Earth may be on a runaway trajectory towards a ‘hothouse’ climate which will see huge swathes of the planet become uninhabitable and 200ft sea level rises, an international team of scientists has warned.
A new review found that even if targets to cap global warming at 2C are met, it may already be too late because of a ‘domino effect’ of other factors such as the ongoing reduction in Arctic sea ice and the deforestation of the Amazon rainforest.
Lead author Professor Will Steffen of the Stockholm Resilience Centre said Earth was reaching a tipping point where it would be impossible to control devastating climate change.
"Human emissions of greenhouse gas are not the sole determinant of temperature on Earth,” said Prof Steffen.
“Our study suggests that human-induced global warming of 2°C may trigger other Earth system processes, often called "feedbacks", that can drive further warming - even if we stop emitting greenhouse gases.
“Avoiding this scenario requires a redirection of human actions from exploitation to stewardship of the Earth system."
Currently, global average temperatures are just over 1C above pre-industrial levels and rising at 0.17C per decade. Under the Paris Agreement countries have agreed to cut carbon dioxide emissions so that warming does not pass 2C.
But the authors warned there were ten natural feedback processes which could trigger rapid change even if targets are met. Those are: permafrost thaw, loss of methane from the ocean floor, weakening land and ocean carbon sinks, increasing bacterial respiration in the oceans, Amazon rainforest dieback, boreal forest dieback, reduction of northern hemisphere snow cover, loss of Arctic summer sea ice, and reduction of Antarctic sea ice and polar ice sheets.
As an example, permafrost thawing, forest dieback and the biological release of carbon from the soil and ocean would add an extra half a degree alone to the warming climate.
"These tipping elements can potentially act like a row of dominoes,” said co-author Johan Rockström, incoming co-Director of the Potsdam Institute for Climate Impact Research.
"Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if "Hothouse Earth" becomes the reality."
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They said the climate would eventually stabilise at a global average of 4-5C higher than pre-industrial temperatures with sea level 32 to 196 feet higher than today.
The scientists conclude: "Where such a threshold might be is uncertain, but it could be only decades ahead at a temperature rise of 2C above pre-industrial."
Commenting on the findings, climate researcher Dr Phil Williamson, from the University of East Anglia, said: "In the context of the summer of 2018, this is definitely not a case of crying wolf, raising a false alarm. The wolves are now in sight."
The researchers say it is crucial to not only cut emissions but also create new carbon stores through schemes such as planting new forests.
However Chris Rapley, Professor of Climate Science at University College London, said global agreement was unlikely.
"To avoid such a fate, Steffen et al point out that a deep transformation is required based on a fundamental reorientation of human values, equity, behaviour, institutions, economies and technology," he said.
“Given the evidence of human history, this would seem a naive hope at the best of times. But at a time of the widespread rise of Right Wing Populism, and specific denial of climate change as an issue, the likelihood that the combination of factors necessary to allow humanity to navigate the planet to an acceptable intermediate state must surely be close to zero.”
Stephen Cornelius, Chief Adviser on Climate Change at WWF, added: "Climate change is one of the greatest threats facing nature and people. It means extreme weather such as the heatwave scorching the UK and Europe could become the new normal. Meek ambition and mild half measures are not enough in this fight for the planet - we need strong action from the UK Government through rapid and deep cuts to emissions. "
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The new study was published in Proceedings of the National Academy of Sciences (PNAS).