'Off the charts': Scientists sound alarm over Greenland ice melt

Mindy Sparks
December 7, 2018

The ice sheet has the potential to raise global sea levels by 23 feet if it melts in its entirety. The Arctic began to warm as humanity began to pump greenhouse gases (GHG) into the atmosphere.

The surface melting across Greenland's mile-thick ice sheet began to increase in the mid-19 century and then surged dramatically during the 20 century and early 21 century. Another noteworthy aspect of the findings is how little additional warming it now takes to cause huge spikes in ice sheet melting. The melting and sea level rise we've observed already will be dwarfed by what may be expected in the future as climate continues to warm, " said Trusel.

It seems that icebergs which are calving into the ocean from the edge of glaciers are one component of the water re-entering the ocean and this way rising the sea levels.

From these numbers, the researchers estimated that ice sheet-wide levels of meltwater runoff have jumped 50 per cent in the past 20 years compared with pre-industrial times.

To determine how the Greenland ice had melted, researchers used a drill to extract ice cores. Greenland experiences seasonal melt during the warm summer days, and at low elevations, the melting is more intense.

Nowadays, the Greenland ice sheet is the most significant contributor to the world's sea level rise, as it adds about 72 cubic miles of meltwater to the world's oceans, every year. At higher elevations, however, the summer meltwater quickly refreezes from contact with the below-freezing snowpack sitting underneath. This frozen meltwater creates distinct ice bands that pile up over years to form layers of densely packed ice.

"Once the ice sheets reach these tipping points, it's thought that they'll go into a state of irreversible retreat, so they'll be responding to what we do now for centuries and milliennia into the future", Trusel said. Dark bands running horizontally across the cores record the strength of the melting for a given year.

The long-term record the researchers built from these layered ice cores allowed them to spot a slight trend of increased melting across Greenland coinciding with the beginning of modern-day warming in the mid-1800s. This threatens cities such as London and Venice and entire nations such as the Maldives, which within decades could be swallowed by the rising level of the sea.

"We can show that the recent increase in melt and runoff from Greenland over the past two decades, in response to warming temperatures, is exceptional and unprecedented ('off the charts')", stated Sarah Das, a geologist at the Woods Hole Oceanographic Institution and co-author of the study.

"From a historical perspective, today's melt rates are off the charts".

"We have had a sense that there's been a great deal of melting in recent decades, but we previously had no basis for comparison with melt rates going further back in time", he said.

"The melting is not just increasing - it's accelerating", Trusel told Nature.

"We need to be aiming for net-zero emissions before 2050".

Das and her colleagues at Rowan University and elsewhere reached that conclusion by examining three ice cores from central west Greenland, and one from an ice cap off the coast, that contain a history of melt events spanning the past 350 years.

Other reports by Iphone Fresh

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