Politics, Economics and other Stuff

Flooding at 10 meters/day

From Nature, Catastrophic flood of the Mediterranean after the Messinian salinity crisis:

The Mediterranean Sea became disconnected from the world’s oceans and mostly desiccated by evaporation about 5.6 million years ago during the Messinian salinity crisis^{1, 2, 3}. The Atlantic waters found a way through the present Gibraltar Strait and rapidly refilled the Mediterranean 5.33 million years ago in an event known as the Zanclean flood⁴. The nature, abruptness and evolution of this flood remain poorly constrained^{4, 5, 6}. Borehole and seismic data show incisions over 250 m deep on both sides of the Gibraltar Strait that have previously been attributed to fluvial erosion during the desiccation^{4, 7}. Here we show the continuity of this 200-km-long channel across the strait and explain its morphology as the result of erosion by the flooding waters, adopting an incision model validated in mountain rivers. This model in turn allows us to estimate the duration of the flood. Although the available data are limited, our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 10⁸ m³ s^-1 (three orders of magnitude larger than the present Amazon River) and incision rates above 0.4 m per day. Although the flood started at low water discharges that may have lasted for up to several thousand years, our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years. This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than ten metres per day.

'Early hominids and extant apes are remarkably divergent'

Owen Lovejoy looks at Ardipithecus ramidus, dated to 4.4 million years ago.  From a special section of Science. 

Ardipithecus ramidus now reveals that the early hominid evolutionary trajectory differed profoundly from those of our ape relatives from our clade’s very beginning. Ar. ramidus was already well-adapted to bipedality, even though it retained arboreal capabilities (19–25). Its postcranial anatomy reveals that locomotion in the chimpanzee/human last common ancestor (hereafter the CLCA) must have retained generalized above-branch quadrupedality, never relying sufficiently on suspension, vertical climbing, or knuckle walking to have elicited any musculoskeletal adaptations to these behaviors (26–28).

Moreover, Ardipithecus was neither a ripe-fruit specialist like Pan, nor a folivorous browser like Gorilla, but rather a more generalized omnivore (19, 25). It had already abandoned entirely the otherwise universal sectorial canine complex (SCC), in which the larger, projecting upper canine is constantly honed by occlusion against the lower third molar of anthropoid primates (25), demonstrating that the large, projecting, interlocking, and honing male canines of apes had been eliminated before the dawn of the Pliocene and before the emergence of the dentognathic peculiarities of Australopithecus. What’s more, it appears to have been only slightly dimorphic in body size (25). Finally, the environmental context of Ardipithecus suggests that its primary habitat was not savanna or grassland, but instead woodlands (26–28).

In retrospect, clues to this vast divide between the evolutionary trajectories of African apes and hominids have always been present. Apes are largely inept at walking upright. They exhibit reproductive behavior and anatomy profoundly unlike those of humans. African ape males have retained (or evolved, see below) a massive SCC and exhibit little or no direct investment in their offspring (their reproductive strategies rely primarily on varying forms of male-to-male agonism). Although they excel at some cognitive tasks, they perform at levels qualitatively similar to those of some extraordinary birds (29, 30) and mammals (31). The great apes are an isolated, uniquely specialized relict species surviving today only by their occupation of forest refugia (32). Even their gut structure differs substantially from that of humans (33).

How and why did such profound differences between hominids and African apes evolve? Why did early hominids become the only primate to completely eliminate the SCC? Why did they become bipedal, a form of locomotion with virtually no measurable mechanical advantage (34)? Why did body-size dimorphism increase in their likely descendants? These are now among the ultimate questions of human evolution. We can, of course, only hypothesize their answers. Nevertheless, by illuminating the likely morphological structure and potential social behavior of the CLCA, Ar. ramidus now confirms that extant African ape–based models are no longer appropriate. ...

The primitive nature of the craniodental and postcranial anatomies of Ar. ramidus suggest that the CLCA, unlike extant African apes, was predominantly arboreal. However, all of its descendants have since developed relatively sophisticated adaptations to terrestrial locomotion (23). What was the CLCA’s socio-reproductive structure before these events? Whereas African apes have, in the past, almost invariably been selected as CLCA vicars, Ar. ramidus now allows us to infer that they have undergone far too many pronounced and divergent specializations to occupy such a role.

Also some history I'd not known about:

Apes radiated profusely during the Middle Miocene (~16 to 11.5 Ma) yet became largely extinct by its terminus (5.3 Ma), which coincided with the radiation of Old World monkeys (65). The nearly total replacement of great apes by cercopithecids is likely to have been closely associated with advanced K specialization in the former, shared by all surviving hominoids (66, 67). However, in dramatic contrast to all other ape descendants, hominids became remarkably ecologically and geographically cosmopolitan.

I was going to quote more of Lovejoy's thesis, but that started raising substantive issues -- including statements that diverge from my understanding of the literature -- I don't have time to look into or otherwise address.  I liked this summing up from the blog A Primate of Modern Aspect:

Lovejoy’s hypothesis is controversial.  It’s a Theory of Everything, and that should raise flags in everyone’s head.  But at the end of the day, it’s really stinkin’ weird that human males abandoned their canine teeth, and it’s really stinkin’ weird that human females abandoned their ovulatory advertisement.  I think monogamous pair-bonding goes further than any other hypothesis in explaining those two weirdnesses of the human.  However, my little red flag pops up when we connect those things to bipedalism.

Update #1: Lovejoy at.al. also have a more formal article in Science on a subset of the claims above:  Careful Climbing in the Miocene: The Forelimbs of Ardipithecus ramidus and Humans Are Primitive

The Ardipithecus ramidus hand and wrist exhibit none of the derived mechanisms that restrict motion in extant great apes and are reminiscent of those of Miocene apes, such as Proconsul. The capitate head is more palmar than in all other known hominoids, permitting extreme midcarpal dorsiflexion. Ar. ramidus and all later hominids lack the carpometacarpal articular and ligamentous specializations of extant apes. Manual proportions are unlike those of any extant ape. Metacarpals 2 through 5 are relatively short, lacking any morphological traits associable with knuckle-walking. Humeral and ulnar characters are primitive and like those of later hominids. The Ar. ramidus forelimb complex implies palmigrady during bridging and careful climbing and exhibits none of the adaptations to vertical climbing, forelimb suspension, and knuckle-walking that are seen in extant African apes. ...

The forelimb has played a definitive role in most chronicles of human evolution since Huxley’s and Keith’s original accounts (55, 56). Most recent narratives of its anatomical and behavioral evolution have emphasized a heritage of suspensory locomotion, vertical climbing, and knuckle-walking in the common ancestors that humans shared with extant African apes. Encouraged by human and chimpanzee genetic similarity and cladistic analyses, such views have come to dominate recent explications of early hominid evolution (27, 40), although alternative interpretations based on classical comparative anatomy have long differed (3, 57, 58). Ar. ramidus now permits resolution of these controversies. It indicates that, although cranially, dentally, and postcranially substantially more primitive than Australopithecus, these known Late Miocene to Early Pliocene hominids probably all lacked the numerous, apparently derived, forelimb features of extant African apes. The most probable hypothesis to explain these observations is that hominids never passed through adaptive stages that relied on suspension, vertical climbing, or knuckle-walking. Further fossil remains from the Late Miocene, including those before and after the African ape–hominid phyletic divergences, will test this hypothesis derived from our analysis of Ar. ramidus.

The Ancestors of African Americans

To follow up on the post below, I tried to google recent articles on African American genetic origins. 

Lind et. al., Elevated male European and female African contributions to the genomes of African American individuals, Human Genetics (2007).

The differential relative contribution of males and females from Africa and Europe to individual African American genomes is relevant to mapping genes utilizing admixture analysis. The assessment of ancestral population contributions to the four types of genomic DNA (autosomes, X and Y chromosomes, and mitochondrial) with their differing modes of inheritance is most easily addressed in males. A thorough evaluation of 93 African American males for 2,018 autosomal single nucleotide polymorphic (SNP) markers, 121 X chromosome SNPs, 10 Y chromosome haplogroups specified by SNPs, and six haplogroup defining mtDNA SNPs is presented. A distinct lack of correlation observed between the X chromosome and the autosomal admixture fractions supports separate treatment of these chromosomes in admixture-based gene mapping applications. The European genetic contributions were highest (and African lowest) for the Y chromosome (28.46%), followed by the autosomes (19.99%), then the X chromosome (12.11%), and the mtDNA (8.51%). The relative order of admixture fractions in the genomic compartments validates previous studies that suggested sex-biased gene flow with elevated European male and African female contributions. There is a threefold higher European male contribution compared with European females (Y chromosome vs. mtDNA) to the genomes of African American individuals meaning that admixture-based gene discovery will have the most power for the autosomes and will be more limited for X chromosome analysis.

I'm a bit doubtful about fractions to 1/10,000 with a sample of 93...still, supports the ballpark figure of a bit under 1/3rd for European ancestry for male DNA.  1/5th for autosomal DNA.    

Tishkoff et.al., The Genetic Structure and History of Africans and African Americans, Science (2009)

Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies.

So a lower figure, 13% European, 8% other non-African.  Indeed, it appears that recent studies have lead to downward revisions of the estimated European ancestry of African Americans from what they were a even decade ago. Tishkoff et.al. also find very low (essentially no?) Native American ancestry in their sample of African Americans.  Which raises the issue of getting a good sample of African Americans, if there's lots of heterogeneity. 

I'm also revising my estimate of how much African DNA is US self-identified whites down...there's no presumption that there's symmetry in gene flow.  That's not how this works.  So were' probably under 10 million but over a million (weighting by fraction -- we're in the tens of millions if you look for whites with small amounts of African ancestry). 

Reintroducing Cheetahs in India

The BBC reports.  I had no idea there even were cheetahs in Indian in historical times.  I'd heard of the Indian lion, but lions have been in many places in historical times. 

What I don't understand is how cheetahs in India lines up the well known low diversity of cheetahs, attributed to a recent population bottleneck, presumably in Africa.  Did cheetahs radiate out of Africa since then?  Thinking about it, it probably does make some sense, with ice age driven climate change -- with its massive impact on tropical vegetation cover -- pushing environmental change.  Still, what drove cheetahs so close to extinction in the recent past?  Wouldn't ice age climate conditions -- with savannah replacing forest -- favor the cheetah at least in some areas?   

Wiki writes:

The Asiatic Cheetah once ranged from Arabia to India, through Iran, central Asia, Afghanistan, and Pakistan. In Iran and the Indian subcontinent, it was particularly numerous. Cheetahs are the only big cat that can be tamed and trained to hunt gazelle. The Mughal Emperor of India, Akbar, was said to have had 1,000 cheetahs at one time, something depicted in many Persian and Indian miniature paintings. The numerous constraints regarding the Cheetah’s conservation contribute to its general susceptibility and its very complex conservation: e.g., its low fertility rate, the high mortality rate of the cubs due to genetic factors, and the fact that females are the ones who select mates, have been reasons why captive breeding has had such a poor record. A Cheetah-specific issue is its gene pool. Scientists are aware of the fact that all the Cheetahs in the world have a very similar immune system which means that they all have the same vulnerability to the same diseases; this is due to an interbreeding – approximately 12,000 years ago – that influenced the Cheetah’s gene pool dramatically. The Cheetah will not be a “robust, vigorous species anytime in the foreseeable future"^[10]

By the beginning of the twentieth century, the species was already heading for extinction in many areas. The last physical evidence of the Asiatic Cheetah in India was three shot by the Maharajah of Surguja in 1947 in eastern Madhya Pradesh. By 1990, the Asiatic Cheetah appeared to survive only in Iran. Estimated to number more than 200 during the 1970s, more recently Iranian biologist Hormoz Asadi estimated that the number of Asiatic Cheetahs left to be between 50 and 100 and figures for 2005-2006 are between 50 and 60 in the wild. Most of these 60 Asiatic Cheetahs live in Iran on the Kavir desert. A remnant population inhabits the dry terrain covering the border of Iran and Pakistan. In the areas in which the cheetah lives, locals say they have not seen it for more than fifteen years.

The (re)introduced cheetahs would be from Africa.  Probably good enough.  A reminder that Africa serves as a refuge for large animals driven to extinction recently in Europe and Asia. 

"Hunting of Blackbuck with Cheetah" Drawn by James Forbes in South Gujarat. Oriental Memoirs, Vol. I, 1812.

Living with one sort of severe brain damage

Neuroskeptic writes up the paper Feinstein, J., Rudrauf, D., Khalsa, S., Cassell, M., Bruss, J., Grabowski, T., & Tranel, D. (2009). Bilateral limbic system destruction in man Journal of Clinical and Experimental Neuropsychology:

What happened to Roger's mind when his brain suffered such injury? In many ways, remarkably little. His only major impairment is profound anterograde amnesia: he is unable to remember anything that has happened since the infection, which was 28 years ago.

For Roger, not much has changed over the past 28 years. He has virtually no episodic memories for any events that have transpired over the past three decades. For example, he has no recollection of 9/11, and when shown pictures of the planes crashing into the World Trade Center he often responds with bewilderment, speculating that Russia must be attacking America.

This is, obviously, a disabling deficit: Roger cannot lead a normal life. But in other areas of mental functioning, he is quite normal. His IQ is above average; his speech and language abilities are excellent; his vision and hearing are normal, although he has no sense of taste or smell. His short term (working) memory, attention, and reasoning abilities are unimpaired. His motor abilities are fine - he is reportedly an excellent bowler - and he is able to improve motor skills through practice. And his recall of things which happened before the infection is largely preserved, although the few years just before the infection are partially lost. ...
Fascinatingly, Roger's personality and emotional life seems to have been changed by the infection as well, but in a rather fortunate way -

Roger appears remarkably unconcerned by his condition. He hardly ever complains and, in general, shows little worry for anything in life. Both of his parents and his sister fervently claim that “Roger is always happy,” an observation that is consistent with our own impression. Moreover, based on his family’s report, Roger is paradoxically happier now than he was before his brain damage. ... His premorbid disposition of being somewhat reserved and introverted has shifted to being outgoing and extroverted...

Most conversations with Roger involve animated speech that is replete with prosody, gesture, and, often times, laughing. He readily displays signs of positive emotion including happiness, amusement, interest, and excitement. As previously noted, Roger’s positive mood has remained essentially unchanged over nearly three decades.

His only other reported quirks are an insatiable appetite, and a habit of collecting and holding onto everyday items. ...
For me, Roger provides two main lessons, both rather satisfying ones. Firstly, even after losing large parts of the brain, life goes on. The brain is modular, and we can live without many of the modules. And secondly, if our emotional circuitry is damaged, we generally feel better, rather than worse. To put it another way, perhaps, happiness is our default state, and emotions just have a habit of getting in the way.

Faked DNA Evidence

The NYT reports.  Something I expect to hear more about in the future.  Surprising this hasn't been more on the radar screen until now. 

Tallest Mountain Range in the Solar System

Since I was trying to figure out how McKinley can be so tall in a glacial climate I was trying, unsuccessfully so far, to find a list of mountain heights from the mountain base.  But I did run into a mention of the tallest mountain range in the Solar System.  I'd known that Olympus Mons on Mars is the highest mountain at a bit over 21km from its base (compared to Hawaii's Mauna Kea with a bit over 10km height from its base), but I'd not known about the tallest mountain range, the equatorial ridge of Iapetus, the 3rd largest moon of Saturn.  It is about 1,300 km long, 20 km wide and 13 km high, with some peaks over 20km high (potentially beating Olympus Mons?).  Discovered in 2004 by Cassini.  Obviously mountain formation on a moon with low gravity, a large neighbor and 80% water content is different than on earth. 

Update #1:

The orbit of Iapetus is somewhat unusual. Although it is Saturn's third-largest moon, it orbits much farther from Saturn than the next closest major moon, Titan. It has also the most inclined orbital plane of the regular satellites; only the irregular outer satellites like Phoebe have more inclined orbits. The cause of this is unknown.

'Differences in the height of mountain ranges mainly reflect variations in climate rather than tectonic forces'

D. L. Egholm, S. B. Nielsen, V. K. Pedersen & J.-E. Lesemann writing in the most recent issue of Nature: Glacial effects limiting mountain height.  The key technical term is 'glacial buzzsaw'.  Totally obvious once you think about it, but not something that had crossed my mind previously. 

I still want to know about Mount McKinley and the Antarctic mountain ranges. Ah, it appears that they don't include McKinley or Antarctica in the data set...here is their figure 1:

a, Hypsometric distributions from a fluvial (northern Andes) and a glacial (Cascade Range, USA) landscape. Both hypsometries contain local maxima, but at different elevations. The hypsometric distributions each represent a 1°  1° DEM with coordinates (lower left corner) (09° N, 71° W) for the fluvial landscape and (48° N, 121° W) for the glacial. b, Global distribution of hypsometric maxima as function of latitude and elevation. Each hypsometric maximum found in the data set is represented by a circle coloured by its DEM database entry (upper left inset). Hypsometric maxima derived from DEMs with more than 5% data gaps are white. The grey shaded area represents the total data coverage set by the maximum elevation at each latitude. Also shown are the modern (black line) and LGM (dashed line) snowline transects along the east Pacific (EP) coasts of North and South America¹⁷ and more than 13,000 modern snowline observations from the World Glacier Inventory¹⁸ averaged in bins of 1° latitude where available (red line). c, Distribution of surface area (A) based on latitude (L) and elevation (E) within the data set. Colours show area at a given latitude and elevation normalized by the total area (A_total) of the data set. Note the logarithmic colour scale. The grey zone has very little area and falls outside the colour scale, but serves to outline the total data range. Ellipses mark tectonically uplifted plateaus: 1, South Africa; 2, the Altiplano (Andes), 3, the Tibetan plateau; and 4, the Tarim basin. (See also Supplementary Figs 1–4.)

Animals mix the ocean

This recent article in Nature gave me on of those occaional 'am I dreaming?' sensations.  The notion that animals may contribute a similar amount to ocean mixing as winds and tides was novel, almost shocking, for me. 

Kakani Katija & John O. Dabiri, A viscosity-enhanced mechanism for biogenic ocean mixing

Recent observations of biologically generated turbulence in the ocean have led to conflicting conclusions regarding the significance of the contribution of animal swimming to ocean mixing. Measurements indicate elevated turbulent dissipation—comparable with levels caused by winds and tides—in the vicinity of large populations of planktonic animals swimming together¹. However, it has also been noted that elevated turbulent dissipation is by itself insufficient proof of substantial biogenic mixing, because much of the turbulent kinetic energy of small animals is injected below the Ozmidov buoyancy length scale, where it is primarily dissipated as heat by the fluid viscosity before it can affect ocean mixing². Ongoing debate regarding biogenic mixing has focused on comparisons between animal wake turbulence and ocean turbulence^{3, 4}. Here, we show that a second, previously neglected mechanism of fluid mixing—first described over 50 years ago by Charles Darwin⁵— is the dominant mechanism of mixing by swimming animals. The efficiency of mixing by Darwin's mechanism is dependent on animal shape rather than fluid length scale and, unlike turbulent wake mixing, is enhanced by fluid viscosity. Therefore, it provides a means of biogenic mixing that can be equally effective in small zooplankton and large mammals. A theoretical model for the relative contributions of Darwinian mixing and turbulent wake mixing is created and validated by in situ field measurements of swimming jellyfish using a newly developed scuba-based laser velocimetry device⁶. Extrapolation of these results to other animals is straightforward given knowledge of the animal shape and orientation during vertical migration. On the basis of calculations of a broad range of aquatic animal species, we conclude that biogenic mixing via Darwin's mechanism can be a significant contributor to ocean mixing and nutrient transport.

I got the same 'am I dreaming' feeling with another Nature paper: Ju Young Lee, Byung Hee Hong, Woo Youn Kim, Seung Kyu Min, Yukyung Kim, Mikhail V. Jouravlev, Ranojoy Bose, Keun Soo Kim, In-Chul Hwang, Laura J. Kaufman, Chee Wei Wong, Philip Kim & Kwang S. Kim, Near-field focusing and magnification through self-assembled nanoscale spherical lenses:

It is well known that a lens-based far-field optical microscope cannot resolve two objects beyond Abbe's diffraction limit. Recently, it has been demonstrated that this limit can be overcome by lensing effects driven by surface-plasmon excitation^{1, 2, 3}, and by fluorescence microscopy driven by molecular excitation⁴. However, the resolution obtained using geometrical lens-based optics without such excitation schemes remains limited by Abbe's law even when using the immersion technique⁵, which enhances the resolution by increasing the refractive indices of immersion liquids. As for submicrometre-scale or nanoscale objects, standard geometrical optics fails for visible light because the interactions of such objects with light waves are described inevitably by near-field optics⁶. Here we report near-field high resolution by nanoscale spherical lenses that are self-assembled by bottom-up integration⁷ of organic molecules. These nanolenses, in contrast to geometrical optics lenses, exhibit curvilinear trajectories of light, resulting in remarkably short near-field focal lengths. This in turn results in near-field magnification that is able to resolve features beyond the diffraction limit. Such spherical nanolenses provide new pathways for lens-based near-field focusing and high-resolution optical imaging at very low intensities, which are useful for bio-imaging, near-field lithography, optical memory storage, light harvesting, spectral signal enhancing, and optical nano-sensing.

I have no idea how this works. 

Thinking about the Palaeocene–Eocene Thermal Maximum as a model of our time

Richard E. Zeebe, James C. Zachos & Gerald R. Dickens, Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming, Nature Geoscience

The Palaeocene–Eocene Thermal Maximum (about 55 Myr ago) represents a possible analogue for the future and thus may provide insight into climate system sensitivity and feedbacks. The key feature of this event is the release of a large mass of 13C-depleted carbon into the carbon reservoirs at the Earth's surface, although the source remains an open issue. Concurrently, global surface temperatures rose by 5–9 °C within a few thousand years. Here we use published palaeorecords of deep-sea carbonate dissolution and stable carbon isotope composition along with a carbon cycle model to constrain the initial carbon pulse to a magnitude of 3,000 Pg C or less, with an isotopic composition lighter than -50permil. As a result, atmospheric carbon dioxide concentrations increased during the main event by less than about 70% compared with pre-event levels. At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration1, this rise in CO2 can explain only between 1 and 3.5 °C of the warming inferred from proxy records. We conclude that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Palaeocene–Eocene Thermal Maximum. Once these processes have been identified, their potential effect on future climate change needs to be taken into account.

I've been using the Palaeocene–Eocene Thermal Maximum as my benchmark historical event for global warming given the surprising similarity in short term carbon forcing [current annual anthropic carbon emissions are around 8.5 PG, so 850 Pg in a century, and they are still going up, so we could easily get past 1,000 or 2,000 Pg in the near future, which is about where recoverable fossil fuel reserve estimates are now...]...glad to see this is respectable. 

Which Mimosa is this?

This was going to be a post on the question of why this mimosa tree has such a strange color, but I don't know if the color comes through in these photos with the late afternoon lighting and I cannot determine which of the ~400 mimosa species this is. I assume the color has something to do with the metabolism of the tree, a metabolism presumably well adapted to the temperature, moisture, soil, sun exposure and foragers of the tree in its typical environment.  There is a whole theory of leaf size and appearance based on metabolic function, but I couldn't outline who the theory works. 

Besides color, leaf size is also not standard for trees in the Northeast.

Color Illusion

via Matt Steinglass, Discover magazine's blog has an impressive optical illusion.  This illusion suggests why white balance isn't a straightforward problem in photography.  

The original was apparently posted on Buzzhunt Akiyoshi Kitaoka’s incredible optical illusion website.  The green and the blue spirals are the same color.  For pedantry sake, the RGB colors in both spirals are 0, 255, 150. So they are mostly green with a solid splash of blue.

Earth to (potentially) collide with Mars and Venus

Something I'd not expected from last week's Nature: J. Laskar & M. Gastineau, Existence of collisional trajectories of Mercury, Mars and Venus with the Earth.

It has been established that, owing to the proximity of a resonance with Jupiter, Mercury's eccentricity can be pumped to values large enough to allow collision with Venus within 5 Gyr. This conclusion, however, was established either with averaged equations that are not appropriate near the collisions or with non-relativistic models in which the resonance effect is greatly enhanced by a decrease of the perihelion velocity of Mercury. In these previous studies, the Earth's orbit was essentially unaffected. Here we report numerical simulations of the evolution of the Solar System over 5 Gyr, including contributions from the Moon and general relativity. In a set of 2,501 orbits with initial conditions that are in agreement with our present knowledge of the parameters of the Solar System, we found, as in previous studies, that one per cent of the solutions lead to a large increase in Mercury's eccentricity—an increase large enough to allow collisions with Venus or the Sun. More surprisingly, in one of these high-eccentricity solutions, a subsequent decrease in Mercury's eccentricity induces a transfer of angular momentum from the giant planets that destabilizes all the terrestrial planets approx 3.34 Gyr from now, with possible collisions of Mercury, Mars or Venus with the Earth.

Nature also provides a bit of context for this result:

Orbital predictions obtained from numerical integration of the planets' equations of motion demonstrated that the planetary orbits will indeed become chaotic, with typical Lyapunov times — the time required for chaos to significantly degrade the predictability of a system — of the order of 5 million years. Statements regarding the stability of the Solar System must therefore be expressed in terms of probabilities. Computers are now fast enough to be able to produce forward models of the Solar System throughout the Sun's remaining 5-billion-year hydrogen-burning lifetime. One insight that has emerged is that, from a dynamical point of view, the Solar System is effectively two systems of planets. The gas giants — Jupiter, Saturn, Uranus and Neptune — constitute an extremely stable constellation, whereas the rocky terrestrial planets are on a far less solid footing. Were one to eliminate the Sun's eventual mass loss and its damaging encounters with passing stars in the far future, the outer planets would evolve with substantially unaltered orbits for about 10¹⁸ years before succumbing to a weak orbital resonance, in which the perturbative attractions between Jupiter, Saturn and Uranus would generate large-scale instability.

Controlled Nuclear Fusion with Net Energy Release is still in the Future

Now the proof of principle is scheduled for 2025, only 16 years from now, a delay of only 5 years since 2006.  Delays have been reliably mounting at about a one year per year rate since I started following this stuff in the late 1970s.  Nature writes:

ITER — a multi-billion-euro international experiment boldly aiming to prove atomic fusion as a power source — will initially be far less ambitious than physicists had hoped, Nature has learned.

Faced with ballooning costs and growing delays, ITER's seven partners are likely to build only a skeletal version of the device at first. The project's governing council said last June that the machine should turn on in 2018; the stripped-down version could allow that to happen (see Nature 453, 829; 2008). But the first experiments capable of validating fusion for power would not come until the end of 2025, five years later than the date set when the ITER agreement was signed in 2006.

Okay, this is only the tokamack, but still...first controlled fusion in a tokamack was 1968. 

Jellyfish replacing fish as top predators in parts of the ocean?

Anthony J. Richardson, Andrew Baku, Graeme C. Hays and Mark J. Gibbons, The jellyfish joyride: causes, consequences and management responses to a more gelatinous future is a nice thought piece on possible jellyfish threat (via. Climate Shifts).  I cannot judge its quality, but Trends in Ecology and Evolution is a respected journal. The big story is possible strong positive feedbacks by which jellyfish overcome control on their population by fish in stressful environments by suppressing fish populations. 

The most prominent regional jellyfish outbreaks of recent decades have followed collapses of formerly dominant local stocks of small filter-feeding pelagic fishes....Major jellyfish outbreaks have followed overexploitation and collapse of a locally dominant, small filter-feeding fish stock (e.g. anchovy, sardine or herring) in situations where another rapidly responding, similar fish species is not available as an adequate replacement. For example, in the northern Benguela upwelling system, where intense fishing decimated sardine stocks and jellyfish now dominate [11], maximum anchovy abundance has historically been limited to ~10% of maximum sardine biomass [64] (possibly because the weakly swimming anchovy might be incapable of coping as well as the larger sardine in this highly energetic upwelling system [21]). There is thus no obvious filter-feeding replacement for sardine in this ecosystem. This pattern was replicated in the energetic ocean context off Japan, where anchovies have not historically built populations comparable to those of sardines [64], and where the infestation of giant Nomura jellyfish has occurred following the collapse of what was an enormous Japanese sardine population [65]. When translocated ctenophores exploded in abundance following the anchovy collapse in the Black Sea [10], there was no obvious replacement. A similar episode of anchovy collapse and ctenophore explosion occurred in the Caspian Sea [43] and, following a similar general pattern, there was a decade-long increase in jellyfish abundance in the Bering Sea [55] following a lasting decline in herring abundance [66].

Equally informative are fishery collapses that have not led to jellyfish outbreaks. With the collapse of the largest fish stock in the world, the Peruvian anchoveta (Engraulis ringens) during the 1970s [64], there was no switch to increased jellyfish outbreaks. One possible explanation is that there were healthy stocks of an alternate rapidly responding filter-feeding species (i.e. highly migratory sardines) that quickly built up a large biomass and spread throughout the system to replace the collapsed anchoveta [64].

Finally, many of the instances in which fisheries collapses have not led to jellyfish outbreaks involve predatory rather than planktivorous fish [19]. Many fisheries collapses in the North Atlantic shelf and peripheral seas have been of bottom-dwelling predators such as cod and haddock. In these cases, the filter-feeding small pelagic prey of the collapsed species have increased rapidly (e.g. herring off New England [22] and sprat in the Baltic Sea [51]). Lower predatory fish biomass can release predation pressure on planktivorous fish, enabling their biomass to increase (top-down control) and, thus, lead to increased predation on, and competition with, jellyfish. Thus, many well-known collapses of piscivorous fish should have favoured increased planktivorous fish abundance and could have suppressed rather than encouraged jellyfish outbreaks.  ....

Thus, it is not unreasonable to suggest that jellyfish proliferations are held in check via a combination of competition for planktonic food and (perhaps) predation on ephyrae, small medusae or polyps by filter-feeding fishes. If this is the case, heavy fishing and other aspects of global change that appear to favour jellyfish could act to increase the abundance of jellyfish relative to that of filter-feeding fish until a crucial ‘tipping point’ [22,50,51] is reached. Here, jellyfish begin to overwhelm any significant control of their vulnerable life-cycle stages by fish predators, while progressively eliminating that control via their predation on fish eggs and larvae [52]. Moreover, as jellyfish abundance increases, successful sexual combination of planktonic reproductive products becomes more efficient. For jellyfish with entirely pelagic life cycles, this might involve infesting recirculating ocean currents, permanent eddy structures and other retention zones. For those species with obligate sessile stages, it might entail sequential colonisation of new seafloor habitat. A rapidly self-enhancing feedback loop could then ensue in which the jellyfish infestation spreads by sequentially invading habitats where fish might have formerly controlled jellyfish numbers.

Once established, a jellyfish infestation might quickly exclude competitive or predatory fish stocks, resulting in a durable regime shift in ecosystem structure and operation [51], with diverse fish communities replaced by a relative monoculture of jellyfish. As uncontrolled growth continues, local overproduction is available for export to new areas, where the jellyfish could again overwhelm resident predators and precipitate local outbreaks. ... This type of feedback mechanism, where the hunted becomes the hunter, is specific to marine environments, as illustrated by Bakun and Weeks [22]: ‘Imagine trying to maintain stability in an African veldt ecosystem if antelopes and zebras were to voraciously hunt and consume the young of the adult lions and cheetahs that prey on them.’ The potentially durable switch to a jellyfish- dominated system is reminiscent of the ancient, rudimentary ecosystems of the Cambrian, and has convinced some authors [26,53] that human stressors are propelling marine ecosystems ‘way back to the future’ (Box 3).

Fern Prairie

I continue to be fascinated by fern prairies.  Turns out that one of the most common illustrations of Quetzalcoatlus northropi, an animal I've blogged about previously, is of it foraging on a fern prairie.

A group of flying reptiles called Quetzalcoatlus may have strolled along a fern prairie eating baby dinosaurs for lunch. Credit: Mark Witton, University of Portsmouth. (link)

Shade intensive forests are a modern biome

I've been slowly assimilating the fact that shade intensive forests with a stratified closed canopy are a relatively modern biota.  In particular, modern ferns are not like ancient ferns since ancient ferns did not live in forests with deep shade. Instead, many ancient ferns were more like modern grasses, even forming 'fern prairies.'

For instance, Davis et.al., who support the earliest date for the origin of modern forests, survey the literature in Explosive Radiation of Malpighiales Supports a Mid-Cretaceous Origin of Modern Tropical Rain Forests, 2005:

Modern tropical rain forests are one of the most important and species rich biomes on the planet. They can be defined as having a stratified closed canopy, as receiving abundant precipitation, as experiencing equable temperatures, and as containing woody angiosperm species, at least in the understory (Richards 1996; Whitmore 1998; Morley 2000). During the past 20 years the view has become widespread that the expansion and diversification of this vegetation type occurred principally during the past 65 million years, following the mass extinction event at the Cretaceous- Tertiary (K/T) boundary (∼65 Ma [Tiffney 1984; Wing and Boucher 1998; Morley 2000; Johnson and Ellis 2002; Ziegler et al. 2003]; Cretaceous and Cenozoic timescales following Gradstein et al. [1995] and Berggren et al. [1995]). This hypothesis was initially supported by the rarity of large stems (Wheeler and Baas 1991; Wing and Boucher 1998) and large diaspores (Tiffney 1984; Wing and Boucher 1998) of angiosperms in the Cretaceous and by the marked increase in diaspore size in the Early Tertiary. Large seeds facilitate the establishment of seedlings under a rain forest canopy (Grime 1979).

Studies of fossil leaves and wood (Upchurch and Wolfe 1987, 1993; Wolfe and Upchurch 1987) partially corroborated this pattern by indicating that most Late Cretaceous floras of southern North America, which was tropical or nearly so, represented open and subhumid (though not deciduous) forests. This contrasts with fossil floras in the same areas after the recovery from the K/T extinction event, which resemble modern tropical rain forests (Wolfe and Upchurch 1987; Johnson and Ellis 2002). However, floras from the early Late Cretaceous (Cenomanian; ∼100 Ma) of Kansas, Nebraska, and New Jersey have leaf sizes and morphologies characteristic of wetter climates (Wolfe and Upchurch 1987). Upchurch and Wolfe (1993) interpreted one flora (Fort Harker, KS) as typical megathermal (>20C mean annual temperature [Upchurch and Wolfe 1987]) rain forest and as evidence against the view that such forests did not originate until the Tertiary.

Temperate intensive shade forests also appear to be extant only since the mid-Cretaceous at the earliest.  It is not clear to me yet what the standard theory is, except that the 'mid-Cretaceous is a period of sudden turnover from gymnosperm to angiosperm dominated floras' as Coiffard et. al. write.  As to causality, I cannot tell what is going on yet. 

But back to modern ferns for a moment:

Leptosporangiate ferns, with more than 9000 extant species, are truly exceptional among the non-flowering lineages of vascular plants. However, this rather remarkable diversity was not simply a consequence of being able to “hold on” as flowering plants rose to dominance. Instead, it appears to be the result of an ecological opportunistic response to the establishment of more complex, angiosperm-dominated ecosystems. The proliferation of flowering plants across the landscape undoubtedly resulted in the formation of a plethora of new niches into which leptosporangiate ferns could diversify. Many of these were evidently on shady forest floors, but many others were actually within the new angiosperm-dominated canopies. Today, almost one third of leptosporangiate species grow as epiphytes on angiosperm trees.

Finally, it seems the modern steppe with its highly productive heat tolerant grasses and occasional trees is an even more modern biome, just 8 or so million years old.  More later...

Yet More Late Quaternary Extinctions

Darren Naish writes:

[U]ntil just a few thousand years ago, small crocodilians inhabited the tropical islands of the South Pacific and elsewhere. In fact, judging from recent discoveries, small terrestrial crocodilians were an ordinary component of many tropical island groups, and they presumably still would be, had they not been made extinct by people.

More at the link. 

The most dominant land animal ever: Lystrosaurus

Lystrosaurus was one of the very few large survivors of the Permian mass extinctions.  More later....

"Everyone generalizes from one example. At least, I do."

Is this true?  Yvain writes:

There was a debate, in the late 1800s, about whether "imagination" was simply a turn of phrase or a real phenomenon. That is, can people actually create images in their minds which they see vividly, or do they simply say "I saw it in my mind" as a metaphor for considering what it looked like?

Upon hearing this, my response was "How the stars was this actually a real debate? Of course we have mental imagery. Anyone who doesn't think we have mental imagery is either such a fanatical Behaviorist that she doubts the evidence of her own senses, or simply insane." Unfortunately, the professor was able to parade a long list of famous people who denied mental imagery, including some leading scientists of the era. And this was all before Behaviorism even existed.

The debate was resolved by Francis Galton, a fascinating man who among other achievements invented eugenics, the "wisdom of crowds", and standard deviation. Galton gave people some very detailed surveys, and found that some people did have mental imagery and others didn't. The ones who did had simply assumed everyone did, and the ones who didn't had simply assumed everyone didn't, to the point of coming up with absurd justifications for why they were lying or misunderstanding the question. There was a wide spectrum of imaging ability, from about five percent of people with perfect eidetic imagery to three percent of people completely unable to form mental images. 

Googling reveals that there is indeed a famous 1880 psychology paper by Galton on this topic, as well as later work. 

I couldn't actually say, off the cuff, how much mental imagery I have --- none flashes immediately into my mind.  I do have pretty good physical imagination, in the sense of being able to imagine how spacial relationships, movement/flow and forces work.  Pushing things around and imagining how to manipulate them falls into this category and the standard 3-D mental rotation tasks are pretty straightforward.  Imagining full faces, on the other hand, isn't so obvious.  Colors are also, for the most part, not important in my mental imagery, while temperature or blinding light is.  

If mental imagery is actually as diverse as suggested above, this strikes me as extremely intriguing and puzzling.  Why is this? 

Asian Deserts and Forests during the Last Glacial Maxium

Asia 18,000 years before present.  Note the extensive deserts and limited and regional forests.  Temperate forests are basically only in southern Japan and around the coast of the Yellow Sea. 

 

Testimony of Dr. E. Calvin Beisner to the Subcommittee on Energy and Environment of the Committee on Energy and Commerce of the United States House of Representatives Wednesday, March 25, 2009

via Deltoid, the Testimony of Dr. E. Calvin Beisner to the Subcommittee on Energy and Environment of the Committee on Energy and Commerce of the United States House of Representatives Wednesday, March 25, 2009, which I ran across since I was googling for information on today's Climate Change hearings with Al Gore and Newt Gingrich:

I am convinced that policies meant to reduce alleged carbon dioxide-induced global warming will be destructive, devising mischief by decree. As Lord Monckton points out in his own testimony today, the best, most recent empirical scientific discoveries have shown that even the mid-range scenarios of the IPCC exaggerate the warming effect of increased CO2 by at least seven times; atmospheric CO2 concentration is rising at a fraction of the rate forecast by the IPCC; and Earth has been cooling for the last seven years at a rate of 3.5F per century.

These findings, opposite the expectations of the IPCC, are consistent with the Biblical world view. The naturalist, atheistic world view sees Earth and all its ecosystems as the result of chance processes and therefore inherently unstable and fragile, vulnerable to enormous harm from tiny causes. The Biblical world view sees Earth and its ecosystems as the effect of a wise God’s creation and providential preservation and therefore robust, resilient, and self-regulating–like the product of any good engineer who ensures that the systems he designs have positive and negative feedback mechanisms to balance each other and prevent small perturbations from setting off a catastrophic cascade of reactions. The IPCC’s work rests on the naturalist, atheistic world view. Every one of its computer climate models, without exception, assumes that positive feedback mechanisms vastly outnumber and outweigh negative feedbacks, which is the root of fears of a runaway greenhouse effect and a “tipping point” beyond which there is no return.

The IPCC exaggerates the rate of carbon buildup because it doesn’t recognize the capacity of Earth’s plants and oceans to absorb vast amounts of carbon from the atmosphere and turn it into the building blocks of life. But that is precisely what has been happening, with wild and cultivated plants growing larger and more numerous because of increased CO2, and raising crop yields (and so lowering food prices. And the IPCC exaggerates the warming effect of CO2 in the atmosphere largely because its computer models all assume that clouds are a positive feedback–that they respond to rising surface temperature by trapping still more heat. But University of Alabama climatologist Roy Spencer, using data from NASA satellites, has shown the opposite: warming clouds diminish as surface temperature rises, allowing more heat to radiate out to space. The system works like a thermostat, keeping surface temperature within a narrow range well suited to human and other life on Earth.

But empirical observation–the very soul of scientific method–has shown otherwise.  The Biblical world view prepares us for just such findings. When God finished His creation, “God saw all that He had made, and behold, it was very good” (Genesis 1:31). Do you think he would have judged a fragile system biased by unidirectional feedbacks toward destruction that way? No, He would not. Indeed, the global destruction of the Flood required His supernatural intervention (Genesis 6–8), after which He promised Himself, “I will never again curse the ground on account of man . . .; and I will never again destroy every living thing, as I have done. While the earth remains, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease” (Genesis 8:21–22)–the repeated pairs of opposites being the poetic device called merism, implying that God had committed Himself to ensuring that all the cycles needed for human (and other) thriving would continue.

Deltoid comments: "In other words, if climate sensitivity to the doubling of CO2 is 3 degrees, there is no God."  Hm, I think god may just test Beisner's faith -- isn't that what god does?   

My wife comments that her study of the bible shows that god has a long history of smiting societies run by idiots.  God may hate Republicans, which puts us all at risk. 

Update #1: to the extent that Beisner believes in god guaranteed self-regulation of the earth, there are lots of ways this could occur that are quite destructive to normal conceptions of human welfare, such as the plague and economic collapse.  Not to forget war.  Why does this god guaranteed self-regulation have to occur via non-human biological processes (all the extra plant growth) and not the decline of human civilization as punishment for bad stewardship over the earth?  Punishing societies that have deviated from god's plan isn't unheard of in the bible.  Or are we simply relying on the second coming to bail us out if necessary?  

Update #2: What's the deal with Beisner's claim that 

The IPCC exaggerates the rate of carbon buildup because it doesn’t recognize the capacity of Earth’s plants and oceans to absorb vast amounts of carbon from the atmosphere and turn it into the building blocks of life.

The IPCC spends lots of time discussing terrestrial carbon sinks (for instance Chapter 7.3.2 of the 2008 Summary), including plant growth, a difficult to measure and model phenomena with lots of heterogeneity across many dimensions.  I could see how Beisner might claim that the IPCC underestimates these carbon sinks, but how can he claim that the IPCC "doesn’t recognize" them? 

What about the claim, often mentioned by Republicans, that

Earth has been cooling for the last seven years at a rate of 3.5F per century.

Even taking the 3.5F per 100 years (i.e. 0.25F over seven years) as true, this does not look to me like a statistically significant deviation from the IPCC's trend warming projections given the variability of global surface temperatures.  For instance, here is the National Climatic Data Center's data on mean world surface temperatures (land and ocean -- it would be worthwhile to look into how these are constructed and sampling errors over time and space, for instance do better sampled locations get more weight?) as a deviation from the 1901-2000 average temperature for each month.  The statistical significance is even less that it appears, since there is, it seems, some positive autocorrelation in temperature even more than a year out, after taking out the trend.  And 3.5F per century sure isn't statistically different than 0F over a seven year period. 

 
Not clear to me what the basis for the claim that

atmospheric CO2 concentration is rising at a fraction of the rate forecast by the IPCC.

I've seen this claim before, but never with much documentation or citation of specific IPCC projections, the main claim being that CO2 concentrations seem to be growing linearly and not exponentially in the last decade or so.  And even if true, the interpretation Beisner puts on it seems odd. 

No major glacial cycle extinctions before the Late Quaternary Extinctions?

S. Kathleen Lyons, Felisa A. Smith and James H. Brown, Of mice, mastodons and men: human-mediated extinctions on four continents, Evolutionary Ecology Research, 2004 write:

There were more than 20 glacial–interglacial cycles during the ∼1.6 million years of the Pleistocene, but only in the last one, and only in North and South America, were these climatic changes associated with wholesale extinctions of large mammals.

Lyons et. al. don't, as far as I can tell, cite a source for this claim.  They do recognize that there are lots of debates about climate change and extinctions of large animals outside of the Americas, especially in Northern Eurasia and Australia, so in part what is important here is what 'wholesale' means and how close other glacial cycles and other locations come to 'wholesale' extinctions of large animals.  My gut instinct from reading a bit of this literature is that humans are the main cause of large animal extinctions in the 50,000 - 8,000 BP period, with the lack of these types of mass extinctions in prior glacial cycles and far fewer extinctions in Africa (where modern humans originated and coevolved with large animals) the most suggestive evidence, but it would be nice to know the extent that this suggestive line of evidence is actually true. 

Update #1: the standard reference seems to be Alroy J. 1999, 'Putting North America’s end-Pleistocene megafaunal extinction incontext: large-scale analyses of spatial patterns, extinction rates, and size distributions', but I cannot get it online [ah here it is, but not as a pdf and not complete].  Paul L. Koch and Anthony D. Barnosky, Late Quaternary Extinctions: State of the Debate, 2006, summarize Alroy as

[R]recent analyses that account for temporal and sampling biases in the fossil record recognize a LQE spike that exceeds all but one other extinction in the past 55 million years (Alroy 1999). Even taking into account that larger animals are preferentially impacted by extinction events, and that smaller species are increasingly affected as extinction intensity rises, by Alroy’s metrics the LQE appears more selective than any extinction event in the preceding 65 million years of mammalian history in North America.

Not clear what that one larger extinction in the past 55 million years is, or even what the extinction event 55 million years ago is. The Eocene-Oligocene transition is the obvious candidate -- indeed, it would be very noteworthy if the  LQEs are similar in size to the ones associated with one of the major climate changes (the glaciation of the Antarctic for the first time in more than 100 million years to an ice volume above where it is now, along with a fall in tropical mean temperatures of more than 4C, more likely 8C or more, a larger fall in non-tropical temperatures and a major increase in seasonality -- basically the transition from a still Cretaceous-like climate to today's basic climate structure) in the geological record. 

So yes, the LQEs do sound like they are the one major extinction even in 1.6 million years of glacial cycles.  Still, it would be nice to see the numbers (corrected for sampling biases). 

Finally, from Koch and Barnosky the size dependency of the LQEs by animal size and location:

Earth Science Factoids

I'm not sure what to make of these two claims I ran across this week.  It would be nice to know more.

RealClimate:

There is a standard theorem of oceanography called Sandström's theorem which basically states that it is really hard to do any work on a system, like the ocean, if you are cooling and heating at the same level (i.e. the surface). By contrast, the atmosphere is heated from below (since the atmosphere is mostly transparent to solar radiation), and cooled from above and so can behave as a relatively efficient heat engine. Since we observe however that the ocean does have a large-scale deep circulation, it can't therefore be 'driven' (in an energetic sense) from the cooling of waters in the high latitudes. The alternate name, 'the Thermohaline Circulation', does tend to perpetuate the idea that it is the temperature and salinity fluxes that 'drive' the circulation, and so is slowly falling into disfavour (though it is still widely used and defended).

But if this deep circulation doesn't derive its energy from density contrasts, where does it get the energy from? Most of the energy in the oceans is derived from two sources, the winds and the tides. Both of these forces generate small scale turbulence and internal waves which cause mixing of ocean waters. It is this mixing which energetically fuels the deep ocean circulation.

Since the winds will continue to blow and the Earth continue to turn, does this mean that there can't be any changes to the MOC? Emphatically no. The circulation may well derive it's energy from the winds and tides, but it is heavily steered by density contrasts and the stratification of the ocean (witness the difference between the North Pacific and the North Atlantic). Changes in that modulation can have profound effects on the currents, and in particular, additions of fresh water from massive lake drainages (i.e. the 8.2 kyr event) or ice sheet collapses (the Heinrich events) most likely caused severe slowdowns or shutdowns of the MOC in the past. Wunsch is a little sceptical of this research (he calls fresh water the 'deus ex machina' of climate change), but in this he is probably mistaken - for instance, there is enough information from the 8.2 kyr event to reasonably attribute it to the drainage of Lake Agassiz into Hudson Bay.

Thus while density changes don't 'drive' the circulation (in an energetic sense) they can 'drive' (in a modulating sense) changes in that circulation. If this seems complicated, think of the example of greenhouse gases - they don't drive the climate in an energetic sense (the sun does), but they can drive changes in the climate (by modulating radiation flow in the atmosphere).

Time to find a good ocean circulation book. I do have Wunsch's book from the 1990s, but I may want to find a different treatment. Ah, here is a Wunsch 2008 review article: Ocean Circulation Kinetic Energy: Reservoirs, Sources, and Sinks. Or a 2004 Ferrari and Wunsch article, VERTICAL MIXING, ENERGY, AND THE GENERAL CIRCULATION OF THE OCEANS: 

The coexistence in the deep ocean of a finite, stable stratification, a strong meridional overturning circulation, and mesoscale eddies raises complex questions concerning the circulation energetics. In particular, small-scale mixing processes are necessary to resupply the potential energy removed in the interior by the overturning and eddy-generating process. A number of lines of evidence, none complete, suggest that the oceanic general circulation, far from being a heat engine, is almost wholly governed by the forcing of the wind field and secondarily by deep water tides. In detail however, the budget of mechanical energy input into the ocean is poorly constrained. The now inescapable conclusion that over most of the ocean significant “vertical” mixing is confined to topographically complex boundary areas implies a potentially radically different interior circulation than is possible with uniform mixing. Whether ocean circulation models, either simple box or full numerical ones, neither explicitly accounting for the energy input into the system nor providing for spatial variability in the mixing, have any physical relevance under changed climate conditions is at issue.

Wiki on the geothermal gradient:

If [the] rate of temperature change were constant, temperatures deep in the Earth would soon reach the point where all known rocks would melt. We know, however, that the earth's mantle is solid because it transmits S-waves. The temperature gradient dramatically decreases with depth for two reasons. First, radioactive heat production is concentrated within the crust of the Earth, and particularly within the upper part of the crust, as concentrations of uranium, thorium, and potassium are highest there: these three elements are the main producers of radioactive heat within the Earth. Second, the mechanism of thermal transport changes from conduction, as within the rigid tectonic plates, to convection, in the portion of Earth's mantle that convects. Despite its solidity, most of the Earth's mantle behaves over long time-scales as a fluid, and heat is transported by advection, or material transport. Thus, the geothermal gradient within the bulk of Earth's mantle is of the order of 0.3 kelvin per kilometer, and is determined by the adiabatic gradient associated with mantle material (peridotite in the upper mantle).

How do we know that uranium, thorium and potassium are concentrated in the upper mantle crust?  I assume there are theoretical reasons to believe this, but what are they? Ah, this is crust, not upper mantle...so yes, I can see how we might know this.  I was wondering how we'd know about concentrations in the upper vs. lower mantle. 

Which reminds me, how much radiative vs. convective heat flow is there in different layers of the sun?  I assume it's mostly radiative heat flow. Ah, flow from the solar core to the surface convective zone is radiative, some convective heat flow in the convective zone.  

The convection zone is the outer-most layer of the solar interior. It extends from a depth of about 200,000 km right up to the visible surface. At the base of the convection zone the temperature is about 2,000,000° C. This is "cool" enough for the heavier ions (such as carbon, nitrogen, oxygen, calcium, and iron) to hold onto some of their electrons. This makes the material more opaque so that it is harder for radiation to get through. This traps heat that ultimately makes the fluid unstable and it starts to "boil" or convect. Convection occurs when the temperature gradient (the rate at which the temperature falls with height or radius) gets larger than the adiabatic gradient (the rate at which the temperature would fall if a volume of material were moved higher without adding heat).

Recently Extinct Megafauna Update

Dennis M. Hansen and Mauro Galetti write in Science:

Scientists have argued that in continental Central and South America, the extinction of the classic mammalian megafauna--such as giant ground sloths and gomphotheres--caused disruption of seed dispersal for large fruits (4, 5). However, on islands, the extinction of large birds and reptiles in the past two or three millennia has led to similar disruptions (8, 9). ....
[T]he largest frugivores in South America were gomphoteres (7580 kg), whereas the largest living frugivores are the tapirs (300 kg). On the continental island of Madagascar, the role of largest frugivore has passed from the elephant bird (450 kg) to the radiated tortoise (10 kg). On Mauritius, giant tortoises weighing up to 100 kg were the largest native frugivores; today, the title goes to a fruitbat weighing only 0.54 kg. Thus, the loss of the island giants--tortoises, lizards, and flightless birds such as the dodo that were once found on many islands--has, in relative terms, led to a greater megafaunal downsizing than the extinction of even the largest gomphotheres in South America.  ....
If all currently threatened vertebrate frugivores were to go extinct, the relative ecological shrinkage in many continental ecosystems would equal that of islands. For instance, if all threatened frugivores in South America were to go extinct, the largest remaining frugivore would be the howler monkey, weighing 9 kg--a factor of 700 less than the giant ground sloth. Even some islands stand to suffer further losses; in Mauritius, the largest nonthreatened native frugivore is the gray white-eye, a bird weighing a mere 0.009 kg.

Here are two gomphotheres -- which did have overlap with humans, with many now extinct or marginal fruit plants specialized for dispersal via them (see Janzen 1982 and more critically Howe 1985).  BTW, this is part of the backdrop for the 'Rewildering North America' movement (see also a critique of the movement). 

Update #1: some examples of megafauna fruit (not clear if these are all from South America and I'm not going to spend time figuring it out):

The Ground is not a good conductor

The ocean has most of the heat capacity linked to the climate system, with the ground playing a very second tier role, with 5% of the heat absorption of the oceans.  For instance Hugo Beltrami et. al., Continental heat gain in the global climate system, GEOPHYSICAL RESEARCH LETTERS 2002:

Recent estimates have shown the heat gained by the ocean, atmosphere, and cryosphere as 18.2 *10^22 J, 6.6 * 10^21 J, and 8.1 * 10^21 J, respectively over the past half-century. However, the heat gain of the lithosphere via a heat flux across the solid surface of the continents (29% of the Earth’s surface) has not been addressed. Here we calculate that component of Earth’s changing energy budget, using ground-surface temperature reconstructions for the continents. In the last half-century there was an average flux of 39.1 mW m^-2 across the land surface into the subsurface, leading to 9.1 * 10^21 J absorbed by the ground. The heat inputs during the last half-century into all the major components of the climate system—atmosphere, ocean, cryosphere, lithosphere-reinforce the conclusion that the warming during the interval has been global.

5% is actually higher than I would have guessed, which may illustrate how low ocean overturning and mixing is.  Some people do (low temporal resolution?) climate reconstruction from borehole temperature measurements, for instance Henry N. Pollack and Jason E. Smerdon, Borehole climate reconstructions: Spatial structure and hemispheric averages, JOURNAL OF GEOPHYSICAL RESEARCH 2004 or Henry N. Pollack and Shaopeng Huang, CLIMATE RECONSTRUCTION FROM SUBSURFACE TEMPERATURES, Annu. Rev. Earth Planet. Sci. 2000.  The guys who do climate reconstruction from measuring ice sheet temperature profiles get much higher resolution: D. Dahl-Jensen, et. al., Past Temperatures Directly from the Greenland Ice Sheet , Science 1998, which I thought was very very cool when it came out, and a nice illustration of how slow heat diffusion is:

Figure 3. The contour plots of all the GRIP temperature histograms as a function of time describes the reconstructed temperature history (red curve) and its uncertainty. The temperature history is the history at the present elevation (3240 m) of the summit of the Greenland Ice Sheet (21). The white curves are the standard deviations of the reconstruction (18). The present temperature is shown as a horizontal blue curve. The vertical colored bars mark the selected times for which the temperature histograms are shown in Fig. 2. (A) The last 100 ky BP. The LGM (25 ka) is seen to have been 23 K colder than the present temperature, and the temperatures are seen to rise directly into the warm CO 8 to 5 ka. (B) The last 10 ky BP. The CO is 2.5 K warmer than the present temperature, and at 5 ka the temperature slowly cools toward the cold temperatures found around 2 ka. (C) The last 2000 years. The medieval warming (1000 A.D.) is 1 K warmer than the present temperature, and the LIA is seen to have two minimums at 1500 and 1850 A.D. The LIA is followed by a temperature rise culminating around 1930 A.D. Temperature cools between 1940 and 1995.

Arguing Successfully in Public: The Plausible vs. The True

Since I'm on a climate change bender, here a comment from Julian Sanchez  about how the climate change debate works with anthropogenic climate change skeptics who come up with counterarguments:

Obviously, when it comes to an argument between trained scientific specialists, they ought to ignore the consensus and deal directly with the argument on its merits. But most of us are not actually in any position to deal with the arguments on the merits.  ...

Sometimes, of course, the arguments are such that the specialists can develop and summarize them to the point that an intelligent layman can evaluate them. But often...that’s just not the case. Give me a topic I know fairly intimately, and I can often make a convincing case for absolute horseshit. Convincing, at any rate, to an ordinary educated person with only passing acquaintance with the topic. A specialist would surely see through it, but in an argument between us, the lay observer wouldn’t necessarily be able to tell which of us really had the better case on the basis of the arguments alone—at least not without putting in the time to become something of a specialist himself.  Actually, I have a plausible advantage here as a peddler of horseshit: I need only worry about what sounds plausible. If my opponent is trying to explain what’s true, he may be constrained to introduce concepts that take a while to explain and are hard to follow, trying the patience (and perhaps wounding the ego) of the audience.

Come to think of it, there’s a certain class of rhetoric I’m going to call the “one way hash” argument. Most modern cryptographic systems in wide use are based on a certain mathematical asymmetry: You can multiply a couple of large prime numbers much (much, much, much, much) more quickly than you can factor the product back into primes. Certain bad arguments work the same way—skim online debates between biologists and earnest ID afficionados armed with talking points if you want a few examples: The talking point on one side is just complex enough that  it’s both intelligible—even somewhat intuitive—to the layman and sounds as though it might qualify as some kind of insight. (If it seems too obvious, perhaps paradoxically, we’ll tend to assume everyone on the other side thought of it themselves and had some good reason to reject it.) The rebuttal, by contrast, may require explaining a whole series of preliminary concepts before it’s really possible to explain why the talking point is wrong. So the setup is “snappy, intuitively appealing argument without obvious problems” vs. “rebuttal I probably don’t have time to read, let alone analyze closely.”

If we don’t sometimes defer to the expert consensus, we’ll systematically tend to go wrong in the face of one-way-hash arguments, at least our own necessarily limited domains of knowledge.  Indeed, in such cases, trying to evaluate the arguments on their merits will tend to lead to an erroneous conclusion more often than simply trying to gauge the credibility of the various disputants. The problem, of course, is gauging your own competence level well enough to know when to assess arguments and when to assess arguers. Thanks to the perverse phenomenon psychologists have dubbed the Dunning-Kruger effect,  those who are least competent tend to have the most wildly inflated estimates of their own knowledge and competence. They don’t know enough to know that they don’t know, as it were. 

You get the same sort of problem with economics debates once they hit a wider audience.   And there is also a feedback where skeptics tear into popularized presentations of academic experts designed to appeal to a lay audience on grounds of plausibility and find, surprise, lots of omissions, sloppy arguments, misstatements or worse, and the skeptics conclude from this the experts are either clueless or deceptive, in either case not to be trusted as authorities.

On the other hand, there are academic fields, mostly in the humanities but not limited to the humanities, that do occasionally go off on dead ends where 'truth' is defined in a somewhat self-referential manner that does occasionally need to be overthrown.  Still, real subject matter outsiders aren't able to do so, while some institutional outside status does at times help.  More later...

Update #1: David comments

I really liked this post. It's important and very hard to explain why intelligent discourse is so hard, even impossible. The heuristics that we need to get through life also can make it impossible to correctly understand what's going on.
I have these sort of arguments with global-warming "skeptics" all the time. I admit that I'm not an expert either, of course. I just have better heuristics, I think.
There's only a couple of things that I might qualify myself as an expert. Even then, I sometimes can't convince people.
Come to think of it, these sort of problems are present in medical debates too.
What I'm missing is how to improve the situation. Any ideas?

I thought you might like the post and see the analogy to medical debates.  I don't know how to improve the situation -- I don't want to suggest developing better skills to exploit this problem, though that is what public relations and marketing is about, and to some extent career advancement in organizations.  Decisions get made all the time by people who miss out on very important context that they are simply unaware of and which cannot be communicated to them efficiently by experts.   Views that are not pre-marketed then don't fall on fertile ground and get filtered out by time-constrained decision makers looking for solutions that, well, look like neat solutions that fit preexisting understandings and organizational contexts, not further complications that are going to result in the need to reorganize things that currently don't look like they need reorganization. 

How to deal with climate skeptics?  I don't run into any in my world.  I do run into climate model skeptics -- I am one in some ways --, but they also understand that model uncertainty combined with greater climate forcing via CO2 should make one more cautious about putting more forcing into the climate system.  So I have no experience with climate skeptics.  But I would suggest you push exactly this view: we are increasing very persistent climate forcing quite a bit in a system with lots of positive and at times slow feedbacks that we don't understand all that well, which should make us cautious about doing more of it.  The more you're a skeptic about how good the modeling is, the more cautious you should be about CO2 emissions.  My world if full of people who build and use models, and model skepticism is our daily bread.  It isn't model nihilism.  If we know we're kicking a system hard and don't have a good reason to believe it will take the kicking well we don't rely on 'well, nothing bad happened recently before we kicked it hard so nothing bad will happen because that would suck' thinking. [1]

The only out here for the climate skeptic is that the climate forcing effect of CO2 is much lower than the standard calculation or 'there is no CO2 greenhouse effect'.  I don't know if you've run into this and it is hard to counter without recounting lots of hard big science radiative transfer physics done in the 1940-70 period, stuff I now want to read up on.  The physics is hard enough that good physicists got it wrong for quite some time. (see this recent post) 

[1] Though we -- or rather our employers --  may take the fees we get for kicking the system, but that's because it is money, not because we are sure about the modeling.  That's a topic for another post.  

Update #2: Doug comments:

I'm something of a climate model skeptic, too (though not of anthropogenic explanations for climate changes). I am particularly skeptical of claims of economic harm that are grafted onto somewhat dubious climate models. Anyone who is claiming to have an "estimated" dollar figure for the welfare impacts from climate change a century from now should probably have his/her license to practice economics revoked.

At the same time, we make social choices all the time that involve spending real resources today to avert potential but uncertain -- and even unlikely -- harm in the future. For example, a lot of the same politicians who oppose spending money on climate remediation have vocally advocated spending money on missile defense. In both cases, we are talking about allocating real resources to avert low probability (but very bad) outcomes at some uncertain future date. And in both cases, the science is a bit sketchy.

To offer a couple of other examples, we devote a lot of social resources to medical research and military research in areas where the success probabilities may be low but the potential payoffs are large.

In my mind, a high degree of skepticism about climate change models and impacts is not inconsistent with believing that we need to take strong action fairly soon. What I don't understand is why so many of the climate change skeptics have trouble understanding this. You could have a constructive argument over how much to spend on remediation today, or about what the decision tree should look like. But even if you don't believe that the case is proven that people cause climate change and that climate change is harmful, you should probably believe that there is some possibility that both claims are true. And if so, you should be willing to act on that possibility.

Clouds

V. Ramanathan writes

Extra-tropical storm track cloud systems provide about 60% of the total cooling effect of clouds [6]. The annual mean forcing from these cloud systems is in the range of –45 to –55 W m–2 and effectively these cloud systems are shielding both the northern and the southern polar regions from intense radiative heating. Their spatial extent towards the tropics moves with the jet stream, extending farthest towards the tropics (about 35 deg latitude) during winter and retreating polewards (polewards of 50 deg latitude) during summer. This phenomenon raises an important question related to past climate dynamics.
During the ice age, due to the large polar cooling, the northern hemisphere jet stream extended more southwards. But have the extra tropical cloud systems also moved southward? The increase in the negative forcing would have exerted a major positive feedback on the ice age cooling. There is a curious puzzle about the existence of these cooling clouds. The basic function of the extra tropical dynamics is to export heat polewards.
While the baroclinic systems are efficient in transporting heat, the enormous negative radiative forcing (Fig. 2) associated with these cloud systems seems to undo the poleward transport of heat by the dynamics. The radiative effect of these systems is working against the dynamical effect. Evidently, we need better understaning of the dynamic- thermodynamic coupling between these enormous cooling clouds and the equator-pole temperature gradient, and greenhouse forcing.
Another major interesting feature in Fig. 2 is the smaller forcing over the highly reflective (high albedo) tropical cloud systems. It is well known that over the western tropical Pacific, equatorial Africa, South America, and the monsoon regions of Asia, deep cumulonimbus- cirrus systems give rise to extensive high albedo clouds, but Fig. 2 does not show this cooling effect. The fundamental reason is that the greenhouse effect of these cloud systems are very large (because their tops are located in the cold upper troposphere) and the large positive forcing from the cloud greenhouse effect nearly cancels out the large negative forcing from the high albedo of these clouds.  ...

While the atmospheric circulation determines the location and extent of clouds and water content, aerosols are the nuclei for cloud drops and thus determine the size and number distribution of cloud drops. The aerosol properties, in turn, are determined by the chemistry (e.g. oxidation of sulfur dioxide) and the biology (dimethyl sulfide and organics). The aerosol-cloud interactions in turn determine the precipitation efficiency of clouds and thus regulate lifetimes and spatial extent of clouds. All of these parameters including the aerosol concentration and composition undergo significant temporal (minutes to years) and spatial (meters to planetary scales) variations. It is remarkable that general circulation climate models (GCMs) are able to explain the observed temperature variations during the last century solely through variations in greenhouse gases, volcanoes and solar constant. This implies that the cloud contribution to the planetary albedo due to feedbacks with natural and forced climate changes has not changed during the last 100 years by more than ±0.3%; i.e, the cloud forcing has remained constant within ±1 Wm–2. If indeed, the global cloud properties and their influence on the albedo are this stable (as asserted by GCMs), scientists need to validate this prediction and develop a theory to account for the stability.

I'm not sure what Ramanathan means when he writes that "If indeed, the global cloud properties and their influence on the albedo are this stable (as asserted by GCMs), scientists need to validate this prediction and develop a theory to account for the stability" --- if the GCMs predict this, why do we need theory?  Better intuition might be helpful, but I don't see why we need a theory.  On the other hand, it would be nice to know if this stability is there outside of the 20th century, for times when we don't have good observational data and in which the models may break down.  For the most part, this seems like Ramanathan saying he doesn't trust the models here and thinks (correctly?) that the modeling community may have gotten lucky or fooled itself by calibrating models to get this fact just right without actually getting the physics right. 

Ramanathan was Chair of the NAS Committee on Strategic Advice on the US Climate Change Science Program, so he has some standing. 

Half of all mammal species heavier than 100 lbs extinct

Barry Brook writes introducing one of his papers on the the relative contribution of people and climate in driving the late Pleistocene and Holocene megafauna extinctions:

End-Quaternary (late Pleistocene and Holocene) extinctions eliminated half of all mammal species heavier than 44 kg (100 lbs) and other large-bodied fauna across most continents (Australia, Eurasia, North and South America) and large islands (West Indies, Madagascar and New Zealand), between 50,000 and 600 years before present. The losses included large mammals (e.g., mammoth, giant wombats), reptiles (e.g. huge monitor lizards about three times bigger than Komodo dragons), and massive flightless birds (e.g. moa, Elephant birds).

How the US Military-Industrial Complex discovered Global Warming

Just musing about a title for a possible blog post.  The US military did fund good geo- and atmospheric physics research, especially for understanding atmospheric physics. Though it may be more the military research side of the complex than the private industrial side.  Which reminds me that the Office of Naval Research is still the lead auditor for Harvard's federal grants:

Harvard University receives approximately $500 million annually in Federal research funds and is required to maintain a Federally approved purchasing system. An approved purchasing system complies with Federal procurement regulations and internal purchasing policies and procedures. The Office of Naval Research (ONR) conducts a Contractor Procurement Systems Review (CPSR) at Harvard every three years to evaluate compliance.

When did this start at Harvard?

In any case, for global warming research the Office of Naval Research's support of Roger Revelle at Scripps one of the big contributions of the military supported research in overcoming the view that

the oceans would absorb any excess gases that came into the atmosphere. Fifty times more carbon is dissolved in sea water than in the wispy atmosphere. Thus the oceans would determine the equilibrium concentration of CO2, and it would not easily stray from the present numbers.

First step here: blow up some nuclear weapons in the Pacific. 

Greenhouse Effect History of Thought

One argument that shows up in global warming denial discourse is that CO2 cannot matter since a) CO2 is an efficient absorber of IR radiation and adding more CO2 cannot make the greenhouse blanket over the earth any thicker, b) CO2 absorbs in the same spectral bands as water, so again adding more CO2 cannot matter.  In short, CO2 and water do create a greenhouse effect, but it cannot be pushed further by more CO2. 

An interesting aspect of this is that exactly these objections kept the initial global warming theory of Svante Arrhenius from becoming established science back around 1900 (even though Arrhenius did win the Nobel Prize for Chemistry in 1903 and had a good platform to work from, even writing a popularizing book on the topic).  In particular, as described in an AIP retrospective:

Experts could dismiss the hypothesis because they found Arrhenius's calculation implausible on many grounds. In the first place, he had grossly oversimplified the climate system. Among other things, he had failed to consider how cloudiness might change if the Earth got a little warmer and more humid.(6) A still weightier objection came from a simple laboratory measurement. A few years after Arrhenius published his hypothesis, another scientist in Sweden, Knut Ångström, asked an assistant to measure the passage of infrared radiation through a tube filled with carbon dioxide. The assistant ("Herr J. Koch," otherwise unrecorded in history) put in rather less of the gas in total than would be found in a column of air reaching to the top of the atmosphere. The assistant reported that the amount of radiation that got through the tube scarcely changed when he cut the quantity of gas back by a third. Apparently it took only a trace of the gas to "saturate" the absorption — that is, in the bands of the spectrum where CO2 blocked radiation, it did it so thoroughly that more gas could make little difference.(7*)

Still more persuasive was the fact that water vapor, which is far more abundant in the air than carbon dioxide, also intercepts infrared radiation. In the crude spectrographs of the time, the smeared-out bands of the two gases entirely overlapped one another. More CO2 could not affect radiation in bands of the spectrum that water vapor, as well as CO2 itself, were already blocking entirely.(8)

These measurements and arguments had fatal flaws. Herr Koch had reported to Ångström that the absorption had not been reduced by more than 0.4% when he lowered the pressure, but a modern calculation shows that the absorption would have decreased about 1% — like many a researcher, the assistant was over confident about his degree of precision.(8a) But even if he had seen the1% shift, Ångström would have thought this an insignificant perturbation. He failed to understand that the logic of the experiment was altogether false.

The greenhouse effect will in fact operate even if the absorption of radiation were totally saturated in the lower atmosphere. The planet's temperature is regulated by the thin upper layers where radiation does escape easily into space. Adding more greenhouse gas there will change the balance. Moreover, even a 1% change in that delicate balance would make a serious difference in the planet’s surface temperature. The logic is rather simple once it is grasped, but it takes a new way of looking at the atmosphere — not as a single slab, like the gas in Koch's tube (or the glass over a greenhouse), but as a set of interacting layers.

As the AIP retrospective explains in a separate section:

Not until the mid-20th century would scientists fully grasp, and calculate with some precision, just how the effect works. A rough explanation goes like this. Visible sunlight penetrates easily through the air and warms the Earth’s surface. When the surface emits invisible infrared heat radiation, this radiation too easily penetrates the main gases of the air. But as Tyndall found, even a trace of CO2, no more than it took to fill a bottle in his laboratory, is almost opaque to heat radiation. Thus a good part of the radiation that rises from the surface is absorbed by CO2 in the middle levels of the atmosphere. Its energy transfers into the air itself rather than escaping directly into space. Not only is the air thus warmed, but also some of the energy trapped there is radiated back to the surface, warming it further.

That’s a shorthand way of explaining the greenhouse effect — seeing it from below, from "inside" the atmosphere. Unfortunately, shorthand arguments can be misleading if you push them too far. Fourier, Tyndall and most other scientists for nearly a century used this approach, looking at warming from ground level, so to speak, asking about the radiation that reaches and leaves the surface of the Earth. So they tended to think of the atmosphere overhead as a unit, as if it were a single sheet of glass. (Thus the "greenhouse" analogy.) But this is not how global warming actually works, if you look at the process in detail.

What happens to infrared radiation emitted by the Earth's surface? As it moves up layer by layer through the atmosphere, some is stopped in each layer. (To be specific: a molecule of carbon dioxide, water vapor or some other greenhouse gas absorbs a bit of energy from the radiation. The molecule may radiate the energy back out again in a random direction. Or it may transfer the energy into velocity in collisions with other air molecules, so that the layer of air where it sits gets warmer.) The layer of air radiates some of the energy it has absorbed back toward the ground, and some upwards to higher layers. As you go higher, the atmosphere gets thinner and colder. Eventually the energy reaches a layer so thin that radiation can escape into space. What happens if we add more carbon dioxide? In the layers so high and thin that much of the heat radiation from lower down slips through, adding more greenhouse gas means the layer will absorb more of the rays. So the place from which most of the heat energy finally leaves the Earth will shift to higher layers. Those are colder layers, so they do not radiate heat as well. The planet as a whole is now taking in more energy than it radiates (which is in fact our current situation). As the higher levels radiate some of the excess downwards, all the lower levels down to the surface warm up. The imbalance must continue until the high levels get warmer and radiate out more energy. As in Tyndall's analogy of a dam on a river, the barrier thrown across the outgoing radiation forces the level of temperature everywhere beneath it to rise until there is enough radiation pushing out to balance what the Sun sends in.

While that may sound fairly simple once it is explained, the process is not obvious if you have started by thinking of the atmosphere from below as a single slab. The correct way of thinking eluded nearly all scientists for more than a century after Fourier. Physicists learned only gradually how to describe the greenhouse effect. To do so, they had to make detailed calculations of a variety of processes in each layer of the atmosphere.

Finally:

The subtle difference did not occur to anyone for many decades, if only because hardly anyone thought the greenhouse effect was worth their attention. For after Ångström published his conclusions in 1900, the few scientists who had taken an interest in the matter concluded that Arrhenius's hypothesis had been proven wrong. Theoretical work on the question stagnated for decades, and so did measurement of the level of CO2 in the atmosphere.(9)

A few scientists dissented from the view that changes of CO2 could have no effect. An American physicist, E.O. Hulburt, pointed out in 1931 that investigators had been mainly interested in pinning down the intricate structure of the absorption bands (which offered fascinating insights into the new theory of quantum mechanics) "and not in getting accurate absorption coefficients." Hulburt's own calculations supported Arrhenius's estimate that doubling or halving CO2 would bring something like a 4°C rise or fall of surface temperature, and thus "the carbon dioxide theory of the ice ages... is a possible theory."(10*) Hardly anyone noticed this paper. Hulburt was an obscure worker at the U.S. Naval Research Laboratory, and he published in a journal, the Physical Review, that few meteorologists read. Their general consensus was the one stated in such authoritative works as the American Meteorological Society's 1951 Compendium of Meteorology: the idea that adding CO2 would change the climate "was never widely accepted and was abandoned when it was found that all the long-wave radiation [that would be] absorbed by CO2 is [already] absorbed by water vapor."(11)

Or as James R. Fleming writes:

By 1929, G.C. Simpson had pointed out that it was "now generally accepted that variations in carbon-dioxide in the atmosphere, even if they do occur, can have no appreciable effect on the climate." Simpson provided three reasons why this was so: (1) The absorption band of carbon dioxide is too narrow to have a significant effect on terrestrial radiation; (2) The current amount of atmospheric carbon dioxide exerts its full effect and any further addition would have little or no influence; and (3) The water vapor absorption band overlaps and dominates the carbon dioxide band. Such negative assessments of the carbon dioxide theory reached wide audiences through articles on climate change in the U.S.D.A. Yearbook for 1941 and in the Compendium of Meteorology in 1951.

After a few isolated pre-WWII attempts at figuring out how atmospheric radiative equilibrium worked, WWII and especially the early Cold War with the needs of the Air Force and military funding for research lead researchers, including astrophysicists, to start figuring out how multilayer models of the atmosphere work. 

Update #1: I've been looking for a nice popular write up of how the greenhouse effect responds to CO2 forcing in terms of how it raises the emission height at the tropopause...but annoyingly, I cannot find one.  Nor can I find my standard Climate Modeling book in my basement, though I did find Thomas and Stamnes, Radiative Transfer in Atmosphere and Ocean.  But they don't seem to have short intuitive treatment.  

Climate Change Link Dump

David Archer & Victor Brovkin, The millennial atmospheric lifetime of anthropogenic CO2, Climatic Change (2008)

The notion is pervasive in the climate science community and in the public at large that the climate impacts of fossil fuel CO2 release will only persist for a few centuries. This conclusion has no basis in theory or models of the atmosphere/ocean carbon cycle, which we review here. The largest fraction of the CO2 recovery will take place on time scales of centuries, as CO2 invades the ocean, but a significant fraction of the fossil fuel CO2, ranging in published models in the literature from 20–60%, remains airborne for a thousand years or longer. Ultimate recovery takes place on time scales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste. The glacial/interglacial climate cycles demonstrate that ice sheets and sea level respond dramatically to millennial-timescale changes in climate forcing. There are also potential positive feedbacks in the carbon cycle, including methane hydrates in the ocean, and peat frozen in permafrost, that are most sensitive to the long tail of the fossil fuel CO2 in the atmosphere.

Alvaro Montenegro et.al., Long term fate of anthropogenic carbon, Geophy Res Let 2007

Two earth-system models of intermediate complexity are used to study the long term response to an input of 5000 Pg of carbon into the atmosphere. About 75% of CO2 emissions have an average perturbation lifetime of 1800 years and 25% have lifetimes much longer than 5000 years. In the simulations, higher levels of atmospheric CO2 remain in the atmosphere than predicted by previous experiments and the average perturbation lifetime of atmospheric CO2 for this level of emissions is much longer than the 300–400 years proposed by other studies. At year 6800, CO2 concentrations between about 960 to 1440 ppmv result in global surface temperature increases between 6C and 8C. There is also significant surface ocean acidification, with pH decreasing from 8.16 to 7.46 units between years 2000 and 2300.

Gerard H. Roe and Marcia B. Baker, Why Is Climate Sensitivity So Unpredictable? Science 2007 [supporting material]

Uncertainties in projections of future climate change have not lessened substantially in past decades. Both models and observations yield broad probability distributions for long-term increases in global mean temperature expected from the doubling of atmospheric carbon dioxide, with small but finite probabilities of very large increases. We show that the shape of these probability distributions is an inevitable and general consequence of the nature of the climate system, and we derive a simple analytic form for the shape that fits recent published distributions very well. We show that the breadth of the distribution and, in particular, the probability of large temperature increases are relatively insensitive to decreases in uncertainties associated with the underlying climate processes.

Reto Knutti and Gabriele C. Hegerl, The equilibrium sensitivity of the Earth’s temperature to radiation changes, Nature Geoscience 2008

The Earth’s climate is changing rapidly as a result of anthropogenic carbon emissions, and damaging impacts are expected to increase with warming. To prevent these and limit long-term global surface warming to, for example, 2 °C, a level of stabilization or of peak atmospheric CO2 concentrations needs to be set. Climate sensitivity, the global equilibrium surface warming after a doubling of atmospheric CO2 concentration, can help with the translation of atmospheric CO2 levels to warming. Various observations favour a climate sensitivity value of about 3 °C, with a likely range of about 2–4.5 °C. However, the physics of the response and uncertainties in forcing lead to fundamental difficulties in ruling out higher values. The quest to determine climate sensitivity has now been going on for decades, with disturbingly little progress in narrowing the large uncertainty range. However, in the process, fascinating new insights into the climate system and into policy aspects regarding mitigation have been gained. The well-constrained lower limit of climate sensitivity and the transient rate of warming already provide useful information for policy makers. But the upper limit of climate sensitivity will be more difficult to quantify.

Margaret B. Davis and Ruth G. Shaw, Range Shifts and Adaptive Responses to Quaternary Climate Change, Science 2001

Tree taxa shifted latitude or elevation range in response to changes in Quaternary climate. Because many modern trees display adaptive differentiation in relation to latitude or elevation, it is likely that ancient trees were also so differentiated, with environmental sensitivities of populations throughout the range evolving in conjunction with migrations. Rapid climate changes challenge this process by imposing stronger selection and by distancing populations from environments to which they are adapted. The unprecedented rates of climate changes anticipated to occur in the future, coupled with land use changes that impede gene ßow, can be expected to disrupt the interplay of adaptation and migration, likely affecting productivity and threatening the persistence of many species.

Petit et. al., Glacial Refugia: Hotspots But Not Melting Pots of Genetic Diversity, Science 2003

Glacial refuge areas are expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. To test this hypothesis, we studied chloroplast DNA variation in 22 widespread European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. However, the genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugia.

Godfrey Hewitt, The genetic legacy of the Quaternary ice ages, Nature 2000

Global climate has fluctuated greatly during the past three million years, leading to the recent major ice ages. An inescapable consequence for most living organisms is great changes in their distribution, which are expressed differently in boreal, temperate and tropical zones. Such range changes can be expected to have genetic consequences, and the advent of DNA technology provides most suitable markers to examine these. Several good data sets are now available, which provide tests of expectations, insights into species colonization and unexpected genetic subdivision and mixture of species. The genetic structure of human populations may be viewed in the same context. The present genetic structure of populations, species and communities has been mainly formed by Quaternary ice ages, and genetic, fossil and physical data combined can greatly help our understanding of how organisms were so affected.

John W Williams and Stephen T Jackson, Novel climates, no-analog communities, and ecological surprises, Front Ecol Environ 2007;

No-analog communities (communities that are compositionally unlike any found today) occurred frequently in the past and will develop in the greenhouse world of the future. The well documented no-analog plant communities of late-glacial North America are closely linked to “novel” climates also lacking modern analogs, characterized by high seasonality of temperature. In climate simulations for the Intergovernmental Panel on Climate Change A2 and B1 emission scenarios, novel climates arise by 2100 AD, primarily in tropical and subtropical regions. These future novel climates are warmer than any present climates globally, with spatially variable shifts in precipitation, and increase the risk of species reshuffling into future no-analog communities and other ecological surprises. Most ecological models are at least partially parameterized from modern observations and so may fail to accurately predict ecological responses to these novel climates. There is an urgent need to test the robustness of ecological models to climate conditions outside modern experience.

Stephen T. Jackson and Chengyu Weng, Late Quaternary extinction of a tree species in eastern North America, PNAS 1999

Widespread species- and genus-level extinctions of mammals in North America and Europe occurred during the last deglaciation [16,000–9,000 yr B.P. (by 14C)], a period of rapid and often abrupt climatic and vegetational change. These extinctions are variously ascribed to environmental change and overkill by human hunters. By contrast, plant extinctions since the Middle Pleistocene are undocumented, suggesting that plant species have been able to respond to environmental changes of the past several glacialy interglacial cycles by migration. We provide evidence from morphological studies of fossil cones and anatomical studies of fossil needles that a now-extinct species of spruce (Picea critchfieldii sp. nov.) was widespread in eastern North America during the Last Glacial Maximum. P. critchfieldii was dominant in vegetation of the Lower Mississippi Valley, and extended at least as far east as western Georgia. P. critchfieldii disappeared during the last deglaciation, and its extinction is not directly attributable to human activities. Similarly widespread plant species may be at risk of extinction in the face of future climate change.

C.W. Woodall at. al., An indicator of tree migration in forests of the eastern United States, Forest Ecology and Management 2009

Changes in tree species distributions are a potential impact of climate change on forest ecosystems. The examination of tree species shifts in forests of the eastern United States largely has been limited to simulation activities due to a lack of consistent, long-term forest inventory datasets. The goal of this study was to compare current geographic distributions of tree seedlings (trees with a diameter at breast height <2.5 cm) with biomass (trees with a diameter at breast height > 2.5 cm) for sets of northern, southern, and general tree species in the eastern United States using a spatially balanced, region-wide forest inventory. Compared to mean latitude of tree biomass, mean latitude of seedlings was significantly farther north (>20 km) for the northern study species, while southern species had no shift, and general species demonstrated southern expansion. Density of seedlings relative to tree biomass of northern tree species was nearly 10 times higher in northern latitudes compared to southern latitudes. For forest inventory plots between 448 and 478 north latitude where southern tree species were identified, their biomass averaged 0.46 tonnes/ha while their seedling counts averaged 2600 ha-1. It is hypothesized that as northern and southern tree species together move northward due to greater regeneration success at higher latitudes, general species may fill their vacated niches in southern locations. The results of this study suggest that the process of northward tree migration in the eastern United States is currently underway with rates approaching 100 km/century for many species.

Global Warming Commitment by Emissions up to Today

The standard models indicate that the long-persistence fraction of emissions already made up to today commits us to global warming for the long-run, most of which is not yet realized.  See, for instance, the first graph in Ramanathan and Feng, On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead, PNAS 2008, showing the probability distribution for current models of where we'll end up if we stop emitting today.  Note the list of threshold temperatures for different effects.  I've not figured out what long-term feedbacks are included or excluded here.  For instance, I suspect changes in the themohaline circulation or the cores of large ice sheets aren't included, and some vegetation changes may also be excluded.  And this just emissions up to now -- we could put four times this amount into the air in the next 100 years.  [See also Susan Solomon, Gian-Kasper Plattner, Reto Knutti, and Pierre Friedlingstein, Irreversible climate change due to carbon dioxide emissions, PNAS 2009, which puts assumptions in Ramanathan and Feng in context. Hans Joachim Schellnhuber, Global warming: Stop worrying, start panicking? discusses Ramanathan and Feng.  Finally, Timothy M. Lenton et. al., Tipping elements in the Earth’s climate system, PNAS 2008.]

Climate Change

I'm on a climate change reading binge, with several preliminary observations that might be interesting to blog about, but learning quite a bit about the literature is keeping me busy enough.

My gut feeling on going into this reading binge is that insufficient attention is paid to long-run --  meaning more than 100 or more than 1000 year -- effects of carbon emissions today, given the long persistence of CO2 in the climate system (about 25% of carbon emitted into the atmosphere persists as a higher carbon concentration in the atmosphere 10,000 years out in standard models), bad tail effects, given the difficulty of ruling out high climate sensitivities with all feedbacks asymptotically (the standard quoted sensitivity appears to be for a medium range sensitivity excluding slow feedbacks [1]). In terms of my policy preferences I don't really care much about what the climate change in the next few decades is going to be, except to the extent we learn about the earth's behavior and the political effects this has, since these effects are relatively small and mostly predetermined by now compared to what might be coming later.  I also have the sense that a bit of well mitigated warming might not even be bad, but after a bit of warming things will get much more interesting and may have big downsides that are much harder to adapt to. 

[1] See Gavin Schmidt:

First, it probably needs to be made clearer that generally speaking radiative forcing and climate sensitivity are useful constructs that apply to a subsystem of the climate and are valid only for restricted timescales - the atmosphere and upper ocean on multi-decadal periods. This corresponds in scope (not un-coincidentally) to the atmospheric component of General Circulation Models (GCMs) coupled to (at least) a mixed-layer ocean. For this subsystem, many of the longer term feedbacks in the full climate system (such as ice sheets, vegetation response, the carbon cycle) and some of the shorter term bio-geophysical feedbacks (methane, dust and other aerosols) are explicitly excluded. Changes in these excluded features are therefore regarded as external forcings.

Why this subsystem? Well, historically it was the first configuration in which projections of climate change in the future could be usefully made. More importantly, this system has the very nice property that the global mean of instantaneous forcing calculations (the difference in the radiation fluxes at the tropopause when you change greenhouse gases or aerosols or whatever) are a very good predictor for the eventual global mean response. It is this empirical property that makes radiative forcing and climate sensitivity such useful concepts. For instance, this allows us to compare the global effects of very different forcings in a consistent manner, without having to run the model to equilibrium every time.

Which means there might be some nasty non-linear action in the longer term feedbacks.  Also note that sensitivities look like s = 1/(1-f_1 - f_2 - ...), so even small additional long-run feedbacks start becoming important once medium-run sensitivity is already high, so non-linearities are pretty much globally built in here. I need to look into this more to see if I have this right.

Schmidt continues:

To see why a more expansive system may not be as useful, we can think about the forcings for the ice ages themselves. These are thought to be driven by the large regional changes in insolation driven by orbital changes. However, in the global mean, these changes sum to zero (or very close to it), and so the global mean sensitivity to global mean forcings is huge (or even undefined) and not very useful to understanding the eventual ice sheet growth or carbon cycle feedbacks. ....

So in order to constrain the climate sensitivity from the paleo-data, we need to find a period under which our restricted subsystem is stable - i.e. all the boundary conditions are relatively constant, and the climate itself is stable over a long enough period that we can assume that the radiation is pretty much balanced. The last glacial maximum (LGM) fits this restriction very well, and so is frequently used as a constraint. From at least Lorius et al (1991) - when we first had reasonable estimates of the greenhouse gases from the ice cores, to an upcoming paper by Schneider von Deimling et al, where they test a multi-model ensemble (1000 members) against LGM data to conclude that models with sensitivities greater than about 4.3ºC can't match the data. In posts here, I too have used the LGM constraint here to demonstrate why extremely low (< 1ºC) or extremely high (> 6ºC) sensitivities can probably be ruled out.

But extremely high sensitivities are ruled out only if 'all the boundary conditions are relatively constant'.  Which begs the question of what the long-run effects that we are committing ourselves to now are. And to the extent the relevant boundary conditions are going to change, they are going to change in a direction the earth system hasn't explored for at least 4 million years, a warmer earth that has a different geography (i.e. sufficiently different ocean basins, especially in the arctic, and sufficiently different mountain ranges, especially Himalayan height) than when it last encountered these temperatures and CO2 forcings. We know what this earth does when it gets colder and can assess climate sensitivities with some confidence based on historical data.  More than 1C warmer -- or are we there already? -- and we're in different territory. 

The Green Wet Sahara

One thing you'll notice if you look at the world map of forest cover and extreme desert during the last glacial maximum from my post yesterday is that the Sahara is, well, extreme desert, more extreme than today extending further south.  So when was the green wet Sahara of lore? 

Turns out the 'green wet Sahara' -- not that green, green here means savannah and not desert --  was in the period immediately after the Ice age until before the beginnings of Ancient Egypt. See for instance Rudolph Kuper and Stefan Kropelin, Climate-Controlled Holocene Occupation in the Sahara: Motor of Africa’s Evolution, Science 2006:

Radiocarbon data from 150 archaeological excavations in the now hyper-arid Eastern Sahara of Egypt, Sudan, Libya, and Chad reveal close links between climatic variations and prehistoric occupation during the past 12,000 years. Synoptic multiple-indicator views for major time slices demonstrate the transition from initial settlement after the sudden onset of humid conditions at 8500 B.C.E. to the exodus resulting from gradual desiccation since 5300 B.C.E. Southward shifting of the desert margin helped trigger the emergence of pharaonic civilization along the Nile, influenced the spread of pastoralism throughout the continent, and affects sub-Saharan Africa to the present day.  ...

During the Allerod interstadial (about 11,900 to 10,800 B.C.E.), when Northwest Europe witnessed temporarily waning ice sheets, and the following Younger Dryas, the final cold phase of the Pleistocene, the Eastern Sahara was still void of any aquatic environments and as hyper-arid as it was during the Last Glacial Maximum at 20,000 B.C.E. The first signal of a changing climate occurred in the early Preboreal with the establishment of postglacial conditions in the mid-latitudes, supported by evidence of a sudden appearance of carbonate lake formations in the Sudanese Sahara and of siliceous mud deposits in the Egyptian Sahara.
Radiocarbon dates of the base levels of these paleolakes and playa-type rain pools reveal the almost contemporaneous onset of pluvial conditions between latitudes 16-N and 24-N at about 8500 B.C.E., indicating an abrupt northward shift of the tropical rainfall belts over as much as 800 km within just several generations (7, 8). This decisive climate change can be attributed to tropical summer rains owing to a major extension of the paleomonsoon system, whereas the contribution of Mediterranean winter rain systems north of 24-N remains vague. As a result, notably improved environmental conditions spread over the entire Eastern Sahara (7–15), with semihumid climates in its southern part and semi-arid conditions in its center.

One question, which I'll try to discuss later, is why we are not, it seems, seeing a wetter Sahara now, if only briefly, with increased CO2 climate forcing, reversing the drying of the Sahara since 5,300 BCE that accompanied global cooling since that time.   

Update #1: see also S. Kröpelin et. al. Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years, Science 206. 

Update #2: Timothy M. Lenton et. al., Tipping elements in the Earth’s climate system, PNAS 2008 discusses the future:

Sahara/Sahel and West African Monsoon (WAM). Past greening of the Sahara occurred in the mid-Holocene (71–73) and may have happened rapidly in the earlier Bo¨lling-Allerod warming. Collapse of vegetation in the Sahara 5,000 years ago occurred more rapidly than orbital forcing (71, 72). The system has been modeled and conceptualized in terms of bistable states that are maintained by vegetation–climate feedback (71, 74). However, it is intimately tied to the WAM circulation, which in turn is affected by sea surface temperatures (SSTs), particularly antisymmetric patterns between the Hemispheres. Greenhouse gas forcing is expected to increase the interhemispheric SST gradient and thereby increase Sahel rainfall; hence, the recent Sahel drought has been attributed to increased aerosol loading cooling the Northern Hemisphere (75). Future 21st century projections differ (75, 76); in two AOGCMs, the WAMcollapses, but in one this leads to further drying of the Sahel, whereas in the other it causes wetting due to increased inflow from the West. The latter response is more mechanistically reasonable, but it requires a 3°C warming of SSTs in the Gulf of Guinea (76). A third AOGCM with the most realistic present-day WAM predicts no large trend in mean rainfall but a doubling of the number of anomalously dry years by the end of the century (76). If the WAM is disrupted such that there is increased inflow from the West (76), the resulting moisture will wet the Sahel and support greening of the Sahara, as is seen in mid-Holocene simulations (73). Indeed, in an intermediate complexity model, increasing atmospheric CO2 has been predicted to cause future expansion of grasslands into up to 45% of the Sahara, at a rate of up to 10% of Saharan area per decade (11). In the Sahel, shrub vegetation may also increase due to increased water use efficiency (stomatal closure) under higher atmospheric CO2 (77). Such greening of the Sahara/Sahel is a rare example of a beneficial potential tipping element.

Forest Cover during the Last Glacial Maximum

I'd not realized how little forest cover there was during the last glacial maximum, worldwide and especially in Europe.(image below, also here)  Very small forest enclaves in the Southern Alps (or their foothills) and Carpathia, from which Europe's forests were  recolonized.  I do remember reading a few times that the ecological communities of today did not exist during the LGM and assembled from different sources afterward, instead of migrating together.  Conversely, ecological communities of the LGM don't exist today. It wold be nice to know more. 

Also note the massive reduction in forest cover in the Amazon and Africa. 

Ah, here is more:

Some areas of woodland present. In southern Europe, some areas of open pine (Pinus) and birch (Betula) woodland seem to have existed in the plains of northern Italy and to the south-east of the Alps, although these were not extensive (C. Tzedakis, August 1995). Scattered pockets of woodland or isolated trees occurred through the mid-altitudes (e.g. with a belt about 500m above [present] sea level in Northern Greece) of the southern Balkans and Apennines, according to reviews of the pollen evidence by van Zeist & Bottema (1982), Bennett et al. (1990) and Willis (1994). S. Bottema (pers. comm. April 1996) suggests from the pollen diagrams that the refugia for deciduous and needle-leaved species were mainly on the western side of the Mountains of Greece.

In the Balkans, the several scattered pollen sites indicate that the predominant vegetation was an open Artemisia steppe with a small component of Pinus, but with many other tree taxa present and locally abundant at mid elevations (around 500m altitude), possibly due to the orographic rainfall and reduced evaporation supplying just enough moisture to enable them to survive.

In Iberia, scattered patches of pine woodland may have been present in valleys and other sheltered sites in the mountains of Spain (Turner & Hannon 1988), showing up to some extent in the pollen diagrams. Yet although a Pinus and Quercus element was present, it seems to have been only locally important. For the most part, the LGM vegetation of Spain and Portugal seems to have been drought-tolerant, open and semi-desert or steppe-like, with abundant Artemisia, and also chenopods and grasses. Several cores scattered around the Iberian peninsula and off the south-west coast all indicate the same general vegetation type (Hooghiemstra et al. 1992). The most recently published core confirms the same picture of an almost treeless cold-tolerant, arid steppe for the region close to the Mediterranean, inland from Barcelona in the north-east of Spain (Pérez-Obiol & Julià 1994). In the south-west of Spain, the vegetation on the exposed continental shelf areas seems to have been sparse enough to allow extensive dune mobility at the LGM (Zazo pers. comm., May 1994), even well inland from coastal areas. In south-eastern Spain, sparse vegetation cover and semi-arid conditions punctuated by sudden storms are indicated by slope wash deposits which are thought to date from the last glacial (Harvey 1984). ...

Scattered pockets of woodland. The Caucuses is thought to have been a glacial refuge for many temperate tree taxa, although there is little direct evidence of these trees surviving there during the LGM. In the Colchis region of Southern Russia, along the eastern shores of the Black Sea and the high ranges of the Caucuses, pollen evidence indicates that there were scattered pine and birch forests but broad-leaved trees were probably very localised in distribution (Tumajanov 1971). In contrast to the large area of surviving forest suggested in the maps Grichuk (1980, 1992), Velichko & Kurenkova (1990) and Frenzel (1992) also show only small areas of closed temperate forest surviving in the lowlands of the southern Caucasus, with dry steppe and open woodlands or localised woody pockets prevailing. The map by van Zeist & Bottema (1988) similarly suggests that there was virtually no temperate forest present in the main Caucasus region at the LGM. It is not clear from these sources what evidence is used to justify this choice of vegetation types or to what extent more recent research on this area has been published.

Update #1: Paul Colinvaux believes there was extensive forest cover in the Amazonian lowlands during the LGM.  I cannot judge this issue....Colinvaux also appears just to have come out with a popular book on this. Yes, other recent papers seem to reflect a shift since the mid-1990s towards a more continuous forest cover view of the LGM Amazon, though still reduced compared to modern times by measures other than area, for instance here:

Although there are very few palaeoecological records extending to the LGM, there is accumulating evidence to indicate that most of the Amazon Basin was forested at this time (Fig. 1), contrary to Haffer’s (1969) hypothesis of widespread savanna with isolated, disjunct forest refugia. Colinvaux et al. (1996) and Bush et al. (2002) have provided pollen, sedimentological, and geochemical data that show that the Lake Pata catchment in the central Amazon (0816VN, 66841VW) was continuously forested over the last 170,000 years. De Freitas et al. (2001) collected soil carbon isotope data from a 200 km transect, spanning small, isolated pockets (ca. 10–100 km2) of seasonally flooded savannas, between Porto Velho (Rondonia State) and Humaita (Amazonas State), Brazil, between the coordinates 8843VS, 63858VW and 7838VS, 63804VW. These savanna dislandsT are surrounded by rainforest and located ca. 450 km north of the southern limit of rainforest communities in Bolivia. De Freitas et al. show that these savanna islands at 17 14C ka BP (ca. 20.5 cal ka BP) were no larger than today, indicating that there was no expansion of savanna at the expense of forest at this time.

Nature causing Nurture

Sandra Aamodt and Sam Wang write in the NYT  on an at times under appreciated phenomena:

We tend to think of the environment as something that just happens to us, but in fact animals actively seek out surroundings that are compatible with their genetic predispositions. Teenagers in the chess club choose to be exposed to different influences from their hockey-player counterparts. Such differences don’t even have to be voluntary: tall kids may be picked more often for the basketball team and end up better at the game because they have more opportunities to develop their skills.

Certain people are much more likely than others to be exposed to stressful life experiences, including specific traumas like car accidents, industrial injuries or being a crime victim. Some of this variation is traceable to genetics.

Psychiatric geneticists have formalized this idea by studying “heritability,” the amount of the variation within a population that can be explained by genetic differences between individuals. Identical twins are more likely to both experience a variety of life events than fraternal twins, who, like siblings of different ages, share only half their genes. About one-fourth of the variation in life experiences — from strictness of parents to difficulties with friends — can be traced to genetic origins. This finding emerges from dozens of studies.  ...

What connects our genetic inheritance to environmental experiences? Most likely it is personality, which is known to depend on genes. In one study, three common measures of personality — extraversion, neuroticism and openness to experience — were enough to explain the entire heritability of some life events. In general, neurotic people are more likely to experience negative life events, while extraverted people are more likely to experience positive and controllable life events.  ...

The interaction between genetic tendencies and life experiences may explain another puzzling finding: the heritability of many psychological traits — from intelligence to anxiety — increases as people mature. This result seems odd at first glance, since genes are most important in brain development in babies and children. But children also have less control over their environment than adults. As people get older, they become more able to determine their own circumstances, and they may be able to choose environments that reinforce their natural personality tendencies. Apparently those of us who suspect we are turning into our parents as we get older may have a valid point.

Flynn and Dickens have a paper that suggests that some (large fraction of) IQ heritability works like this as well, but they (not surprisingly) never tie up their case. Heritable life expectancy, especially for long lived adults, is similar. 

Update #1: Jody comments:

The only issue I'll raise (and it's a mild one) is that I've been less-than-impressed by every twin study I've ever seen. Granted it's the best measurement tool we have for some of this stuff, it rests on some assumptions that have yet to convince me.

The major one: that multiple-birth children have the "same" parenting experiences and household environment, so if there's a difference in the trait being measured, it must be genetic. Problem is, from experience and observation -- MZ twins in triplet pairs being relatively common these IVF days -- I'd say that the assumption is weak at best.

It's a confounding issue, because in the case of DZ multiples, some of the difference in parental interactions can be traced to genes -- the meshing of different personalities, as it were. But the fact remains that not all MZ twins have, for example, colic, and so right from the beginning, they have different familial environments (rates of parental interaction, etc.) It's just not the case that, simply because you were born at the same time, your "nurture inputs" were the same.

Throw in placental differences and you've got another layer of uncertainty.

Also, parents of MZ twins have certain culture-based assumptions in the first place, which create a different parenting environment for MZ twins than that faced by DZ twins or by singletons. How to untangle those factors? Cross-culture studies might be a route. But in the same way that babies are treated differently because of their parents' expectations about gender, twins are also raised in a non-neutral environment of their own.

I just think we're wise to look for alternative routes when studying culture vs. genes in human-trait expression.

Again, I'm not entirely discounting twin studies. The studies based on twins raised apart are fascinating. But in general, I have serious doubts about the underlying assumptions on which many twins studies are based.

Homo Erectus in recent Times

From last week's Nature a claim about the persistence of Homo erectus into recent times that I had missed until now:

Fossil evidence now points to an origin of H. erectus about 2.0 Myr ago in equatorial Africa, followed by dispersal northwards and eastwards into Eurasia⁸. Incontestable evidence of that dispersal comes from the site of Dmanisi (Transcaucasia, Republic of Georgia) at 1.75 Myr ago and from southeast Asia (Java) by 1.6 Myr ago. Homo erectus survived to as late as 0.35 Myr ago in continental east Asia, and isolated populations persisted longer on the Indonesian archipelago. One group on Java, commonly known as 'Solo Man', may have survived until 50,000 years ago¹².

The citation to Solo Man is a 1996 article in Science:

Hominid fossils from Ngandong and Sambungmacan, Central Java, are considered the most morphologically advanced representatives of Homo erectus. Electron spin resonance (ESR) and mass spectrometric U-series dating of fossil bovid teeth collected from the hominid-bearing levels at these sites gave mean ages of 27 ± 2 to 53.3 ± 4 thousand years ago; the range in ages reflects uncertainties in uranium migration histories. These ages are 20,000 to 400,000 years younger than previous age estimates for these hominids and indicate that H. erectus may have survived on Java at least 250,000 years longer than on the Asian mainland, and perhaps 1 million years longer than in Africa. The new ages raise the possibility that H. erectus overlapped in time with anatomically modern humans (H. sapiens) in Southeast Asia.

Note that persistence to 50,000 years ago is the upper bound -- it could more recent that that.   Another species wiped out by the arrival of modern man? 

Context for the interpretation of Homo floresiensis that I'd missed, even if Flores island is to the East of Java and seperated from the Asian mainland even during recent (all?) ice ages.