We use cointegration procedures that are designedto estimate and test relations among integrated time series to develop a modelof the relation between surface temperature and the radiative forcing of solarirradiance, greenhouse gases, and tropospheric sulfates. We use this modelto test some basic hypotheses regarding the relation between surface temperatureand radiative forcing. We find that there is a statistically meaningful relationbetween surface temperature and changes in the radiative forcing associatedwith natural variability and human activity. We also find that hemispherictemperatures cannot be explained by hemispheric forcings alone: Hemispherictemperatures are linked. Differences in hemispheric temperatures are associatedwith differences in the hemispheric temperature effects of greenhouse gases,anthropogenic sulfur emissions, and solar irradiance. Estimates for the temperaturesensitivity (ΔT2x) are consistentwith the middle and lower range of values estimated by physically based models.