Dependence of the land-sea contrast in surface climate response on the nature of the forcing

The land-sea contrast in surface warming is a phenomenon of both transient and equilibrium climate change. Its magnitude, while model-dependent, is invariant with forcing amplitude. Here we demonstrate that the land-sea contrast is dependent on whether the climate forcing is mainly caused by changes to CO2 or other mechanisms such as solar or volcanic forcing: this is mainly because a CO2 change affects stomatal conductance in plants, and therefore changes the amount of evaporation from regions with vegetation present. In addition, solar or volcanic radiative forcing has a different latitudinal distribution to CO2 forcing: when this effect is removed by normalising the land temperature response by the average ocean temperature response at the same latitude, spatial differences between the CO2 forced run and the solar forced run become more apparent. Our results affect prediction of the land/sea contrast, as well as the interpretation of proxy climate data.