Scientists have warned that the Earth could be approaching a “hothouse” state that would be extremely difficult to reverse.
Several key parts of the Earth’s climate system appear closer to destabilising than previously believed, a new analysis finds.
These include critical “tipping points” – such as the Greenland and Antarctic ice sheets, the Amazon rainforest and major ocean currents – that could shift abruptly once certain temperature limits are crossed.
When one system destabilises, it can intensify warming elsewhere. Melting ice reduces the planet’s ability to reflect sunlight, causing further warming. Thawing permafrost and dying forests release additional greenhouse gases, which trap more heat.
The study published in One Earth said that interactions between these systems could create a chain reaction, locking the planet into a self-reinforcing “hothouse” trajectory – a state of sustained extreme warming and rising sea levels, even if emissions are later reduced.
“After a million years of oscillating between ice ages separated by warmer periods, the Earth’s climate stabilised more than 11,000 years ago, enabling agriculture and complex societies,” said William Ripple, who led the study.
“We’re now moving away from that stability and could be entering a period of unprecedented climate change.”
The warning comes as global temperatures have exceeded 1.5C above pre-industrial levels for 12 consecutive months. Earlier in December, the EU’s Copernicus Climate Change Service said that 2025 would complete the first three-year period in which the average global temperature exceeded by 1.5C. The Paris Agreement aims to limit long-term warming to 1.5C, measured over a 20-year average. But researchers say the sustained breach suggests the long-term threshold may already be at or near that level.
“Temperature limit exceedance is usually evaluated using 20-year averages, but climate model simulations suggest the recent 12-month breach indicates the long-term average temperature increase is at or near 1.5 degrees,” said Christopher Wolf, a co-author of the study.
“It’s likely that global temperatures are as warm as, or warmer than, at any point in the last 125,000 years and that climate change is advancing faster than many scientists predicted.”
Atmospheric carbon dioxide concentrations now exceed 420 parts per million – around 50 per cent higher than before the Industrial Revolution – and are likely the highest in at least two million years, the researchers said.
The tipping elements examined include the Greenland and West Antarctic ice sheets, mountain glaciers, Arctic sea ice, boreal forests and permafrost, the Amazon rainforest and the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that helps regulate global climate.
Weakening of the AMOC could disrupt rainfall patterns and increase the risk of Amazon rainforest collapse.
“The AMOC is already showing signs of weakening, and this could increase the risk of Amazon dieback,” Ripple said. “Carbon released by an Amazon dieback would further amplify global warming and interact with other feedback loops. We need to act quickly on our rapidly dwindling opportunities to prevent dangerous and unmanageable climate outcomes.”
Scientists first outlined the prospect of a Hothouse Earth in 2018, warning that cascading tipping points could lock the planet into sustained warming well above 4C for thousands of years. The new assessment suggests several Earth systems may be closer to destabilisation than previously thought.
“Uncertain tipping thresholds underscore the importance of precaution – crossing even some of those thresholds could commit the planet to a hothouse trajectory with long-lasting and possibly irreversible consequences,” Wolf said. “While averting the hothouse trajectory won’t be easy, it’s much more achievable than trying to backtrack once we’re on it.”
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