The Global Water Cycle and Salinity in CMIP5

The global water cycle is expected to intensify in a warming climate. To identify potential patterns and magnitudes of change, we analyze outputs from a high emissions scenario (RCP8.5) of the Coupled Model Intercomparison Project 5 (CMIP5) for evaporation (E), precipitation (P), atmospheric vapor transport (Q), and sea surface salinity (SSS) over the coming century. The models predict with high confidence that convergence and divergence of Q increase with warming, leading to increased P in wet areas and decreased P in dry areas. These changes in the surface freshwater flux are reflected in the SSS field, but with strong modification by ocean dynamics. Meridional SSS contrasts between equatorial, subtropical, and polar oceans increase following the pattern of E - P change, but interbasin salinity contrasts between Atlantic, Pacific, and Indian also increase. These interbasin SSS changes are due to accelerated convergence and divergence of Q on the basin scale. Furthermore, the salinity outputs from CMIP5 suggest that much of the additional surface freshwater forcing from warming becomes relatively well mixed across the ocean surface from approximately 40°S - 40°N. The Atlantic becomes saltier across this entire latitude band despite increased P near the equator, and the Pacific becomes fresher despite decreased P in the subtropics. Several strategies to test this behavior of the ocean models using existing observational data and salt budgets will be discussed.