Early warning of future rapid Arctic sea ice loss

The Arctic is currently transitioning toward a new climatic state that will be characterized by seasonally sea-ice-free conditions almost every year from the 2050s, with widespread ecological, climatic, and societal consequences. There is growing evidence that the future summer sea ice retreat will not occur at a constant rate. Indeed, climate model simulations are suggestive of pronounced sub-decadal fluctuations on top of the long-term trend, leading to periods of relative stability followed by abrupt sea ice decline in hardly 3-5 years. A lot remains to be understood regarding the precursors, mechanisms, predictability, and impacts of these rapid events. In particular, it is unclear how close we might be to the next one.The overall objective of this project, ArcticWATCH, is to build an integrated early warning system that alerts on the possibility of rapid Arctic sea ice loss for the following summer up to five years. This system will provide annually updated assessments and will synthesize multiple lines of evidence harvested from various data sources (pre-existing and generated during the project), including climate model projections, initialized climate model and machine-learning-based predictions, satellite observations, and climate reconstructions.By introducing innovative targeted numerical experiments, ArcticWATCH will also identify the new pathways of sea ice predictability in a warmer world and will thereby provide evidence-based guidance regarding the design of the Arctic observing system for the next 30 years. Finally, ArcticWATCH will make a leap forward in depicting environmental impacts during and after rapid sea ice loss events, from short (Arctic heatwaves and precipitation extremes) to long (interactions with the Arctic and North Atlantic oceanic circulation) timescales.The hypothesis that, after a decade of relatively stable conditions, Arctic sea ice is poised to an abrupt decline before 2030, will be paid utmost attention.