A "global cascade of tipping points" *
Scientists warn that the planet faces a "global cascade of tipping points" posing an “existential threat to civilisation” unless nations slash their greenhouse gas emissions much faster than agreed under the Paris Climate Agreement. The consequences include an abrupt shift to a warmer world and huge disruption to human societies and ecosystems.
Tipping points, many of them interconnected, include:
Melting ice sheets
- The ice sheets in West Antarctica which are dangerously close which alone would raise sea levels by three metres if they melted.
- Those in the Wilkes Basin of eastern Antarctica with another four metres of potential sea-level rise if they disintegrated.
- The interconnected nature of the giant mixing processes that distribute heat around the world's oceans: a key reason why one region's changes could reinforce other shifts. For instance, the melting of Greenland's ice sheets is driving an influx of fresh water into the North Atlantic, slowing the Gulf Stream – also known as the Atlantic Meridional Overturning Circulation (AMOC) – by 15 per cent since the middle of the 20th century.
- Another outcome is a further heating of the Southern Ocean, resulting in more Antarctic ice melt.
Other effects include:
- drought for the Sahel region of Northern Africa because of disruptions to the West African monsoon, and worse fires in the Amazon as that region dries out.
- Amazon dieback alone has the potential to release about 90 billion tonnes of CO2 while boreal forests (coniferous forests consisting mostly of pines, spruces, and larches growing in high-latitude environments where freezing temperatures occur for 6 to 8 months of the year) could add another 110 billion tonnes. Even without including the methane, emissions from melting permafrost could total 100 billion more tonnes of CO2, the report said. (By contrast, humans directly contribute to about 40 billion tonnes of CO2 a year. We also have a total emissions budget of 500 billion tonnes if the world is to have a 50:50 chance of hitting the Paris climate target of keeping warming to 1.5 degrees)
- Entire ecosystems, such as the Great Barrier Reef, are also facing tipping points. Half the reef's coral cover had been lost in recent bleaching and only a tiny fraction would remain if warming reached 2 degrees.
- Australia is among the nations most exposed to "a tipping point cascade" given it is already exposed to droughts and heatwaves, making it a much tougher climate for us to live in.
Overall consequence
The risk is not of runaway global warming but rather of a world stabilising at perhaps 5 degrees warmer. It will be a much tougher climate for us to live in.
"The schoolchildren are right," says Professor Stefan Rahmstorf, head of Earth system analysis at Germany's Potsdam Institute for Climate Impact Research. "We indeed have a climate emergency, and an emergency-level response is now needed to ensure that we don’t activate the tipping cascade".
* This is an edited summary of an article by Peter Hannam "Tipping points 'dangerously close'", which appeared in the Sydney Morning Herald on 28 November 2019, based on an article appearing in Nature on the same day.
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The risk is not of runaway global warming but rather of a world stabilising at perhaps 5 degrees warmer. It will be a much tougher climate for us to live in.
"The schoolchildren are right," says Professor Stefan Rahmstorf, head of Earth system analysis at Germany's Potsdam Institute for Climate Impact Research. "We indeed have a climate emergency, and an emergency-level response is now needed to ensure that we don’t activate the tipping cascade".
* This is an edited summary of an article by Peter Hannam "Tipping points 'dangerously close'", which appeared in the Sydney Morning Herald on 28 November 2019, based on an article appearing in Nature on the same day.
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