Anthropogenic warming forces extreme annual glacier mass loss

Glaciers are unique indicators of climate change. While recent global-scale glacier decline has been attributed to anthropogenic forcing, direct links between human-induced climate warming and extreme glacier mass-loss years have not been documented. Here we apply event attribution methods to document this at the regional scale, targeting the highest mass-loss years (2011 and 2018) across New Zealand's Southern Alps. Glacier mass balance is simulated using temperature and precipitation from multiple climate model ensembles. We estimate extreme mass loss was at least six times (2011) and ten times (2018) (>90% confidence) more likely to occur with anthropogenic forcing than without. This increased likelihood is driven by present-day temperatures ~1.0 °C above the pre-industrial average, confirming a connection between anthropogenic emissions and high annual ice loss. These results suggest that as warming and extreme heat events continue and intensify, there will be an increasingly visible human fingerprint on extreme glacier mass-loss years in the coming decades. Detecting a human role in a given year of extreme glacier mass loss is difficult at regional scales. Event attribution methods estimate that two extreme mass-loss years in the New Zealand Southern Alps, 2011 and 2018, were at least six and ten times more likely with anthropogenic climate warming.