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In from the cold: May 2009 Archives

How many glaciers are there? For quite some time the standard estimate, offered in the 1990s by Mark Meier, was about 160,000. But when you dig a little deeper it becomes clear that there are probably a lot more than that. And of course the question connects with a closely-related question: Who cares how many glaciers there are?

The World Glacier Inventory is the place to go for a really long list of glaciers. The idea of listing the world's glaciers originated more than 50 years ago with the Special Committee for the International Geophysical Year, which resolved in 1955 that "at the conclusion of the International Geophysical Year there be published as complete a list as possible of all known glaciers".

I always like the definiteness and clarity of this directive. The International Geophysical Year ended in December 1958. The first recommendations about how to present the list of glaciers were published in 1959, in which year the first actual list, of some of the glaciers of Italy, also appeared. Since then, although there have been several ups and downs, the story has unfolded at about the pace with which it began.

Today the World Glacier Inventory exists as a computer database at the National Snow and Ice Data Center in Boulder, Colorado, containing records for just over 100,000 glaciers. I have made available a version, called WGI-XF, with records for 131,000 glaciers. If we kept counting glaciers at the average 1959-2009 rate, a little over 2,000 a year, we would have the Special Committee' s complete list 15-30 years from now, only about 70 years late. By that time a fair proportion of the glaciers that were there in the 1950s will have disappeared.

Why so slow? Part of the problem is remoteness. Surprisingly, for some parts of the world there are still no maps of large enough scale to show individual glaciers. For others there are maps but they are closely-guarded military secrets, or are very hard to obtain, or are not accurate enough. Nowadays satellite imagery is making a big difference, but even with modern data sources we come up against the second big problem, which is that compiling a useful list of glaciers, even for a single region, is very time-consuming. To be useful, the list has to give not just a position but an outline or at least an area for each glacier, and preferably a good deal of other information as well.

The third major problem is money, combined with indifference. Apparently the more money you have, the less do you care how many glaciers you have. Bhutan has a complete inventory of its glaciers. There are 677. The two least complete national inventories are those of the United States and of my country, Canada. It is true that both of these countries have a great many glaciers, and therefore a lot of work to do, but this is what makes Mark Meier's estimate of a total of 160,000 glaciers worldwide seem improbable. Guessing very roughly, there may be tens of thousands of unlisted glaciers in the U.S.A., and more than that in Canada. Add numbers like those to the 131,000 we have in hand, and speculate that there might be another 50-100,000 in the uncovered regions in the rest of the world, and you end up with an answer to the original question that has to be in the region of 300 to 500 thousand.

Who cares? I don't think anybody actually cares about the count. It is the ancillary information for which glaciologists are hungry. For the study of global change, you can't get a proper handle on glaciological change until you have a proper list of glaciers. You need to know, for example, how big each glacier was at some initial date before you can assess the significance of its size at a later date. The general picture is that all of them are smaller now, but that is an imprecise generalization. For informing policy in a responsible way we have to do better, if only because incomplete samples are vulnerable to the objection that they might be biased.

The Wilkins Ice Shelf in West Antarctica has been in the news again lately. As ice shelves go, it is rather small, but it has claimed attention because it is falling to pieces. This is not the breaking off and drifting away of one large iceberg, but a disintegration into lots of slivers, each a few tens of metres thick.

Why not one big chunk? Evidently forces are at work that cause cracks to appear and to propagate through a previously homogeneous block of floating ice, but they are more distributed in the Wilkins collapse than in the really big calving events we sometimes hear about. The slab of ice, weakly supported by the water underneath but pinned more firmly at its sides and at the grounding line, is not strong enough to resist what the engineers call "bending stresses", originating from variations in the vigour of ice flow or perhaps from the ocean tides.

Why now? Why has the Wilkins joined the growing list of spectacular recent ice-shelf failures? The trouble with the bending explanation is that it does not account for change. Ice shelves are always at risk of bending until they crack, and I know of no evidence that they are suffering more of this now than in the past. In the ordinary way, the loss by calving of icebergs (and perhaps melting on the underside) would balance the gain by snowfall and flow across the grounding line. The shelf would stay roughly the same size.

At this point, enter a now-familiar suspect: global warming. Cracks in ice shelves behave very differently when they have water in them. It is a thousand times denser than air, and magnifies greatly the forces encouraging the tip of the crack to propagate downwards. If the crack propagates all the way to the bottom of the shelf, and also sideways until it meets another crack or the shelf edge, then the job of making a new sliver is done. If there are lots of cracks, and they all fill with water and propagate right through the shelf, then the shelf falls to pieces. This seems to have happened to the Wilkins in recent months. On the other side of the Antarctic Peninsula, continuing study of the collapse of the Larsen B Ice Shelf, an even more dramatic event in summer 2002, is showing that it too disintegrated when, and probably because, its cracks filled with meltwater.

The water can only have come from melting at the surface. All of the West Antarctic ice shelves that have collapsed recently, in whole or in part, are now on the warm side of the -5ºC isotherm of mean annual air temperature at the surface. This isotherm has been migrating rapidly southwards in West Antarctica, a part of the world which, according to weather-station records, has warmed faster than almost any other during the past 50 years.

It would be wrong to think that -5ºC is a kind of tipping point. All it means, given the rather equable climate of West Antarctica, is that an ice shelf which crosses from the cold to the warm side of the isotherm begins to suffer a "significant" summer melt season. At the other end of the world, the ice shelves which once fringed the north coast of Ellesmere Island in Canada have all but disappeared over the last century. The mean annual temperature is much colder than in West Antarctica, but the annual range is much greater, and in northern Canada too the culprit seems to be increased summertime melting.

Why worry? The shelf ice made its contribution to sea-level rise when it flowed across the grounding line, roughly balancing the sea-level fall due to snow accumulating on the grounded ice. The main reason for concern is back stress. At the grounding line, just as there is a force pushing the shelf ice further out to sea, where it will eventually calve and drift away, so there is an opposing force - the back stress - discouraging the grounded ice from accelerating seawards. Take away the ice shelf and you remove the back stress.

Again Larsen B is instructive. Its collapse has provoked the land-based glaciers which formerly fed it to calve icebergs from their grounding lines at greatly increased rates. So the loss of an ice shelf is indeed a cause for concern in the context of sea-level rise. And we think we know why these losses are happening more frequently now.

Lunar Race

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The effects of the gravitational pull of the moon on the seas, coupled to a lesser extent with that of the sun, provide a significant potential source of renewable energy. There is a race underway to tap into it.

Tidal power extraction technology comes in various shapes and forms. Barrages across estuaries, trapping high tides to create a head of water, may be the most familiar, but free-standing tidal current turbines, working on the horizontal flows rather than the vertical tidal range, are a less environmentally invasive and easier to install option. There are now reputed to be 150 or so tidal current turbine projects of various types and scales underway in the UK and elsewhere, with the most developed being MCT's 1.2MW Seagen, now installed in Strangford Narrows in Northern Ireland.

Other UK projects include the nicely named 'Lunar energy' seabed-mounted ducted rotor, the 'Pulse Tidal' oscillating hydroplane system being tested in the Humber, and the 'Tidal Delay' system, which feeds power to a heat store, so that power can be generated continuously. There is also a proposal for a permeable 'tidal fence' across the Severn estuary, housing a series of tidal turbines, as an alternative to a solid 'tidal range' barrage, which would in effect dam the estuary.

There are many more tidal current projects and devices at various stages of development- there is very much a flurry of innovation going on, with tidal technology being seen as basically simpler than wave energy technology. That's hardly surprising since, with wave energy, we are trying to tap into complex chaotic wave motions in an interface between air and water, whereas tidal flows, running smoothly below the surface, are by comparison much more linear.

Although the UK still leads in this field, challenges are emerging from overseas. For example, Singapore-based Atlantis is planning to install some of their ducted rotor units in a 30MW project in Pentland Firth in Scotland. And Irelands Open Hydro is planning to install a series of 1MW versions of its novel Open Centre turbine in France, Canada- and Alderney. In addition, Voith Siemens have developed a novel gearless 1MW propellor turbine design, which is to be used in a 100 MW array in the Wando project in South Korea. Canada and the USA are also pushing ahead with a range of systems- the US Dept of Energy has allocated its first Marine Energy Grants- $7.3m in all, to 14 projects, with more now being planned.

Cleary tidal power has gone international and there is a race to be first in what could be a very large global market. In the end what will probably decide the winners is economics There is talk of some tidal current devices getting down to 2-3p/kWh in time, so the prospects look good, while there are dark mutterings amongst some of the tidal current enthusiasts about the cost of the main rival approach in the UK- the proposed Severn Tidal Barrage, put by some at 9p/kWh.

The race is on

Although it's often seen as the front-runner in the UK, the large Cardiff to Weston Barrage isn't the only tidal range option. There have been proposals for even larger barrages further down the Severn estuary. Alternatively, smaller barrages on the Severn and elsewhere (e.g. the Mersey Solway Firth, Humber etc) might be less invasive, and offshore tidal lagoons even less so.

There are also various different operational options. In terms of increasing the continuity of power output, there is the option of having segmented lagoons, so that some degree of storage might be possible, and it is also possible to pump water uphill behind barrages or lagoons, using excess off-peak power from the grid. Barrage operation on the incoming tidal flow is also an option, although that means using two-way turbines, which are more complex, expensive and prone to excessive wear and breakdown.

Although pumped storage is sometimes included as an option, most new barrage designs use conventional one-way turbines. The problem then is that they will only fire off twice roughly every twenty-four hours, with large pulses of energy for a couple of hours, which may not be matched to electricity demand. So, for example, although the 8.6GW Severn Barrage might be able to generate 4.6% of UK's electricity, only some of that could actually be used effectively in practice- unless we also spent money on major electricity storage facilities. According to the generally pro-barrage Sustainable Development Commission, by some time after 2020, when it was working, the barrage would only reduce UK emissions by about 0.92% - not very much for £20 billion, the expected construction cost.

By contrast, a network of smaller tidal turbines around the coast could deliver more continuous output, since peak tide occurs progressively later in time at each site. Tidal turbines can also be designed to swivel around to run on the flow and the ebb i.e. four times per 24 hour period. And they can be installed on a modular basis relatively quickly.

All in all, with most UK environmental groups strongly opposed to large estuary-wide barrages like that proposed for the Severn, the tidal current option looks like to one the watch. But who will win in that race is far from clear. The UK may be ahead technologically, but for example, S. Korea has plans for installing a total of around 500MW of tidal current projects.

Why don't they get the message? Environmentalists take different approaches to putting the message across. Some have allowed distinguished careers to evolve into activism. James Hansen, the director of NASA's Goddard Institute for Space Studies, is a leading example. Having spent several decades modelling climatic change and charting the course of global warming, he now wants energy producers to stop building coal-fired power stations, and is telling them why in increasingly emphatic terms. But they aren't listening to him.

bp.0901.f1.thumb.png
Fingerprint of glacier mass balance

I am not saying Hansen's approach isn't right, but in my little corner of the problem, in which I try to document the rate at which glaciers are shedding mass, I have followed most of my fellow-scientists by trying to present the facts deadpan, with due attention to all the caveats and uncertainties. The dinosaurs aren't listening to me either.

Of course, it isn't a small problem, but human inertia has a lot to do with the reluctance of the dinosaurs. Recently the politicians have realized that, apart from survival, there is money to be made out of trying to be a mammal instead. Perhaps this new message from a new quarter will help. On the whole, though, I am not disposed to be too hard on the dinosaurs, considering the scale of the problem, my own familiarity with inertia, and the fact that I am part of the problem. I buy the stuff they sell.

But we have lost a lot of time already. After Waterloo, Wellington said that it had been "a damn close-run thing", and solving this problem is going to be like that.

What can I do to help? The best I can think of is to keep sending the message. Time is running out, but it is not yet time to panic, and you can't beat facts if you want a cumulative effect. I will try in this blog to write about some of the ways in which the field of glaciology helps to pile up the facts.

I will try to show why the facts are not just important but interesting, but if I get carried away sometimes - if the facts seem more exciting to me than they do to you - you will have to bear with me if you can.

I want to begin, though, by regretting that scientists' caveats and uncertainties are not equally interesting to everybody. In my experience numbers, the scientist's stock in trade, tend to turn people off as soon as there are more than about three of them. Error bars are even less popular, but your average scientist probably spends more time on the error bars than on the measurements themselves.

The errors, of course, help to explain why we have spent more than two decades arguing about climatic change rather than taking action. But you have to be able to see the measurements in their context before you can know what they allow you to say. It is a risky mistake to think that science, because it seems to be about numbers, must therefore be crisp and focussed. In fact we spend most of our time wandering around in a fog, looking for clear patches.

Not long ago I was asked an interesting question about the fingerprint of glacier mass balance: has it changed in recent decades? It is quite clear, as we will see in a moment, that the pattern has become stronger. But has its geographical shape changed?

Consider the graph. The top panel shows the fingerprint for 1961-1990, presented as a sea-level equivalent (the result of spreading the mass lost by the glaciers uniformly over the ocean). The blip near 50 degrees south is the Patagonian icefields, the blip at 30-40 north is the Himalaya, Karakoram and so on, and most of the loss is from glaciers at high northern latitudes. We are in a fog about several of the latitude belts, because their error bars cross the zero line (no detectable change of mass).

But we are not in a fog about the global total. Add up the losses from all of the latitude belts, allowing for the uncertainty of each, and it becomes clear that in 1961-1990 the ocean was gaining mass from the glaciers as meltwater.

The lower panel shows the fingerprint for the more recent period 1993-2007, divided by the 1961-1990 fingerprint. First, the signal has grown stronger everywhere, although our confidence about this is low in many latitude belts (the error bars cross the 1 line which means no change). But second, where it matters (that is, where the signal was strong to begin with, north of 30 north, say), the signal is now two to five times stronger. Third, as in the upper panel, finding number two holds for the whole world when we average the ratios with due attention to their error bars. Glacier mass loss is much greater now than it was 20-50 years ago. We are not in a fog about this.

Fourth, the answer to the original question is Don't Know. The error bars, some of them grotesque, make it certain that we cannot say anything about whether the shape of the fingerprint has changed. We are definitely in a fog about this.

We are not entirely clueless about how to search for the nearest clear patch. For example, more measurements would help. It looks as though the glaciers in the Himalaya and Karakoram may have begun to suffer more than glaciers elsewhere. Tackling this question would require measuring them. So if the Taleban would kindly get out of the way, we could travel to the head of the Swat valley and produce an answer to a question which is more important than any of those they are asking.

We will know we are out of the fog when the error bars shrink to a more reasonable size. And at that point neither the Taleban nor the dinosaurs will be able to reject the message of the measurements, whatever it turns out to be.