Earth may be decades away from a climatic tipping point that triggers runaway global warming and threatens the future of humanity, scientists have warned.
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, writes John von Radowitz
Feedback mechanisms acting “like a row of dominoes” will then spin the world into a “Hothouse Earth” state of uncontrollable climate change.
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, 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 research highlighted 10 feedback 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.
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, 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.
Avoiding a Hothouse Earth would require “deep cuts” in greenhouse gas emissions as well as concerted efforts to remove carbon dioxide from the atmosphere, both by preserving natural carbon sinks and using technology, 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.”
The warnings come as twin northern California blazes fuelled by dry vegetation and hot, windy weather have become the state’s largest wildfire in history. The two fires burning a few miles apart and known as the Mendocino Complex are being treated as one incident. It has scorched 283,800 acres (443.4 sq m), according to fire officials. The fires, north of San Francisco, have burned 75 homes and are only 30% contained.
The size of the fires surpasses a blaze last December in southern California that burned 281,893 acres (440.5 sq m). It killed two people, including a firefighter, and destroyed over 1,000 buildings.
Hotter weather attributed to climate change is drying out vegetation, creating more intense fires that spread quickly from rural areas to city subdivisions, say climate and fire experts.
But they also blame cities and towns that are expanding housing into previously undeveloped areas.