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Warming could push Greenland ice sheet beyond ‘tipping points’

An ice-floe

The Greenland ice sheet covers an area of about 1.7 million km2 and is the second largest body of ice in the world. As our climate warms, the ice sheet will melt and reduce in size. Scientific research has shown that if global temperatures rise unchecked, then it could melt completely over a few thousand years — pushing up global sea levels by up to seven metres.

Met Office scientists sought to find out if the ice sheet could recover if our climate cooled, with temperatures returning to pre-industrial levels — before man-made global warming began.

They used a sophisticated climate model coupled to a 3D simulation of the ice sheet to predict changes over thousands of years — a method pioneered by the Met Office Hadley Centre. The results showed there were tipping points in the melting of the ice sheet which, when crossed, meant it would not recover even if temperatures did cool.

  • If the ice sheet shrinks by more than 15% (which could occur within 300 years) it would be locked into a decline from which it could only recover to 80% of its current size. This would cause a 1.3 m sea-level rise.
  • If the ice sheet reduces to about 50% of its current size it would be locked into further reduction, only stabilising again at 25% of its current size — creating a sea-level rise of five metres.

This damage could only be undone if the global temperatures plunged back into an ice age — where temperatures would be cool enough for the ice to rebuild. Current predictions estimate this is unlikely to happen for tens of thousands of years.

Graph of ice-sheet volume following return to pre-industrial atmospheric CO2 forcing

Graphic of changes in size of the Greenland ice-sheet
Fig 1. Changes in ice-sheet volume from initial state toward final equilibrium as a percentage of present-day ice volume. The graph suggests convergence toward three equilibrium states at about 100, 80 and 20%

Jeff Ridley, a Met Office climate scientist specialising in polar regions, said that while the time frames for this melting were over centuries, the time to act to prevent melting beyond the tipping points is now.

“The effects of the greenhouse gases we emit today will still be felt long into the future.”

“We will need to start taking action now to stop temperature rises that will still be happening at the end of this century. Only by tackling warming temperatures now can we prevent the ice sheet melting past these tipping points, and prevent irreversible sea-level rise.”

Our expertise in this area is now being used to assess how global warming could impact the world’s biggest ice sheet, in the Antarctic. Covering an area of about 14 million km2, it contains about 60% of all the fresh water on Earth and any melting could have a significant effect on sea-levels.

Greenland ice-sheet facts

  1. 2,400 km at its longest point.
  2. 1,100 km at its greatest width.
  3. Up to 3 km thick.
  4. The ice sheet covers roughly 80% of the surface of Greenland.
  5. Ice in the current sheet is up to 110,000 years old.
  6. Has a total volume of about 2.85 million km3.
  7. Total melting of the sheet could cause a seven-metre sea-level rise.
  8. Previous studies show about 195 km2 of ice is melting each year.

Read the full article Thresholds for irreversible decline of the Greenland ice sheet (external site).