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

The large-scale moistening of the atmosphere in response to increasing greenhouse gases amplifies the existing patterns of precipitation minus evaporation (P - E), which, in turn, amplifies the spatial contrast in sea surface salinity. Here, by performing a series of transient CO2 doubling experiments, we demonstrate that surface salinification driven by the amplified dry conditions (P - E < 0), primarily in the subtropical ocean, accelerates ocean heat uptake. The salinification also drives the sequestration of upper-level heat into the deeper ocean, reducing the thermal stratification and increasing the heat uptake through positive feedback. The change in Atlantic Meridional Overturning Circulation due to salinification has a secondary role in heat uptake. Consistent with the heat uptake changes, the transient climate response would increase by approximately 0.4 K without this process. Observed multidecadal changes in subsurface temperature and salinity resemble those simulated, indicating that anthropogenically forced changes in salinity are probably enhancing ocean heat uptake. A climate model shows that hydrological cycle change drives ocean salinity increases, enhancing heat transport into the ocean and modulating near-term climate warming. This suggests that model spread in near-term climate sensitivity may be due in part to hydrological cycle and salinity differences.

Automated summary

Climate change leading to atmospheric moistening exacerbates the spatial contrast in sea surface salinity, impacting ocean heat uptake. Salinification-driven surface salinity increase plays a key role in heat absorption by the ocean.