High temperatures and anomalous high-pressure conditions triggered the melting of enormous quantities of ice, causing a rapid rise in sea levels.
The Greenland ice sheet, the second largest in the world, is melting very rapidly, seven times faster than in the 1990s. In August 2019, in a single day, 11 billion tonnes of ice melted, the most severe episode in the Arctic ice retreat season.
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A new study, published in the journal The Cryosphere, has analysed this alarming trend and highlighted the risks posed by a sharp rise in sea levels.
The melting of the ice sheet was caused by the extraordinarily high temperatures affecting the Arctic regions, but that is not all. According to the researchers, the main cause of the record melting was a vast and persistent high-pressure system over the region. High-pressure conditions lasted for 63 of the 92 summer days in 2019, compared with an average of just 28 days between 1981 and 2010.
Ice melt is linked to a series of factors, including the amount of snowfall, the capacity to reflect sunlight, and cloud cover. These factors were influenced by the persistent high-pressure zone, which produced clear skies, high temperatures and a lack of snowfall in the southern part of the island, and drove humid air towards the northern areas of the ice sheet.
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The prolonged absence of clouds in the southern part of the island meant that a greater amount of sunlight was absorbed by the ice, accelerating its melting. The lack of clouds also entailed a drastic drop in snowfall, depriving the ice sheet of approximately 50 billion tonnes of snow. The absence of snow also exposed the darker ice to solar radiation; darker ice reflects less light than a bright surface such as fresh snow, thus resulting in greater melting.
Extreme melting events, such as the one that occurred in Greenland in 2019, are becoming increasingly frequent, exacerbated by climate change. "In just a few decades we are destroying ice that formed over thousands of years," Marco Tedesco, a researcher at Columbia University in New York and lead author of the study, told Reuters. "What happens here has enormous implications for every other part of the world."
Read also: Greenland, the rate of ice melting has quadrupled in just 10 years
Last year, Greenland's ice sheet recorded its greatest decline since 1948, the year measurements began, due to the extraordinary imbalance between new snowfall and ice melt.
The climate models used by the Ipcc to predict ice melt and the resulting rise in sea levels, the study's authors warned, do not account for these unusual climatic and meteorological conditions, which could become increasingly frequent. If that were the case, ice could melt at twice the speed hypothesised by Ipcc scientists, with serious consequences on a global scale.
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"This melting event is a warning sign reminding us that we urgently need to change our way of life to limit global warming, as the Ipcc projections are likely to be too optimistic for the Arctic," said co-author of the research Xavier Fettweis, from the University of Liège.
Greenland's ice sheet is seven times the area of the United Kingdom and, in some places, is 2–3 kilometres thick. It contains so much frozen water that if it all melted, it would raise sea levels by up to 7 metres worldwide. The 600 billion tonnes of ice that melted in 2019 caused a rise in global sea levels of 1.5 millimetres in just two months.
In recent decades, Greenland has contributed 20–25 per cent of sea level rise. If carbon emissions continue to grow, Tedesco warned, this share could rise to around 40 per cent by 2100.
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Average temperatures in the Arctic have risen by two degrees since the mid-nineteenth century, twice the global average. The massive melting of Arctic ice threatens hundreds of millions of people around the world, and the enormous quantities of fresh water pouring into the seas would also alter the salinity of the oceans, disrupting their ecosystems.
