Bosong Zhang

Forcing and Feedback • Ocean Heat Uptake

Nature Climate Change (2021)

Enhanced Hydrological Cycle Increases Ocean Heat Uptake and Moderates Transient Climate Change

Transient CO2-doubling experiments show that subtropical surface salinification from an amplified hydrological cycle strengthens ocean heat uptake and reduces near-term surface warming.

DOI: 10.1038/s41558-021-01152-0 Transient CO2 Doubling Salinity Pattern Effect Ocean Heat Uptake
Map from Liu et al. 2021 showing ocean heat uptake response pattern
Ocean heat-uptake anomaly pattern associated with CO2-driven salinity changes.

TCR Shift: ~0.4 K

Without salinity-pattern adjustment, transient warming is substantially larger.

Subtropical Salinification

Dry-get-drier freshwater forcing increases salinity and weakens upper-ocean stratification.

Deeper Heat Sequestration

Salinity-driven buoyancy changes enhance penetration of heat into the ocean interior.

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Paper Citation

Liu, M., G. Vecchi, B. Soden, W. Yang, and B. Zhang, 2021: Enhanced hydrological cycle increases ocean heat uptake and moderates transient climate change. Nature Climate Change, 11, 848-853. https://doi.org/10.1038/s41558-021-01152-0

View Journal Article Open PDF

Scientific Logic

  • Question: Does CO2-driven surface salinity change alter ocean heat uptake enough to change transient warming?
  • Method: Coupled 1% yr-1 CO2 increase experiments comparing a standard run with a fixed-SSS configuration.
  • Mechanism: Amplified P−E patterns produce subtropical salinification, reduce near-surface density stratification, and increase downward heat transport.
  • Main Findings: Salinity-pattern evolution enhances ocean heat uptake and lowers transient warming; fixing SSS raises TCR by about 0.4 K.

Scientific Objective

Quantify how hydrological-cycle amplification feeds back on ocean heat uptake and transient surface temperature response through sea-surface salinity changes.

Approach

  • Run transient CO2-doubling simulations in FLOR with and without dynamic SSS response.
  • Compare TOA imbalance, OHC tendency, and vertical heat distribution between experiments.
  • Diagnose regional salinity, freshwater flux, and overturning contributions to heat uptake changes.

Key Findings

  • Hydrological-cycle-driven salinification increases low-latitude and subtropical ocean heat uptake.
  • Additional salinity buoyancy forcing shifts warming deeper, reducing upper-ocean warming and transient surface temperature rise.
  • AMOC changes contribute secondarily; the dominant control is salinity-mediated stratification change.

Figures from the Study

From Liu et al. (2021), Nature Climate Change, https://doi.org/10.1038/s41558-021-01152-0.

Figure 1

Transient global temperature and ocean heat uptake time series
Transient response showing stronger surface warming when salinity evolution is suppressed.

Figure 2a

Spatial pattern of ocean heat uptake changes with salinity feedback
Regional ocean heat-uptake response associated with salinity-pattern amplification.

Figure 2b

Spatial pattern of sea surface salinity changes
Sea-surface salinity response pattern linked to amplified freshwater-flux contrast.

Figure 2c

Spatial pattern of precipitation minus evaporation changes
P−E changes highlighting wet-get-wetter and dry-get-drier structure tied to salinity feedback.
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