Climate Change: Rainfall Drives Rapid Ice Melt in Greenland Ice Sheet

The Greenland ice sheet is continuing to melt. Now, scientists have found another factor that's contributing; it turns out that the ice sheet melt has accelerated in response to surface rainfall associated with late-summer and autumnal cyclonic weather events.

"It is like an urban sewerage system that is temporarily overwhelmed by an intense rainstorm," said Alun Hubbard, one of the researchers, in a news release. "The ice sheet plumbing-literally a network of pipes, cavities and channels-gets backed up by the sheer quantity of runoff draining into it, leading to flooding and high water pressures, which literally hydraulically lifts the ice sheet up off its bed, reducing basal friction and sending it on its way."

The influence of rain events hadn't been considered in assessments of ice sheet melt and flow response. Although cyclonic conditions are relatively rare across Greenland now, they're likely to increase in the future. This could mean that rain may play an important role in driving mass loss from the Greenland ice sheet.

Since measurements began in the 1980s, the proportion of precipitation now falling as rain rather than snow has both increased and extended into the late summer and autumn in line with increased circulation and moisture availability within a warmer, more energetic atmosphere.

"We're seeing that warm wet weather is increasing with climate change and is driving more melt of the Greenland ice-sheet than we thought," said Jason Box, co-author of the new study. "And worryingly, this melt is now reaching ever higher elevations on the ice sheet."

Observed climate warming doesn't just mean hotter summers and milder winters; it's more complex than that. That's why scientists aren't sure whether or not the rainfall events will have a lasting influence. That said, current evidence points to the fact that this may just be the case.

The findings are published in the journal Nature Geoscience.

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