HAs the Greenland Ice Sheet Reached Peak Ice Discharge - HAGRID

During recent decades, the glaciological community has become familiar with statements in numerous papers, and high-profile reports, highlighting that ‘Greenland’s marine-terminating glaciers are retreating, accelerating and thinning’. However, while the vast majority of Greenland’s 200+ marine terminating glaciers have both retreated and thinned in recent decades, and many have certainly accelerated, the net impact of these changes on ice mass flux has been somewhat limited and extremely variable between individual glaciers. Indeed, a brief consideration of dynamic ice-flux data suggests that with the exception of a ~10% increase between 2000 and 2005, ice flux from these systems has shown minimal increase (<2%) in the two decades since the early millennial dynamic shift with the contribution from the largest 15 outlet glaciers remaining largely invariant. This observation not only brings in to question the suggestion of ubiquitous acceleration; it also raises the question that if one considers ice-flux, which is the most critical determinant for future sea-level rise, have we already or will we shortly reach peak ice flux from the Greenland Ice Sheet? It is clear that at some point, and in a corollary with ‘peak water’ in deglaciating valley glaciers, that each tidewater glacier will reach peak discharge and that this will occur prior to each glacier retreating on to land. This paper investigates in detail recent patterns of ice-flux change, both in terms of regional variability and glacier size, in order to consider the likelihood of future acceleration in ice-mass loss via solid ice-discharge from the Greenland Ice Sheet.