This study provides new estimates of historical and projected changes in pan-Arctic runoff, with emphasis on the impact of permafrost changes and sub-surface flows on large scale hydrology. The impact of permafrost change on hydrological processes is a key uncertainty facing the cold regions hydrology community, and requires comprehensive model-based analysis as presented in this study. The analysis also addresses changes to the terrestrial runoff contribution to the freshwater budget of the Arctic, and so is of interest to a wide range of disciplines.

This study addresses an important question regarding the stability of ice shelves, a question that is highly relevant for Greenland and Antarctica. Using a unique combination of observations, the authors document extensive thinning and extremely high basal melt rates at the floating tongue Nioghalvfjerdsbræ, North Greenland, an important and fast-changing part of the Greenland Ice Sheet. The increase in melt rates are suggested to be caused by an increase in surface melt that is funneling surface water under the ice shelf.

The history and extent of the Greenland ice sheet is a widely debated and poorly understood question. In this study, the authors show that the childhood of the Greenland ice sheet took place in the southern and eastern highlands of Greenland, and further suggest that the continental ice sheet we observe today first emerged between 7 million years and 2.6 million years ago.