The Greenland Ice Sheet has lost 1,965 square miles (5,091 square km) of ice since 1985, a study has found.
The world’s second-largest ice sheet has shrunk by an area more than three times the size of London, and has been collapsing at an accelerating since the 1990s.
Researchers from NASA‘s Jet Propulsion Lab found that previous research has underestimated the ice retreat by up to 20 per cent.
Their new estimate suggests that 1,034 gigatonnes, or 1,034 trillion kilograms, of ice has been lost in the last 40 years.
The scientists warn that this is enough to risk destabilising ocean currents, weather patterns, ecosystems, and even global food security.
Researchers have found that the Greenland Ice Sheet has been disappearing at an accelerating rate since the 1990s, often calving into enormous icebergs like this one, which detached from the Jakobshavn glacier
This graph shows how the Jakobshavn glacier has retreated since 1985. The darker purple colours show the extent of the glacier in the past while the bright yellow shows more recent measurements
Researchers analysed over 230,000 satellite images of the Greenland Ice Sheet to create a month-by-month measurement of how the ice sheet has changed.
This new data, published in Nature, reveals that every glacier in the ice sheet bar one has been losing ice at an accelerating rate since the 1990s.
Despite previously having been relatively stable, the ice sheet shrunk by an average of 84 square miles (218 square kilometres) every year since January 2000.
In the most extreme case, the Zachariæ Isstrøm glacier lost 378 square miles (980 square km) or 160 gigatonnes of ice.
The Jakobshavn Isbræ glacier meanwhile retreated by 73 square miles (188 square km), but lost 88 gigatonnes of ice due to its thickness.
Only Qajuuttap Sermia has grown at all, and this has only gained 0.54 square miles (1.4 square km) of ice.
All along the Greenland Ice Sheet, glaciers are moving backwards from their older positions (shown in purple) and retreating further inland towards their current extents (shown in bright yellow)
Chad Greene, a satellite expert at NASA’s Jet Propulsion Lab, discovered that ice was being lost much faster than had previously been thought.
Mr Greene and his co-authors write: ‘We report a widespread glacier terminus retreat in Greenland that has resulted in more than 1,000 Gt of ice loss that has not been accounted for in current observation-based estimates.’
They suggest that there has been 43 trillion kilograms of ice lost every year, which previous measures have been unable to detect.
While glaciers do grow in the winter and shrink in the summer, since the 1990s the summer losses have become increasingly larger than what is regained during the colder months.
Interestingly, the researchers found that the glaciers which showed the biggest seasonal fluctuations also retreated the most over the last four decades.
They suggest that seasonal variation could be a good predictor for longer-term retreat.
For example, Jakobshavn Isbræ gains almost 14 gigatonnes of ice every winter but has seen the second largest overall mass loss.
Rising global temperatures due to climate change are the driving reason that the Greenland Ice Sheet has been shrinking faster each year.
This graph shows the cumulative mass change caused by glacier retreat since 1985. The glaciers have grown and shrunk with the seasons but have continued to lose mass overall at an accelerating rate
Between 2001 and 2011 the Greenland Ice Sheet experienced its warmest decade in 1,000 years.
At high elevations, temperatures were 2.7°F (1.5°C) warmer than in the 20th century.
Last year, scientists from the British Antarctic Survey warned that humans ‘may have lost control of the West Antarctic Ice Sheet due to climate change.
Dr Greene says that his study serves as a measure of how sensitive the Greenland Ice Sheet may be to future climate change.
These graphs show how much ice has been lost since 1985 (left) and how large the seasonal fluctuations are (right) on each glacier. The glaciers with the biggest seasonal changes (shown by darker colours) also have lost the most mass overall
While the collapse of the Greenland Ice Sheet is unlikely to contribute very much to rising sea levels, the bigger concern is that it might affect ocean currents.
The Atlantic Meridional Overturning Circulation (AMOC)is a major system of ocean currents that circulates water from North to South.
As warm water flows northwards, it cools and becomes saltier, becoming dense enough to sink deep into the ocean.
As it falls, the cold water pulls more water behind it before warming and rising back to the surface, creating a current that moves like a conveyor belt.
But, when fresh water from land melts into the sea it becomes less salty and so isn’t dense enough to sink.
The worry is that if too much of the Greenland Ice Sheet melts, the seas will no longer be salty enough to drive the currents.
The researchers concluded: ‘There is some concern that any small source of freshwater may serve as a “tipping point” that could trigger a full-scale collapse of the AMOC, disrupting global weather patterns, ecosystems, and global food security.’
