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Earth at risk of entering ‘hothouse’ state from which there is no return

  • Climate change made European heatwave ‘more than twice as likely’
    Even if countries succeed in meeting their CO2 targets, we could still lurch on to this "irreversible pathway". Climate change made European heatwave ‘more than twice as likely’
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Climate change made European heatwave ‘more than twice as likely’
While it is unclear how likely this scenario is, experts agree that were it to happen the runaway warming after this tipping point would be an existential threat to humanity.

It may sound like the title of a low budget sci-fi movie, but for planetary scientists, "Hothouse Earth" is a deadly serious concept.

Researchers believe we could soon cross a threshold leading to boiling hot temperatures and towering seas in the centuries to come.

Even if countries succeed in meeting their CO2 targets, we could still lurch on to this "irreversible pathway".

Their study shows it could happen if global temperatures rise by 2C.

An international team of climate researchers, writing in the journal, Proceedings of the National Academy of Sciences, says the warming expected in the next few decades could turn some of the Earth's natural forces - that currently protect us - into our enemies.

Each year the Earth's forests, oceans and land soak up about 4.5 billion tonnes of carbon that would otherwise end up in our atmosphere adding to temperatures.

Many parts of the world would be significantly disrupted in a Hothouse Earth scenario
But as the world experiences warming, these carbon sinks could become sources of carbon and make the problems of climate change significantly worse.

So whether it is the permafrost in northern latitudes that now holds millions of tonnes of warming gases, or the Amazon rainforest, the fear is that the closer we get to 2 degrees of warming above pre-industrial levels, the greater the chances that these natural allies will spew out more carbon than they currently now take in.

Back in 2015, governments of the world committed themselves to keeping temperature rises well below 2 degrees, and to strive to keep them under 1.5. According to the authors, the current plans to cut carbon may not be enough if their analysis is correct.

"What we are saying is that when we reach 2 degrees of warming, we may be at a point where we hand over the control mechanism to Planet Earth herself," co-author Prof Johan Rockström, from the Stockholm Resilience Centre, told BBC News.

"We are the ones in control right now, but once we go past 2 degrees, we see that the Earth system tips over from being a friend to a foe. We totally hand over our fate to an Earth system that starts rolling out of equilibrium."

In a summer marked by global heatwaves, wildfires

Even if greenhouse gas emissions are reduced, there is a chance human-induced global warming could trigger other processes which will lead to uncontrollable warming, the team at the Stockholm Resilience Centre said. 

As Amazon rainforest is destroyed, Arctic permafrost thaws and Antarctic sea ice melts, these natural feedback mechanisms that currently help store Earth’s carbon will instead begin emitting it, scientists at the Swedish institute warned.  

Climate change made European heatwave ‘more than twice as likely’
While it is unclear how likely this scenario is, experts agree that were it to happen the runaway warming after this tipping point would be an existential threat to humanity.

“These tipping elements can potentially act like a row of dominoes,” said Professor Johan Rockstrom, Executive Director of the Stockholm Resilience Centre. “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