Anthropogenic and natural causes of twentieth century temperature change

We analyse spatio-temporal patterns of near-surface temperature change to p rovide an attribution of twentieth century climate change. We apply an "opt imal detection'' methodology to seasonal and annual data averaged over a ra nge of spatial and temporal scales. We find that solar effects may have con tributed significantly to the warming in the first half of the century alth ough this result is dependent on the reconstruction of total solar irradian ce that is used. In the latter half of the century, we find that anthropoge nic increases in greenhouses gases are largely responsible for the observed warming, balanced by some cooling due to anthropogenic sulphate aerosols, with no evidence for significant solar effects.