The Earth’s global temperature is 1C away from a climatic tipping point that threatens the future of humanity, scientists have warned.
Experts added that the planet is just decades away from the event that would trigger runaway global warming.
The threshold will be reached when average global temperatures are only around 2C higher than they were in pre-industrial times, research suggests.
The findings show that the Earth’s temperature is already half way there.
If the tipping point is reached it would create a “Hothouse Earth” state of uncontrollable climate change.
The event would pose “severe risks for health, economies, political stability, and ultimately, the habitability of the planet for humans”, international scientists wrote in the journal Proceedings of the National Academy of Sciences.
Their research highlighted 10 feedback processes that were predicted to kick in at around 2C of global warming.
Feedback mechanisms would act “like a row of dominoes”, spinning the world into a state of climate change that will alter the landscape of the planet.
In the long-term, the Hothouse Earth climate will stabilise at a global average of 4C – 5C above pre-industrial levels, the study shows.
If that happens it will render swathes of the planet around the equator uninhabitable, with sea levels up to 60 metres (197ft) higher than they are today threatening coastal cities.
The research refers to “tipping elements” that 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 and weakening land and ocean carbon sinks.
Others include increased carbon dioxide production by ocean bacteria, 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.
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.
“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.”
“Deep cuts” in greenhouse gas emmissions as well as concerted efforts to remove carbon dioxide from the atmosphere are required to avoid a Hothouse Earth state, the researchers added.
They argued that this could be done both by preserving natural carbon sinks and using technology.
Dr Phil Williamson, a climate researcher 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.”
The scientists warning comes as the Met Office said Britain’s heatwave could continue for several months, with higher than average temperatures likely until October.