Tipping points leading to ‘Hothouse Earth’ already “active”, scientists warn

A group of the world’s leading climate scientists warn that many climate change ‘tipping points’ are already active and rapid and irreversible changes to the Earth’s climate may be unavoidable unless urgent action is taken on climate change.

In a comment piece published in leading scientific journal Nature, the scientists warn that the world is beginning to trigger “abrupt and irreversible changes” in the earth’s climate, and political and economic action is necessary.

The scientists highlight the fact that current national climate change pledges are insufficient to limit warming to safe levels, and that the world is likely heading to warming of at least 3°C above pre-industrial levels.

“Currently we are seeing much higher risk, and we are rapidly running out of time to respond,” co-author and emeritus professor at the Australian National University Will Steffen says.

“All nations need to recognise the seriousness of the situation and go well beyond their Paris Agreement pledges to cut emissions.”

Scientists have long warned about the impacts of tipping-points, where initial levels of global warming trigger processes within the earth’s climate that reinforce and accelerate further global warming and amplify climate change impacts like sea-level rise.

“As soon as one or two climate dominoes are knocked over, they push Earth towards others,” Steffen says.

“We fear that it may become impossible to stop the whole row of dominoes from tumbling over, forming a cascade that could threaten the existence of human civilisations.”

The group of scientists say that tipping points, which include the significant loss of Arctic sea ice, loss from Greenland and Antarctic ice sheets, thawing of permafrost and ongoing destruction of the Amazon rainforest are already “active”.

Such tipping points will contribute to further warming of the earth, and could lead to irreversible impacts driven by climate change.

“The collapse of major ice sheets on Greenland, West Antarctica and part of East Antarctica would commit the world to around 10 metres of irreversible sea-level rise,” Steffen said.

“Even if these polar ice sheets are ‘tipped’, reducing emissions could slow this process, allowing more time for low-lying populations to move.”

The scientists issued an “urgent call” for rapid reductions in global greenhouse gas emissions, saying governments must act to reduce emissions to avoid the activation of further tipping-points and a rapid increase in global temperatures.

“In our view, the clearest emergency would be if we were approaching a global cascade of tipping points that led to a new, less habitable, ‘hothouse’ climate state,” the scientists say.

The scientists say that the world’s researchers must increase their understanding of the potential, complex impacts of tipping points, saying that they could push the Earth into climate scenarios that are substantially different to anything seen in human history.

“Atmospheric CO2 is already at levels last seen around 4 million years ago, in the Pliocene. It is rapidly heading towards levels last seen some 50 million years ago — in the Eocene — when temperatures were up to 14 °C higher than they were in pre-industrial times,” the paper says.

“It is challenging for climate models to simulate such past ‘hothouse’ Earth states.”

The scientists say that the observation of active tipping-points would justify a global declaration of a climate change emergency.

“In our view, the evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute,” the paper says.

“The stability and resilience of our planet is in peril. International action — not just words — must reflect this.”

Earlier in the month, a group of 11,000 scientists called for a declaration of a climate change emergency, saying that the world was on the path to “untold human suffering” caused by climate change unless stronger action was taken to reduce global greenhouse gas emissions.