Friday, May 08, 2020

Sea-levels to rise higher than projected

Oceans rising faster than previously thought, according to survey of 100 specialists. Sea-level rise could exceed 1 metre by the end of the century unless global emissions are reduced and could reach as high as 5 metres by 2300.

“A global sea-level rise by several metres would be detrimental for many coastal cities such as Miami, New York, Alexandria, Venice, Bangkok, just to name a few well-known examples. Some may have to be abandoned altogether as they cannot be defended,” said co-author Stefan Rahmstorf, from the Potsdam Institute for Climate Impact Research in Germany. “Like in the Covid pandemic, timing is critical to prevent devastation. If you wait until you already have a serious problem, then it is too late. Unlike with corona, sea-level rise cannot be stopped for many centuries or even millennia once ice sheets have been destabilised past their tipping points,” Rahmstorf said.

In the worst-case scenario – with rising emissions and global heating of 4.5C above pre-industrial levels – the study estimates the surface of the world’s oceans in 2100 will be between 0.6 and 1.3 metres higher than today, which would potentially engulf areas home to hundreds of millions of people If humanity succeeds in cutting carbon dioxide and holding the increase in temperature to 2C, the rise would be a more manageable 0.5 metre.

The figures for both are more pessimistic than those outlined by the UN intergovernmental panel on climate change (IPCC), which predicts the worst possibility is a 1.1-metre rise by 2100.  The new survey – published in the journal Climate and Atmospheric Science – aggregates the views of 106 specialists, who were chosen because they have published at least six peer-reviewed papers on the subject in major academic journals. As a result, the predictions are more representative of a range of views in the field.

The higher estimates highlight growing concern about the world’s two biggest ice sheets, in Antarctica and Greenland. Satellite data and on-the-ground measurements show these regions are melting faster than most computer models predicted. Many of the scientists said there was now greater understanding of the risks posed by marine ice-cliff instability, which can lead to the collapse of ice shelves.

The study was led by scientists at the Nanyang Technological University in Singapore with support from seven research institutions across the world, including Durham University in the UK, Tufts University in the US and the Potsdam Institute for Climate Impact Research in Germany.
“Although emissions are reducing this year, this does not mean the build-up of CO2 in the atmosphere will reverse – it will just be slightly slower” the Met Office’s chief CO2 forecaster, Richard Betts, said in a blogpost. “An analogy is filling a bath from a tap – it’s like we are turning down the tap, but because we are not turning off the tap completely, the water level is still rising.”

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