Read more of this story here from Truthdig RSS by Tim Radford / Climate News Network.
The speed of Antarctica’s melting has begun to gather pace. Between 1992 and 2017, the rate of loss of ice from West Antarctica has risen threefold, from 59 billion metric tons per year to 159bn. The West Antarctic peninsula, one of the fastest warming places on Earth, has seen ice loss soar from 7bn to 33bn tonnes a year in that timespan, as ice shelves have collapsed.
Altogether, in those 25 years, Antarctica has lost more than a trillion tonnes of ice. Since the southern continent is the biggest store of freshwater on the planet – if it all melted, the sea levels would rise by 58 metres – the news is ominous. It means that melting in Antarctica alone has raised global sea levels by 8mm, as global average temperatures rise, in response to ever-higher levels of carbon dioxide in the atmosphere.
And if the world’s economies go on burning the fossil fuels that have driven rising levels of greenhouse gases, then by 2070 global sea levels will rise even faster – by a metre, with one fourth of that from Antarctic meltwater – and ever more ice will be lost from the Southern Ocean.
This in turn will drive big changes in the marine ecosystems of the Antarctic and for the first time permit invasive pests to colonise what was once a pristine, unspoiled landscape.
But such an outcome is not inevitable. “The future of Antarctica is tied to that of the rest of the planet and human society,” said Steve Rintoul, of the Centre for Southern Hemisphere Oceans Research in Hobart, Tasmania, and one of the research team.
“Actions can be taken now that will slow the rate of environmental change, increase the resilience of Antarctica, and reduce the risk that we commit to irreversible changes with widespread impact.”
A series of research papers in the journal Nature tells a story of ice loss and global concern. A team of 84 scientists from 44 international organisations have amalgamated 24 satellite surveys of change in the farthest south with greater precision that any other study so far.
“According to our analysis, there has been a steep increase in ice losses from Antarctica during the last decade, and the continent is causing sea levels to rise faster today than at any time in the past 25 years,” said Andrew Shepherd of the University of Leeds, UK, who led the assessment. “This has to be a concern for the governments we trust to protect our coastal cities and communities.”
None of this is a surprise: what is new about the latest research is the confidence with which the researchers speak. Human exploration of Antarctica began little more than a century ago, and systematic scientific observation began only in the mid-20th century.
Antarctic ice has retreated and advanced and retreated again many times over the millennia: there has always been argument about how much of the change is because of natural cycles, how much because of human-induced climate change. In the last few years, the contribution of warmer oceans and warmer atmosphere has begun to become obvious.
Using both direct observation and remote sensing, they have watched fresh water running off the polar surface in the summer and recorded the first signs of invasive plants on rocks that were once all but barren.
And now data from satellites launched by the European Space Agency, Japan, Canada, NASA, Italy and Germany has been combined into something known as the Ice Sheet Mass Balance Inter-comparison Exercise, or IMBIE for short. And it has settled one of the great uncertainties.
While the western Antarctica ice sheet has been steadily melting, there has been evidence that East Antarctica itself was stable, or even growing. The latest study settles an old argument: the combined evidence suggests that East Antarctica is more or less stable, gaining if anything 5bn tonnes a year on average, perhaps because of greater snowfall.
Overall, though, the continent is losing the mass of its ice, and if the world continues to warm, this loss can only accelerate.
“Unfortunately, we appear to be on a pathway to substantial ice-sheet loss in the decades ahead, with longer-term consequences for enhanced sea-level rise; something that has been predicted in models for some time.
“If we aren’t already alert to the dangers posed by climate change, this should be an enormous wake-up call,” said Martin Siegert, of the Grantham Institute at Imperial College London, and one of the authors.
“Antarctica is being affected by global warming, and unless we curtail our CO2 emissions within the next decade, and have a zero carbon economy within a few decades, we will be locked into substantial global changes, including those in Antarctica and the Southern Ocean.”Read more