Simon F. B. Tett (1), Gareth S. Jones (1), Peter A. Stott (1), David C. Hill (2), John F. B. Mitchell (1), Myles R. Allen (2), William J. Ingram (1), Tim C. Johns, Colin Johnson (1), Andy Jones (1), David L. Roberts (1), David M. H. Sexton (1) and Margaret J. Woodage (1)

(1) Hadley Centre for Climate Prediction and Research, The Met. Office London Road, Bracknell UK. sfbtett@meto.gov.uk (2) Space Science and Technology Dept, Rutherford Appleton Laboratory, UK Department of Astronomy, Yale University, New Haven CT, USA

"Estimation of natural and anthropogenic contributions to 20th Century Temperature Change"
The ability of the coupled ocean/atmosphere model HadCM3 to simulate observed changes in temperature during the 20th century, near the surface and throughout the atmosphere is assessed. A variety of simulations forced with changes in solar irradiance, aerosol optical depth due to explosive volcanic eruptions, stratospheric and tropospheric ozone, direct and indirect effects of sulphates, and greenhouse gases are compared with observations. We find that near-surface temperature change over the 20th century is explained by a combination of natural and anthropogenic forcings. Total anthropogenic forcings are the principal agent of change over the last 30 years but the early 20th century warming is explained by changes in solar irradiance, a lack of explosive volcanic eruptions, total global-mean anthropogenic forcing close to zero and a large contribution from internal climate variability. We find that over the last 30 years temperature changes in both the free atmosphere and the surface are largely a response to anthropogenic forcings. This is despite the near balance between positive radiative forcing due to greenhouse gases and the negative forcings due to stratospheric ozone decline and the indirect effect of sulphate aerosols.