They warn that the window of opportunity for reducing emissions is now small, and that the speed at which we are currently emitting carbon into the atmosphere could result in the Earth suffering damage lasting for tens of thousands of years.
Writing in Nature Climate Change journal, they say too much of the climate policy debate has focused on the past 150 years and their impact on global warming and sea level rise by the end of this century.
Peter Clark, professor of geology and geophysics at Oregon State University in the US, and the study’s lead author, says: “Much of the carbon we are putting in the air from burning fossil fuels will stay there for thousands of years – and some of it will be there for more than 100,000 years.”
Long-term view
Co-author Thomas Stocker, professor of climate and environmental physics at the University of Berne, Switzerland, and former co-chair of Working Group I of the Intergovernmental Panel on Climate Change (IPCC), warns of “the essential irreversibility” of greenhouse gas emissions.
He writes: “The long-term view sends the chilling message of what the real risks and consequences are of the fossil fuel era. It will commit us to massive adaptation efforts so that, for many, dislocation and migration becomes the only option.”
The authors say sea level rise is one of the most graphic impacts of global warming, yet its effects are only just starting to be felt. The latest IPCC report, for example, expects that likely sea level rise by the year 2100 will be no more than one meter.
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But with just 2°C of warming in the low scenario examined in the study, sea levels are predicted eventually to rise by about 25 metres. And with 7°C expected in the high scenario, the rise is estimated at 50 metres, over several centuries to millennia.
“It takes sea level rise a very long time to react – on the order of centuries,” Professor Clark says. “It’s like heating a pot of water on the stove; it doesn’t boil for quite a while after the heat is turned on – but then it will continue to boil as long as the heat persists. Once carbon is in the atmosphere, it will stay there for tens or hundreds of thousands of years.”
An estimated 122 countries have at least 10% of their population in areas that will be directly affected by rising sea levels in the low scenario. About 1.3 billion people – 20% of the Earth’s population – may be directly affected.
“We can’t keep building seawalls that are 25 metres high,” Clark says. “Entire populations of cities will eventually have to move.”
Read more at Chilling Warning on Warming’s Future Legacy
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