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Arctic and Antarctic

Con Allègre, ma non troppo

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Guest Commentary by Georg Hoffmann (LSCE)

Climate change denial is not necessarily a speciality of Washington DC think tanks – sometimes it can also be found in old Europe. Right now there is a little media storm passing by in France evoked by an article from Claude Allègre in L’Express. Who is Claude Allègre? He is one of the most decorated french geophysicists specializing in geochemistry and the use of paleomagnetism. Being a longtime friend of the former prime minister, Lionel Jospin, he even became Minister of Education and Research in the former Socialist government. He still plays an active role within the Socialist party and though he has never published anything directly related to anthropogenic climate change, one would assume that he has some understanding of the scientific matter. But this assumption would be wrong.

In the French weekly journal l’Express he exposed his “sceptical” views in an article entitled “The snows of Kilimanjaro”. In the short editorial, he somehow became lost when following Ernest Hemingway to East Africa. Allègre mentions two scientific examples to demonstrate that there is something fundamentally wrong in the IPCC statements on the reality of climate change. First, he commented on the disappearing glaciers of the Kilimanjaro, sometimes treated as the “Panda” of anthropogenic climate change. Citing a “Nature” study (which was in fact published in Science) by Pierre Sepulchre and colleagues from my laboratory, he claimed that this modelling study demonstrated that Kilimanjaro’s glaciers are controlled by tectonic activity. In fact, the article describes the impact of tectonics of the East African Highlands on Indian ocean moisture transport —- on a time scale of millions of years! This confuses glacier variability over the last ~100 years with rainfall trends extending back to the time of the early hominids (such as Lucy).

In fact, there are good reasons to believe that the situation on the Kilimanjaro is a bit more complicated than a simple “atmosphere gets warmer/ glaciers are melting” equation (for instance, see this previous post on tropical glacier retreat). Furthermore, the real link to climate change does not come from the retreat of one single tropical glacier, but from the fact that, to my knowledge, all studied tropical glaciers have retreated over the 20th century, and the retreat rates have generally increased in recent decades.

Allègre’s misunderstanding was immediately followed by another one. Citing a recent study on relatively stable Antarctic snowfall over the last 30 years (Monaghan et al, 2006, discussed here) , he highlighted what he thought was a clear contradiction to future climate simulations of global circulation models (melting of the Antarctic ice sheet). However, that’s not what they predict. All models predict a comparably stable Antarctic ice sheet for the 21th century in which comparably moderate temperature changes in Antarctica are compensated by slight increase in snowfall. The Monaghan et al study does not contradict these model scenarios.

The French climate research community was of course not very pleased about this short sequence of misrepresentations and personal attacks (“les Cassandres”) and corrected Allègre in an open letter published here on the website of the Institute Pierre Simon Laplace (which includes links to the ongoing back and forth, for those that speak French).

Curiously enough, twenty years ago Allègre wrote in “Clés pour la géologie”, (éd. Belin/France Culture):

“En brûlant des combustibles fossiles, l’homme a augmenté le taux de gaz carbonique dans l’atmosphère, ce qui fait, par exemple, que depuis un siècle la température moyenne du globe a augmenté d’un demi-degré.”

(Translation)
“By burning fossil fuels man enhanced the concentration of carbon dioxide in the atmosphere which has raised the global mean temperature by half a degree in the last century”.

But at that time he used this argument against the anti-nuclear energy movement. It might be that there is simply a bit too much politics in Allègre’s life…

Is Antarctic climate changing?

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Is the Antarctic ice sheet getting bigger or smaller? Is it warming or cooling?

As we’ve reported in earlier posts (here and here), getting accurate answers to these questions is non-trivial, because the available instrumental data remain sparse and generally date back only a few decades, at best. While modern satellite-based techniques such as laser altimetery and gravity anomaly measurements provide important information on very recent changes, to get at the longer term we must rely on less direct methods. In the last 5 years or so, an effort has been under way, much of it under the banner “International Trans Antarctic Scientific Expedition” (ITASE), to do this by collecting many dozens of ice cores from across the Antarctic continent. Two papers out this month represent the first major compilations of results from these efforts. The first, in Science on August 11th, provides a new estimates of Antarctic snowfall changes over the last 50 years. The second, in Geophysical Research Letters (August 30th) provides the first statistical reconstruction of Antarctic temperature change, extending about 200 years into the past.
[Read more…] about Is Antarctic climate changing?

Peter Doran and how misleading talking points propagate

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Peter Doran, the lead author on a oft-cited, but less-often read, Nature study on Antarctic climate in 2002 had an Op-Ed in the NY Times today decrying the misuse of his team’s results in the on-going climate science ‘debate’. As we discussed a while back (Antarctic cooling, global warming?), there is a lot of interesting stuff going on in Antarctica: the complexities of different forcings (ozone in particular), the importance of dynamical as well as radiative processes, and the difficulties of dealing with very inhomogeneous and insufficiently long data series. But like so many results in this field, it has become a politicized ‘talking point’, shorn of its context, that is mis-quoted and mis-used by many who should (and often do) know better. Doran complained about the media coverage of his paper at the time, and with the passage of time, the distortion has predictably increased. Give it another few years, maybe we’ll be having congressional hearings about it…

Ice Sheets and Sea Level Rise: Model Failure is the Key Issue

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Guest post by Michael Oppenheimer, Princeton University

A plethora of research articles has appeared over the past year reporting new observations of the Greenland and West Antarctic ice sheets along with associated modeling results. RealClimate has reviewed the issues raised by these articles and attempted to clarify the sometimes conflicting inferences about the current mass balance of the ice sheets, as well as their future contributions to global mean sea level rise (see here and here).

Nevertheless, the issue still seems to perplex many journalists and others because there are two entirely distinct aspects of the sea level rise problem that are emphasized, depending on which scientists are speaking. On the one hand, these ices sheets are large enough to ultimately raise sea level by 7m and about 5m, for Greenland and West Antarctica, respectively. On the other, the recent observations that caused such a stir report a current contribution to the rate of sea level rise not exceeding ~1mm/yr from both ice sheets taken together. If this rate were maintained, the ice sheets would make a measurable but minor contribution to the global sea level rise from other sources, which has been 1-2mm/yr averaged over the past century and 3mm/yr for 1993-2003, and is projected to average 1-9mm/yr for the coming century (see IPCC Third Assessment Report).

The key question is whether the ice sheet contribution could accelerate substantially (e.g., by an order of magnitude) either in this century or subsequently. Sea levels were indeed much higher in the distant, warmer past but the timing of earlier sea level rise is very uncertain. From the point of view of societal and ecosystem adaptation, the timescale over which ice sheets might disintegrate, which may be on the order of centuries or millennia according to the two extremes posited in the literature, is crucial. [Read more…] about Ice Sheets and Sea Level Rise: Model Failure is the Key Issue

Sea level in the Arctic

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A recent conference presentation at AGU (reported here) while confirming that global sea level is indeed rising (in line with other estimates), showed that Arctic sea levels may actually be falling. On the face of it these preliminary results are a little puzzling (though note that this isn’t yet a properly peer reviewed paper, and so may not reflect what ends up in the journal), but it does reveal some of the complexities in analysing sea level in relatively small enclosed basins and so a brief overview of the different factors involved is probably useful. [Read more…] about Sea level in the Arctic

More on the Arctic

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By Michael Mann & Phil Jones (guest)

Svalbard, an Arctic island in the Northern North Atlantic, is predicted to warm considerably more than most of the rest of the earth in many model-based scenarios. See for example the figure to the right, which represents a relatively high-end IPCC Third Assessment Report scenario for the projected surface temperature difference between the period 2071 -2100 and 1961-1990. Svalbard is the island north of Norway at about 80N between 15-30E.

The enhanced warming in this region is related to the issue of polar amplification that we have discussed previously on RC. It also happens that the Svalbard meteorological station is the 2nd station in the World Meteorological Organization (WMO) meteorological station list. This means that it tends to get noticed. The Climatic Research Unit (CRU) of the University of East Anglia maintains one prominent version of the global surface temperature data set and as part of its routine quality control, CRU flags any unusual (anomalous warm or cold) new measurements that come in. Svalbard has now been flagged consistently over the past several months, but the values have been confirmed as accurate by the Norwegian Met Service, which operates the Svalbard station.
[Read more…] about More on the Arctic

Thank you for emitting

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A recent movie, ‘Thank You for Smoking‘, amusingly highlighted the lengths that PR reps for the tobacco companies would go to distort the public discourse on the health effects of smoking. Lest you thought that was of merely historical relevance, we would like to draw your attention to two of the funniest videos around. Lifting a page straight out of the Nick Naylor playbook, the CEI (an industry-funded lobby group) has launched a new ad campaign that is supposed to counteract all those pesky scientific facts about global warming.

The first ad (both available here) deserves to become a classic of the genre. It contains the immortal lines ‘CO2: they call it pollution, we call it Life!’ – it is beyond parody and without content – and so you should definitely see it. The second ad has a little more substance – but is as misleading as you might expect.
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Significant Warming of the Antarctic Winter Troposphere

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The “iconic” Antarctic temperature trends are the large warming seen on the Antarctic Peninsula, which has had various repercussions including the collapse of several ice shelves (some documented in a previous post). Elsewhere, though, the pattern of surface warming is more complex – trends are smaller, and while more are positive than negative they are generally not significant – see this map. Contrary to what you might have heard, this is in general agreement with model predictions.

But meanwhile, there is a record for the upper atmosphere derived from radiosondes, which we have been working on – finding old datasets and digitising them to fill in gaps. What this shows is that around East Antarctica there is a general warming of the troposphere, greatest at around mid-height (at 600 hPa) at 0.7 ºC/decade over the last 30+ years.

In itself, this is an interesting observation. The obvious question is, what does it mean? Is this natural variability; is it a response to global warming, or to changes in ozone; or something else? Ozone is unlikely, because this is winter (which conveniently means that the radiosonde temperature corrections, often a source of potential trouble, are not a problem). Two ways of trying to interpret the record are to see what GCMs run for the same period show; or to look at the re-analyses (essentially, the archived outputs from the weather-prediction models). The latter, of course, incorporate many of the radiosonde observations that we are using, and so don’t count as independant. Despite this, the ECMWF re-analyses show *greater* trends than we see in the observations; and a maximum trend over West Antarctica (which has no radisonde stations to allow us to verify this). A climate model (HadCM3, with an ensemble of four members) shows similar patterns to the observations, but this time too little warming; and a good deal of variation between the ensemble members. So neither of these is helps much with the interpretation.

So we are currently left with an open question; hopefully, this will stimulate us and other researchers to explain it in the future.

[Quick addendum: the paper itself is available via this.]

How much future sea level rise? More evidence from models and ice sheet observations.

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Lots of press has been devoted to four papers in this week’s Science, on the topic of ice sheets and sea level.

We’ve already discussed the new evidence that Greenland’s glaciers are speeding up. What is new this week is an effort to evaluate the impact of future warming on Greenland by looking at what happened to it last time it got very warm — namely during the Last InterGlacial (LIG) period, about 125,000 years ago. The same group of authors looked at this in two ways, using NCAR’s Community Climate System model (CCSM) coupled to a state-of-the-art 3-D ice sheet model.
[Read more…] about How much future sea level rise? More evidence from models and ice sheet observations.

The Greenland Ice

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by Rasmus Benestad, Eric Steig and Gavin Schmidt

In a recent paper in Science, Eric Rignot and Pannir Kanagaratnam present new satellite observations of the speed of glaciers of Greenland, and find that they are sliding towards the sea almost twice as fast as previously thought. Additionally, between 1996 and 2005, they detected a widespread glacier acceleration and consequently an increased rate of ice discharge from the Greenland ice sheet. However, previous papers have recently noted an increase in snow accumulation in the interior (i.e. Johannessen et al., 2005), so how do these different measurements fit into the larger picture of Greenland’s net mass balance?
[Read more…] about The Greenland Ice