West Antarctic Surface Climate Changes Since the Mid-20th Century Driven by Anthropogenic Forcing

Although the West Antarctic surface climate has experienced large changes over the past decades with widespread surface warming, an overall increase in snow accumulation and a deepening of the Amundsen Sea Low, the exact role of human activities in these changes has not yet been fully investigated, which limits confidence in future projections. Here, we perform a detection and attribution analysis using instrumental and proxy-based reconstructions, and two large climate model simulation ensembles to quantify the forced response in these observed changes. We show that surface climate changes since the 1950s were driven by anthropogenic forcing, in particular the greenhouse gas forcing and stratospheric ozone depletion. Therefore, our results indicate that the 21st century changes will depend on both the greenhouse gas emissions and the ozone layer recovery. Plain Language Summary Since the second half of the 20th century, West Antarctica has experienced large climate changes, such as widespread warming, increased snow accumulation, and a deepening of a low-pressure system located off the West Antarctic coasts. The observed climate changes in West Antarctica are influenced by both the internal (related to the chaotic nature of climate) and forced (related to changes in forcings) variability but it is still unclear to what extent human activities are responsible for these changes. We used a statistical method to distinguish between changes caused by humans and by natural influences both for instrumental observations and reconstructions of past climate. Our results show that the observed changes since the 1950s are out of the range of natural variability and can be attributed to human activities-that is, the increase of greenhouse gases and stratospheric ozone depletion. Therefore, our findings indicate that the future state of the West Antarctic surface climate will depend on the greenhouse gas emissions as well as the ozone layer recovery.