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NASA - Measuring Changes to Greenland's Icesheet

Greenland's ice loss is twice 20th century average, study

Leeanna McLean
Digital Reporter

Thursday, December 17, 2015, 12:38 PM - Rather than using computer models, for the first time, scientists have published their direct observations of Greenland's ice loss. 

Findings show the country's ice sheet has melted twice as fast between the years of 2003 and 2010 as it did from 1900 to 1983, according to a new study.

Published in the journal Nature, researchers used historic and aerial photos taken between 1978-87 to estimate ice loss over the course of the 20th century. Together with satellite imagery that shows present-day glacier positioning, they were able to map the rate of retreat in three-dimension.

Credit: Niels Jákup Korsgaard, Natural History Museum, Denmark

"The foundation for our study is a unique set of aerial photographs recorded by the then Danish National Cadastre and Survey, which cover both the ice-free land and extends up to 100 km onto the Inland Ice itself. The digital reconstruction of the past and present elevation, which is based on the aerial photos, is a first of its kind and allows for the unique surveying of the entire ice sheet and the landscape in front of the ice," senior author of the paper, professor Kurt H. Kjær from the Centre for GeoGenetics said.

 RELATED: One of the fastest-melting glaciers may have broken record

Scientists were also able to calculate Greenland's contribution to sea level rise from meltwater, which they estimate to be about 10 to 18 per cent between 1990 and 2010.

The new study fills a gap in the last report conducted by the United Nations Intergovernmental Panel on Climate Change (IPCC), Kjær explained.

"Our paper contributes with an estimated mass loss from Greenland for the first part of the twentieth century, which is exactly the period where there is no data in IPCC's report. As a consequence of this we are one step further in mapping out the individual contributions to global sea level rise. In order to predict future sea level changes and have confidence in the projections, it is essential to understand what happened in the past."

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The photos below show where the glaciers scraped against the rock, eroding vegetation. The boundary between the lighter and darker parts on the mountain slopes is called the "trimline." By using the trimline as a reference and combining thousands of aerial photos with present satellite imagery, researchers were able to measure and reconstruct the extent of ice at different points in time.

Kangiata Nunata Sermia in Southwest Greenland. The upper trimline (transition) between the lighter and darker valley sides marks the extent of the glacier during the Little Ice Age, while the lower lines shows the extent at later points in time. (Hans Henrik Tholstrup/Natural History Museum of Denmark)

Scientists were particularly interested in changes of the ice sheet after the Little Ice Age, a period from c. 1200 AD to the end of the nineteenth century; a time in which which Europe and North America were subjected to much colder winters than during the 20th century.

The information in the study will help scientists further understand the behaviour behind Greenland's ice sheet and in turn, lead to more accurate projections of how it will change in the future.

Source: Study | Natural History Museum of Denmark | Climate Central 

Watch more: Chief meterologist Chris Scott speaks with leading expert on glaciers and climate change

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