Greenland's massive ice sheet may have melted by a record amount this year, scientists have warned. During this year alone, it lost enough ice to raise the average global sea level by more than a millimetre. Researchers say they're "astounded" by the acceleration in melting and fear for the future of cities on coasts around the world.
One glacier in southern Greenland has thinned by as much as 100 metres since I last filmed on it back in 2004. Essentially because its ice sheet is seven times the area of the UK and up to 2-3km thick in places. It stores so much frozen water that if the whole thing melted, it would raise sea levels worldwide by up to 7m.
No one is suggesting that could happen for hundreds or even thousands of years but even a small increase in the rate of melting in coming decades could threaten millions of people living in low-lying areas. Bangladesh, Florida, and eastern England are among many areas known to be particularly vulnerable to rises in sea level over the course of the century.
And although the island of Greenland is remote, stretching from the north of the Atlantic high into the Arctic, its fate could have major implications for the severity of future flooding and may even alter coastlines and force communities to move inland. One of the scientists studying the ice sheet, Dr Jason Box of the Geological Survey of Denmark and Greenland (GEUS), says he's unnerved by the potential dangers and that coastal planners need to "brace themselves".
"Now that I'm starting to understand more of the consequences, it's actually keeping me awake at night because I realise the significance of this place around the world and the livelihoods that are already affected by sea level rise," he told me. Image caption Dr Jason Box, Geological Survey of Denmark How much is Greenland melting?
Until recently, the ice sheet was generally in a state of balance - the amount of snow falling in winter was roughly equal to the amount of ice melting in summer. Last year, there was actually a gain in ice but that was relatively unusual. Over the last 30 years, decade-by-decade, Greenland has tended to shed more ice.
Either the ice melts at the surface which sends torrents of water down to the surrounding seas or huge chunks of ice break off from the margins and float away as icebergs, gradually to melt. Recent years have seen hundreds of billions of tonnes of ice lost - and a rough guide to the effect on sea level is that 362 billion tonnes of melt raises the average ocean level by a millimetre.
That doesn't sound a lot but in 2012 Greenland's loss totalled about 450 billion tonnes, and this year's melt is on course to produce about the same, or even slightly more, with some researchers suggesting it could raise sea levels by up to 2mm. And on top of that you have to factor in the ice melting in Antarctica plus the effect of water expanding as it warms. It all raises the level of the oceans.
According to Dr Box, it's the recent increase in the average temperature that's being felt in Greenland's ice: "Already effectively that's a death sentence for the Greenland ice sheet because also going forward in time we're expecting temperatures only to climb," he said. "So, we're losing Greenland - it's really a question of how fast." How rapidly is the ice sheet changing?
I've seen for myself what's happened to one corner of it. Sermilik glacier at the southern end is not one of Greenland's largest but it does rank as one of the fastest-shrinking streams of ice anywhere in the world. To reach it back in 2004, we flew past towering cliffs of ice, the front of the glacier an immense wall of pale grey and blue standing high above the sea.
At that time, we accompanied a scientist who checked instruments positioned on the ice and he was stunned to see how the surface of the glacier was dropping by as much as a metre every month. And over the past 15 years, that rate of shrinking has continued so aggressively that now, on a return visit to the same glacier, the ice looks diminished, almost battered, and far less dominating in the landscape.
Jason Box is with me and he gathers the latest readings which show that over this summer alone the glacier has shrunk by an estimated 9m. "That's an astounding rate of loss," he said. Since my last visit, the surface of this margin of the ice sheet has lowered by an extraordinary 100m, more than halving in thickness, exposing the remaining ice to the relatively warmer temperatures of lower altitudes.
