Un total de 28 bilions de tones de gel han desaparegut de la superfície de la Terra des de 1994. Aquesta és la sorprenent conclusió dels científics del Regne Unit que han analitzat enquestes per satèl·lit sobre els pals, muntanyes i glaceres del planeta per mesurar la cobertura de gel perduda a causa de la calefacció global. provocada per l’augment de les emissions de gasos d’efecte hivernacle.
The scientists – based at Leeds and Edinburgh universities and University College London – describe the level of ice loss as “staggering” and warn that their analysis indicates that sea level rises, triggered by melting glaciers and ice sheets, could reach a metre by the end of the century.
“To put that in context, every centimetre of sea level rise means about a million people will be displaced from their low-lying homelands,” said Professor Andy Shepherd, director of Leeds University’s Centre for Polar Observation and Modelling.
The scientists also warn that the melting of ice in these quantities is now seriously reducing the planet’s ability to reflect solar radiation back into space. White ice is disappearing and the dark sea or soil exposed beneath it is absorbing more and more heat, further increasing the warming of the planet.
In addition, cold fresh water pouring from melting glaciers and ice sheets is causing major disruptions to the biological health of Arctic and Antarctic waters, while loss of glaciers in mountain ranges threatens to wipe out sources of fresh water on which local communities depend.
“In the past researchers have studied individual areas – such as the Antarctic or Greenland – where ice is melting. But this is the first time anyone has looked at all the ice that is disappearing from the entire planet,” said Shepherd. “What we have found has stunned us.”
The level of ice loss revealed by the group matches the worst-case-scenario predictions outlined by the Intergovernmental Panel on Climate Change (IPCC), he added.
The group studied satellite surveys of glaciers in South America, Asia, Canada and other regions; sea ice in the Arctic and Antarctic; ice sheets that cover the ground in Antarctica and Greenland; and ice shelves thatprotrude from the Antarctic mainland into the sea. The study covered the years 1994 to 2017.
A glacier melting in Svalbard archipelago. Photograph: Jan Tove Johansson/Getty Images
The researchers’ conclusion is that all the regions have suffered devastating reductions in ice cover in the past three decades and these losses are continuing.
“To put the losses we’ve already experienced into context, 28 trillion tonnes of ice would cover the entire surface of the UK with a sheet of frozen water that is 100 metres thick,” added group member Tom Slater from Leeds University. “It’s just mind-blowing.”
As to the cause of these staggering losses, the group is adamant: “There can be little doubt that the vast majority of Earth’s ice loss is a direct consequence of climate warming,” they state in their review paper, which is published in the online journal Cryosphere Discussions.
“On average, the planetary surface temperature has risen by 0.85C since 1880, and this signal has been amplified in the polar regions,” they state. Both sea and atmospheric temperatures have risen as a result and the resulting double whammy has triggered the catastrophic ice losses uncovered by the group.
In the case of the melting ice sheet in Antarctica, rising sea temperatures have been the main driver while increasing atmospheric temperatures have been the cause of ice loss from inland glaciers such as those in the Himalayas. In Greenland, ice loss has been triggered by a combination of both sea and atmospheric temperatures increasing.
Meltwater rushes from Boyabreen glacier in Fjaerland, Norway – a process accelerated by global heating. Photograph: Sean Gallup/Getty Images
The team stressed that not all the ice that was lost over that period would have contributed to sea level rises. “A total of 54% of the lost ice was from sea ice and from ice shelves,” said Leeds University researcher Isobel Lawrence. “These float on water and their melting would not have contributed to sea level rises. The other 46% of meltwater came from glaciers and ice sheets on the ground, and they would have added to sea level rise.”
The group’s results were published 30 years after the first assessment report of the IPCC was published, at the end of August 1990. This outlined, in stark terms, that global warming was real and was being triggered by increasing emissions of greenhouse gases from the burning of fossil fuels.
Despite warnings from scientists, these emissions have continued to rise as global temperatures continued to soar. According to figures released by the Met Office last week, there was a 0.14C increase in global temperatures between the decade 1980-89 and the decade 1990-1999, then a 0.2C increase between each of the following decades. This rate of increase is expected to rise, possibly to around 0.3C a decade, as carbon emissions continue on their upward trajectory.