By Paul Homewood

 

European satellites have detailed the abrupt change in behaviour of one of Greenland’s most important glaciers.

In the 2000s, Jakobshavn Isbrae was the fastest flowing ice stream on the island, travelling at 17km a year.

As it sped to the ocean, its front end also retreated and thinned, dropping in height by as much as 20m year.

But now it’s all change. Jakobshavn is travelling much more slowly, and its trunk has even begun to thicken and lengthen.

"It’s a complete reversal in behaviour and it wasn’t predicted," said Dr Anna Hogg from Leeds University and the UK Centre for Polar Observation and Modelling (CPOM).

"The question now is: what’s next for Jakobshavn? Is this just a pause, or is it a switch-off of the dynamic thinning we’ve seen previously?"

The rapid flow, thinning and retreat of Jakobshavn’s front end in the mid to late 2000s were probably driven by warm ocean water from Disko Bay getting into the fjord and attacking the glacier from below.

The phase change, scientists think, may be related to very cold weather in 2013. This would have resulted in less meltwater coming off the glacier, which in turn might have choked the mechanism that pulls warm ocean water towards Jakobshavn.

"Fjord overturning, the circulation that draws warm ocean water in from Disko Bay to melt the glacier at its base is, in part, forced by surface melting on the Greenland Ice Sheet. If you don’t get a lot of fresh, cold meltwater going into the fjord, this circulation is weaker," said Dr Hogg.

“All this is a reminder of how unpredictable glaciers can be," she told BBC News. "We didn’t predict this change in behaviour, and if Jakobshavn does start thinning and retreating again – we can’t predict when that will happen.

"The rate of sea-level contribution from Greenland has slowed in recent years and it’s because some of the biggest ice evacuators like Jakobshavn aren’t contributing as much as they used to."

https://www.bbc.co.uk/news/science-environment-48265217

 

It is nice to know that these scientists admit they can’t predict what is going on!

And if Jonathan Amos had bothered reading this blog, he would have already known that most of Greenland’s glaciers stopped retreating six years ago. As I noted in March, DMI’s annual Polar Portal report for 2018 stated:

glaciers have continued the development seen during the last six years in which they have more or less maintained their area

 

 

 Satellite monitoring of Greenland’s glaciers only began in 1999, so we have no idea of what went on before then, and whether recent trends are in any way unusual.

 

The full report from DMI makes clear that there has only been a minor loss in glaciers’ area since 2012/13, and that there was even a small overall increase last year:

 

 http://polarportal.dk/en/news/2018-season-report/

 

 

Bear in mind as well that the surface mass of the Greenland ice sheet has been growing at close to record levels for the past two years:

 

 

 http://polarportal.dk/en/news/2018-season-report/

 

As DMI explain, the total ice sheet balance depends on both the SMB and glacial melting/calving:

 

 

 

As the SMB has been increasing whilst glacier area has remained fairly stable in the last few years, it means that the Greenland ice sheet has actually been growing in recent years.

 

I can guarantee you won’t hear that from the BBC!

via NOT A LOT OF PEOPLE KNOW THAT

http://bit.ly/2WXFiDn

May 22, 2019 at 09:09AM