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Recent trends in CO2 emissions

Filed under: — group @ 14 June 2010

Guest commentary by Corinne Le Quéré, Michael R. Raupach, and Joseph G. Canadell

There is a letter in Nature Geoscience this month by Manning et al (sub. reqd.) “Misrepresentation of the IPCC CO2 emission scenarios” discussing some recent statements about the growth rates of CO2 emissions compared to the IPCC scenarios that informed the climate modeling in the last IPCC report. In it they refer to results published by us and colleagues in a couple of recent papers (Raupach et al. 2007; Le Quéré et al. 2009), and to statements made by others on the basis of our results (Ganguly et al. 2009; Anderson et al. 2008; Reichstein 2010). Specifically, Manning et al object to the claim that “current CO2 emissions from fossil fuel burning were higher than the values used in climate projections by the IPCC”.

We agree with the Manning et al’s main point, and appreciate the chance to provide some clarification on the graph in question and subsequent use of our result. To be specific, recent emissions were not higher than each and every one of the climate projections by the IPCC, as has been claimed by some other studies citing our work, although they were near the top end of the range.

So what is the claim of ‘misrepresentation’ based on?
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A conclusion of the 4th International Polar Year

Filed under: — rasmus @ 13 June 2010 - (Español) (Italian)

This week, the “Oslo Science conference” the largest conference ever -it was claimed – was held on polar sciences at Lillestrøm, just outside Oslo. Some of the web-casts from that meeting are worth watching, and I found especially the talk by David Barber (“On Thin Ice: The Arctic and Climate Change”, video link here) both a bit alarming as well as fascinating.

Storms and snow affect sea-ice growth, since a layer of snow on top of the ice insulates against the cold atmosphere and prohibits ice growth. Winds and extra mass can lead to break-up, and the amount of multi-annual ice is lower than expected; it has decayed and ‘rotted’. A mission with the Canadian ice breaker apparently managed to break ice slabs much thicker than expected, due to weaker ice. Also more recent reversals of the Beaufort gyre, unexpected long swells, and new ice on top of clumps of old ice fooling the satellites to think there is more multi-year ice than really the case, are just part of the story. In the mean while, the sea-ice for this season from NSIDC is on a low note.

The main message that I took home from this was that the sea-ice is more important than I previously thought. It appears clearer now that it plays a role in the Arctic amplification – which clearly is really emerging.

Some claim that reduced sea-ice can explain cold winters in the northern hemisphere, but I’m not yet convinced. The cold winters are due to weak Arctic Oscillation, and hence a shift in the air masses bringing frigid polar southwards, and this air is replaced by milder air in the polar region. Hence, a shift in the wind system as well as milder temperatures may favour less Arctic sea-ice.

The Antarctic sea-ice cover has increased on average in the last 30 years, but not everywhere. Both the general increase around East Antarctica and the large decrease off West Antarctica are attributed to the ozone hole and corresponding changes in the Southern Annular Mode (SAM, or the ‘Antarctic Oscillation’), though this probably doesn’t explain what is happening in winter. There is no clear polar amplification observed over Antarctica, such as seen as in the Arctic, and one explanation for this may be that the Antarctic continent has large ice sheets with enormous thermal inertia. But ice core data suggest that there have been amplification there in the past too. Nevertheless, the Arctic is characterized by a polar ocean with retreating sea-ice in the northern hemisphere. In both cases, changing air masses and the winds are important for inter-annual to inter-decadal variations, both in explaining cold winters over Eurasia and sea-ice around Antarctica.

Climate Change Commitment II

Filed under: — gavin @ 2 June 2010 - (Español)

A couple of months ago, we discussed a short paper by Matthews and Weaver on the ‘climate change commitment’ – how much change are we going to see purely because of previous emissions. In my write up, I contrasted the results in M&W (assuming zero CO2 emissions from now on) with a constant concentration scenario (roughly equivalent to an immediate cut of 70% in CO2 emissions), however, as a few people pointed out in the comments, this exclusive focus on CO2 is a little artificial.

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