Earth at risk of 'hothouse climate' where efforts to reduce emissions will have no impact, study finds
If humans cause the earth's global average temperature to increase by a further 1 degree Celsius, the world could face a "hothouse" climate and trigger further warming — even when all human emissions cease, an international study has found.
Key points:
- Study found the climate is heading for a tipping point that could make the planet uninhabitable
- It could cause temperatures up to 5C higher than pre-industrial averages
- Current global efforts to curb emissions are "unlikely" to prevent the dangerous situation
The study titled Trajectories of the Earth System in the Anthropocene, which involved researchers from around the world, was published in the international journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).
It found the Earth was heading for a tipping point, known as a "hothouse" climate, which could lead to average temperatures up to 5C higher than pre-industrial temperatures and rises in sea level of between 10 and 60 metres.
Lead researcher Professor Will Steffen from the Australian National University (ANU) said at that point much of the earth would be uninhabitable.
He explained that if human emissions raised global temperatures to 2C above pre-industrial temperatures it could trigger earth system processes — or feedbacks — that could then cause further warming.
"The real concern is these tipping elements can act like a row of dominoes," Professor Steffen said.
"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."
Current efforts 'unlikely' to help avoid tipping point
Professor Steffen said global average temperatures were currently just over 1C above pre-industrial temperatures and rising at 0.17C each decade.
And he said while humans were not the sole cause of temperature changes on Earth, the current efforts by nations to reduce emissions and stop average temperatures rising by a further 1C were "unlikely to help avoid this very risky situation".
"Even if the Paris Accord [Agreement] target of a 1.5C to 2C rise in temperature is met, we cannot exclude the risk that a cascade of feedbacks could push the Earth system irreversibly onto a 'hothouse Earth' pathway," the study said.
"As yet [these initiatives] are not enough to meet the Paris target."
Professor Steffen said countries needed to work together to "greatly accelerate the transition towards an emission-free world economy".
"If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies," the study said.
"Collective human action is required to steer the Earth system away from a potential threshold and stabilise it in a habitable interglacial-like state."
The authors of the study examined 10 feedback processes, some of which could cause "the uncontrollable release" of carbon back into the atmosphere, after it had been stored in the earth.
Some of the processes also included permafrost thaw, Amazon rainforest dieback, a reduction of northern hemisphere snow cover, a loss of Arctic summer sea ice, and a reduction of Antarctic sea ice and polar ice sheets.
The study did not lay down a timeframe for when such events would begin to occur, but theorised — if the threshold was crossed — it could be within a century or two.
"The impacts of a hothouse earth pathway on human societies would likely be massive, sometimes abrupt, and undoubtedly disruptive," the study said.