Antarctic Tipping points triggered by the mid-Pliocene warm climate
Abstract. Tipping elements, including the Antarctic Ice Sheet (AIS), are Earth system components that can reach critical thresholds due to anthropogenic emissions. Increasing our understanding of past warm climates can help to elucidate the future contribution of the AIS to emissions. The mid-Pliocene warm period (mPWP, 3.3–3.0 million years ago) serves as an ideal benchmark experiment. During this period, CO2 levels were similar to present-day (350–450 ppmv), but global mean temperatures were 2.5–4.0 degrees higher. Sea-level reconstructions from that time indicate a rise of 10–20 meters compared to the present, highlighting the potential crossing of tipping points in Antarctica. In order to achieve a sea-level contribution far beyond 10 m not only the West Antarctic Ice Sheet (WAIS) needs to largely decrease, but a significant response in the East Antarctic Ice Sheet (EAIS) is also required. A key question in reconstructions and simulations is therefore which of the AIS basins retreated during the mPWP. In this study, we investigate how the AIS responds to climatic and bedrock conditions during the mPWP. To this end we use the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) general circulation model ensemble to force a higher-order ice-sheet model. Our simulations reveal that the West Antarctic Ice Sheet experiences collapse with a 0.5 K oceanic warming, the Wilkes basin shows retreat at 3 K oceanic warming, although higher precipitation rates could mitigate such a retreat. Totten glacier shows slight signs of retreats only under high oceanic warming conditions (greater than 4 K oceanic anomaly). We also examine other sources of uncertainty related to initial topography and ice dynamics. we find that the climatologies yield a higher uncertainty than the dynamical configuration, if parameters are constrained with PD observations and that starting from Pliocene reconstructions lead to smaller ice-sheet configurations due to hysteresis behaviour of marine bedrocks. Ultimately, our study concludes that cliff instability is not a prerequisite for the retreat of Wilkes basin. Instead, a significant rise in oceanic temperatures can initiate such a retreat. Our research contributes to a better understanding of Antarctic tipping points and the likelihood of crossing them under future emission scenarios.
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