RealClimate. What is the long term sensitivity to increasing CO2? What, indeed, does long term sensitivity even mean? Jim Hansen and some colleagues (not including me) have a preprint available that claims that it is around 6ºC based on paleo-climate evidence. Since that is significantly larger than the ‘standard’ climate sensitivity we’ve often talked about, it’s worth looking at in more detail. We need to start with some definitions. Traditionally, the decision to include or exclude a feedback from consideration has been based on the relevant timescales and complexity. Not coincidentally, the Charney sensitivity corresponds exactly to the sensitivity one gets with a standard atmospheric GCM with a simple mixed-layer ocean, while the Earth System sensitivity would correspond to the response in a (as yet non-existent) model that included interactive components for the cryosphere, biosphere, ocean, atmospheric chemistry and aerosols.
So what does this mean for the future? Reuters AlertNet - Giant kangaroo image gives clues on climate. NASA GISS: NASA Goddard Institute for Space Studies.