IS +2°C TOO WARM FOR ANTARCTICA? DIATOM LESSONS FROM A 400 PPM WORLD (Invited Presentation)

When the Paris Agreement was adopted in late 2015, it represented a multi-national commitment to adopt carbon policies that would keep the global average temperature in they year 2100 well below 2° C relative to pre-industrial levels, while pursuing efforts to limit the temperature increase to 1.5° C. The Late Pliocene is the most recent interval in Earth’s history to sustain global temperatures within the range of warming anticipated under Paris Agreement commitments. Published global reconstructions and climate models find an average +2° C summer SST anomaly relative to modern during the ~3.3-3.0 Ma PRISM interval, when atmospheric CO₂ concentrations last reached 400 ppm, providing a natural analog to test the impact of the maximum permissible Paris Agreement warming.

Here, we present the view from the Southern Ocean and Antarctic margin, compiling marine diatom assemblage reconstructions of Plio-Pleistocene interglacial sea surface conditions from sediment cores collected by multiple Antarctic drilling initiatives. We use these reconstructions to demonstrate that Antarctic ice sheets and ocean circulation responded sensitively to comparatively modest climate forcing in the late Pliocene, suggesting that overshooting the Paris Agreement’s more ambitious target of +1.5° C risks nudging the Antarctic / Southern Ocean system across a tipping point.