Analysis of observational temperature records for the Northern and Sou
thern hemispheres indicates a statistical relationship in which Northe
rn Hemisphere temperature depends on temperature in the Southern Hemis
phere. This pattern, which has strengthened over time, can be explaine
d by the climatic effects of anthropogenic trace gases and tropospheri
c sulphate aerosols. A similar statistical pattern is produced by mode
l simulations of the historical atmosphere.