13 June 2018

Melting ice sheet accelerates rising sea levels

Ice loss on Antarctica tripled in 10 years

Unusual iceberg at Rothera Research Station, Antarctic Peninsula (Andrew Shepherd, University of Leeds)
Unusual iceberg at Rothera Research Station, Antarctic Peninsula / Andrew Shepherd, University of Leeds

Antarctica is losing more ice at an accelerating rate. Over the past 10 years, the rate of ice melt has tripled, from 73 billion tonnes per year, to 219 billion tonnes. As a result, sea levels are rising faster as well, as shown by a combination of measurements conducted by 24 international research groups. The results of this study will be published on Thursday, 14 June in the scientific periodical Nature. One of the five research leaders is Prof. Michiel van den Broeke from Utrecht University.

For the publication in Nature, the researchers combined data about Antarctica that have been collected by 24 different research groups over the past 25 years. They then determined the changes in the thickness and mass of the ice sheet that covers Antarctica. Their results show that the ice loss has tripled over the past 10 years, to an average of 219 billion tonnes per year for the period 2012-2017.

In a single generation

Prof. Michiel van den Broeke, Universiteit Utrecht
Prof Michiel van den Broeke, Utrecht University

The ice loss in Antarctica has caused sea levels to rise by an average of 7.6 mm world-wide over the past 25 years. Forty percent of that, or 3 mm, occurred just over the past five years. “The mass loss from the ice sheet fluctuates due to variations in snowfall from year to year, but the general trend is clear. And this increase occurred in just a single generation. That’s a big deal”, says Van den Broeke, Professor of Polar Meteorology at Utrecht University.

Tipping point

Van den Broeke’s concern is based on the fact that the accelerated ice melt and its consequences can eventually reach a tipping point beyond which some parts of the ice sheets will melt irreversibly. Van den Broeke: “The Paris climate accord aimed to limit global warming to a maximum of 2°C. But it’s unclear as to whether that will be enough for Antarctica. At the moment, we can’t accurately predict the maximum temperature increase at which these tipping points can occur.”

Bijdrage van de ijskappen van Antarctica aan de stijging van de zeespiegel sinds begin jaren '90 (IMBIE/Planetary Visions)

Complex relationships

In order to accurately predict the future ice loss on Antarctica, scientists require an accurate model of the extremely complex interactions between the oceans, the atmosphere, and the ice sheets. “We don’t have a model like that right now, but people all over the world are working hard on developing one”, according to Van den Broeke.

Greatest ice loss

British Antarctic Survey two-man field camp next to The Obelisk on Alexander Island, Antarctic Peninsula (Hamish Pritchard, BAS)
A field camp next to The Obelisk on Alexander Island, Antarctic Peninsula / Hamish Pritchard

The study published on Thursday indicates that the greatest ice loss was from the immense Pine Island glacier and the nearby Thwaites glacier in West Antarctica. The bedrock under these glaciers is located under sea level, and it slopes down land-inwards, so the glaciers have an unstable flow, which exacerbates the ice melt problem.

Coldest place on earth

No ice loss has yet been observed at the coldest place on earth, the gigantic mass of East Antarctica. The group led by Van den Broeke has shown that snowfall there has remained constant for decades, and the ice flow seems to be stable too. But due to the expansive size of East Antarctica, there are still many uncertainties. “A change of 1% of the mass of the East Antarctic ice sheet would mean a half-meter change in the sea level. So it’s important to keep a close eye on that area.”

This research was funded in part by the Netherlands Earth System Science Centre (NESSC), and the NWO’s Netherlands Polar Programme and is part of Utrecht University’s interdisciplinary research programme Pathways to Sustainability.

Publication

'Mass balance of the Antarctic Ice Sheet from 1992 to 2017
The Utrecht University researchers involved in the study are: Michiel van den Broeke, Bert Wouters, Melchior van Wessem, Brice Noël and Willem Jan van de Berg, from the Institute for Marine and Atmospheric Research (IMAU).
Nature, 14 June 2018, doi 10.1038/s41586-018-0179-y.

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