Greenland's biggest glacier suddenly slows down and thickens, baffling scientists

Jakobshavn Isbrae glacier gaining thickness of 20 metres a year

Greenland’s largest glacier has not only slowed its retreat, but has also thickened in recent years, surprising scientists studying the impacts of global warming on ice in the northern hemisphere.

The island is home to the second-largest ice sheet in the world after Antarctica and rapid warming in the northern hemisphere has major implications for continuing global sea-level rise.

The Jakobshavn Isbrae glacier on Greenland’s west coast used to lose more ice from this than anywhere else in the country.

It is known for the huge blocks of ice it calves into Disko Bay, which then drift south into the Atlantic Ocean. It is believed to have calved the iceberg which sank the Titanic.

Between 2000 and 2010, Jakobshavn Isbrae contributed the largest solid ice discharge in all of Greenland’s ice sheet and is estimated to have contributed to nearly 1mm of global sea rise.

But despite the trend of rising temperatures, it is no longer the place where the territory loses most of its ice.

Since 2013, when the glacier’s ice loss was at its fastest, the ice at the terminus of the glacier has stopped decreasing in height and started to thicken.

The overall effect is that it is now flowing more slowly, thickening and advancing towards the ocean instead of retreating further inland.

Measurements of the glacier’s elevation changes on its narrow trunk show that instead of losing 20 metres in height a year as it had previously, the glacier is now thickening by 20 metres a year.

New data processing techniques applied to the information gathered by satellites have given a clearer picture of the extent to which the ice is returning to the glacier, the European Space Agency (ESA) said.

“The dynamic speedup of Jakobshavn Isbrae observed from the late 2000’s to 2013 was triggered by warm ocean waters in Disko Bay, entering Jakobshavn Fjord and melting ice at the glacier terminus," said Anna Hogg, a researcher in the Centre for Polar Observation and Modelling at the University of Leeds.

“In recent years, however, temperature measurements show that ocean water in Disko Bay has experienced a series of cooler years – more than one degree lower than mean temperature previously observed. This has reduced the rate of ice melt on Jakobshavn Isbrae.”

However, the glacier does not indicate greater stability in the ice sheet overall. It drains just 7 per cent of all ice on Greenland.

Scientists at the Living Planet Symposium in Milan heard the glacier’s drainage basin as a whole is still losing more ice to the ocean than it gains as snowfall.

It is therefore still contributing to global sea-level rise, albeit at a slower rate.

Dr Hogg said: “The key question we need to answer now is whether the slowdown of Jakobshavn Isbrae just a pause, or is it more permanent? We will use ESA satellite observations combined with models to monitor change and predict this colossal glacier’s future evolution.”

The ESA’s Mark Drinkwater said further research was required and noted that “large seasonal and year-to-year variability in the dynamics of the Jakobshavn Isbrae Glacier … can easily hide the longer-term climate trend in ice loss.”

The research appears to fit with a study published earlier this year, indicating Greenland’s ice sheet was melting four times faster now than it was in 2003. However, it found the largest amount of ice loss was sustained away from the country's glaciers.

“Whatever this was, it couldn’t be explained by glaciers, because there aren’t many there,” Michael Bevis, the study’s lead author said in January.

He added: “It had to be the surface mass – the ice was melting inland from the coastline. It’s because the atmosphere is, at its baseline, warmer."

Another study of Jakobshavn Isbrae’s unexpected thickening indicated the cooling period will pass as ocean temperatures rise, which will then see the glacier retreat even faster than it was before.