Impact of Stratospheric Water Vapor Decadal Variability on Surface Temperature

Satellite and in-situ observations reveal a sharp decrease of stratospheric water vapor after the year 2000: lower stratospheric water vapor dropped about 10% between 2001-2005 and 1996-2000. It has been hypothesized that this large stratospheric water vapor decadal change strongly affected the surface temperature. In order to test this hypothesis, two time-slice simulations under constant year 2000 conditions are conducted with the coupled ocean Goddard Earth Observing System Chemistry-Climate Model. The setups of the two simulations differ only in the prescribed stratospheric water vapor field: the differences are constructed from observed decadal stratospheric water vapor changes in the 1996-2005 period. The simulations show that the stratospheric water vapor decrease forces significant tropospheric and surface cooling, particularly in the Northern Hemisphere extratropics. The surface radiation budget is diagnosed to quantify the responses of shortwave and longwave radiation, and cloud radiative effect to stratospheric water vapor decrease. The impact of stratospheric water vapor on sea surface temperature is also investigated.