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In from the cold: January 2010 Archives

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.