Downwind control of oceanic air by land: the land wake and its sensitivity to CO2

Abstract

Abstract Oceans are well-known to be directly altered by global climate forcings such as greenhouse gas changes, but how oceans are indirectly influenced by land and its response to such forcings remains less explored. Here, we assess the present-day and projected future state of a little-explored feature of the climate system—a ‘land wake’ in relative humidity downwind of the east coast of North America, consisting of low-humidity continental air extending roughly 1000 km over the Atlantic ocean. The wake exists throughout the year, but is supported by high continental temperatures in summer and low continental moisture in winter. The wake is well represented in an ensemble of global climate models (GCMs), qualitatively matching reanalysis data. Under increasing atmospheric CO2, the land wake intensifies in GCM simulations through two pathways: the radiative effects of CO2 on surface temperatures, and the biogeochemical effect of CO2 on terrestrial vegetation. Vegetation responses to increased CO2 alter the summer wake from Florida to Newfoundland, and both the radiative and biogeochemical effects of CO2 drive reductions in coastal cloud cover. These changes illustrate the potential of rapidly changing terrestrial climate to influence coastal regions and the ocean environment downwind of continents through both light conditions and the energy balance of the surface ocean.