Global warming could trigger an irreversible domino effect of dying forests, melting ice and hotter oceans that push temperatures up to 5˚C above pre-industrial levels.
That is the grim warning from an international team of climate scientists, which says the carbon-storing trees and ice that were once ‘friends’ could turn into ‘foes’, spewing gases uncontrollably in a warmer world. If this occurs, it may no longer matter whether humans cut greenhouse gas emissions or not, as the ‘hothouse’ conditions could render parts of planet uninhabitable.
The scientists also warn that restricting global warming to the Paris Agreement’s upper limit of 2˚C may not be enough to prevent the series of cataclysmic climate events unfolding. “These potentially act like a row of dominoes,” said study co-author Johan Rockström. “It may be very difficult or impossible to stop the whole row of dominoes from tumbling over.”
These domino events include permafrost thaw, weakening of land and ocean carbon sinks, Amazon rainforest loss, reduction of northern hemisphere snow cover, and loss of ice at the poles. Once a critical temperature threshold is crossed, these events could release an abundance of gas into the atmosphere, causing long-term heating of 4-5˚C above pre-industrial levels and the sea level rising to 10-60m higher than it is today.
The scientists highlight the urgent need to accelerate the transition towards an emission-free world economy but say that biological carbon stores such as improved forest and soil management are also necessary. Technologies that remove carbon dioxide from the atmosphere and store it underground may also be required to halt temperature rises, which are already increasing by 0.17°C per decade.
Critically, the study emphasises that these measures must be underpinned by the fundamental societal changes that are required to maintain a “stabilised Earth”.
“What we do not know yet is whether the climate system can be safely ‘parked’ near 2°C above pre-industrial levels, or if it will, once pushed so far, slip down the slope towards a hothouse planet,” said Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research.
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