Clear skies and warm temperatures in 2019 are responsible for the worst year on record for Greenland’s vast ice sheet, a study reveals.
It also found that atmospheric factors, such as clear skies and high pressure, are currently not included in climate predictions for the future.
Therefore, the researchers from Columbia University state, models may be underestimating future melt of the world’s second largest ice sheet by around half.
Last year, Greenland ice sheet’s mass balance — which accounts for melting and snowfall — increased by only 50 billion tons, 320 billion tons less than the average for 1981-2010.
However, when researchers also accounted for ice that calves away and drifts into the ocean, it revealed Greenland’s ice sheet lost 600 billion tons in mass.
According to the researchers, this is equivalent to a global sea level rise of around 1.5mm.
Unusually persistent bouts of high pressure over the country prevented the formation of ice, which led to a decrease in snowfall and an increase in ice melt.
The Greenland ice sheet contains enough frozen water to raise sea levels by as much as 23 feet (7m) if it was to disappear entirely.
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Pictured, how 2019 was different to the average for 1981-2010 Red indicates something is happening at an above average rate while blue indicates it is occurring at a below average rate. (a) number of total melting days (b) amount of snowfall (c) amount of reflected light from the sun (d) cloudiness (e) temperature two meters above the ice. The data reveals more melting, less snowfall and less cloud cover than normal in 2019
The study used satellite data, ground measurements and climate models to analyse changes in the ice sheet during the summer of 2019.
The scientists compared the data to the average annual surface mass difference between 1981 and 2010, which was a 375 billion ton gain.
Previously, the worst year on record was 2012, which experienced a 310 billion ton drop compared to the pre-2010 average.
The principle issue last year was the fact Greenland’s skies were often clear, and not cloudy, due to persistent area of high pressure.
As a result of these so-called anticyclonic conditions, approximately 50billion ton of snow did not fall, the scientists say.
The lack of snowfall also left dark, bare ice exposed in some places, and because ice doesn’t reflect as much sunlight as fresh snow, it absorbed more heat and exacerbated melting and runoff.
‘Imagine this vortex rotating in the southern part of Greenland,’ Professor Tedesco explained
‘It is literally sucking in like a vacuum cleaner the moisture and heat of New York City, for example, and dumping it in the Arctic – in this case, along the west coast of Greenland.
‘When that happened, because you have more moisture and more energy, it promoted the formation of clouds in the northern part.’
Average pressure over Greenland in summer 2019, with arrows showing wind direction. The high pressure led to less cloud cover and this, in turn, increased ice loss. The red circles reveal the country was experiencing far higher pressure, and less cloud, than normal
Last year, Greenland ice sheet’s mass balance — which accounts for melting and snowfall — increased by only 50 billion tons, 320 billion tons less than the average for 1981-2010. Pictured, blue icebergs Saqqaq village, west coast of Greenland
Surface mass balance takes into account gains in the ice sheet’s mass, such as through snowfall, as well as losses from surface meltwater runoff.
Professor Tedesco said: ‘You can see the mass balance in Greenland as your bank account. In some periods you spend more, and in some periods you earn more.
‘If you spend too much you go negative. This is what happened to Greenland recently.’
The study, published in the journal The Cryosphere, shows climate models may be vastly underestimating how much ice will melt in Greenland in the future.
According to Dr Tedesco, current global climate models are not able to capture the effects of a ‘wavier jet stream’ – a phenomenon that can lead to extreme weather.
As a result, he believes simulations of future impacts are significantly underestimating the mass loss due to climate change.
He says: ‘Because climate models that project the future melting of the Greenland ice sheet do not currently account for these atmospheric patterns, they may be underestimating future melting by about half.’
The researchers believe these conditions will become more common in Greenland.
Dr Tedesco said: ‘These atmospheric conditions are becoming more and more frequent over the past few decades.
‘It is very likely that this is due to the waviness to the jet stream, which we think is related to, among other things, the disappearance of snow cover in Siberia, the disappearance of sea ice, and the difference in the rate at which temperature is increasing in the Arctic versus the mid-latitudes.’
HOW MUCH WILL SEA LEVELS RISE IN THE NEXT FEW CENTURIES?
Global sea levels could rise as much as 1.2 metres (4 feet) by 2300 even if we meet the 2015 Paris climate goals, scientists have warned.
The long-term change will be driven by a thaw of ice from Greenland to Antarctica that is set to re-draw global coastlines.
Sea level rise threatens cities from Shanghai to London, to low-lying swathes of Florida or Bangladesh, and to entire nations such as the Maldives.
It is vital that we curb emissions as soon as possible to avoid an even greater rise, a German-led team of researchers said in a new report.
By 2300, the report projected that sea levels would gain by 0.7-1.2 metres, even if almost 200 nations fully meet goals under the 2015 Paris Agreement.
Targets set by the accords include cutting greenhouse gas emissions to net zero in the second half of this century.
Ocean levels will rise inexorably because heat-trapping industrial gases already emitted will linger in the atmosphere, melting more ice, it said.
In addition, water naturally expands as it warms above four degrees Celsius (39.2°F).
Every five years of delay beyond 2020 in peaking global emissions would mean an extra 20 centimetres (8 inches) of sea level rise by 2300.
‘Sea level is often communicated as a really slow process that you can’t do much about … but the next 30 years really matter,’ lead author Dr Matthias Mengel, of the Potsdam Institute for Climate Impact Research, in Potsdam, Germany, told Reuters.
None of the nearly 200 governments to sign the Paris Accords are on track to meet its pledges.
Source: Daily Mail – Articles