Kevin Krajick/Earth Institute
Ice melt from winter rainfall in Greenland tripled from 1979 to 2012.
DRIPPLE EFFECT

It really shouldn’t be raining on the Greenland ice sheet in winter

By Zoë Schlanger

When scientists say we need to stay below 2 degrees Celsius of warming to avoid catastrophic climate change, they’re talking about a global average two degrees above pre-industrial levels.

But for the Arctic, where warming is happening much, much faster, those two degrees sound almost quaint. For example, over the Greenland Ice Sheet, which is currently causing about a quarter of global sea level rise as it melts, temperatures have risen by 3 °C (5.4 °F) in winter. And that’s not compared to “pre-industrial levels,” which refers to levels around the year 1850. That’s just since 1990.

(Summer temperatures over the ice sheet have risen about 1.8 °C [3.2°F] since then.)

Rapidly warming winters have brought about a bizarre phenomenon: Rain. On Greenland. In winter.

Rain, quite simply, melts ice. In a paper published Thursday (March 7), researchers at Germany’s GEOMAR Centre for Ocean Research and the Columbia University Earth Institute compiled satellite data and on-the-ground observations to learn that Greenland ice melt triggered by winter rain tripled between 1979 and 2012. Melt from rainfall during summer doubled in that time frame.

Researchers believe the Greenland ice sheet is losing around 270 billion tons of ice per year, a rate of loss likely greater than it has seen in 8,000 years or more. About 70% of that loss is from meltwater runoff (the other 30% is from calving icebergs). Rainy weather, say the study authors, is increasingly becoming the trigger for that runoff, accounting for almost 30% of the melt.

“The ice should be gaining mass in winter when it snows,” Marilena Oltmanns, a researcher at Germany’s GEOMAR Centre and lead author on the study, said in a statement. Instead, the gains are being overwhelmed by melt. Researchers already knew the ice sheet was melting in winter, but the share of melt caused by rain is a new twist.

For now, the winter rainfall is confined to the lower elevations of Greenland, particularly in the south and southwest. But as temperatures rise, the rain area will likely expand northwards, covering more of the ice sheet.

Kevin Krajick/Earth Institute
A meltwater stream runs through Greenland’s Russell Glacier.

The rain in Greenland is another reminder of the interconnected global climate system: The rain is the product of moist, warm wind blowing in from the south, which the researchers say is being propelled by changes in the jet stream caused by climate change.

The melting ice itself is likely triggering further melting, they write; as it runs off the ice sheet, it might refreeze before it reaches the ocean, transforming even snowy places into darkened ice. Whereas snow reflects the vast majority of the sun’s light and heat, protecting the ice beneath it, darker ice absorbs solar energy, melting faster.

Plus, as more of the formerly-snowy ice sheet hardens with runoff, its slicker surface more efficiently delivers meltwater to the ocean. In short, the cascade effects of winter rain on Greenland are likely contributing to the speed-up of the melt.

As other researchers have pointed out, Greenland is melting faster than it ever has before, and it’s doing so in a “nonlinear” way—meaning that each one-degree increase in global air temperature cannot be correlated to a standardized melt rate; instead, the ice melt is outpacing warming.

So, yeah. It really shouldn’t be raining on the Greenland ice sheet in winter.