Rain fell at the highest point on the Greenland ice sheet last week for the first time on record, another worrying sign of warming for the ice sheet already melting at an increasing rate.

Not only is water warmer than the usual snow, it's also darker – so it absorbs more 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% of global sea level rise seen over the last few decades. 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, where temperatures remained above freezing for around nine hours.

Temperatures at the ice cap almost never lift above freezing, but have now done so three times in less than a decade.

In total, 7 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 August 15 that was seven times above the average for mid-August.

Source: Reuters