It’s raining on Greenland’s ice sheet. That’s a big problem.

Changing weather patterns have triggered a stark change in how Greenland is melting

photo-Martin Zwick / REDA&CO / UIG via Getty Images

Changing weather patterns have triggered a stark change in how Greenland is melting, according to a new paper published on Thursday. By combining data from satellites and weather stations, a team of scientists found that rainstorms are now driving nearly one-third of the frozen island’s rapid melt.

In terms of sea-level rise, meltwater runoff from the top of the Greenland ice sheet has recently surpassed the contribution of icebergs breaking off from its edges. Those runoff events are increasingly tied to rainstorms — even during winter — that trigger extensive new ice melt.

“That was a surprise to see,” lead author Marilena Oltmanns of the Helmholtz Center for Ocean Research in Germany said in a statement. The researchers looked at more than 300 sudden melt episodes from 1979 to 2012, the most recent year available.

Warmer air temperatures are having a big effect on Greenland, but warm water falling as rain is apparently disastrous to the ice — tunneling through divots and cracks and melting surrounding snow with abandon. The rain-on-snow process transforms the surface of the ice sheet from fluffy and reflective to compact and dimmer, a dangerous feedback loop that’s perfect for encouraging further melt on sunny days.

“If it rains in the winter, that preconditions the ice to be more vulnerable in the summer,” Marco Tedesco, a glaciologist at Columbia University and co-author of the study, said in the statement. “We are starting to realize, you have to look at all the seasons.”

It seems increasingly clear that the Greenland ice sheet crossed a tipping point around 2002. In the decade after that year, melting increased nearly four-fold, coming mostly from the southern part of the island that’s especially prone to these rain-on-ice events.