Projected Impacts of Antarctic Meltwater Anomalies over the Twenty-First Century

Antarctic margin and Southern Ocean surface freshening has been observed in recent decades and is pro-jected to continue over the twenty-first century. Surface freshening due to precipitation and sea ice changes is represented in coupled climate models; however, Antarctic ice sheet/shelf meltwater contributions are not. Because Antarctic melting is projected to accelerate over the twenty-first century, this constitutes a fundamental shortcoming in present-day projec-tions of high-latitude climate. Southern Ocean surface freshening has been shown to cause surface cooling by reducing both ocean convection and the entrainment of warm subsurface waters to the surface. Over the twenty-first century, Ant-arctic meltwater is expected to alter the pattern of projected surface warming as well as having other climatic effects. How-ever, there remains considerable uncertainty in projected Antarctic meltwater amounts, and previous findings could be model dependent. Here, we use the ACCESS-ESM1.5 coupled model to investigate global climate responses to low and high Antarctic meltwater additions over the twenty-first century under a high-emissions climate scenario. Our high-meltwater simulations produce anomalous surface cooling, increased Antarctic sea ice, subsurface ocean warming, and hemispheric dif-ferences in precipitation. Our low-meltwater simulations suggest that the magnitude of surface temperature and Antarctic sea ice responses is strongly dependent on the applied meltwater amount. Taken together, these findings highlight the importance of constraining projections of Antarctic ice sheet/shelf melt to better project global surface climate changes over the twenty-first century.

Automated summary

Antarctic margin and Southern Ocean surface freshening has been observed and is projected to continue in the future. While precipitation and sea ice changes are accounted for in climate models, contributions from Antarctic ice sheet/shelf meltwater are not considered, which is a fundamental flaw in current projections. Surface freshening in the Southern Ocean has been shown to cause surface cooling and alter the pattern of projected surface warming. However, there is still uncertainty in projected meltwater amounts, and previous findings may be model-dependent. It is important to better constrain projections of Antarctic meltwater to accurately predict global surface climate changes in the future.