On Feb 25, 10:06 pm, Robert I Ellison <[email protected]> wrote: > This article on climate computing was published recently. Only fair > that I link to it here as well. > > http://www.quadrant.org.au/blogs/doomed-planet/2010/02/ellison > > Climate sensitivity is always a fiction. There are non-linear > processes sorted out in computer programs. So the idea of climate > sensitivity as a number is related to a doubling of CO2. It is not > the same number at 0.5 or 1.5 times CO2 because of the non-linear > responses. > > More generally climate sensitivity is thought of in qualitative terms > - higher or lower sensitivity to greenhouse gas changes. In terms of > abrupt climate change - I think both are answers to the wrong > question.
http://www.realclimate.org/index.php/archives/2007/08/the-co2-problem-in-6-easy-steps/ [...] Step 5: Climate sensitivity is around 3ºC for a doubling of CO2 The climate sensitivity classically defined is the response of global mean temperature to a forcing once all the ‘fast feedbacks’ have occurred (atmospheric temperatures, clouds, water vapour, winds, snow, sea ice etc.), but before any of the ’slow’ feedbacks have kicked in (ice sheets, vegetation, carbon cycle etc.). Given that it doesn’t matter much which forcing is changing, sensitivity can be assessed from any particular period in the past where the changes in forcing are known and the corresponding equilibrium temperature change can be estimated. As we have discussed previously (www.realclimate.org/ index.php/archives/2004/12/index/#ClimateSensitivity ), the last glacial period is a good example of a large forcing (~7 W/m2 from ice sheets, greenhouse gases, dust and vegetation) giving a large temperature response (~5 ºC) and implying a sensitivity of about 3ºC (with substantial error bars). More formally, you can combine this estimate with others taken from the 20th century, the response to volcanoes, the last millennium, remote sensing etc. to get pretty good constraints on what the number should be. This was done by Annan and Hargreaves (2006), (www.realclimate.org/index.php/archives/2006/03/ climate-sensitivity-plus-a-change/ ) and they come up with, you guessed it, 3ºC. -- You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/globalchange
