Excerpts from The Register, coverage of the Nic Lewis paper.
This graph below from Bishop Hill shows that it isn’t just one paper, but several now that show lower climate sensitivity to a doubling of CO2.
More and more likely that double CO2 means <2°C: New study
Yes, it warms the planet – just not as much as thought
The results of a new approach to calculating the effect of CO2 – using empirical observations – suggest it has a lower impact on the climate than previously thought, and its effects are being over-estimated by the IPCC.
Publishing in the American Meterological Society’s Journal of Climate, a new paper called An improved, objective Bayesian, approach for applying optimal fingerprint techniques to estimate climate sensitivity, Nicholas Lewis applies objective Bayesian techniques and uses more up-to-date observational data to derive his conclusions.
Very few people disagree with the basic fact that the greenhouse gas CO2 warms the climate, but without some kind of positive feedback mechanism, it doesn’t add very much: around 1°C-1.2°C per doubling of CO2. (See this discussion on no-feedback sensitivity). The global warming “crisis” emerged from a belief that small rises in CO2 concentrations result in large knock-on effects, or strong positive feedbacks. These remain conjectural, as the forcings and feedbacks are poorly understood. Just how much of an effect does a rise in CO2 have – a little, or a lot? Hence the importance of new and better studies in the area of climate science dealing with “attribution”.
Lewis finds that in recent years neither the global temperature nor ocean heat uptake have changed very much, while CO2 concentrations have continued to rise. Therefore, the climate sensitivity must be lower.
Full article here: http://www.theregister.co.uk/2013/04/22/climate_sensitivity_down_down/