Earth could be plunged into irreversible 'Hothouse' state even if CO₂ emissions are slashed, scientists warn

The Earth could be just decades away from being plunged into a “Hothouse” state that threatens the future of humanity with boiling temperatures and towering seas.

Leading scientists have warned that the planet is not far off a climatic tipping point that triggers an irreversible level of “runaway” global warming, even if countries meet CO2 targets.

The threshold will be reached when average global temperatures are only around 2C higher than they were in pre-industrial times, new research suggests.

They are already 1C higher, and rising.

Long term, the “Hothouse Earth” climate will stabilise at a global average of 4C-5C above pre-industrial levels, according to a new study from a group of international scientists.

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If that happened, swathes of the planet around the equator will become uninhabitable, with sea levels up to 60 metres (197ft) higher than they are today threatening coastal cities.

A Hothouse Earth would pose "severe risks for health, economies, political stability, and ultimately, the habitability of the planet for humans", the international scientists wrote in the journal Proceedings of the National Academy of Sciences.

The domino effect of melting ice, warming seas, shifting currents and dying forests could tilt the Earth into a “hothouse” state
AP

The research highlighted 10 processes that were predicted to kick in at around 2C of global warming. The "tipping elements" could turn natural carbon storage systems or "sinks" into powerful greenhouse gas emitters

Professor Johan Rockstrom, a leading member of the team from the University of Stockholm, Sweden, said: "These tipping elements can potentially act like a row of dominoes. 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.

"Places on Earth will become uninhabitable if Hothouse Earth becomes the reality."

The tipping point dangers were identified as thawing permafrost, the release of methane trapped on the ocean floor, weakening land and ocean carbon sinks, increased carbon dioxide production by ocean bacteria.

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Amazon rainforest die-back, coniferous forest die-back, reduced northern hemisphere snow cover, loss of Arctic summer sea ice, reduced Antarctic sea ice and melting polar ice sheets were also identified as factors.

The scientists wrote: "Our analysis suggests that the Earth system may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions - Hothouse Earth. This pathway would be propelled by strong, intrinsic, biogeophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered or substantially slowed.

Pollution seen hanging over the city of London early in the morning as the Capital enjoys warm weather (Jeremy Selwyn
Jeremy Selwyn

"Where such a threshold might be is uncertain, but it could be only decades ahead at a temperature rise of (around) 2C above pre-industrial."

Avoiding a Hothouse Earth would require "deep cuts" in greenhouse gas emissions and concerted efforts to remove carbon dioxide from the atmosphere, said the researchers.

Commenting on the findings, climate researcher Dr Phil Williamson, from the University of East Anglia, said: "In the context of the summer of 2018, this is definitely not a case of crying wolf, raising a false alarm. The wolves are now in sight."

Chris Rapley, Professor of Climate Science at University College London said: "Previous research has shown that an increase in the mean global temperature of 11-12C would make more than half of the land area currently occupied by humans uninhabitable. So, a 'runaway' warming to a new and uncontrollable hot state would represent an existential threat to humanity and the majority of existing species."

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