April 23, 2019

expert reaction to study looking at loss of Greenland ice sheet mass

Research published in PNAS describes changes in the mass of the Greenland Ice Sheet over the past 46 years.

Prof Edward Hanna, Professor of Climate Science and Meteorology, University of Lincoln, said:

“I’m happy that the press release reflects the science, and the conclusions seem reasonable and well backed up by the data presented. I do not think there is over-speculation or hyperbole, and – due to natural climate variability which is superimposed on the long-term warming – the authors do point out the difficulties and dangers of extrapolating their mass trends into the future.

“This new study adds to an existing body of evidence of significant and increasing mass loss of the Greenland Ice Sheet in response to global warming. The authors have taken advantage of an improved historical database of satellite velocity measurements and several other recently improved datasets and models which together indicate that the loss of solid ice into the ocean may have a bigger role than previously thought in the overall mass budget of the ice sheet. This together with recently much increased surface melt water losses since the 1990s highlights the vulnerability of the Greenland Ice Sheet to ongoing climate change as well as its growing impact on global sea-level rise.

“Increasing runoff (and surface mass balance losses) from Southwest Greenland are also likely to be of increasing importance in a warming climate, as indicated by the authors’ own results – as several recent studies have shown that runoff losses from the ice sheet have approximately doubled since the 1990s.”

Dr Colin Summerhayes, Emeritus Associate of the Scott Polar Research Institute, said:

“This is an excellent piece of work by a well-established research group using novel methods to extract more information from the available data.

“The story is very similar to the recent one by Rignot et al on the Antarctic (even to the colours used in the diagrams). As we join the dots, so the picture emerges progressively more clearly. There are no surprises here for those familiar with the Arctic scientific literature, where Gifford Miller and his crew are now finding mosses emerging from beneath the Baffin Island ice cap that last saw daylight 44,000 years ago. Polar amplification is doing its deadly work – destroying reflective ice and exposing darker sea that absorbs heat in a positive feedback that warms the Arctic more than anywhere else on the planet. And if you warm your fridge, what do you get? Puddles.”

Dr Amber Leeson, Senior Lecturer in Environmental Data Science, Lancaster University, said:

“This paper uses an interesting combination of observations and computer simulations to perform an assessment of ice loss from Greenland from 1972 until now, and quantifies the impact this has had on global sea level.

“The work is important because previous observation-based estimates tend to go back only as far as the early 90s and this paper shows us that the ice sheet was already out of balance by then.

“This new data better enables us to put recent, dramatic, changes to Greenland’s contribution to global sea level rise into a longer-term context – the ice loss we’ve seen in the last eight years is as much as was lost in the preceding four decades.

“We know that Greenland will continue to lose ice in coming years, however it is less certain whether ice loss will continue to accelerate at the current rate because ice sheets are incredibly complex systems.

“The next step is for scientists to use these data, in conjunction with ice sheet modelling, in order to constrain our projections of future ice sheet change.”

Dr Jeffrey Kargel, Senior Scientist, Planetary Research Institute, Tucson, AZ, said:

“I read the embargoed paper by Jeremie Mouginot, Eric Rignot and others about ‘Forty six years of Greenland Ice Sheet mass balance: 1972 to 2018.’ The results fortify previous understanding that Greenland ice balance has become more negative recently. The new results appear solidly based, and place the accelerating negative mass balance into a longer context. The Greenland ice sheet shifted dramatically to increased melting at the start of the 21st century. The paper is observational, not attributive. Such changes have been attributed by others to anthropogenic climate warming due to rising greenhouse gases. Here I offer my own thoughts on attribution.

“The abruptness of increased melting all around Greenland, as this paper documents, is beyond that expected from gradually increasing warming. Greenland’s sudden shift was like the sudden turning of a key, thus opening a door to new behaviour. For attribution, I point to a drastic change whereby increased rainfall – even in winter – is driving surface melting and faster sliding of Greenland’s glaciers into the sea. A recent paper in The Cryosphere by Marilena Oltmanns and others points out that recent years have seen winter rains falling in Greenland. This could be driven by Arctic warming and melting of sea ice, which has caused a shift in stratospheric jet streams, according to Jennifer Francis at the Woods Hole Research Center. This shift has caused eastern North America to plunge to frigid and often severely snowy winter conditions for months on end (“Snowmageddon”), the West Coast of the U.S. to suffer rainless winters, heat waves, and extreme wildfires and other protracted extreme weather from the U.K. to Siberia, and is driving nearly unheard-of winter and summer warmth and rain onto Greenland. These shifts are indirect responses to rising greenhouse gases and global warming.

“What does this mean for the future? Greenland has begun deglaciating, which will drive rising seas century after century, reaching seven meters (23 feet) of increase over the next couple of thousand years. It is probably past a point of no return. What else is in store for our planet this century, even this generation? What is still reversible or at least manageable? These are the key questions.”

‘Forty six years of Greenland Ice Sheet mass balance: 1972 to 2018’ by Jeremie Mouginot et al. was published in PNAS at 20:00 UK time on Monday 22 April 2019.

Declared interests

Dr Jeffrey Kargel: “I have no conflicts of interest regarding this paper.”

None others received.