Identifying global climate change using simple indices

Several simple indices of surface air temperature patterns are used to desc ribe global climate variability and change. The indices include the land-oc ean temperature contrast, the hemispheric contrast, the meridional gradient , and the magnitude of the seasonal cycle, as well as the global-mean tempe rature. The behaviour of the indices is investigated using global observati onal data for the period 1881-1994 and long control and anthropogenic clima te change simulations with two different climate models. The indices repres ent the key features of the "fingerprint" of greenhouse climate change. For natural climate variations, they contain information independent of the gl obal-mean temperature. The observed trends over the last 40 years in all th e indices, except for the hemispheric contrast, are unlikely to have occurr ed due to natural climate variations and all are consistent with model simu lations of anthropogenic climate change.