Climate Science - the certainties and the uncertainties

Keith Shine

(Reading University)

The recent Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report concluded that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations". This talk discussed the background to this statement. In particular, although this is the strongest statement yet from IPCC, what are the current uncertainties in climate science that prevented IPCC from using a wording stronger than "likely"? In IPCC-speak, they could have used "very likely" or "virtually certain". Inadequate observations and an incomplete understanding of climate processes are currently preventing a more assertive statement. An area of particular emphasis in the talk concerned our understanding of the way changes in cloud characteristics both cause and respond to climate change.