August 20, 2020

expert reaction to paper on Greenland ice loss

A study, published in Communications Earth & Environment, reports on the rate of Greenland ice loss.

Prof Stuart Cunningham, an oceanographer from the Scottish Association for Marine Science (SAMS), said:

“The UK is leading international efforts to continuously observe the strength and structure of North Atlantic Circulation with an array of moorings from Newfoundland to Greenland to Scotland. 

“We know the strength of the North Atlantic circulation which moderates UK climate – contributing to the UK and NW Europe being 5-10 degrees Celsius warmer than elsewhere at similar latitudes – is sensitive to the Greenland freshwater input.  

“Climate models show this circulation can be switched off by adding fresh water to the North Atlantic. Paleo climate data demonstrates the circulation abruptly changed during the end of the last ice-age due to melting of glaciers and that such changes can be abrupt (a decade or less) and lower mean temperatures by 5-10 degrees Celsius.

“Recent modelling results suggest that much of the Greenland Freshwater is retained in the North Atlantic and we know the North Atlantic is now fresher than at any time in the past 100 years. This is due to circulation changes. 

“Freshwater from Greenland is a potential tipping point by adding yet more fresh water. This tipping point in the climate system is one of the potential climate disasters facing us.” 

Dr Andrew Sole, Senior Lecturer in Physical Geography at the University of Sheffield, said:

“I am not at all surprised that 2019 was a record melt year for the Greenland Ice Sheet, as there has been a lot of anecdotal and localised evidence suggesting that it would be. Indeed, in early July 2019 I was on an expedition to north-east Greenland in Kronprins Christian Land at 80N where we measured an unusually high temperature of 17C in the shade.

“It is of course essential to justify such suppositions with robust scientific measurements. The authors have done this using new data from the Gravity Recovery and Climate Experiment – Follow On (GRACE-FO) satellite mission. Extremely precise measurements of changes in the distance between the two GRACE-FO satellites, which orbit the Earth in tandem, enable the spatial distribution of Earth’s mass, and changes in this distribution over time, to be estimated. Using a suite of numerical models, the mass lost from ice sheets to the ocean can be identified.

“The authors found that mass loss from the Greenland Ice Sheet in 2019 was 532 ± 58 Gt, 15 per cent greater than the previous record set in 2012. (Note that the melting of one gigatonne or Gt (1 × 10 9 tonnes) of ice produces a cubic kilometre of meltwater). In each case, anticyclonic atmospheric circulation transported relatively warm air from the mid-latitudes over the ice sheet for a prolonged period, leading to enhanced surface melting.

“The 2019 record follows two relatively low mass loss years in 2017 and 2018 (caused by reduced melt and increased snowfall), highlighting both the large interannual variability in the ice sheet’s
mass time-series, but crucially also the importance of using longer-term trends for determining the effects of climate change. As well as quantifying the overall ice sheet mass loss, the authors have
demonstrated measurement continuity with the previous GRACE mission (2002 – 2017) using regional climate and ice sheet surface process models – a very useful contribution for the wider
scientific community.”

Dr Twila Moon, Research Scientist, University of Colorado at Boulder, said:

“The GRACE and GRACE-FO satellites provide a valuable data source for assessing ice loss, and their measurements continue to confirm that we are in a critical state of global ice loss, including in Greenland. While scientific measurements are able to tell us about the changing state of Greenland ice, it is up to all of us to take action to ensure that ice does not disappear too quickly. 

“It is devastating that 2019 was another record year of ice loss. In 2012, it had been about 150 years since the ice sheet had experienced similar melt extent, and then a further 600+ years back to find another similar event. We have now had record breaking ice loss twice in less than 10 years, and the ice sheet has lost ice every year for the past 20. If everyone’s alarm bells were not already ringing, they must be now. 

“While we cannot expect to add ice to the Greenland Ice Sheet, human action plays the key role in determining how quickly we lose ice. Slowing the rate of ice loss by lowering global emissions means protecting our coastal communities and economies for a longer time as we adapt to the coming changes in sea level.

“The research further confirms that we are in a dire state of ice loss in Greenland. This ice loss translates directly to rising seas around the world. The goods news is that by taking climate action, we can slow the rate of ice loss. With less ice lost, our coastal homes, schools, military sites, shipping ports, and other infrastructure will not be so quickly drowned by rising seas and we can better plan to protect our people and resources and adapt to coming changes.

Prof Andrew Shepherd, Director of the Centre for Polar Observation and Modelling, University of Leeds, said:

“It’s incredible to think that even in cool years, Greenland is now losing more than a hundred billion tons of ice. 

“But the record melting has returned, and the ice sheet is once again tracking the IPCCs worst-case climate warming scenario. This means we need to prepare for an extra 10 cm or so of global sea level rise by 2100 from Greenland alone. And at the same time we have to invent a new worst-case climate warming scenario, because Greenland is already tracking the current one.

“It’s important of course because every centimetre of sea level rise leads to coastal flooding and erosion, disrupting people’s lives around the planet. And if Greenland’s ice losses continue on their current trajectory, an extra 25 million people could be flooded each year by the end of this century.”

Prof Martyn Tranter, Professor of Polar Biogeochemistry, University of Bristol, said:

“These data show that successive years can produce very different melt amounts across the Greenland Ice Sheet. This arises because the warming climate over Greenland has different characteristics from year to year. Melt from Greenland is a major contributor to sea level rise and we need accurate models to forecast melt rates in the coming decades for coastal defence. It is reassuring to see that the melt models currently being used are in tune with the melt that is observed, so we can be confident the models are getting it right now. We need to continue working hard as a research community to make sure that our melt models work this well in the warming climates of our future.”

Prof Ed Hawkins, Climate research scientist, University of Reading, said:

“To put this 2019 Greenland melt rate into context, 532 gigatonnes in one year is equivalent to around 6 Olympic-sized swimming pools every single second of the year.”

Prof Chris Rapley, Professor of Climate Science, University College London (UCL), said:

“In a 1983 study for the European Space Agency on the potential of polar orbiting satellites to transform the study of Earth’s icy regions, we wrote: ‘At present we do not know if the ice sheets of Greenland and Antarctica are growing or shrinking’. Considering a specific example of possible collapse we noted: ‘By the time increasing sea level became apparent, it would be too late to take evasive action, such as reducing atmospheric pollution, because the residence time in the atmosphere of the most important pollutant (carbon dioxide) is too long. Moreover, ice sheet collapse may in any case become dynamically irreversible.’

“Twenty-two years later, at the Exeter conference on ‘Avoiding Dangerous Climate Change’, based on early satellite data, I spoke of the ice sheets as having shifted from being ‘Slumbering Giants’ to ‘Awakening Giants’. Now here we are a further 15 years later – and from the results reported here and another study last week suggesting Greenland may already have passed its ’Tipping Point”, we may draw the conclusion that the Slumbering Giant is in fact us – humanity.

“To transform the way we power, finance and run the world in the way we know we should is proving entirely beyond us. Torpor, incompetence and indifference at the top may kill people in a health crisis, and torpedo the careers of young students in an education crisis; but the damage they are generating in the pipeline from climate change is on another scale.”

‘Return to rapid ice loss in Greenland and record loss in 2019 detected by the GRACE-FO satellites’ by Ingo Sasgen et al. was published in Communications Earth & Environment at 4pm UK TIME on Thursday 20 August 2020.

DOI: 10.1038/s43247-020-0010-1

Declared interests

Prof Rapley: none to declare

No others received.