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.
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The NCEI ocean salinity and temperature data are available online (https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/). The JMA data are available online (https://climate.mri-jma.go.jp/pub/ocean/ts/v7.3/). The IAP data are available at http://18.104.22.168/cheng/. The ORAS4 data are available at ftp://ftp-icdc.cen.uni-hamburg.de/EASYInit/ORA-S4/. The input data for running the FLOR experiments presented in this work and processed data for graphics from the four datasets and FLOR model outputs are available at tigress-web at Princeton University (http://tigress-web.princeton.edu/~maofeng/SSS_OHU_TCR/data/).
The climate model used in this study is GFDL FLOR with code available at the NOAA/GFDL website (https://www.gfdl.noaa.gov/cm2-5-and-flor/). All graphics were produced using Python v.3.6 (https://www.python.org/downloads/release/python-360/). The codes needed to set up the FLOR experiment and Python scripts used for analyses and producing main figures are available at GitHub (https://github.com/maofeng2012/SSS_OHC_TCR; https://doi.org/10.5281/zenodo.5149277).
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This work was supported by award 80NSSC20K0879 from the National Aeronautics and Space Administration and award DE-SC0021333 from the US Department of Energy. The simulations presented in this paper were performed on computational resources managed and supported by Princeton Research Computing at Princeton University.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Veronique Lago, M. Cameron Rencurrel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Liu, M., Vecchi, G., Soden, B. et al. Enhanced hydrological cycle increases ocean heat uptake and moderates transient climate change. Nat. Clim. Chang. 11, 848–853 (2021). https://doi.org/10.1038/s41558-021-01152-0