Josh Gabbatiss: Earth at risk of entering ‘hothouse’ state from which there is no return, scientists warn
In a summer marked by
global heatwaves, wildfires and
drought, scientists have warned that things could get considerably worse under
a future scenario dubbed “hothouse Earth”. 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.
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 over.” The prospect of such a
situation has been laid out by Professor Rockstrom and his colleagues in the journal
Proceedings of the National Academy of Sciences (PNAS). “We address tipping
elements in the planetary machinery that might, once a certain stress level has
been passed, one by one change fundamentally, rapidly, and perhaps
irreversibly,” explained Professor Hans Joachim Schellnhuber, director of the
Potsdam Institute for Climate Impact Research. “This cascade of
events may tip the entire Earth system into a new mode of operation.”
Global average
temperatures are currently 1C above pre-industrial levels and under the Paris
climate agreement world governments have agreed to keep total warming
below 2C. In the worst-case
scenario, the researchers predict the Earth’s climate would stabilise at around
4-5C higher – hotter than any point for 1.2 million years – and with sea level
increase of up to 60m. “Places on Earth will
become uninhabitable if ‘hothouse Earth’ becomes the reality,” Professor
Rockstrom said.
Other scientists
acknowledged the situation laid out in the new PNAS paper as
uncertain, as it is somewhat speculative and not covered by most existing
climate change predictions, but they nonetheless admitted it
was plausible.
“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,” said Dr Phil Williamson, a climate
researcher at the University of East Anglia who was not involved in the work. Pointing out that
evidence from geology shows Earth’s climate system is “inherently nervy”, he
said human processes to the mix could well exacerbate this. To avoid catastrophe,
the researchers behind the new work said there was a need to move “from
exploitation to stewardship” of the Earth, and not only reduce emissions but
create new carbon stores – by planting forests, conserving biodiversity and
creating technologies to remove carbon dioxide form the air.
However, they noted
that while their runaway threshold may well be within the Paris target of 2C,
they suggested this as a point beyond which the risk of hothouse Earth could
increase sharply. As for whether staying below this target
and maintaining a “stabilised Earth” is possible, climate scientists Professor
Chris Rapley of University College London, who was also not involved in the
study, did not have much hope. He said in the face of “right wing
populism” and climate change denial, drastically tackling the problem in the
ways described seemed highly unlikely. “The future habitability of the planet thus
appears to rest on chance,” he said. “That the sensitivity of the climate
system to greenhouse gas emissions and other human disruptions is fortuitously
very low – or that some other global scale social calamity dramatically reduces
human emissions before any runaway planetary threshold is breached. The latter
offers cold comfort.”
https://www.independent.co.uk/environment/climate-change-hothouse-earth-global-warming-rainforests-sea-ice-heatwave-a8479706.html