Persistent High-Latitude Ocean Warming and Global Sea Level Rise
Following Temporary Overshoots
Abstract
As the likelihood of temporarily exceeding 1.5 °C of global warming
rises, understanding the response of the ocean-climate system to
overshooting this warming level is of increasing importance. Here, we
apply the Adaptive Emissions Reduction Approach to the Earth System
Model GFDL-ESM2M to conduct novel overshoot scenarios which temporarily
exceed 1.5 °C of global warming to 2.0, 2.5 and 3.0 °C, alongside a
complementary scenario that stabilizes global temperature at 1.5 °C. The
simulation framework allows to isolate impacts attributable to the
temperature overshoots alone, both during their peaks and after their
reversals, in simulation timeframes spanning from 1861 to 2500. Our
results reveal that, while global sea surface temperatures eventually
retrace to 1.5 °C stabilization levels, substantial residual ocean
surface warming persists regionally, particularly in the North Atlantic
(regional average of up to +3.1 °C in the 3°C overshoot scenario) and
the Southern Ocean (+1.2 °C). The residual warming is primarily
attributed to the recoveries of the Atlantic and Southern Ocean
meridional overturning circulation, resulting in a reversed pattern of
disproportionate surface warming in low-latitude oceans found during the
transient peak of the overshoot. Excess subsurface heat storage in low
and mid-latitudes furthermore prevents steric sea level rise from
reverting to 1.5 °C stabilization levels in any overshoot scenario, with
sea level remaining up to 32 % higher in the 3 °C overshoot scenario.
Both peak overshoot impacts and persistent changes following overshoot
reversal bear significant implications for future assessments of
coastlines, regional climates, marine ecosystems, and ice sheets.