[D66] Climate endgame: risk of human extinction ‘dangerously underexplored’ | Guardian

[René Oudeweg]

theguardian.com
<https://www.theguardian.com/environment/2022/aug/01/climate-endgame-risk-human-extinction-scientists-global-heating-catastrophe>



  Climate endgame: risk of human extinction ‘dangerously underexplored’

Damian Carrington <https://www.theguardian.com/profile/damiancarrington>
Environment editor

Mon 1 Aug 2022 20.00 BST
6-7 minutes
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The risk of global societal collapse or human extinction has been
“dangerously underexplored”, climate scientists have warned in an analysis.

They call such a catastrophe the “climate endgame”. Though it had a
small chance of occurring, given the uncertainties in future emissions
and the climate system, cataclysmic scenarios could not be ruled out,
they said.

“Facing a future of accelerating climate change while blind to
worst-case scenarios is naive risk management at best and fatally
foolish at worst,” the scientists said, adding that there were “ample
reasons” to suspect global heating could result in an apocalyptic disaster.

The international team of experts argue the world needs to start
preparing for the possibility of the climate endgame. “Analysing the
mechanisms for these extreme consequences could help galvanise action,
improve resilience, and inform policy,” they said.

Explorations in the 1980s of the nuclear winter that would follow a
nuclear war spurred public concern and disarmament efforts, the
researchers said. The analysis proposes a research agenda, including
what they call the “four horsemen” of the climate endgame: famine,
extreme weather, war and disease.

They also called for the Intergovernmental Panel on Climate Change to
produce a special report on the issue. The IPCC report on the impacts of
just 1.5C <https://www.ipcc.ch/sr15/> of heating drove a “groundswell of
public concern”, they said.

“There are plenty of reasons to believe climate change could become
catastrophic, even at modest levels of warming,” said Dr Luke Kemp at
the University of Cambridge’s Centre for the Study of Existential Risk,
who led the analysis. “Climate change has played a role in every mass
extinction event. It has helped fell empires and shaped history.

“Paths to disaster are not limited to the direct impacts of high
temperatures, such as extreme weather events. Knock-on effects such as
financial crises, conflict and new disease outbreaks could trigger other
calamities.”

The analysis is published in the journal Proceedings of the National
Academy of Sciences
<https://www.pnas.org/cgi/doi/10.1073/pnas.2108146119> and was reviewed
by a dozen scientists. It argues that the consequences of global heating
beyond 3C have been underexamined, with few quantitative estimates of
the total impacts. “We know least about the scenarios that matter most,”
Kemp said.

A thorough risk assessment would consider how risks spread, interacted
and amplified, but had not been attempted, the scientists said. “Yet
this is how risk unfolds in the real world,” they said. “For example, a
cyclone destroys electrical infrastructure, leaving a population
vulnerable to an ensuing deadly heatwave.” The Covid pandemic underlined
the need to examine rare but high-impact global risks, they added.

Particularly concerning are tipping points, where a small rise in global
temperature results in a big change in the climate, such as huge carbon
emissions from an Amazon rainforest suffering major droughts and fires.
Tipping points could trigger others in a cascade
<https://www.theguardian.com/environment/2021/jun/03/climate-tipping-points-could-topple-like-dominoes-warn-scientists>
and some remained little studied, they said, such as the abrupt loss of
stratocumulus cloud decks
<https://www.nature.com/articles/s41561-019-0310-1.pdf?proof=t> that
could cause an additional 8C of global warming.

The researchers warn that climate breakdown could exacerbate or trigger
other catastrophic risks, such as international wars or infectious
disease pandemics, and worsen existing vulnerabilities such as poverty,
crop failures and lack of water. The analysis suggests superpowers may
one day fight over geoengineering plans to reflect sunlight or the right
to emit carbon.

“There is a striking overlap between currently vulnerable states and
future areas of extreme warming,” the scientists said. “If current
political fragility does not improve significantly in the coming
decades, then a belt of instability with potentially serious
ramifications could occur.”

There were further good reasons to be concerned about the potential of a
global climate catastrophe, the scientists said: “There are warnings
from history. Climate change has played a role in the collapse or
transformation of numerous previous societies
<https://www.academia.edu/44322625/The_IPCC_A_Primer_for_Archaeologists>
and in each of the five mass extinction events in Earth’s history.”

New modelling in the analysis shows that extreme heat – defined as an
annual average temperature of more than 29C – could affect 2 billion
people by 2070 if carbon emissions continue.

“Such temperatures currently affect around 30 million people in the
Sahara and Gulf Coast,” said Chi Xu, at Nanjing University in China, who
was part of the team. “By 2070, these temperatures and the social and
political consequences will directly affect two nuclear powers, and
seven maximum containment laboratories housing the most dangerous
pathogens. There is serious potential for disastrous knock-on effects.”

The current trend of greenhouse gas emissions would cause a rise of
2.1-3.9C by 2100. But if existing pledges of action are fully
implemented, the range would be 1.9-3C. Achieving all long-term targets
set to date would mean 1.7-2.6C of warming.

“Even these optimistic assumptions lead to dangerous Earth system
trajectories,” the scientists said. Temperatures more than 2C above
pre-industrial levels had not been sustained on Earth for more than 2.6m
years, they said, far before the rise of human civilisation, which had
risen in a “narrow climatic envelope” over the past 10,000 years.

“The more we learn about how our planet functions, the greater the
reason for concern,” said Prof Johan Rockström, at the Potsdam Institute
for Climate Impact Research in Germany. “We increasingly understand that
our planet is a more sophisticated and fragile organism. We must do the
maths of disaster in order to avoid it.”
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