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Atlantic circulation change summary
Nature this week has an excellent summary of the state of the science with regards to possible changes in the ocean thermohaline (or meridional) circulation in the Atlantic and its impact on climate. Even though it quotes a couple of us, it’s still worth reading if you want to understand how results like the Bryden et al paper – that suggested that the Atlantic overturning had reduced by 30% in recent decades – are assimilated into the scientific picture. [Read more…] about Atlantic circulation change summary
New look
Hopefully readers will appreciate the new look we have given the site (you may need to reload for it to work properly). We have added some new features attached to the buttons above – an index which may prove useful in navigating the site, a more prominent Search function (which searches posts and comments), a link to the archives etc. This has allowed us to reduce some of the clutter and hopefully make this site a little more user friendly. If there are any problems, wrinkles that need to be ironed out, or if you have suggestions for further improvement, let us know at contrib -at- realclimate -dot- org.
Was the record Amazon drought caused by warm seas?
On December 11, 2005, The New York Times ran a story on record drought conditions in the Amazonas region of Brasil, linking it to global warming, and specifically the warm ocean temperatures in the North Atlantic that have also been linked to the ferocity of the 2005 Atlantic hurricane season. This prompted a response from Chris Mooney, calling for a comment from RealClimate about whether such an assertion is valid, as we earlier made it very clear that it is impossible to say whether one single extreme event in a very noisy environment – such as Hurricane Katrina – is related to climate change. So we decided to take a look at this phenomena, and address why there might be a connection and what it takes to make an attribution. [Read more…] about Was the record Amazon drought caused by warm seas?
Scientists baffled!
Every so often a scientific paper comes out that truly surprises. The results of Keppler et al in Nature this week is clearly one of those. They showed that a heretofore unrecognised process causes living plant material to emit methane (CH4, the second most important trace greenhouse gas), in quantities that appear to be very significant globally. This is surprising in two ways – firstly, CH4 emission is normally associated with anaerobic (oxygen-limited) environments (like swamps or landfills) but chemistry in plants is generally thought of as ‘aerobic’ i.e. not oxygen-limited, and secondly, because although the total budget for methane has some significant uncertainty associated with it (see the IPCC assessment here), the initial estimates of this effect (between 62–236 Tg/yr out of a total source of 500+ Tg/yr!) give numbers that might be difficult to incorporate without some significant re-evaluations elsewhere.
Reactions so far have been guarded, and there will undoubtedly be a scramble to check and refine the estimates of this process’s importance. Once the dust settles though, the situation may not be so different to before – some emissions may turn out to have been mis-identified, this source may not be as large as these initial estimates (10-30% of total sources) suggest, or it might radically challenge our current understanding of methane’s sources and sinks. However, the process by which this is decided will demonstrate clearly that the scientific method is alive and well in the climate sciences. That is, as long as a work is careful and the conclusions sound, papers that upset the apple cart can appear in the major journals and have a good chance of ending up being accepted by the rest of the field (providing the conclusions hold up of course!).
Update 19 Jan: The authors of the study have released a clarification of their study to counter some of the misleading conclusions that had appeared in the press.
Polar Amplification
Guest commentary by Cecilia Bitz, University of Washington
“Polar amplification” usually refers to greater climate change near the pole compared to the rest of the hemisphere or globe in response to a change in global climate forcing, such as the concentration of greenhouse gases (GHGs) or solar output (see e.g. Moritz et al 2002). Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow. There are a host of other lesser reasons that are associated with the atmospheric temperature profile at the poles, temperature dependence of global feedbacks, moisture transport, etc. Observations and models indicate that the equilibrium temperature change poleward of 70N or 70S can be a factor of two or more greater than the global average. [Read more…] about Polar Amplification
One year on…
RealClimate has been online for just over a year, and so this is probably a good time to review the stories we’ve covered and assess how well the whole project is working out.
Over the last 12 months, we’ve tackled a 100+ scientific topics that range from water vapour feedbacks, the carbon cycle, climate sensitivity, satellite/surface temperature records, glacier retreat, climate modelling to hurricanes. We’ve had guest postings that span questions of Martian climate change to Arctic ozone depletion and solar forcing. We’ve crossed virtual swords with Michael Crichton, the Wall Street Journal’s editorial board, George Will, Nigel Lawson, Fox News and assorted documentary makers (though only one person ever threatened to sue us). Hopefully our contributions have interested, intrigued and occasionally amused (at least a few of you…). [Read more…] about One year on…
How to be a real sceptic
Scepticism is often discussed in connection with climate change, although the concept is often abused. I therefore thought it might be interesting to go back and see what the epitome of 20th Century sceptics, Bertrand Russell, had to say on the subject. This is extracted from the Introduction to his ‘Sceptical Essays’ (1928):
[Read more…] about How to be a real sceptic
Naturally trendy?
From time to time, there is discussion about whether the recent warming trend is due just to chance. We have heard arguments that so-called ‘random walk‘ can produce similar hikes in temperature (any reason why the global mean temperature should behave like the displacement of a molecule in Brownian motion?). The latest in this category of discussions was provided by Cohn and Lins (2005), who in essence pitch statistics against physics. They observe that tests for trends are sensitive to the expectations, or the choice of the null-hypothesis .
2005 temperatures
Due to a historical quirk (of unknown origin), the World Meterological Organisation releases its summary for each year based on the Dec to Nov ‘meteorlogical year’ means (rather than the more usual calendar year). Anyway, the WMO summary is now available, as is the NASA GISS analysis and the CRU summary. The point upon which all the analyses agree is that 2005 was exceptionally warm and that it continues the long term mean warming trend. All show record warmth in the Northern Hemisphere since 1860, while GISS gives 2005 as the warmest year globally as well (CRU/WMO have it second after 1998). As the summaries indicate, the differences in ranking are on the order of a few hundredths of a degree (smaller than the accuracy of the analysis) and so a definitive ranking is not possible. Differences in how the separate analyses deal with missing data are responsible for most of the apparent variations. Note too that the convention for the base periods for the anomalies differ between the analyses (1961-1990 for CRU/WMO, 1951-1980 for GISS), but this does not affect the rankings.
Update 7pm: The GISS analysis curiously appears to have gone off line….
Update 8am 16 Dec: The GISS summation is still not back up, but the raw data and new figures do seem to be available http://data.giss.nasa.gov/gistemp . Note that as pointed in comment #5, the WMO/CRU/Hadley Centre analysis is for Jan-Nov, and not for the met. year as stated above (though the GISS analysis is). Don’t ask us why!
Final Update 11pm 16 Dec: The GISS analysis is back!
(traduit par T. de Garidel)