Combined surface solar brightening and increasing greenhouse effect support recent intensification of the global land-based hydrological cycle

The surface net radiation (surface radiation balance) is the key driver behind the global hydrological cycle. Here we present a first-order trend estimate for the 15-year period 1986-2000, which suggests that surface net radiation over land has rapidly increased by about 2 Wm(-2) per decade, after several decades with no evidence for an increase. This recent increase is caused by increases in both downward solar radiation (due to a more transparent atmosphere) and downward thermal radiation (due to enhanced concentrations of atmospheric greenhouse-gases). The positive trend in surface net radiation is consistent with the observed increase in land precipitation (3.5 mmy(-1) per decade between 1986 and 2000) and the associated intensification of the land-based hydrological cycle. The concurrent changes in surface net radiation and hydrological cycle were particularly pronounced in the recovery phase following the Mount Pinatubo volcanic eruption, but remain evident even when discarding the Pinatubo-affected years.