New estimates of water cycle change from sea water salinity and its interplay with ocean warming
The talk will cover two critical topics in climate science, water cycle change and ocean warming, and their interplay.
Warming-induced water cycle change is expected to amplify the pattern of sea surface salinity. A puzzle has however emerged. The surface salinity pattern has amplified by 5%–8% since the 1950s while the water cycle is thought to have amplified at close to half that rate. This discrepancy is also replicated in climate projections of the 21st century. Using targeted numerical ocean model experiments collaborators at the NOC and I find that, while surface water fluxes due to water cycle change and ice mass loss amplify the surface salinity pattern, ocean warming exerts a substantial additional influence. Warming increases near-surface stratification, inhibiting the decay of existing salinity contrasts and further amplifying surface salinity patterns. Observed ocean warming can explain approximately half of observed surface salinity pattern changes from 1957–2016 with ice mass loss playing a minor role. Water cycle change of 3.6% ± 2.1% per degree Celsius of surface air temperature change is sufficient to explain the remaining observed salinity pattern change.
Recognising the significant impact variability in mixing has on the ocean’s role in climate I will discuss new work with collaborators at UNSW Sydney. New methods we have developed are able to accurately diagnose the role of different processes (parameterised, resolved and spurious) in both the geographical distribution and temporal variability in mixing in ocean climate models.