Rain fell at the highest point on the Greenland ice sheet last week for the first time on record, another worrying sign of warming, with the ice sheet already melting at an alarming rate, scientists said on Friday.
“That's not a healthy sign for an ice sheet,” said Indrani Das, a glaciologist with Columbia University's Lamont-Doherty Earth Observatory. “Water on ice is bad. … It makes the ice sheet more prone to surface melt.”
Not only is water warmer than the usual snow, it's also darker — causing it to absorb sunlight rather than reflecting it away.
That meltwater is streaming into the ocean, causing sea levels to rise. Already, melting from Greenland's ice sheet ——the world's second largest after Antarctica's — has caused around 25 per cent of global sea level rise over the last few decades, scientists estimate. That share is expected to grow as global temperatures increase.
The rain fell for several hours at the ice sheet's 3,216-metre summit on August 14, when temperatures remained above freezing for around nine hours, scientists at the US National Snow and Ice Data Centre said.
Temperatures at the ice cap almost never lift above freezing, but have now done so three times in less than a decade.
In total, seven billion tonnes of rain fell across Greenland over three days, from August 14 through August 16 — the largest amount since records began in 1950.
The rain and high temperatures triggered extensive melting across the island, which suffered a surface ice mass loss on Aug. 15 that was seven times above the average for mid-August.
The record-breaking rain is the latest in a string of warning signs showing how climate change is affecting Greenland's ice sheet.
Greenland experienced a major melting event in late July, when enough ice melted in a single day to cover the US state of Florida in five centimetres of water.
That melting event and last week's rain were both caused by air circulation patterns in which warm, moist air temporarily covered the island.
“This alarming rain at the summit of Greenland is not an isolated event,” said Twila Moon, deputy lead scientist with the US National Snow and Ice Data Centre.
Along with rising floods, fires and other extreme events, it is one of many “alarm bells” signalling the need to reduce greenhouse gas emissions, she said.
“We really have to stay laser-focused on adapting as well as reducing the potential for those to become truly devastating.”
