Illusory early-warning signals of Greenland Ice Sheet destabilization

Interannual variability of surface mass balance over the Greenland Ice Sheet has been increasing, which has been cited as an early-warning signal of ice sheet destabilization under current climatic conditions. A destabilized ice sheet would continue to lose mass and contribute to global sea level rise, even if climate stopped changing in the future. Here, we investigate the mechanisms driving nonstationarity of surface mass balance variability in a high-fidelity surface mass balance reconstruction, and a calibrated simple model. We show that, regardless of the proximity to destabilization, increasing variability in surface mass balance is an expected consequence of atmospheric warming on low-accumulation parts of the ice sheet. Autocorrelation of surface mass balance exhibits spurious multidecadal trends under a wide range of climatic conditions due to the slow response of ice sheets to climatic fluctuations, making this a poor early-warning signal of destabilization. Though these findings do not rule out the potential for destabilization under current or future climate, they provide a conceptual framework for understanding the drivers of surface melt variability.