CPOM research on the impact of surface melting on radar penetration in Greenland

CPOM research on the impact of surface melting on radar penetration in Greenland

An article led by CPOM PhD researcher Inès Otosaka “Surface Melting Drives Fluctuations in Airborne Radar Penetration in West Central Greenland” has been published in Geophysical Research Letters (August 2020).

Radar waves emitted by satellites can be used to measure changes in surface elevation of the Greenland Ice Sheet. However, they do not reflect off the ice sheet surface itself, but penetrate into the snow to a depth of about 15 m for radar wavelengths of 2.3 cm. When the snow melts, meltwater can percolate into the snow or refreeze at the surface. Layers of refrozen ice sharply reduce the degree of radar penetration and may be mistaken for an elevation increase in radar measurements. In this paper, the researchers combine firn cores and modelled firn densities with seven years of airborne radar data collected during field campaigns in West Central Greenland to quantify this effect. They identify internal layers corresponding to annual stratigraphy within the snowpack and show that more melt means less radar penetration into the firn. The unprecedented surface melting which occurred across Greenland in 2012 caused a sharp reduction in the degree of radar penetration, from 11.5 m to 5.3 m. However, if the effects of penetration are corrected for, radar altimeters can accurately measure the surface elevation of the ice sheet.

The earth has lost 28 trillion tonnes of ice in less than 30 years

A CPOM-led study, which shows that 28 trillion tonnes of ice have disappeared from the surface of the Earth since 1994 due to greenhouse gas emissions, has captured media and public attention.

CPOM researchers Professor Andy Shepherd, Dr Tom Slater (first author on the paper, and Dr Isobel Lawrence are quoted in a number of articles, including The Guardian:

“To put the losses we’ve already experienced into context, 28 trillion tonnes of ice would cover the entire surface of the UK with a sheet of frozen water that is 100 metres thick,” added group member Tom Slater from Leeds University. “It’s just mind-blowing.

The research has been translated in to at least 9 different languages, and high-profile attention includes Greta Thunberg, Caroline Lucas and the World Economic Forum.

Past evidence supports complete loss of Arctic sea-ice by 2035

A new study, published this week in the journal Nature Climate Change, supports predictions that the Arctic could be free of sea ice by 2035.

High temperatures in the Arctic during the last interglacial “the warm period around 127,000 years ago“ have puzzled scientists for decades. Now the UK Met Office’s Hadley Centre climate model has enabled an international team of researchers to compare Arctic sea ice conditions during the last interglacial with present day.  Their findings are important for improving predictions of future sea ice change.

During spring and early summer, shallow pools of water form on the surface of Arctic sea-ice.  These “melt ponds” are important for how much sunlight is absorbed by the ice and how much is reflected back into space.  The new Hadley Centre model is the UK’s most advanced physical representation of the Earth’s climate and a critical tool for climate research and incorporates sea-ice and melt ponds.

Using the model to look at Arctic sea ice during the last interglacial, the team concludes that the impact of intense springtime sunshine created many melt ponds, which played a crucial role in sea-ice melt.  A simulation of the future using the same model indicates that the Arctic may become sea ice-free by 2035.

Dr David Schroeder, CPOM staff researcher at the University of Reading, who developed and co-led the implementation of the melt pond scheme in the climate model, said: “This shows just how important sea-ice processes like melt ponds are in the Arctic, and why it is crucial that they are incorporated into climate models.”

Professor Danny Feltham, CPOM Sea Ice Lead, and Professor Julienne Stroeve, CPOM Associate Investigator, were also co-authors of the study.