Enhanced hydrological cycle increases ocean heat uptake and moderates transient climate sensitivity

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Maofeng Liu , Gabriel Vecchi, Brian Soden, Wenchang Yang, Bosong Zhang


The large-scale moistening of the atmosphere in response to the greenhouse gas increases tends to amplify the existing patterns of precipitation minus evaporation (P-E) which, in turn, amplifies the spatial contrast in sea surface salinity (SSS). We propose that subtropical surface salinification due to the intensified hydrological cycle provides a buoyancy sink that increases the rate of ocean heat uptake and moderates transient climate sensitivity. We quantify the impact of these SSS changes in a series of CO2 doubling experiments using two configurations of a coupled climate model: a standard configuration and a modified one in which SSS is held constant by restoring it back to its seasonally-varying climatology from the control run. In response to CO2-induced warming, dry conditions (P-E < 0) over the subtropical oceans are amplified due to an enhanced hydrological cycle, increasing the SSS in salty regions. There is an increased rate of ocean heat uptake in the standard CO2 doubling experiment relative to the fixed-SSS version. The largest increase in ocean heat content (OHC) for the standard run occurs in the southern subtropical Pacific and the tropical and subtropical Atlantic Ocean, where SSS shows the largest increase, highlighting the role of salinification in accelerating heat uptake. The weakening of the Atlantic Meridional Overturning Circulation in response to high latitude freshening and warming also plays a role in modulating the OHC. Consistent with a smaller rate of ocean heat uptake, the fixed-SSS version produces a transient climate response approximately 0.4K greater than the standard run. Observed multi-decadal changes in subsurface temperature and salinity resembles those simulated, indicating that anthropogenically-forced changes in salinity are likely enhancing the rate of ocean heat uptake.




Climate, Oceanography, Oceanography and Atmospheric Sciences and Meteorology


Ocean heat uptake, Global hydrological cycle, Salinity, Transient climate sensitivity


Published: 2020-11-25 14:31

Last Updated: 2020-11-25 14:50

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CC BY Attribution 4.0 International

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