My other hobby

Sometimes I go to parties and start beatboxing. Everybody just starts going wild, I'm that good. Here's a live recording from the last party I went to. Pretty sweet, right? I know, it's pretty impressive.

Some pictures [too large for palewis]

Racist

I just took tests at two sites to determine if I have subconscious racist biases. Here they are:

U Chicago
Harvard [the race IAT]

I first read about these in Malcolm Gladwell's Blink and then today in Nicholas Kristof's NY Times column. Apparently whites and blacks alike tend to associate blacks with negative things and whites with positive things. The tests are designed to access the subconscious through mind-numbingly repetitive tasks that measure implicit associations.

So go give them a try.

The U Chicago test has you shooting or choosing to not shoot a series of white and black men holding guns or cell phones. I shot whites with guns faster than blacks and I holstered my gun faster with blacks than with whites [no error bars were quoted, so I don't know if the results were statistically significant, but the difference appeared "large"]. This means that I am subconsciously biased anti-white. The second test is an association test and I scored dead even with no bias. I have many questions/complaints about the methodology but the general conclusion is that I test marvelously bias-free!

Everybody let me know how you do... and whether you measure up to my lofty precedent of high-minded anti-European American bigotry.

Evolution of Toxicity

How does defensive toxicity evolve? Being as I am completely ignorant of scientific orthodoxy on the topic, I am free to wildly speculate regarding this mystery.

Consider the monarch butterfly for a well-known example. As caterpillars, monarchs acquire a store of cardenolide aglycones from eating milkweed. These cardenolides are steroids that, in high enough doses, can stop the heart and thus are toxic to most animals. The monarchs then are permanently toxic to most predators from cardenolides ingested as a caterpillar and are thus protected from predation.

Storing cardenolides is a trait that must have evolved. Any investigation into the evolutionary history of a trait must begin with the Occam's Razor of evolutionary theory: the trait arose through random genetic mutation; it was beneficial to the reproductive viability of an individual monarch; this increase in viability eventually led to universal trait ownership in the global monarch population.

But how can this explanation be correct? Let us try to explicitly paint this story of the cardenolides-storing "gene" [standard euphemism for "gene or set of genes"]. We will start with a single monarch since identical genetic mutation in two distinct individuals is probabilistically impossible:

• A single monarch is endowed through genetic mutation with the cardenolides-storing gene. Until the first interaction with a predator, this gene has no effect on the reproductive viability of the single butterfly.
  
• A bird eats the butterfly and dies or is injured from the toxin.
  
• The gene disappears.

The gene conferred no survivability advantage to its host since its first effect occurred only after the monarch was killed. If the monarch had offspring before it was killed, those offspring would have no survivability advantage over their cousins without the special gene. Genes that confer no reproductive viability advantage do not become universal.

Consider further the role of the predator, in this example a bird. If not killed, the bird might learn not to eat monarchs again. Through cultural transmission the bird could possibly teach other birds not to eat monarchs. Even if such cultural transmission is likely, this benefits both the monarchs endowed with this gene and not, giving no evolutionary advantage to the gene itself [using a Dawkinsian gene-level evolutionary argument which is clearly valid trait-level as well]. If the bird was killed, on the other hand, then birds with a gene instructing them to not eat monarchs might replace the old ones after many generations. This scenario is less likely than the first; it requires a long period of large-scale predator/prey interactions with a monarch population significantly endowed with the gene, while simultaneously never giving any viability advantage to the cardenolides-storing monarchs. Neither explanation can account for selective pressures favoring the toxic gene.

Is there still some way to invoke basic adaptive natural selection for monarch toxicity? There is a candidate solution: taste. Cardenolides taste horrible. Is it possible that the bird tasted our monarch and rejected it? The butterfly then has received the ultimate survivability boost from the gene: it lives where its cousins would certainly have died. This is certainly possible, but I have strong doubts about this hypothesis. For one thing, I wonder about the state of a butterfly after being tasted by a bird. Is it likely that a tasted butterfly can survive and have offspring? It is true that this tasting could possibly leave the butterfly alive; this is why beak-marks on the wings of butterfly specimens are common. But what are a monarch's chances of reproducing after this injury? Additionally, any lesson the bird learned from the tasting the monarch--that all monarchs or even all butterflies taste terrible and are possibly toxic--will confer no specific advantage to the monarchs with the mutation. Remember that our one monarch, in order to pass on beneficial genes, will need to live in a situation where a monarch without the genes would die. Unless birds habitually sample butterflies in a non-fatal way before deciding to eat them, I find it extremely unlikely that it is taste that conferred the viability advantage for the monarchs with the toxic gene.

It is clear to me that the standard adaptive natural selection argument can't explain the toxicity trait of monarch butterflies. But exaptation--my old friend of herons and voles--could explain it well. Here's my explanation:

Cardenolides are not only toxic to birds, but insects as well. In fact, the toxins are used by plants specifically as a defense against being eaten by insects. Let us paint a different evolutionary story:

• A single monarch is endowed through genetic mutation with some kind of immunity to cardenolides
  
• This monarch has access to food plants [as a caterpillar] that other monarchs do not. The immunity gene confers a strong advantage to this monarch at its most vulnerable stage of life.
• Because of increased survival rates as caterpillars, monarchs with the mutant genes proliferate and replace those without it

This sounds very probable. But where does the toxicity fit in? I have only explained how monarchs might have evolved tolerance to cardenolide. Here is the "wild speculation" I promised:

Suppose the gene for "immunity" is actually a gene for removing the cardenolides from the plant matter before digestion. This is one of several plausible methods for tolerating a toxin. The toxin thus must be excreted or stored. If the toxin is stored--or even if it persists a significant amount of time before being excreted--the monarchs will be toxic to birds. This toxicity is a by-product of the natural selection of the cardenolide-tolerant gene.

The benefit of this approach is that it allows the monarchs to acquire the toxic gene as a species. The downfall of the adaptive natural selection argument in the first place was that the gene had to be beneficial to the first butterfly in order to propagate. If the mutation had an initial evolutionary benefit--allowing access to new abundant food sources--then it will prevail throughout the species. Only then will the pressures of predation influence the evolution of these monarchs. Remember that all of our explanations for how the presence of the gene in the first individual gave it an evolutionary edge failed because all of those explanations gave the same advantage to the monarchs not possessing the mutation as to the monarchs with it. This failing is erased when the evolutionary impetus for the gene's survival is not dependent on being eaten or "tasted" to be expressed.

Now, as a species, the monarchs evolve better and better storage mechanisms for the toxins to be more effective at deterring predators. The predators evolve in parallel to learn not to eat monarchs.

This is exaptation.

This is also a "just-so story." But I would be surprised if toxicity in most prey animals is not a result of exaptation [there is a tantalizing genetic correlation between toxicity and coloration that broadcasts toxicity--like the red/black monarch wings--which seems to support my argument].


Update: I just found a paper [Ecological factors influencing the evolution of insects' chemical defenses, J. Skelhorn et al., Behavioral Ecology, doi:10.1093/beheco/arm115 ] discussing the evolution of defensive toxicity in insects. It says that the subject is relatively unexplored but gives this insight:

One potential explanation [for the evolution of defensive toxicity] is that chemically defended individuals suffer less from predation than those that do not invest in costly chemical defenses. However, chemical defense often cannot be detected prior to attack, meaning that in order for chemically defended individuals to suffer less from predation than visually similar undefended individuals, they must be more likely to survive predatory attacks. Although there is now some evidence that aposematic insects often survive predatory attacks relatively unharmed and that predators selectively reject prey based on their chemical content, it is currently unclear under what ecological circumstances such differences in survival would allow costly chemical defenses to evolve...
...[A]lthough sequestered chemicals may be stored systemically in body tissues, many species store a large proportion of the chemicals in the integument and wings. This may increase the speed with which predators perceive an individual to be defended and as a result reduce damage to the insect.

This vindicates the premise for my theory but sheds some doubt on the need for it [the paper nowhere discusses the transmission of the gene from the first individual to further generations, but points to evidence that birds taste and release butterflies. And I was right about storing the toxic chemicals, it seems]. I still think exaptation is a cleaner explaination, but pure adaptative natural selection is more plausible in light of this. The paper is really good, it's worth a read.

Update 2: I just realized that toxicity can be manufactured by the prey species, not just acquired through feed. This strongly suggests that the adaptive route is possible.

Encyclopedia of Life

Last night I had the urge to look up the ecology of tank bromeliads. Not having a university biology library in my apartment, I turned to the internet. And found nothing. The "information superhighway" is supposed to be a glut of information; a curious Googler is supposed to be able to find anything. I have found this to be increasingly not the case. Very, very few resources provide deep, detailed, well-written material for the purpose of free information. Most of my searches return a superfluity of corporate garbage, functionally empty blogs, and woefully incomplete or inaccurate official pages. There are a few well-respected sites which provide high-quality information consistently--like the OED and Encyclopedia Britannica--but all have significant flaws; too narrow a scope, too little free content, or too-shallow coverage. Wikipedia has immensely broad but shallow and frighteningly inconsistent coverage. General Google searches are a major headache for anybody trying to find quality information. At every turn a researcher is bombarded with hundreds of irrelevant ads, search results, and links. I have found the internet to fall well short of its promise of being a powerful and accessible repository of the sum of human knowledge.

For these reasons I have been nearly beside myself with excitement for the last year in anticipation of the unveiling of the Encyclopdia of Life. The EOL will be the culmination of the internet, and by far its most important resource. In the words of E. O. Wilson, one of the coolest guys on the planet and the inspiration for the EOL:

Imagine an electronic page for each species of organism on Earth available everywhere by single access on command.

And it's even better than that. Each page will eventually contain all known information about each species. It will accept user content, but only after screening by an expert, so the EOL will have the breadth of Wikipedia [within biology] with the information quality of a scientific journal. But the depth of information will be unlike any resource ever created by man. Seriously.

This morning I received this message in my inbox:

The new Encyclopedia of Life portal has gone live with more than one million
species pages! In celebration of this big event, our first EOL newsletter is
available at:

Click here to read the newsletter.

You can see the new pages at http://www.eol.org/. We also invite you to take the
survey at the site so you can help us improve.We thank you for your interest and
support over the past year. Enjoy.

Woohoo! It is here--in abbreviated form, but it is here. I strongly urge you to go take it for a spin; the information format in revolutionary and brilliant.

Now when Little wakes up in the morning and asks to look at a picture of a kinkajou I don't have to rely on the crummy random pictures that Google image search returns...

Update: nytimes.com has a nice article on the unveiling of the EOL.

Sub-bullet b: Antarctica

Sub-bullet b: "A clear warming trend is evidenced by the Antartctic ice sheets"
Hierarchy: Part II:1:A:iv:b

Back to Intro - Back to Outline - Up to Bullet iv - Back to Sub-bullet a - Forward to Sub-bullet c

Introduction:
Antarctica, like Greenland, has a complex climate and thus the logical structure of Sub-bullet a will be followed. Simply, this means that we will use current understanding of how warming could effect the ice in Antarctica and data showing the trends of the distribution of that ice to conclude whether warming is occurring. The issue of causality will be left at this point unless evidence can be found which attributes the observed behavior to effects other than warming.

The bulk of the ice on Antarctica consists of two main sheets: the East Antarctic Ice Sheet [EAIS] and the West Antarctic Ice Sheet [WAIS]. The EAIS is much higher in elevation and therefore colder and less susceptible to warming than the lower WAIS. Below is a map compiled by NASA's ICESat showing the altitude of the upper surface of the Antarctic ice sheet.
This uneven distribution of ice mass and altitude will be critical for understanding the behavior of the Antarctic ice sheet.


In most respects Antarctica is as different from Greenland as two polar ice sheets can possibly be. In contrast with Greenland, Antarctica is naturally very cold; a large majority of the surface area of the continent averages below freezing year-round. Since Anatarctica is less marginal for ice than Greenland, a small rise in temperature isn't likely to be the difference between ice and liquid water except at the extreme edges. This means that melting is relatively less important in Antarctica as a factor for mass loss. The interior is large and very cold and in this region scientists expect that a warming climate would increase the ice mass since precipitation would increase--perhaps even enough to make the total mass balance increase due to warming. The Antarctic peninsula sticks much farther north and thus is more susceptible to warming trends than the coasts. Antarctica also does not rely on an exterior ocean current to cool it, and contains over 10 times the ice that Greenland does. All of these factors make Antarctica theoretically much less sensitive to small climate effects as Greenland is.


Despite all of these differences, we are looking for the same warming signature for Antarctica as we were for Greenland: positive mass balance in the interior, potentially negative and accelerating mass balance at the edges [since thinning is not just related to melting but to ice dynamics like glacier flow], and glacial dynamics features like accelerating flow. A refinement of the mass balance model predicts that the WAIS will see mass loss and the EAIS will see mass gain; this is the signature we are looking for.
[Refer to bullet iv for further introductory material]

Study 1 : GRACE weighs in on mass balance
Measurements of Time-Variable Gravity Show Mass loss in Antarctica
Isabella Velicogna and John Wahr, Science 311, 1754 (2006)



Antarctic mass rates from GRACE
J. L. Chen et al., GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L11502

Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE
G. Ramillien et al., Global and Planetary Change 53:3, 198-208 (2006)

Simple: The researchers who conducted two of the three of our GRACE studies for the Greenland mass balance trend also conducted similar studies for Antarctica, and another group worked on the data as well. Their conclusions are the same: interior mass is increasing, peripheral mass is decreasing, with a net decrease in mass that is quickly accelerating. See Sub-bullet a: Greenland for more GRACE discussion.

Details: All three studies found large negative mass balances in the WAIS and mass gain or balance in the EAIS. A figure from Velicogna and Wahr illustrates this [the green line is the EAIS trend and the red line is the WAIS trend]:


Mass balance findings for these three studies are summarized in the table below.

All three studies also corrected the data for post-glacial rebound--the upward swelling of the crust resulting from the loss of glacial period ice--which yields more accurate but less precise data, since the post-glacial rebound is poorly known. Chen et al. describes the limit of knowledge [units, parenthetical statement and emphasis mine]:


"The calculations here show that the estimates of Antarctic snow/ice mass rates from GRACE data are completely dependent on the adopted PGR [post-glacial rebound] model, with uncertainties that might be on the order of 100% Our estimate of -99 or -77 cubic kilometers per year mass loss in West Antarctica is consistent with that of Velicogna and Wahr of -148 cubic kilometers per year, given the large PGR uncertainty and that here we only compute the mass loss of the Amundsen Sea Embayment in West Antarctica."

The take-home message is that we shouldn't have much faith in the exact numerical values of the mass balance, but that the trend of mass loss in the WAIS and mass gain in the EAIS is clear.


Discussion: The two studies with the most comprehensive geographical scope [Velicogna and Wahr and Remillien et al. ] agree within quoted error limits. The total mass balance isn't the first clue to a warming climate that Antarctica offers anyway [although it's the driving global factor in sea-level change, which has the potential for enormous effects]. What is important is also what is clear from the data: Antarctica is undeniably showing the signs of warming--decreasing ice mass in the WAIS and increasing or stable ice mass in the EAIS.

Conclusion: The GRACE data constitute strong evidence of a south polar warming trend.

Study 2: Sattelite radar altimetry measures mass balance
Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002
H. Jay Zwally et al., Journal of Glaciology, Vol. 51, No. 175, 2005

Not-yet-published sattelite radar altimetry Antarctic mass balance study
Eric Rignot

Simple: The European remote sensing sattelites ERS-1 and -2 used radar altimetry to measure the altitude of ice in the Antarctic ice sheets. The first study is comprised of data from 1992-2002 which shows a mass loss in the WAIS and a mass gain in the EAIS which contributed to an overall negative mass balance. Additionally, the as-yet-unpublished second study--another by Eric Rignot--apparently fuses newer ERS-1 and -2 data with similar data from Japanese and Canadian sattelites and finds that ice loss in the WAIS increased extremely sharply during the decade 1996-2006.

Details: Covering a time period prior to most of the studies we've seen so far, the first ERS data is crucial in establishing a longer-term trend. This analysis is the most sophisticated to come out of the ERS program; the authors attempt to correct for some small but important factors which most other studies ignore, having to do with the dynamics of ice compaction. The dH/dt [rate of change of ice sheet altitude] map below represents the corrected data from Zwally et al.:


Rignot's technique is different than Zwally's; Rignot measures the amount of ice leaving the continent indirectly, by monitoring the flow of ice off the continent in glaciers. The benefit of this method is that it allows the researchers to ignore the problems that Zwally had to design sophisticated corrections for, such as the sensitivity of compactibility of new ice to temperature. Additionally, Rignot combined many different large datasets and has data up to 2006, greatly enhancing the completeness and relevancy of the data.

Quote from article on Rignot's upcoming paper: "The team found that the net loss of ice mass from Antarctica increased from 112 (plus or minus 91) gigatonnes a year in 1996 to 196 (plus or minus 92) gigatonnes a year in 2006."

Zwally et al. Quote: "The ice sheet inWest Antarctica (WA) is losing mass (–47 +/- 4Gt per year) and the ice sheet in East Antarctica (EA) shows a small mass gain (+16 +/- 11 Gt per year) for a combined net change of –31
+/- 12 Gt per year (+0.08mma–1 SLE). "

Discussion: The data from this study solidly confirms the existence of the bimodial east/west mass gain/loss signature in Antarctica; the signature of warming. Furthermore, Rignot's study--which used data from the same sources and identical analysis--found solid evidence that the ice mass loss in Antarctica is accelerating at a phenomenal pace; a solid sign of warming. Two more sattelite radar altimetry studies, Wingham et al. and Davis and Li found a slight mass increase. However, both of these studies found it difficult to analyze the peripheral regions and thus left them out of the analysis altogether. Since a majority of the loss we see occurs at the periphery, these studies do nothing but confirm the other studies' findings of a mass increase in the interior.
[Zwally et al. study also analyzed the Greenland ice sheet and found a small positive mass balance, which is not inconsistent with the studies reported in the Greenland section for this time period]

Conclusion: The ERS data constitutes evidence of a south polar warming trend.

Study 3: Laser altimetry analyzes glacial dynamics
Accelerated sea-level rise from West Antarctica
Thomas, Rignot, et al., Science 8 October 2004:Vol. 306. no. 5694, pp. 255 - 258

Simple: Using laser altimetry data from sattelites and aircraft, Thomas et al. have measured the discharge from the glaciers in a section of the WAIS. They discovered a steeply accelerating flow from the 1990's until 2003; a glacier dynamics marker indicative of warming.

Details: Thomas et al. found that 60% more ice was flowing out of the catchment basin feeding the Amundsen sea in west Antarctica than was accumulating due to precipitation. They collected precise ice thickness data from aircraft flown from Chile and compared it with various sattelite data sets to create a map of ice thinning rates for the catchment area. A quote: "The catchment regions of Amundsen Sea glaciers contain enough ice to raise sea level by 1.3 m. Our measurements show them collectively to be 60% out of balance, sufficient to raise sea level by 0.24 mm/year. Although these glaciers are the fastest in Antarctica, they are likely to flow considerably faster once the ice shelves are removed and glacier retreat proceeds into the deeper part of glacier basins."

Discussion: Not only does this large imbalance of outflow/inflow point to conditions now being different than they were previously, but the study reports an acceleration of the imbalance, which signifies compounding factors in recent years. Even more impressive is the potential for yet higher rates of mass loss when/if the ice shelves melt, effectively pulling the rug out from under the glaciers.

Conclusion: This glacial dynamics study constitutes strong evidence of south polar warming.

Other studies
Recent sea-level contributions of the Antarctic and Greenland ice sheets
Andrew Shepherd and Duncan Wingham, Science 315, 1529 (2007)

Simple: This is a review of mass-balance data. It does a much better job than I can, and it reviews most of the same data I have.

Mass balance of polar ice sheets
Eric Rignot and Robert H. Thomas

Simple: Another review but older. Same conclusions.

[Further studies requested]

Discussion
The evidence is accumulating and the doubt is thinning; the Antarctic ice sheets are shrinking at fantastic rates, and the rate of increase is itself increasing at a fantastic rate. Two years ago there might have been argument, but at this point it is obvious that something big is cooking at the south pole. The issue of causality is less complicated than Greenland, but still the strongest statement we can make is that warming is the only candidate known for the cause of the changes observed. Given the scale of the changes--and the recently discovered fact that ice outflow increases dramatically after ice shelves melt--I feel comfortable agreeing with the large majority of these researchers in this point: the loss of ice in Antarctica will likely reach astonishing proportions in the near future if current conditions persist. Two ice shelves collapsed in the last few years, triggering massive acceleration of glacial flow, and similar events should be expected in the near future.


A summary of the mass balance studies cited in this post:


Conclusion
This data constitutes strong evidence of north polar warming.

Sub-bullet value: TRUE

Sub-bullet a: Greenland

Sub-bullet a: "A clear warming trend is evidenced by the Greenland ice sheet"
Hierarchy: Part II:1:A:iv:a

Back to Intro - Back to Outline - Up to Bullet iv - Forward to Sub-bullet b

Introduction:
Greenland holds nearly 10% of all the ice in the world. Given its relatively southerly location, Greenland's ice is balanced precariously between its current state and cataclysmic melting, kept stable only by virtue of a microclimate controlled by the ice itself and by friendly and cold arctic ocean currents. The ice is so thick that the crust of Greenland is depressed in the interior from the weight of it. Warming should be relatively easy to spot here; many scientists think that Greenland is close to a sharp equilibrium point and that warming will cause a chain of " positive feedbacks"--some warming will trigger factors which compound the warming and trigger other factors, etc. Thus the changes in the Greenland ice sheet might happen quicker than expected given the large thermal inertia that such a huge block of ice has.

Greenland's climate is an anomaly when placed in the context of other land masses at its latitude. When my family traveled to Prudhoe Bay, AK this last summer, we found it warm and ice-free. Prudhoe Bay is at the northern edge of Alaska, at a latitude of 70 N [for comparison, Anchorage is at 61 N]. Greenland's permanent ice extends down to about 60 N, so far south that almost all of Alaska and the northern territories of Canada would be under ice if Greenland's ice sheet was typical. Why is Greenland covered in ice when most of the latitudes it occupies are free of ice elsewhere?

The glib answer is: because Greenland is colder than other areas at the same latitude. A little background is needed before we can answer why.

Greenland's ice sheet was formed during one of the many colder periods in the earth's history. These glacial periods have caused the latitude marking the ice sheet boundary to move southward, at times reaching down into the continental United States. About 10,000 years ago the last major ice age ended and temperatures returned to roughly what they are now. The equilibrium latitude shifted much farther north in a short period of time. The bulk of the ice sheets were now below the equilibrium latitude, and thus started slowly retreating northward. The retreat was so slow that it is probable that the remaining continental glaciers are still retreating to this day. For some reason, though, Greenland never got the message; some particular climate conditions caused the local equilibrium latitude around Greenland to be stuck farther south than it is for the rest of the Northern Hemisphere. It turns out that this effect is due to two main things: the East Greenland Current, an ocean current that cools Greenland's climate through shipping cold water right along the east coast Greenland from the Arctic; and the high altitude of the ice sheet in Greenland, which keeps the sheet colder than its latitude would dictate.

Warming would effect Greenland in very complex ways, and since the climate is dictated by an ocean current, understanding the subtleties of the current's response to warming would normally be critical to understanding the effect on Greenland's ice sheets. It would be impossible to delve into those subtleties here--albedo, salinity, feedback--but we can still draw some conclusions if the effects are clear enough. This requires an explicit logic that needs explaining: given the "well, duh" aspect of the statement "ice will melt more if temperatures increase" and also given that regional models predict a certain pattern of melting occurring as the result of the warming, IF expected melting patterns are conclusively observed, THEN the region is almost certainly warming. The burden of proof to the contrary will rest on those who wish to prove that the melting proceeds by some other mechanism.

I am not trying to cover up a logical flaw. Rather, I'm using the strongest logic that is possible in any kind of analysis of complex systems. A researcher can never be 100% confident in a causality solution in a system this complex, but it is not wrong to draw conclusions based on the best available data, assuming that as much rigor as is possible is dedicated to trying to understand the underlying causes and effects. Such a case this is. What this means practically is that we will look at the data, conclude confidently based on this data that it is TRUE or FALSE that the behavior of Greenland proves regional warming. The bullet value will only stay TRUE if sufficient evidence is not found for mechanisms other than warming causing the observed effects.
[Refer to bullet iv for further introductory material]

Study 1
Greenland mass balance from GRACE
Isabella Velicogna and John Wahr, GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L18505

Satellite gravity measurements confirm accelerated melting of Greenland ice sheet
J. L. Chen, et al., Science 313, 1958 (2006)

Recent Greenland ice mass loss by drainage system from sattelite gravity observations
S. B. Luthcke, et al., Science 314, 1286 (2006)

Basic: These papers utilize data from the GRACE experiment, with newer data in the second and third papers. This is the type of experiment every researcher would love to be part of. GRACE is a fantastic idea: two orbiting satellites working in tandem to measure the gravitational field above the earth. This is an exquisitely delicate experiment, but it was pulled off and is very successful. The idea is that ice will "pull" on the spacecraft through gravitational acceleration. This pull is measured each time the satellite passes over and compared across time. If the pull changes, that means that ice is accumulating or being lost on the ice sheet. The beauty of this approach is that it is independent of ice transport mechanism and is the first experiment that is directly measuring the quantity of ice present as opposed to indirect studies of depth or flow which use generous extrapolations and interpolations. The first study includes data from 2002-2004 and the second and third studies adds 2005 to that. The studies concluded that the mass balance of Greenland in the time period was large, negative, and accelerating, consistent with regional warming.

Details: Velicogna and Wahr: "We recover a decrease in total ice mass of 82 ± 28 km3 of ice per year." I am unable to access the rest of the paper, so I would appreciate anybody with an AGU membership to help me on this one. Again, although static or increasing mass balance is inconclusive, negative mass balance, especially one this large, is very strong evidence of warming. The image below, taken from the NASA site supporting this research, shows a very strong net mass loss around the periphery of Greenland and a small mass gain in the interior.

This figure, from Velicogna and Wehr, shows the total Greenland ice sheet mass observed by GRACE during the study:

The second study confirms this data and adds a crucial fact: melting accelerated even within the limited time scale of the study. This acceleration is evident in the following plots from Chen:
The second study revises the yearly net mass loss upwards and confirms the acceleration of mass lost at least on this small time scale.

The third study confirms the main results of the other studies but lowers the mass loss estimate from the second study.

GRACE tells us that the Greenland ice sheet is melting and by how much. But even more significant is that this melting is accelerating on a seasonal timescale. This is a crucial piece of the puzzle; receding glaciers can be attributed to "ice age rebound"--the still on-going process of ice retreat from the last ice age, when the ice sheets were much more expansive. But acceleration of melting can only be due to warming: rebound predicts a gradual deceleration of ice loss as the equilibrium point is approached.

Conclusion: GRACE data provides very strong evidence of north polar warming.

Study 2
Greenland ice sheet: high-altitude balance and peripheral thinning
W. Krabill, et. al., Science 21 July 2000:Vol. 289. no. 5478, pp. 428 - 430

Basic: Greenland ice sheet: high-altitude balance and peripheral thinning. What more to say?

Details: This study was conducted using laser altimetry from aircraft; this is how it was done before GRACE. Laser altimitry can only tell you the altitude of the surface of the ice so this approach is most useful for mass balance studies. The study specifically addressed the mass balance of Greenland. Above 2000m of altitude, there was a mass balance: net accumulation in the northern latitudes counteracted net loss in the southern latitudes. However, at all latitudes around the periphery there was widespread net loss. An included figure best describes the findings [flight tracks shown; also note that this is an elevation chart, not a mass chart like for GRACE]:

Although less comprehensive than the GRACE survey, it is clear that a large negative mass balance at the periphery of Greenland overwhelms the accumulation in the interior.

In sum: "Interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise global sea level by 0.13 millimeter per year--approximately 7% of the observed rise."

Discussion: This study found strong evidence for behavior which points to warming: ice thickening or balance in the interior and aggressive thinning at the periphery. However, the authors admit that the peripheral thinning cannot be explained by the temperature record alone, and that the mechanism for the mass loss is still a mystery. Study 3 below is a partial response to this study and attempts to solve this problem with glacial dynamics studies.

Conclusion: This study gives some evidence for north polar warming.

Study 3
Changes in the velocity structure of the Greenland ice sheet
Eric Rignot and Pannir Kanagaratnam , Science 17 February 2006 311: 986-990

Basic: Using data from satellite radar interferometry [bouncing electromagnetic waves off the surface of ice from space], Rignot and Kanagaratnam have measured the velocity of the glaciers of Greenland over the last decade. Note how this differs from the previous study: the altimetry data presented in Study 2 likewise bounced electromagnetic waves [in that case, lasers] off the surface of the ice sheet, but there it was for the purpose of measuring the altitude of the ice surface and in this study the purpose is to measure the speed at which the ice flows down glaciers. These glaciers are the conveyor belts for ice transportation from the interior of Greenland to the sea, so glacial acceleration is a sign that more ice is leaving Greenland and entering the oceans. The study not only found widespread glacial acceleration, but found that the portion of Greenland experiencing the acceleration is increasing dramatically. The effect is also found to dominate any increase in due to warming, and is presented as an explanation for the mechanisms behind the results found in Study 2.

Detailed: The causes of glacial acceleration are not very well known, although all plausible explanations are products of warming [such as surface meltwater percolating down under the ice and lubricating the interface between ice and rock]. The degree of acceleration is also not a terribly good measure of the warming; all it can say is that warming is occurring. The study found that total mass loss from Greenland doubled in the period 1996-2005. The important point is that acceleration is observed, and this is not a feature of ice age rebound. The authors state: "We detected widespread glacier acceleration below 66 [degrees] north between 1996 and 2000, which rapidly expanded to 70 [degrees] north in 2005. Accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year."

The figure below shows the velocity plots of some of the glaciers from the study. The black lines correspond to the oldest data, blue the next, and red the most recent. Since these are velocity plots, the earmark of acceleration will be the red plots lying "above" the blue ones and the blue ones above the black ones.

Conclusion: This study constitutes strong evidence of north polar warming.

Other studies
Progressive increase in ice mass loss from Greenland
R. Thomas, et al., GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L10503

Basic: Similar results from the ICEsat experiment.

Quote: "Laser altimeter measurements over Greenland show increasing thickening rates bove 2000 m, reflecting increasing snowfall in a warming climate. But near-coastal thinning rates have increased substantially since the mid 1990s, and net mass loss more than doubled from an average of 4–50 Gt per year between 1993/4 and 1998/9 to 57–105 Gt per year between 1998/9 and 2004. This increasing trend is very similar to findings from independent massbudget studies, but differs widely from ERS radar altimeter results."

Runoff and mass balance of the Greenland ice sheet: 1958–2003
Edward Hanna et. al., JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D13108

Quote: "Runoff losses from the ice sheet were 264 (±26) km3 yr−1 in 1961–1990 and 372 (±37) km3 yr−1 in 1998–2003. Significantly rising runoff since the 1990s has been partly offset by increased precipitation. Our best estimate of overall mass balance declined from 22 (±51) km3 yr−1 in 1961–1990 to −36 (±59) km3 yr−1 in 1998–2003, which is not statistically significant."

The Greenland ice sheet and global sea-level rise
Julian A. Dowdeswell

Abstract: "The flow of several large glaciers draining the Greenland Ice Sheet is accelerating. This change,combined with increased melting, suggests that existing estimates of future sea-level rise are too low."

Seasonality and increasing frequency of Greenland glacial earthquakes
Göran Ekström, et al., Science 311, 1756 (2006)

Abstract: "Some glaciers and ice streams periodically lurch forward with sufficient force to generate emissions of elastic waves that are recorded on seismometers worldwide. Such glacial earthquakes on Greenland show a strong seasonality as well as a doubling of their rate of occurrence over the past 5 years. These temporal patterns suggest a link to the hydrological cycle and are indicative of a dynamic glacial response to changing climate conditions."

[Further studies requested]

Discussion
There is no doubt that Greenland is losing ice. And fast. A valid argument against concluding that warming is the cause of the loss is still present, however: since Greenland's climate is so controlled by the East Greenland Current [EGC], it is possible that the current is changing in ways that is encouraging the loss of ice on Greenland. The GRACE mass deficit maps are particularly encouraging to this line of thinking since a large majority of the mass loss occurs along the eastern coast, where Greenland and the current interface. I have dug deep to find evidence that the EGC has changed in any way since before the mass balance turned negative. I found no such evidence. Additionally, any change in the EGC could very well be tied to warming since the Arctic has seen the most dramatic effects attributed to warming of any region on Earth. Until strong evidence emerges that some other factor is forcing these dramatic mass losses, the sub-bullet value is TRUE. However, the evidence strength is demoted from "conclusive" to "strong" due to these concerns.

Brief summary of the issues: A complete description of the behavior of the Greenland ice sheet has to include two behaviors: ice mass loss--the change in the distribution and quantity of ice--and glacial dynamics--the change in the behavior of the ice. The dynamics data [such as Rignot and Kanagaratnam and Ekström] are strongly complementary to the mass balance data since glacial dynamics explains at least some of the mass loss and simultaneously acts as strong evidence of warming. Strong positive signatures of warming were found from both glacial dynamics studies and mass balance studies.

Summary of mass balance data:

Conclusion
This data constitutes strong evidence of north polar warming.

Sub-bullet value: TRUE