Climate Change

Why climate change could be making some sea levels fall

Icebergs are reflected in the calm waters at the mouth of the Jakobshavn ice fjord near Ilulissat in Greenland in this photo taken May 15, 2007. New York, Boston and other cities on North America's northeast coast could face a rise in sea level this century that would exceed forecasts for the rest of the planet if Greenland's ice sheet keeps melting as fast as it is now, researchers said May 27, 2009. Sea levels off the northeast coast of North America could rise by 12 to 20 inches more than other coastal areas if the Greenland glacier-melt continues to accelerate at its present pace, the researchers reported.

Around a trillion tons of ice was lost between 2011 and 2014. Image:  REUTERS/Bob Strong

Simon Torkington
Senior Writer, Forum Agenda
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Climate Change

Greenland’s glaciers are melting fast. Recent measurements from the European Space Agency’s CryoSat project showed around a trillion tons of ice was lost between 2011 and 2014.

And, as you would expect, that water goes into the sea. The melt water pouring into the oceans has caused global sea levels to rise at twice the average rate of the preceding two decades.

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Source: European Space Agency

CryoSat makes its calculations by measuring the surface height of the Greenland ice sheet and then calculating the volume of the remaining ice.

Another view from space

But CryoSat’s picture of climate change is not the only view from space. NASA’s fleet of GRACE satellites (Gravity Recovery and Climate Experiment) monitored the rise and fall of the world’s oceans between April 2002 and July 2013.

The recently released animation of the data gathered shows a dramatic fall in sea levels around Greenland’s coastline.

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Source: NASA

As NASA’s animation progresses, the sea area around Greenland becomes a vivid shade of red. The suggestion from the modelling is that local sea levels fell by up to 50 millimetres (2 inches) over the course of the study.

The wider picture from the animation shows oceans further afield rising as a result of the melting of the Greenland ice sheet. So what is causing these local variations?

Disappearing ice reduces gravity’s effect on the ocean

"When an ice sheet loses mass, for example, the gravity drops locally (remember that gravity is proportional to mass) - meaning the gravitational attraction between the continent and surrounding ocean diminishes, thus causing the ocean mass to move to the far field," explains NASA's Surendra Adhikari, whose research is behind the animation.

At this stage the suggested fall in sea levels around Greenland is only a mathematical model. The researchers are now planning physical measurements to confirm their findings.

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