Greenland is on track to lose ice mass faster this century than during any other century in the last 12,000 years, according to a new study.
US researchers simulated how different levels of carbon emissions would be likely to affect the Greenland Ice Sheet – a 660,000 square mile body of ice that covers around 80 per cent of the surface of the island.
Even if the world goes on a massive ‘energy diet’ the Greenland Ice Sheet’s rate of mass loss this century is likely to exceed anything experienced in the past 12,000 years.
But under a scenario of high greenhouse gas emissions, ice mass loss could be four times higher than anything experienced during that period.
The researchers claim that human societies need to ‘sharply curb’ emissions of greenhouse gases like carbon dioxide, to decrease the contribution of the Greenland Ice Sheet to rising sea levels, which could flood cities in the next 50 years.
The edge of the Greenland Ice Sheet – the second-largest ice body in the world, after the Antarctic Ice Sheet. If human societies don’t sharply curb emissions of greenhouse gases, Greenland’s rate of ice loss this century is likely to outpace that of any century over the past 12,000 years
‘Basically, we’ve altered our planet so much that the rates of ice sheet melt this century are on pace to be greater than anything we’ve seen under natural variability of the ice sheet over the past 12,000 years,’ said lead author Jason Briner at the University at Buffalo in the US.
‘We’ll blow that out of the water if we don’t make severe reductions to greenhouse gas emissions.’
Scientists used new, detailed reconstructions of ancient climate for their simulation model, which was focused on southwestern Greenland.
The model was validated against real-world measurements of the ice sheet’s contemporary and ancient size, taken from samples in the field.
Samples from Greenland boulders, for example, contain chemical isotopes that can help scientists determine the ancient boundaries of the Greenland Ice Sheet.
The team built a detailed geologic history of by measuring beryllium-10, a radioactive isotope, in boulders that sit on moraines – accumulations of glacial debris
‘Moraines are large piles of debris that you can find on the landscape that mark the former edge of an ice sheet or glacier,’ said co-author Professor Nicolás Young at the Lamont-Doherty Earth Observatory in New York.
‘A beryllium-10 measurement tells you how long that boulder and moraine have been sitting there, and therefore tells you when the ice sheet was at that exact spot and deposited that boulder.’
Image (a) is a map of the present-day Greenland Ice Sheet, showing the study area in the box. Images (b) and (c) show moraine sequences – accumulations of unconsolidated glacial debris that help determine the ancient boundaries of the Greenland Ice Sheet
The experts simulated changes in the sheet from the beginning of the Holocene epoch, around 12,000 years ago, and extending into the future up to 2100.
Although the current rate of ice loss in Greenland is comparable to the highest rates during the Holocene, the researchers believe future rates are likely to exceed them.
The research team’s data shows Greenland ice loss has veered below zero at points throughout the last 6,000 years, but is set to soar upwards at the end of the 21st century.
In their simulations, the researchers found that the largest ice mass losses in the past, between 10,000 and 7,000 years ago, was at a rate of around 6,000 billion tonnes per century.
This is similar to the estimated rate during the first two decades of this century (2000–2018) of around 6,100 billion tonnes per century.
However, projected mass losses for the rest of this century are expected to exceed that maximum rate, they say.
The melting of the Greenland Ice Sheet is also currently causing sea levels to rise by about 0.02 inches (0.7mm) per year.
But the new model predicts it could reach somewhere between 0.07 inches and 0.27 inches (2mm to 7mm) per year by 2100.
A rise in sea levels would see many cities around the world exposed to coastal flooding, which could lead to mass evacuations.
Researchers also took into account the different climate eventualities as outlined in the UN Intergovernmental Panel on Climate Change’s ‘RCP’ system.
The RCP trajectory ranges from RCP1.9 – where global warming is limited below 2.7°F (1.5°C) as per the goal of the Paris Agreement – to the dreaded RCP8.5, where emissions continue to rise throughout the 21st century in a worst case scenario.
Researchers used RCP2.6, where carbon dioxide emissions start declining by 2020 and reach zero by 2100, as a best case scenario.
In the RCP2.6 scenario, the predicted mass loss is around 8,800 billion tonnes per century, the team found
The project focused on southwestern Greenland. Data shows Greenland ice loss has veered below zero at points throughout the last 6,000 years, but is set to soar upwards at the end of the 21st century
But this increases to around 35,900 billion tonnes in the scenario with the highest emissions, RCP8.5 – where emissions would continue to rise throughout the 21st century.
‘If the world goes on a massive energy diet, in line with RCP2.6, our model predicts that the Greenland Ice Sheet’s rate of mass loss this century will be only slightly higher than anything experienced in the past 12,000 year,’ said Professor Briner.
‘But more worrisome is that under a high-emissions RCP8.5 scenario – the one the Greenland Ice Sheet is now following – the rate of mass loss could be about four times the highest values experienced under natural climate variability over the past 12,000 years.’
The amount of ice lost this century could also reverse 4,000 years of cumulative ice growth and exceed previous mass-loss rates by about fourfold.
Professor Briner said the findings are ‘yet another wake-up call’, especially for countries like the US that produce huge amounts of carbon-sourced energy.
The US has produced more of the carbon dioxide that currently resides in the atmosphere than any other country, while Americans use more energy per person than any other nation in the world.
Scientists collect samples from boulders in Greenland. These samples contain chemical isotopes that can help scientists determine the ancient boundaries of the ice sheet
‘The most affluent Americans, who have the highest energy footprint, can afford to make lifestyle changes, fly less, install solar panels and drive an energy-efficient vehicle,’ he said.
The authors conclude that unprecedented rates of mass loss will occur unless a low-carbon-emission scenario is followed.
Researchers say the study highlights the ‘extreme and unusual’ projected Greenland ice sheet losses for the 21st century.
‘We have long timelines of temperature change, past to present to future, that show the influence of greenhouse gases on Earth’s temperature,’ said Professor Briner.
‘For the first time we have a long timeline of the impacts of that temperature – in the form of Greenland Ice Sheet melt – from the past to present to future and what it shows is eye-opening.’
Though the project focused on southwestern Greenland, research shows that changes in the rates of ice loss there tend to correspond tightly with changes across the entire ice sheet.
The study has been published in Nature.
SEA LEVELS COULD RISE BY UP TO 4 FEET BY THE YEAR 2300
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.