The world is at risk of reaching ‘hothouse’ conditions, where temperatures rise by four to five degrees Celsius, regardless of whether climate targets from the Paris Agreement are achieved, scientists have found.
The news, published in a report on Monday, comes in the midst of a heatwave summer which has caused the deaths of over 60 people in Japan and sparked wildfires in Greece that killed 91 people.
The study was conducted by researchers from the Stockholm Resilience Center, the University of Copenhagen, Australian National University and the Potsdam Institute for Climate Impact Research. It was published in the Proceedings of the National Academy of Sciences.
Under the terms of the Paris Agreement, around 200 countries pledged to limit temperatures to below the 2°C above pre-industrial levels. However, the research suggests this cap may not be sufficient to protect the world from climate change and nearing this limit may trigger other processes which will continue to drive temperatures up even if greenhouse gas emissions are cut.
These processes include the loss of methane hydrates from the ocean bed –known as permafrost thaw– weakening of land and ocean carbon sinks, the loss of Arctic summer sea ice, and the loss of Antarctic sea ice and polar ice sheets.
Study co-author Johan Rockström said: “These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth toward another.”
He added that once it begins, it will be difficult or even impossible to prevent the chain of events that will lead to the hothouse conditions, which he says will make the world ‘uninhabitable’.
The study says: “Crossing into the hothouse state would lead to a much higher global average temperature than any interglacial in the past 1.2 million years, and to sea levels significantly higher than at any time in the Holocene.”
It adds that reducing greenhouse gas emissions is no longer enough to avoid such a state, saying: “Collective human action is required to steer the Earth System away from a potential threshold.”
The report identifies a need for improvements in forest, agricultural and soil management, as well as biodiversity conservation and technologies that help remove carbon dioxide from the atmosphere, potentially storing it underground if required, to more rapidly decarbonise the world.
Currently, average global temperatures sit at just over 1°C above the pre-industrial period, rising by 0.17°C every ten years.