New Studies Refine Greenland Ice Sheet Melt Estimates, Highlighting Meltwater Retention

Revised Meltwater Runoff Estimates Emerge from Greenland Research

Recent studies affiliated with Brown University suggest that existing measurements and simulations of the Greenland Ice Sheet's meltwater runoff may be overestimations. The research highlights that current climate models often do not fully account for natural processes of meltwater retention and refreezing, leading to potential inaccuracies in predictions of sea-level rise. These findings indicate that corrections of approximately 10% to 15% may be necessary for current models.

Meltwater Retention Mechanisms Detailed

The core of the new understanding lies in two primary mechanisms: meltwater refreezing within porous bare ice and the ponding of meltwater on the ice sheet's surface. Climate models have traditionally assumed that all meltwater from bare ice flows directly into the ocean. However, fieldwork conducted in Greenland's southwestern region, specifically the ablation zone, revealed a different reality. Researchers, including Professor Laurence Smith of Brown University, observed that meltwater produced during the day can fill the pore spaces of the top ice layers and then refreeze at night.

This refreezing process significantly reduces the net runoff. For the southwest Greenland sector alone, meltwater refreezing in bare, porous glacier ice was estimated to reduce runoff by 11 to 17 gigatons per year between 2009 and 2018. This volume is equivalent to 9% to 15% of the annual meltwater runoff simulated by climate models for that area.

The Role of Ponding and Albedo

Beyond refreezing, the studies also investigated the impact of meltwater ponding. In flatter sections of the ablation zone, meltwater tends to accumulate in ponds. These ponds can initiate a positive feedback loop: they darken the ice sheet's surface, which in turn increases its absorption of solar radiation and accelerates further melting. While meltwater ponding accounted for approximately 1% of the total heating from sunlight across the Greenland Ice Sheet in the summer of 2019, its impact can vary significantly based on factors like the time of year, elevation, and specific area.

Implications for Climate Modeling and Sea-Level Rise

The findings underscore the importance of incorporating these detailed physical processes into climate models to achieve more accurate predictions. While Professor Smith noted that these adjustments might be 'more like tinkering around the edges' in the broader context of climate change, he emphasized the necessity of the 'best physical understanding possible' for refining models. The research, which involved direct measurements of river flow rates and the use of drones for imagery, provides crucial data to improve forecasts of ice sheet runoff and its contribution to global sea-level rise.