First published August 27, 2021.
Broken ice and meltwater in Greenland, where the summer of 2021 brought several major melt events.
On 14 August 2021, rain fell at Summit Station, the research camp on the highest point of the Greenland ice sheet, about 3,216 metres above sea level. It was the first rainfall ever recorded there. Air temperatures stayed above freezing for roughly nine hours, and over 14 to 16 August an estimated 7 billion tonnes of rain fell across the ice sheet, the largest such event in records going back to 1950. Scientists at the US National Snow and Ice Data Center (NSIDC) wrote simply that there was "no previous report of rainfall at this location."
Why does a few hours of rain on a remote ice cap matter so much? The answer touches on how ice sheets melt, how warming air reaches the Arctic, and how much the oceans will rise.
What happened at Summit Station
Summit Station sits in the middle of the ice sheet, far from the coast and very high up. Even in summer, temperatures there normally stay well below 0°C, so any moisture falls as snow. That is why the site has been used for decades to drill ice cores that record past climates.
In mid-August 2021, a low-pressure system over Hudson Bay and Baffin Island and a high-pressure system to the south-east of Greenland combined to push a plume of warm, moist air northward over the ice. At Summit, the temperature rose above freezing on the morning of 14 August and stayed there until the afternoon, while rain fell for several hours. Across Greenland, surface melting spread to about 872,000 square kilometres that day.
This was only the third time in under a decade that Summit had reached above-freezing temperatures, after 2012 and 2019. Ice cores suggest that before a short event in 1995, melting at Summit had not occurred since the late 1800s. August 2021 was also the latest date in the year that such warmth had ever been recorded there.
Why rain on an ice sheet is a bad sign
Rain does more damage to ice than the same amount of snow would, for several reasons:
- It brings heat. Liquid water is warmer than snow and releases heat into the surface when it soaks in or refreezes.
- It darkens the surface. Fresh snow reflects most sunlight. Wet snow and bare ice are darker, so they absorb more of the sun's energy and melt faster. Scientists call this a drop in albedo.
- It runs off. Where large areas of bare ice are exposed, rain and meltwater cannot soak in. They flow straight to the ocean, so the ice sheet loses that mass.
- It changes the snowpack. Rain that refreezes can form ice layers that make future meltwater run off more easily.
Glaciologist Indrani Das of Columbia University's Lamont-Doherty Earth Observatory put it plainly to Reuters: "Water on ice is bad." On 15 August, according to NSIDC modelling, the ice sheet lost seven times more surface mass than is normal for mid-August.
Part of a run of extreme melt seasons
The August rain did not come out of nowhere. In late July 2021, a heatwave drove another major melt event, during which Greenland was reported to be losing roughly 8.5 billion tonnes of ice a day, about twice its normal summer rate. News reports at the time noted that one day's melt alone would have been enough to cover the US state of Florida in about five centimetres of water.
Earlier record years included 2012, when melting reached about 97% of the ice sheet's surface, and 2019, when the sheet lost a record amount of ice overall. Twila Moon, deputy lead scientist at NSIDC, told Reuters that the summit rain was "not an isolated event," and she stressed the need both to adapt to change and to cut the emissions behind it.
Greenland and global sea level
The Greenland ice sheet is the second-largest body of ice on Earth after Antarctica. It covers about 1.7 million square kilometres, around 80% of the island, and holds enough water to raise global sea level by roughly 7.4 metres if it ever melted completely.
Nobody expects that within this century, but even partial loss matters. Between 2012 and 2017 Greenland added about 0.7 millimetres a year to sea level, ten times the rate of the 1990s. That is roughly a fifth of today's global sea-level rise, with the rest coming from Antarctica, mountain glaciers and the expansion of warming seawater. For coastal cities, small deltas and island nations, each centimetre brings more frequent flooding and storm-surge damage.
Common misunderstandings
- "It had never rained in Greenland before." Not true. Rain is common on Greenland's coasts. What was new was rain at the high summit of the ice sheet.
- "One event proves the ice sheet is collapsing." A single storm is weather. What concerns scientists is the trend: melt at Summit has gone from absent for about a century to three times in under a decade.
- "Melting sea ice and ice sheets have the same effect." Floating sea ice barely changes sea level when it melts. Land ice like Greenland's adds new water to the ocean.
What it means and what comes next
The summit rain fell a few months before world leaders met in Glasgow for the COP26 climate summit in November 2021, and it became one of the striking examples cited in climate coverage that year. Researchers continue to monitor Greenland using weather stations, satellites that weigh the ice through gravity measurements, and climate models such as MAR, which estimated the rainfall total.
The practical lesson is twofold. Reducing greenhouse gas emissions slows how quickly the ice melts, and coastal communities need to plan now for higher seas, from stronger defences to smarter building rules. Watching the top of Greenland, once one of the most reliably frozen places on the planet, is one of the clearest ways to see how fast the Arctic is changing.
Sources: NSIDC Ice Sheets Today: Rain at the summit of Greenland (August 2021); Live Science: Rain falls on Greenland's summit for first time in recorded history (20 August 2021); Wikipedia: Greenland ice sheet; original report and quotes: Reuters (20 August 2021).
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