Recently in In from the cold Category
The shrinking extent of sea ice in the Arctic has been a cause of concern for some decades, and the record low extent measured with passive-microwave radiometers in September 2007 gathered a good deal of publicity. The September minimum was 7.11 million km2 on average during 1979-1998. In 2007 it was 4.30 million km2. The two minima since then have each been greater. 2008 saw the second lowest and 2009 the third lowest extent.
You can check out the state of Arctic sea ice at the National Snow and Ice Data Center in Boulder, Colorado. Thus far during the present winter, 2009-2010, the extent has been tracking pretty closely the course followed in 2007, so two successive years of increased minimum annual extent do not justify us in concluding that the ice pack might be recovering. Equally, there is no sign of an impending catastrophe at the top of the world, but we would still like to understand why 2007 was a record-breaker. There have been several interesting attempts to explain it.
A particularly interesting attempt by Ron Kwok and colleagues appeared last month. They focus on a detail of the bigger picture, the outflow of sea ice through Nares Strait, the narrow gap between northwest Greenland and Ellesmere Island. To put this study in context, we need to step up from thinking about sea-ice extent to thinking about sea-ice mass.
Very roughly, the ice is 3 m thick on average, for a total mass each average September of about 19 million gigatonnes (but only 12 million Gt in 2007). The mass of the ice pack is the result of a balance between freezing, melting and export. The exported bergs and floes eventually melt, but not within the Arctic Ocean.
Most of the export, about 2000 Gt/yr, is through Fram Strait, between Greenland and Svalbard. Of the other possible outlets, the channels between the islands of the Canadian arctic archipelago contribute little. Apart from being narrow, they are most often blocked at their northward ends by plugs or "arches" of immobile ice. The arches form during the winter and persist until the end of summer, so that for much of the year there is effectively no southward ice export.
Kwok and colleagues found that no arch formed in 2007 at Nares Strait, which was therefore an open passageway for the full 365 days. Between 1998 and 2006, the open-channel state prevailed for only 140 to 230 days per year. From 2004 to 2006, when ice thickness measurements are available from the ICESat laser altimeter, the mass export was about 80-85 Gt/yr, but in 2007 it was 230 Gt/yr.
Why worry about such tiny amounts? The export through Nares Strait in 2007 was only 10% of that through Fram Strait, and insignificant in comparison with the total mass of the pack. The answer is that the ice in the Lincoln Sea, just north of Nares Strait, is some of the thickest, at about 5 m on average, in the whole Arctic Ocean.
The decline of Arctic sea ice is usually discussed in terms of its extent, but that is mainly because we have lots of information about extent. Measurements of thickness are harder to come by, and therefore so are estimates of total mass (area times thickness, multiplied by 900 kg m-3, the density of ice). But one of our main concerns about Arctic sea ice is that apart from shrinking in extent it is also getting thinner.
The impact on ice extent of the free evacuation of thick Lincoln Sea ice in 2007 was small, but it depleted the thick end of the frequency distribution of ice thickness. An ice pack with relatively more thin ice is less likely to survive the summer melt season, so the non-formation of ice arches in Nares Strait constitutes a positive feedback, magnifying the vulnerability of the ice pack as a whole. And it may be a positive feedback in another sense. Presumably arching, that is, blockage, is more likely when the supply of thick chunks of ice is greater. If an episode of free outflow decreases that supply, future episodes of free outflow become more probable.
Palaeogeography is a seductive subject. The appeal of conjuring a vanished landscape out of a few strands of evidence and a good deal of restrained conjecture is irresistible. We know that the reconstructed world is imaginary, but with right treatment of the evidence, under the right constraints, we also know that it must represent a realistic approximation to the way things were.
That is what Douglas Wilson and Bruce Luyendyk appear to have done for West Antarctica at the end of the Eocene, about 34 Ma (million years ago). Records of oxygen isotope ratios in the microfossils preserved in deep-sea sediment suggest that glacier ice began to accumulate in Antarctica at about that time. But models of the palaeoclimate have trouble simulating as much ice on East Antarctica as the isotopes suggest. East Antarctica, palaeoclimatically interesting in itself but not our focus here, is the larger, higher part of the continent.
West Antarctica is not big enough to house the missing ice. Most of it is below sea level. The prevailing wisdom is that you can't grow a marine ice sheet — that is, one with its bed below sea level — from scratch, at least not quickly. So, assuming we are reading the isotopes aright, where was the missing ice?
Enter Wilson and Luyendyk . Their geography of West Antarctica as it may have been at 34 Ma offers a persuasive answer: most of it wasn't below sea level back then.
The first step in the palaeogeographic reconstruction, starting from a map of the modern ice thickness, is to remove the ice and allow the underlying lithosphere to recover from the removed load, rebounding and flexing. You have to juggle with the calculated new surface elevations because in some parts, where the new surface is below sea level, the place of the ice load is taken by a new load of ocean water. This requires care, but it is not a deep problem. On the other hand the result isn't much help. Most of West Antarctica remains under water.
The second step is to account for thermal contraction of the lithosphere. As constrained by palaeomagnetic and other measurements, the main feature of the tectonic-plate system around here until about 28 Ma, the West Antarctic Rift System, was the surface expression of the rising limb of a convection cell in the Earth's mantle. The convection stretched the overlying lithosphere while causing the two sides of the rift to spread apart. Now too high for the fluid mantle rock supporting it, the lithosphere subsided gradually. Wilson and Luyendyk estimate that the subsidence since 34 Ma has varied from 200 to 500 m across West Antarctica.
Apart from correcting for the subsidence, you also have to undo the stretching, moving the Pacific side of the rift some tens of kilometres back towards the East Antarctic side.
A lot of erosion can happen in 34 million years. How do you restore a landscape that has ceased to exist? The answer is that we know, first of all, that the erosive products go downhill, and second that they have to end up somewhere. Most of them end up as sediment offshore, and not too far away. Wilson and Luyendyk rely on sediment thickness estimates for this, their third step. Not all of the sediment is due to erosion, a good deal of it being the fossils of marine microorganisms, and the eroded rock would have been more dense than the deposited sediment. Nevertheless, their approach is very conservative. The volume they restore is only 13% of the volume of offshore sediment.
This step also requires corrections for rebound and subsidence. Shifting loads of sediment are just like shifting loads of water and ice when it comes to the response of the underlying lithosphere.
In the end, Wilson and Luyendyk found another 1.5 million km2 of land, turning the West Antarctica of 34 Ma from an archipelago into a landmass. This plausible landmass, imaginary as it is, is consistent with all the evidence and is constrained by basic principles of physics. In turn it makes what the isotope records imply, that there was quite a lot of ice at 34 Ma, more plausible.
Getting beyond plausibility is a challenge, but one that would be worth rising to because it would allow us to move on to the next questions. Why so much ice? And why then and not earlier or later?
The idea that a super-enormous volcanic eruption — or hypereruption — would alter the climate dramatically has been around for a long time. It fits the facts about the biggest historical eruptions we know of, and also our understanding both of how volcanoes work and how the atmosphere works. But could the drama extend to tipping the climate from an interglacial state to a full-blown ice age?
The answer, as has long been believed, is still No, according to Alan Robock and colleagues in a paper published last year. They added several new kinds of potential cooling mechanism to two climate models, and were unable to trigger an ice age.
When a volcano goes off, it is always unpleasant for those in the immediate neighbourhood. The climatologist's concern, however, is with the broader consequences. A violent enough eruption can loft its products into the stratosphere, where they can persist long enough to spread around the world.
The main culprit is sulphur dioxide, SO2. It reacts with water vapour to form a haze of sulphuric acid droplets. The droplets increase the scattering of incoming solar radiation, making the atmosphere more reflective and cooling the Earth slightly. The more SO2, the more cooling.
The snag is that the haze doesn't last. The atmospheric effects of Pinatubo in 1991, the largest eruption of recent times, were detectable for a few years at most.
Krakatau in 1883 was bigger than Pinatubo. Tambora in 1815 was even bigger, and still stands as the largest eruption in the historical record. If we turn to the geological record, the largest eruption we know of is that of Toba in Sumatra, in about 72,000 BC. Toba yielded a quantity of stratospheric SO2 hundreds of times that of Pinatubo, which was about 20 megatonnes.
Robock and colleagues injected 300 "Pinatubos" of SO2 into the baseline run of their models, but also tried amounts as great as 900 Pinatubos. With a dynamic vegetation module, they explored the feedback on global temperatures of widespread death of vegetation due to the volcanic cooling. The feedback was not very impressive. Precipitation dropped markedly, but cooling reached about 10 degrees at most, and recovery was nearly complete after about a decade. Coupling the climate model to an interactive model of atmospheric chemistry, they found that the SO2 reaction products persist for longer and produce greater total cooling — as much as 18 degrees — but still no permanent, ice-age-like change in the climatic state. The cooling was partly offset by warming influences, such as more water vapour and ozone in the stratosphere, and more methane in the troposphere. All of these are greenhouse gases.
One thing that bothers me about the Robock study, which is a step forward, is that it still may not cover all the bases. For example the model runs may not have been long enough to pick up delayed responses of the ocean to reduced inputs of heat during the cooling episode. And the climate models were unable to follow the behaviour of the other sluggish players in the drama, the glaciers themselves.
On the other hand, look at what actually happened. In an older paper, Zielinski and co-authors found a signal from Toba in an ice core drilled in Greenland: about six years of strongly enhanced deposition of sulphate, followed by a 1,000-year long "stadial". Stadials, identified by looking at ratios of the isotopes of oxygen, are relatively short cool episodes within ice ages. However Toba was preceded by 2,000 years of more moderate cooling, which suggests that the stadial proper might have happened anyway. What is more, the oxygen isotopes repeat a very similar pattern in the 2-3,000 years after the end of the "Toba stadial": rapid warming, moderate cooling, rapid cooling, with no evidence for volcanism at all. In fact, these two excursions look rather like Dansgaard-Oeschger events.
So we have a plausible but not compelling link between our only known hypereruption and a limited amount of long-term cooling. If a Toba happened tomorrow, it might presage a short stadial, but not a long one, and anyway stadials ought not to be at the top of your list of things to worry about. But on the purely intellectual side, the effort to understand Toba nevertheless bears on an important question. How hard do we have to hit the climate system before it really gets upset, or, putting it another way, what does "tipping point" mean?
We have made some astounding intellectual advances in the past few millennia, and we do right to honour our fellows who make these forward leaps. It is proper to regard Isaac Newton, for example, as one of the most important human beings ever. But the 1% of inspiration would be nothing without the necessary 99% of perspiration, and most intellectual advances have been anonymous.
The oldest recognizably modern ideas about glaciers are no older than a couple of centuries, but the way for them was paved by a lot of preparatory observation and thought. Although neither the Greeks nor the Romans had a word for glacier, I cannot believe that nobody had observed or thought about glaciers before the eighteenth century.
Ötzi, the Iceman who died at the main drainage divide of the Alps about 5,300 years ago, probably crossed the divide regularly for pastoral purposes. Surely he must have had a word for the thing, now called the Niederjochferner, on which he died. Besides glacier and its relatives, there are several other words for the thing in alpine languages: vedretta and vadret in Romansch and Friulian, ferner in the dialect of the Tyrol, and kees, another Tyrolean dialect word. Several small neighbours of Ötzi's glacier are called kar. We do not know whether Ötzi used an ancestor of one of these words, but it would have been hard for him to move around and do his work without some such token.
I have not found any information about the history of vadret. The -et may be a diminutive suffix, or a relic of some meaning that has now been lost, but is it naive to wonder whether the vadr- part is a relative of English water? You have to allow a certain slipperiness in the meanings once attached to these tokens. The evidence consists of seeming parallels between the tokens. If you accept the parallelism, you may uncover evidence of thinking. In this case, the implied intellectual achievement is the recognition that ice and water are different aspects of the same thing. Somebody had to be the first to work this out.
Of course the tokens themselves are not unchanging. They gain and lose bits from time to time, which is why the linguistics experts are satisfied that water and Greek hudor, the ancestor of our prefix hydro-, are the same. For some reason speakers of Greek are not keen on the w sound.
kar, kees and ferner seem also to have no known history before the last few centuries, although ferner is interesting because it resembles firn, a German word for compacted snow, and perhaps fonna, Norwegian for an ice cap or snowfield.
Perhaps we can get somewhere by looking for the most basic idea. Latin glacies, ice, is traceable to a reconstructed Indo-European root *gel-, cold, freezing, with descendants in the Italic, Teutonic and possibly Slavic branches of Indo-European. English belongs to the Teutonic branch, and according to The American Heritage Dictionary of Indo-European Roots modern descendants of *gel- in English include chill, cool and cold itself.
When the root acquired its -k suffix, and what it signified, are unknown. Pokorny, in his monumental 1959 Indogermanisches etymologisches Wörterbuch, suggests that it was in fact -g and was simply an example of reduplication of the initial consonant. Pokorny also thinks that *glag became glacies under the influence of other Latin nouns such as facies, appearance, and acies, edge. Some say there is a connection with Greek galaktos, milk, explicable because milk and bubbly ice can resemble each other in colour. If this is correct, which word influenced the other is not clear, and anyway the independent status of Latin *gel- is demonstrated by gelu, frost, and gelidus, frosty, icy cold.
If we have not lost the track, the deepest layer of meaning in the word glacier is the idea of cold. It makes sense to me. Even Isaac Newton showed early promise as a glaciologist. The second sentence of his Mathematical Principles of Natural Philosophy, published in 1687, was about the compaction of snow. It is true that he then lost the track, for which we should be grateful because of the new path he opened up for later glaciologists. But we should also be grateful for all of the thinking that went on before Newton. Somebody had to be first to notice that you only get snow (Indo-European *sneigwh) and ice (Indo-European *eis) where it is cold.
Climatic change in Antarctica is complicated. The northernmost part of the continent, the Antarctic Peninsula, is warming at extreme rates, while elsewhere the pattern is mixed and in some parts there appears to be little or no warming. Up to a point, we glaciologists don't mind whether Antarctica is warming or not. It is so cold that even an implausible temperature increase wouldn't come close enough to the melting point to affect the mass balance.
Indeed, there is a plausible argument that warming would make the mass balance more positive. The Antarctic interior is extremely dry because the capacity of the intensely cold atmosphere to deliver water vapour, and therefore snow, is minimal. Warmer air can carry more water vapour, so snowfall should increase in a warmer Antarctica.
The evolving mass balance of Antarctica is most interesting around the edges, though. Warmer ocean water is increasing melting at the bases of ice shelves and pulling grounded ice across the grounding lines at increasingly scary rates. A modest increase in interior snowfall would not make this picture less scary.
Ice-stream dynamics is not the only interesting thing about the periphery of Antarctica. Here, in the least cold latitudes, we observe what little melting does happen. Spread over the continent, it amounts to a few mm of water-equivalent loss per year, against gains by snowfall of about 150 mm/yr. Losses by discharge across the grounding line are much greater. But melting, if negligible in the big picture, is still interesting.
In a recent paper, Tedesco and Monaghan update a standard measure of melt intensity in Antarctica, the so-called melting index. They watch the ice sheet's emission at microwave wavelengths (8 to 16 mm) and exploit one of the most useful radiative attributes of water. At these wavelengths, the emissivity of frozen water is low, and as conventionally presented in imagery it looks bright, but when it melts its emissivity rises dramatically and it looks black. An intermittently wet snow surface flickers between bright and dark, and we can keep track of melting by noting, in twice-daily overpasses by the imaging satellites, whether the image pixels are bright (cold) or black (warm).
The melting index, summed over a glacierized region for a span of time, is measured in square-kilometre-days, an odd-sounding unit but one that captures what we want to know. For each pixel it is just the number of days on which the pixel was black times the area of the pixel. For the whole region it is the sum of these pixel counts.
The Antarctic melting index has averaged about 35 million km2 days per year (October to September, to be sure of keeping the austral summer months together) between 1980 and 2008. Here comes the intriguing feature: in 2009 it was only 17.8 million km2 days, which is not only a record low but also continues a trend towards lesser annual indices that began in 2005. The melt extent (the area experiencing at least one day of melting) was the second lowest recorded, reaching only half the average of 1.3 million km2.
Tedesco and Monaghan account for this oddity in terms of slow organized variability in how the atmosphere behaves. Two patterns of multi-annual variation in the circulation of the southern atmosphere, the Southern Oscillation and the Southern Annular Mode, together correlate rather well with the melting index. But the authors acknowledge that the correlation breaks down in some Antarctic regions, and that the common variance does not point to a clear-cut physical explanation. (Translation: we don't understand what is happening.)
Antarctica is a happy hunting ground for climate denialists, but they need to be ignored because they are on a wild goose chase. In the first place, anomalous patterns of temperature change haven't stopped melting rates from accelerating, and ice shelves from disintegrating, in the warmest part of the continent. Second, global warming is global. Regional non-warming, and even regional cooling, don't invalidate the main conclusion. The fact that we don't understand why Antarctica is anomalous doesn't invalidate it either. Finally, when it comes to Antarctic change it's the ocean that we need to worry about. From the glaciological standpoint, warmer water is the problem, not warmer air.
It seems that if you want a bunch of comments about your blog you have to say something controversial. At least, that is what happened to this blog last week. I hope that we can get back sooner rather than later to tranquil consideration of the pleasures of studying glaciers, but in response to some of the comments there is more to be said about "denialists".
I will stick with that term, which some do not like, because it emphasizes a valuable distinction between denial and doubt. I was not talking about doubters, and in fact as an antidote to breach of trust I have lately been plugging the wisdom of Bertrand Russell as encapsulated in his first commandment: "Do not feel absolutely certain of anything". There is a world of difference between denial on the one hand and healthy scepticism, or even just asking questions because you don't know what to think, on the other.
There is also a world of difference between genuine ignorance and culpable ignorance. It is a capital mistake to suppose that I know a lot more than you do. I remember a long-ago field trip to look at glacial sediments during which we managed to get, er, lost. I was sitting at the front of the bus and by a fluke managed to get us unlost. One of the students said "How did you do that?!", at which point the bus driver interjected": "That's why you're a student and he's a professor." True, but superficial. There is an infinity of subjects about which I am genuinely ignorant.
I do know a superficially greater amount about glaciers than you (probably), which is why I am the blogger and you are the reader, but that is not important. One of the points I tried to make last time was that the denialists who commented on the news stories about the Himalayan-glacier fiasco are culpably ignorant.
I admit that "trust me, I'm a scientist" makes a lousy sales pitch, but nearly all of the denialist comments that I was deploring boil down to "trust me, even though I'm a dope". Seen from one angle, what I have just put down is a terrible thing for a scientist and university professor to say. It is rude and probably hurtful. It breaks elementary rules about how to make conversations work. (Don't rile your adversary. Give him a way out.) So it cannot possibly advance the discussion. Or can it? I have been worrying a good deal about this recently.
First of all, I am not selling anything. My scientific contributions about glaciers are just contributions, aimed at pushing the frontier of knowledge and understanding forward by a little bit. They are intended to be read critically and accepted or rejected according to the best judgement of the reader. Second, and more fundamentally, there is an awkward attribute of "trust me, even though I'm a dope" that I can't shake out of my mind, namely that whether or not it is helpful or kind or sensible it is a true paraphrase of the denialist comments.
To put it as diplomatically as I can, there is a problem at the core of the debate about climatic change, and the problem is the uniformly low calibre of the arguments on one side. The arguments on the other side vary from pretty good to compelling. There are loopy environmentalists, of course, but none of them contributed to the newspaper discussions I am talking about. I don't know how to solve this problem, but winking at it doesn't make it go away.
One thing about glaciers that doesn't get a lot of attention is that they are independent indicators of the state of the atmosphere. The river of reasoning has the spectral absorption bands of carbon dioxide at one of its sources, but further downstream it is braided. The information from weather stations is one of the channels, but the information from glaciers is a different channel. Even if, against all probability, the denialists were to succeed in knocking out my colleagues at the Climatic Research Unit at the University of East Anglia, they would still have succeeded at most in blocking one of the channels temporarily. The carbon dioxide molecules would still be absorbing and re-emitting infrared radiation. The consequent feedbacks would still be at work. The atmosphere would still be getting warmer. Most awkwardly for the denialist cause, the glaciers would still be shedding mass at an accelerating rate.
If you forget for a moment about the weather-station channel and about the carbon dioxide molecules at the headwaters of the stream, and try to explain why the glaciers are shrinking, and shrinking faster now than formerly, you come up against the considered judgement of the scientific community. Science has agreed that you can't answer these questions satisfactorily if you forget about the carbon dioxide molecules. And even if you persist in forgetting, you still have no coherent basis for tackling the question "What should we do about this?". The denialist answer is "nothing", but that brings me to my last point.
I want to emphasize that my comment-eliciting remarks last time were a direct criticism of those members of the public who can be described accurately as denialist, as opposed to sceptical or doubting. I haven't got a satisfactory answer for Clif Carl's poser about how to have his doubts addressed or for Steve Carson's thoughtful analysis of how best to bring travellers back from the borders of denial. I am not attacking the shadowy "vested interests" that are often blamed for climatic misinformation. Nor am I saying that the denialist citizens who comment on the newspaper articles are the dupes or stooges of these vested interests – which would be truly insulting. I am saying that we have to do something about improving the calibre of the debate, and I have no idea what. When it comes to the study of how the public makes up its mind, I am just another member of the public.
What I am saying seems to lead us to the absurdity of requiring ordinary citizens to spend their evenings and weekends boning up on glaciology, spectroscopy and a long list of other special subjects. The alternative seems to be for them to trust somebody, to which, as we have seen, there are objections. That is why I prefer to write about jam jars, baskets of eggs, fiords that turn out to be astonishing and stuff like that. Boning up on glaciers can be a lot more fun than it sounds like.
This blog is going to be a little bit different, because I need to let off steam about Himalayan glaciers, addressing myself mainly to readers, if any, who don't believe in global warming.
Ben Santer is a climatologist who has done much more than most to advance our understanding of human influence on the climate. In his words from the IPCC's Second Assessment, published in 1995, "The balance of evidence suggests a discernible human influence on climate." Advances since 1995 are encapsulated in the words of the IPCC's Fourth Assessment, published in 2007: "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
In a press conference call last week, Santer asserted that it would be wrong to use the mouse to cast doubt on the elephant. He was reacting to recent excitement in the media about Himalayan glaciers. Himalayan glaciers are the mouse in the room. Denialists evidently have no interest in the fact that sustained dispassionate study of the Earth and its atmosphere shows unequivocally, as summarized in the IPCC's periodical assessments, that there is also an elephant in the room.
Santer is absolutely right about both the elephant and the mouse. I, however, want to focus on the mouse.
I am the guy who found the typo. That is, I found the sources of the mistaken claim, made in the second volume (section 10.6.2) of the IPCC's Fourth Assessment, that Himalayan glaciers are very likely to disappear by 2035 or perhaps sooner. I am also the guy who tipped off Fred Pearce, the author of the 1999 news story in New Scientist that is the de-facto source of the mistaken claim. Pearce's story in last week's New Scientist (16 January) is the spark that ignited the present firestorm threatening the IPCC in general and its chair, Dr Rajendra Pachauri, in particular. I am also the guy who, with three fellow glaciologists, wrote to Science describing the nature of the Himalayan errors.
Finally, I am a guy who like several thousand other scientists holds a tiny share of the 2007 Nobel Prize for Peace along with Dr Pachauri. That is, I contributed to the IPCC's Fourth Assessment.
Rating the news stories on clarity and factual accuracy, the widespread media coverage of the Himalayan mistake has ranged from not very good to very good indeed. On the whole, except for some misattributions and for their addiction to sound bites, I have no substantial fault to find with the journalists. But many of the online news outlets invite comments from readers. With rare exceptions, those comments make unutterably dismal reading.
No scientist can fault members of the public for not being experts. On big questions that are also complicated, they have to trust somebody. Any failure of trust must be painful. But that does not excuse illogic, ignorance and failure to check facts.
The most illogical of the comments on Himalayan-glacier stories last week are those that take the part for the whole. Those commenters who dismiss the entire Fourth Assessment should read the part of it (section 4.5 of the first volume) to which I contributed. If they find anything wrong with it (which I doubt) they should let me know and I will try to fix it. Pachauri is dead right when he says that the Himalayan mistake was a collective failure. We could have fixed section 10.6.2 of the second volume, but failed to because the right mechanisms for making 3000 pages of text all consistent with one another were not in place. We have to do better next time.
Ignorance is unpardonable, or at least very risky, if you feel inclined to shoot your mouth off. Speech is free, but if you want to be taken seriously you need to know your stuff. One point on which many of the newspaper readers are ignorant has to do with money. I don't know how many salaried persons work for IPCC. But none of the contributing authors are paid, up at least as high as the level of Chapter Lead Author. The unknown colleague who wrote the mistaken paragraph about Himalayan glaciers was not paid to do so. I got nothing for the couple of hundred hours I put in on my contribution to the Fourth Assessment, or for tracking down the typo. I do get a salary, but it is for being a university professor. Contributing to IPCC assessments is not what they pay me for.
Failure to check facts is a tough one for an IPCC contributor to tackle, given that we are talking about a failure of IPCC to check its facts. But the difference is that we have to take the consequences and the irresponsible commentator doesn't.
If you write that the atmospheric concentration of carbon dioxide is "widely accepted as being about 350 parts per million", and walk away, it doesn't do much good for me to answer that it is known with high confidence to be between 385 and 390 parts per million (in 2009, on a global annual average). If you write that the hockey-stick graph "has been discredited", you have a good chance of getting away with it, but that doesn't stop it being a wrong fact. Every objection to the hockey-stick graph, and there have been some plausible ones, has been unpicked, found to have no scientific basis, and explained. If you write that "Latest sea level measurements from benchmark island shows sea level is dropping", you need to be told, if you are still there, that that is rubbish. I don't know what "benchmark island" means, but the current best estimate of the rate of sea-level rise, averaged over the world during 2003 to 2008, is +2.5 millimetres/yr, give or take 0.4 mm. (I suspect it might be on the low side, but that is another story.)
You may have noticed that there is nothing about Himalayan glaciers in the last paragraph. That is because there is nothing about Himalayan glaciers in the readers' comments. Although they should be, they aren't interested in Himalayan glaciers.
Probably the least excusable of the failings of the denialist commentators, however, is muddle-headedness. Many of the opinions they express are actually about the levying and spending of tax, and are opinions to which as taxpayers they are clearly entitled. But you need a clear head to grasp that opinions about tax are not a warrant for any opinion whatsoever about Himalayan glaciers or the findings (as opposed to the funding) of the IPCC.
Few as they are, the real facts about Himalayan glaciers are disturbing enough that there is no need, or justification of course, for exaggerating them. Allowing for undersampling, measurement uncertainty and all the other things that make scientific pronouncements fuzzy, Himalayan glaciers are indeed losing mass, and it is more likely than not that they are losing mass faster now than a few decades ago.
When you make a scientific pronouncement about the future, you add new dimensions of fuzziness. Still, it is easy to show on the back of an envelope that there is no chance at all of Himalayan glaciers being gone by 2035. There is no plausible scenario, even with plausible exaggeration of human interference with the climate, that would deliver the energy required to melt the Himalayan ice in the time available. But Himalayan ice is a non-renewable resource. The more of it we pour into the ocean, the less our stock of fresh water, the less our chance of keeping life bearable for the people of the Indian subcontinent, and the less our chance of keeping sea-level rise within reasonable bounds.
Your options as a denialist are limited. You can elect legislators who have accepted the IPCC's findings and will use tax as an instrument for encouraging people to get to work more cheaply. Or you can allow them to use the law, making it an offence to drive to work. Or you can continue to refuse to accept the presence of the elephant in the room, seizing on mice as an excuse. Sooner or later the market will make driving to work too expensive for you, although that will be among the least of your worries. Pick the least unpalatable option.
The term "basket-of-eggs topography" in glacial geomorphology is a metaphor for the appearance of drumlin fields. Drumlin is Gaelic for a rounded but elongate hill or ridge. Where you find one drumlin you usually find a whole field. They tend to be quite tightly packed, and a basket of eggs is a rather apt analogy.
More apt than you might think. Laying an egg is a practical problem in hydrodynamics, solved long ago by our amphibian and reptilian ancestors. Forcing glacier ice over a resistant bed is an analogous problem, at least to the extent that both the bird and the glacier – usually an ice sheet – have to balance force against resistance. One of the most distinctive attributes of drumlins is that they are smooth.
This does not get us very far, though. Drumlins might look like eggs because they represent roughening of an originally smooth (flattish) glacier bed or, equally likely, smoothing of a rough bed. But why did the ice sheet and its bed find it mutually convenient to generate the particular amount of smoothness that we can see today? Why don't we see drumlin fields everywhere? Are there drumlin fields beneath the modern Antarctic and Greenland Ice Sheets? And if so, can we learn about the behaviour of ice sheets, and in particular their behaviour in the worrisome near future, by working out how the ancient ice sheets drumlinized their beds?
The answer to the last question is Yes. Progress, however, has been frustratingly slow. Several intriguing papers demonstrate, either analytically or by numerical modelling, how drumlins could possibly form, but as yet there is no sign of a compelling universal explanation.
Now, Chris Clark and co-authors have fallen back on an old strategy, that of compiling a large sample of simple measurements in the hope that insight will emerge from the sheer weight of the evidence. It is easy to criticize this approach as mindless, and it is true that they have not tackled the big questions, but in my view they have indeed produced food for thought.
The first thing to note about the Clark sample is its impressive scale. They counted all of the drumlins in the British Isles – all 58,983 – and assembled aggregate statistics for half as many more from other glaciated regions. Inadequate sampling is not likely to be one of the major concerns about their results.
They measured the length and, when possible, the width of each drumlin. The average elongation (length divided by width) is 2.9, and the most common elongations are between 2.0 and 2.3, so drumlins are typically two or three times as long as they are wide.
Several non-obvious facts emerge immediately. First, drumlin lengths and widths have unimodal frequency distributions (well-defined single peaks). I buy the argument that this means that "drumlin" is a meaningful single concept and not, for example, a jumble of other concepts. Second, drumlins are no shorter than 100 m. This suggests that, whatever dynamical phenomena are represented by the word "drumlinization", they have a physical lower limit. (To me it smells like a fraction of the ice thickness, but that is as far as my intuition takes me.) Third, the frequency distributions are skewed, meaning that increasingly small proportions of the total sample are very long (or wide, or elongate). There does not seem to be any particular upper limit to the dimensions of drumlins. Perhaps they grade into the very elongate features that geomorphologists call megaflutes.
What Clark and colleagues find most surprising about their sample is that it exhibits a clear scaling law: for any given drumlin length, the greatest observed elongation is equal to the cube root of the length. I agree that this is both clear and surprising, and that it must mean something, although I have no idea what. But for me the most striking thing about their paper is Figure 7, a map that shows that drumlins are essentially lowland landforms. (For some reason, they left the ice-sheet margin off this map, but you can find it in many textbooks. Right now I am looking at Figure 12.1 of Glaciers and Glaciation by Benn and Evans.) Drumlin-free lowlands are not uncommon in the glaciated parts of the British Isles, but all of the uplands, especially the most rugged parts, seem to be entirely free of drumlins. Were they already too rugged, so that drumlinization was unnecessary? Was the ice too thin? Too slow? Too cold? As I said, food for thought.
A little soot can make a big difference to the brightness of snow. Freshly fallen snow, when clean, is one of the brightest of substances, reflecting well over 90% of incident sunlight and presenting the risk of snow blindness to ill equipped travellers on glaciers.
As the snow ages, the snowflakes collapse and become rounded. Opportunities for photons to bounce off and head back into the sky become fewer. Opportunities for absorption become more frequent because the photons spend more of their time passing through grain interiors. Eventually, as the snow turns into glacier ice, the reflected fraction of incoming radiation drops to as low as one half or less.
There is more than this to the radiative physics of snow and ice. For example the wavelength of the impinging photon makes a difference, and so does the angle at which it strikes the surface (more reflection when the angle is closer to horizontal). When a thaw begins, some of the snow turns into liquid water, which, ironically, is one of the darkest of substances. So wet snow is not particularly bright. Dirt also makes a difference.
If the dirt is black enough then even a small amount reduces significantly the brightness, or albedo, of the snow. This was shown dramatically as long as 30 years ago by Warren and Wiscombe. The more soot, the more darkening, but as little as a few parts per billion by weight reduces the albedo of pure snow (that is, collections of grains of ice) by a few per cent in the visible part of the spectrum. We also get significant sunlight in the (invisible) near-infrared, but the effect of soot is much reduced there because ice is itself very dark in the near-infrared. All the same, soot makes a difference.
Photon for photon, exposed glacier ice yields two or more times as much melt water than clean snow, assuming both are at the melting point. So, we are very interested in anything, such as soot, that reduces the radiative contrast between the ice and the overlying snow. What with industrialization, growth of the human population and more intense clearance of forests by burning, there is more soot about now than there used to be. How much of it actually reaches the glaciers, and precisely how large its contribution is to the faster rates of mass loss observed in recent decades, remain open questions. But it would be surprising if we were to look for evidence of a link and failed to find it.
Evidence of a link is just what Xu Baiqing and colleagues, writing in a recent issue of the Proceedings of the National Academy of Sciences, appear to have found. They measured soot concentrations in ice cores from five Tibetan glaciers, and found radiatively significant amounts in all but one, with evidence for recent increases in at least two. These glaciers are downwind of two of the world's largest sources of airborne soot, India and western Europe. (Yes, Tibet is a long way from Europe, but the soot particles are tiny and once they are aloft they can travel thousands of kilometres before being washed out.)
And at the recent Fall Meeting of the American Geophysical Union, Bill Lau of NASA drew attention to another way in which soot can affect glacier mass balance. While the soot is still in the atmosphere it constitutes what he calls an "elevated heat pump". It heats the air (rather than the surface), the heated air rises, and new air is drawn in from elsewhere to replace it. In the Himalayan-Tibetan region, the new air comes from the south and is warm and moist, so this amounts to an induced intensification of the summer monsoon. Warmer air means more melting, but moister air means more precipitation and therefore, where the temperature is right, more snowfall. Working out the net impact on the glaciers, then, will be a challenge.
These studies leave us a long way from nailing down soot as one of the reasons for more negative glacier mass balance, which will require concurrent measurements of sootfall, incident radiation, temperature and rates of snowfall and melting. But at the very least, the soot concentration measurements show that the soot is there, and the most solid part of the deductive chain – the fact that soot makes snow absorb more radiation – is already firmly in place. Greenhouse gas is not the only pollutant we should be worrying about.
The most satisfying experiment that I ever did was done with glass beakers and a cheap thermometer. A student, Mark Aikman, and I were trying to learn more about the composition of our local glacial till – the sediment deposited in our region by the Laurentide Ice Sheet. The till is a mixture of the local limestone, which is soluble in strong acid, and material from the Canadian Shield to the north, which is not soluble. Dissolve the till in acid and you get a measure of the ratio of local to distantly derived components. The distant or "erratic" component must have been delivered by the ice sheet.
One day, Mark wandered into my office wearing a worried look. His samples were still fizzing vigorously even after immersion in acid for the stipulated time, 30 minutes. By pestering my colleagues in chemistry I found that the time was a red herring. The author of the methods textbook we were using had blundered, prescribing an inadequate amount of hydrochloric acid. Mark and I were able to clear up this point with a thermometer because the reaction of hydrochloric acid with calcium carbonate, the basic ingredient of limestone, is exothermic – it releases energy in the form of a known amount of heat per amount of reaction products.
This "finding", new to us if not to chemistry, matched nicely the field work of another student, Dan Stokes. Dan had tried to explain the genesis of the till by counting different-coloured rocks in roadside exposures. The limestone is grey, while the erratics from the Canadian Shield are pink or black, making a striking contrast. The upshot of all this AIS (absurdly inexpensive science) was that most of the till is local, having been carried no more than 2 to 5 km by the ice, but about one eighth is distantly derived, having originated who knows how many hundred kilometres up-glacier. What does this mean? Search me.
When it comes to cheap glaciology, Ernst Sorge has the Trent University geography department beaten soundly. No contest. Sorge overwintered at Eismitte, in the middle of Greenland, during 1930–31, while the leader of the expedition, Alfred Wegener, sledded back towards the coast that he was destined never to reach. Documenting his results in Publication 23 of the International Association of Scientific Hydrology in 1938, Sorge says that he and his companions Fritz Loewe and Johannes Georgi were short not only of many necessities of life, such as a living hut, but also of scientific instruments. They solved the hut problem by digging a hole in the snow, but if they wanted to make measurements they would have to improvise.
Sorge's most important instrument was his Firnschrumpfschreiber or firn compaction recorder. (Firn is snow that has settled part way to the density of ice, but isn't there yet.) It was "contrived out of pieces of board, sheet metal, jam jars, wire, string, paper and ice" and measured the rate at which two horizontal arms frozen into the firn, 1–2 metres apart vertically, approached each other. Sorge smuggled a pen into the apparatus somehow. The jam jars served as recording drums, hand-turned, so that the pen would have something to write on. They worked very well, allowing measurements of the compaction rate with a precision of one part in a thousand.
The stimulus for the instrument was the observation that their cave was settling. Sorge wanted to know whether the settling betokened the impending collapse of his home. It cannot have taken him long to make his five Firnschrumpfschreiber, because during the course of the winter he also dug a 50-foot-deep shaft in which to install them and actually made a large number of measurements. Besides, he remarks that, "During an overwintering one has time to commune with one's self about how Nature is unfolding around one."
The results from the Firnschrumpfschreiber and from density measurements in the walls of the shaft showed that the compaction rate decreases, and the density increases, with depth. More importantly, they are steady at any given depth, and are now immortalized as the basis for Sorge's Law: the density remains constant at any given depth in a cold column of settling snow.
I have nothing against billion-dollar satellite missions, and I bet Sorge and his companions got sticky, but all in all, the jam jars were a sound scientific investment.