The Ocean's Role in Continental Climate Variability and Change

A characteristic feature of global warming is the land-sea contrast, with stronger warming over land than over oceans. Recent studies find that this land-sea contrast also exists in equilibrium global change scenarios, and it is caused by differences in the availability of surface moisture over land and oceans. In this study it is illustrated that this land-sea contrast exists also on interannual time scales and that the ocean-land interaction is strongly asymmetric. The land surface temperature is more sensitive to the oceans than the oceans are to the land surface temperature, which is related to the processes causing the land-sea contrast in global warming scenarios. It suggests that the ocean's natural variability and change is leading to variability and change with enhanced magnitudes over the continents, causing much of the longer-time-scale (decadal) global-scale continental climate variability. Model simulations illustrate that continental warming due to anthropogenic forcing (e. g., the warming at the end of the last century or future climate change scenarios) is mostly (80%-90%) indirectly forced by the contemporaneous ocean warming, not directly by local radiative forcing.