Arctic is Extreme

Arctic is Extreme

A couple of blogs back in August I talked about this summer’s sea ice in the Arctic and the implications of an ice-free Arctic Ocean on national security. Jeff Masters recently had a blog that updated both sea surface temperature and Arctic sea ice. The ocean is still warmer than ever observed, and sea ice was the third lowest observed. The last three years have been the three lowest of a relatively short sea ice observation record.

In the last few weeks there have been a number of reports about the Arctic. Since the 2007 IPCC Report, there has been increased analysis of the uncertainties in the predictions of Arctic climate change and the behavior of ice sheets. There has also been more scrutiny of the observations, and an entire campaign to investigate polar regions (The International Polar Year).

The paper by Darrell Kaufman and many colleagues, entitled Recent Warming Reverses Long-Term Arctic Cooling (Science, 2009), is an elegant analysis that puts together many pieces. This paper uses observations from ice cores and tree rings, and especially, lakes across the Arctic. Sediments are used from the lake. These sediments are laid down and there is a temperature dependence of the sediments. There are both physical and biological reasons that there is temperature dependence. The easiest process to understand is the presence of creatures and creature detritus in the sediments, which is related to the biological activity of the spring and summer. (There are good references in the paper if you want to know more – here’s one: Smol et al. PNAS 2005 , and a simple web resource varve analysis) Therefore, we can get good records of not only each year for the last couple of thousand years, but differences between the warm season and the cold season.

The paper looked at several pieces of the puzzle. One piece is the fact that the orbital parameters of Sun and the Earth are such that there should be less solar heating of the Arctic. Therefore, based on the Sun, the Arctic should be cooling. This is found to be true for much of the last 2000 years, essentially to 1900. For the last century, however, they find systematic and strong warming. The signal sticks out like a sore thumb. So the paper establishes, from observations, that not only is there warming, but the warming overwhelms the cooling expected from the wobbles in the Earth’s motion about the Sun. The paper does not, however, stop here. The authors also add a long model simulation looking to see if the same signal is found in the models. The answer is yes, and it is a remarkably robust signal. The robustness of the signal is likely due to the strong signal found in the Arctic, and the sensitivity of that signal to snow on the land and sea ice. Remember, if there is less snow, less solar energy is reflected, more is absorbed, and the warming is amplified. The amount that the warming of the Arctic in the twentieth century lies outside of the 2000 year average is stunning.

This analysis reminds me of another analysis that I felt especially convincing, that of Osborn and Briffa (see blog)that established that the geographical extent of twentieth century warming was the greatest of, at least, the last 1000 years.

The Arctic is warming, and the magnitude of that warming is so far outside of the natural variability that it is, like the IPCC report said, “unequivocal.” It’s still a hard trip, but two German merchant ships went from Korea to Siberia in the Arctic Ocean, and they are already planning to do it again in 2010.

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Arctic Sea Ice Extent from Snow and Ice Data Center Daily Update