Greenland’s Ice is Melting Seven Percent Faster than Previously Thought
By admin September 29, 2016

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The same hotspot in Earth’s mantle that feeds Iceland’s active volcanoes has been affecting scientists’ calculations of ice loss in the Greenland ice sheet, causing them to underestimate the melting by about 20 gigatons (20 billion metric tons) per year.

According to a new study in the journal, Science Advances, the hotspot softened the mantle rock beneath Greenland in a way that ultimately distorted their calculations for ice loss in the Greenland ice sheet. That means Greenland did not lose about 2,500 gigatons of ice from 2003-2013 as scientists previously thought, but nearly 2,700 gigatons instead — a 7.6 percent difference, said study co-author Michael Bevis of Ohio State University.

The Earth’s crust in that part of the world is slowly moving northwest, he explained, and 40 million years ago, parts of Greenland passed over an especially

hot column of partially molten rock that now lies beneath Iceland. The hotspot softened the rock in its wake, lowering the viscosity of the mantle rocks along a path running deep below the surface of Greenland’s east coast.

During the last ice age, Greenland’s ice sheet was much larger than now, and its enormous weight caused Greenland’s crust to slowly sink into the softened mantle rock below. When large parts of the ice sheet melted at the end of the ice age, the weight of the ice sheet decreased, and the crust began to rebound. It is still rising, as mantle rock continues to flow inwards and upwards beneath Greenland.

The existence of mantle flow beneath Greenland is not a surprise in itself, Bevis said. When the Gravity Recovery and Climate Experiment (GRACE) satellites began measuring gravity signals around the world in 2002, scientists knew they would have to separate mass flow beneath the earth’s crust from changes in the mass of the overlying ice sheet.

Models of this rock flow depend on what researchers can glean about the viscosity of the mantle. The original models assumed a fairly typical mantle viscosity, but Greenland’s close encounter with the Iceland hot spot greatly changed the picture.

To the GNET team, the 7.6 percent discrepancy in overall ice loss is overshadowed by the fact that it concealed which parts of the ice sheet are most affected by climate change. The new results reveal that the pattern of modern ice loss is similar to that which has prevailed since the end of the last ice age.

Computer models can render a fairly accurate estimate of mantle flow and crustal uplift, he said, and GNET’s mission is to make those models better by providing direct observations of present-day crustal motion. That’s why the GNET team includes GRACE scientists and earth modelers as well as GPS experts and glaciologists.

The team used GPS to measure uplift in the crust all along Greenland’s coast. That’s when they discovered that two neighboring stations on the east coast were uplifting far more rapidly than standard models had predicted.

For instance, GNET has a sister network, ANET, that spans West Antarctica. It employs roughly similar numbers of GPS stations, but spread out over a vastly larger area. Unless more stations are added to ANET, anomalous rates of uplift may go undetected, Bevis cautioned, and analyses of GRACE data will lead to inaccurate estimates of ice loss in Antarctica.

As put on the PARIS 2015 UN Climate Change Conference COP21 – CMP11, global warming can be dealt with. The Paris Agreement seeks to accelerate and intensify the actions and investment needed for a sustainable low carbon future. Its central aim is to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius. The Agreement also aims to strengthen the ability of countries to deal with the impacts of climate change.

The Paris agreement, therefore, asks all countries to review these contributions every five years from 2020; they will not be able to lower their targets and are encouraged, on the contrary, to raise them. In addition, emissions should peak as soon as possible and the countries will aim to achieve carbon neutrality in the second half of the century. This is a real turning point. We are going to gradually stop using the most polluting fossil fuels in order to reach this goal.

For more information:

Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.

Land-facing, southwest Greenland Ice Sheet movement decreasing

Greenland ice is melting — even from below: Heat flow from the mantle contributes to the ice melt

Greenland ice sheet may melt completely with 1.6 degrees of global warming Significant contribution of Greenland’s peripheral glaciers to sea-level rise.

Thanks for sharing !

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