Robust attribution of global industrial-era glacier mass loss to anthropogenic climate change

Abstract. We apply formal climate-attribution methods to industrial-era glacier mass loss at both regional and individual glacier scales. Using a combination of observed temperatures and climate-model simulations, we show that warming across all glacierized regions of the globe is attributable to anthropogenic climate change. Our central estimates are that the magnitude of the anthropogenic warming over the industrial era ranges from from 91–98 % of the observed, depending on region.  These temperature changes equate to regional equilibrium-line-altitude (ELA) rises of 107–340 m, all of which are at least extremely likely anthropogenic in origin.

We examine 75 individual glaciers around the world, using realistic geometries and mass-balance profiles to reconstruct approximate preindustrial glacier geometries. Using these preindustrial geometries as reference surfaces, we analyze mass balance on these surfaces and show that anthropogenic ELA rise has produced sweeping changes in ablation and accumulation across all sampled glaciers. We find that a glacier's sensitivity to ELA rise is governed more strongly by local catchment geometry than by climatic setting. Since these industrial-era mass-balance changes are driven by the anthropogenic warming, our central estimates of the anthropogenic contribution are the same as for temperature.

Finally, we compare these anthropogenically driven changes against the distribution of natural mass-balance variability drawn from both climate-model counterfactual simulations and last-millennium reconstructions at each of our 75 glaciers. Across all glacierized regions, it is virtually certain the anthropogenic mass-balance signal is outside the envelope of natural variability, as characterized by both preindustrial climate reconstructions and the CMIP counterfactual ensemble. Within our analysis framework, we conclude it is very likely that anthropogenic warming is the primary driver of industrial-era mass loss.