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The weirdest millennium

Filed under: — stefan @ 29 May 2007

Much research effort over the past years has gone into reconstructing the temperature history of the last millennium and beyond. The new IPCC report compiles a dozen reconstructions for the temperature of the Northern Hemisphere (including of course the original “hockey stick” reconstruction, despite opposite claims by the Wall Street Journal). Lack of data does not permit robust reconstructions for the Southern Hemisphere. Without exception, the reconstructions show that Northern Hemisphere temperatures are now higher than at any time during the past 1,000 years (Figure 1), confirming and strengthening the conclusions drawn in the previous IPCC report of 2001.

Fig. 1: Figure 6.10 (panel b) from the paleoclimate chapter of the current IPCC report (see there for details).

“Climate sceptics” do not like this and keep coming up with their own temperature histories. One of the weirdest has been circulated for years by German high-school teacher E.G. Beck (notorious for his equally weird CO2 curve). This history shows a medieval warm phase that is warmer than current climate by more than 1 ºC (see Figure 2). So how did Beck get this curve?


Fig. 2, modified from E.G. Beck (we added the green parts).

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Why global climate models do not give a realistic description of the local climate

Filed under: — rasmus @ 27 May 2007 - (Português) (English)

Global climate
glasses Global climate statistics, such as the global mean temperature, provide good indicators as to how our global climate varies (e.g. see here). However, most people are not directly affected by global climate statistics. They care about the local climate; the temperature, rainfall and wind where they are. When you look at the impacts of a climate change or specific adaptations to a climate change, you often need to know how a global warming will affect the local climate.

Yet, whereas the global climate models (GCMs) tend to describe the global climate statistics reasonably well, they do not provide a representative description of the local climate. Regional climate models (RCMs) do a better job at representing climate on a smaller scale, but their spatial resolution is still fairly coarse compared to how the local climate may vary spatially in regions with complex terrain. This fact is not a general flaw of climate models, but just the climate models’ limitation. I will try to explain why this is below.

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Glacier Mass Balance: equilibrium or disequilibrium response?

Filed under: — group @ 24 May 2007

Guest Commentary from Mauri S. Pelto

I get asked at least once a day about the future prognosis for alpine glaciers and whether they have a future. I will focus here on North American glaciers whose mass balance measurements in the West from 1984-2005 indicate a declining trend. The trend suggests that all of the glaciers are out of balance and that some will disappear. The question is determining which glaciers are merely out of equilibrium and can retreat to a position of equilibrium, and which are in complete disequilibrium and will melt away? Let me explain.
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Start here

Filed under: — group @ 22 May 2007 - (Slovenčina) (Polski) (English)

A Bulgarian translation is available here (via Ivan Boreev).

A bit of philosophy

Filed under: — eric @ 16 May 2007

Eric Steig and Gavin Schmidt

The two of us participated last week in an interesting meeting at the University of Washington on Ethics and Climate Change. Other scientists in attendance included Dennis Hartmann, who gave an overview of the current state of the science, and sometime RealClimate contributor Cecilia Bitz. Organized by Associate Professor of Philosophy Stephen Gardiner, the conference was dedicated to the particular ethical and moral issues raised by the spectre of anthropogenic climate change. Since we aren’t philosophers by training, and since it would probably stray too far from RealClimate’s focus on science, we won’t comment in great detail. However, we thought it worth making our readers aware that there is a very interesting and growing literature on the subject. Based on their remarks at the conference, we heartily recommend checking out the papers and commentaries written by the various philosphers, scientists, and political theorists who attended. You can get abstracts of their talks on the conference web page. Below, we simply wish to note several issues raised at the conference that we found particularly interesting.
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