“These results are quite strange”, my colleague told me. He analysed some of the recent climate model results from an experiment known by the cryptic name ‘CMIP5‘. It turned out that the results were ok, but we had made an error when reading and processing the model output. The particular climate model that initially gave the strange results had used a different calendar set-up to the previous models we had examined.
Guest post by Brigitte Knopf
Global emissions continue to rise further and this is in the first place due to economic growth and to a lesser extent to population growth. To achieve climate protection, fossil power generation without CCS has to be phased out almost entirely by the end of the century. The mitigation of climate change constitutes a major technological and institutional challenge. But: It does not cost the world to save the planet.
This is how the new report was summarized by Ottmar Edenhofer, Co-Chair of Working Group III of the IPCC, whose report was adopted on 12 April 2014 in Berlin after intense debates with governments. The report consists of 16 chapters with more than 2000 pages. It was written by 235 authors from 58 countries and reviewed externally by 900 experts. Most prominent in public is the 33-page Summary for Policymakers (SPM) that was approved by all 193 countries. At a first glance, the above summary does not sound spectacular but more like a truism that we’ve often heard over the years. But this report indeed has something new to offer.
The 2-degree limit
Guest commentary from Drew Shindell
There has been a lot of discussion of my recent paper in Nature Climate Change (Shindell, 2014). That study addressed a puzzle, namely that recent studies using the observed changes in Earth’s surface temperature suggested climate sensitivity is likely towards the lower end of the estimated range. However, studies evaluating model performance on key observed processes and paleoclimate evidence suggest that the higher end of sensitivity is more likely, partially conflicting with the studies based on the recent transient observed warming. The new study shows that climate sensitivity to historical changes in the abundance of aerosol particles in the atmosphere is larger than the sensitivity to CO2, primarily because the aerosols are largely located near industrialized areas in the Northern Hemisphere middle and high latitudes where they trigger more rapid land responses and strong snow & ice feedbacks. Therefore studies based on observed warming have underestimated climate sensitivity as they did not account for the greater response to aerosol forcing, and multiple lines of evidence are now consistent in showing that climate sensitivity is in fact very unlikely to be at the low end of the range in recent estimates.
- D.T. Shindell, "Inhomogeneous forcing and transient climate sensitivity", Nature Climate change, vol. 4, pp. 274-277, 2014. http://dx.doi.org/10.1038/nclimate2136
More open thread. Unusually, we are keeping the UV Mar 2014 thread open for more Diogenetic conversation and to keep this thread open for more varied fare.
The second part of the new IPCC Report has been approved – as usual after lengthy debates – by government delegations in Yokohama (Japan) and is now public. Perhaps the biggest news is this: the situation is no less serious than it was at the time of the previous report 2007. Nonetheless there is progress in many areas, such as a better understanding of observed impacts worldwide and of the specific situation of many developing countries. There is also a new assessment of “smart” options for adaptation to climate change. The report clearly shows that adaptation is an option only if efforts to mitigate greenhouse gas emissions are strengthened substantially. Without mitigation, the impacts of climate change will be devastating.
Guest post by Wolfgang Cramer