Climate endgame: Risk of human extinction from catastrophic heating ‘dangerously unexplored’, say University of Cambridge researchers

The world must begin preparing for the possibility of “catastrophic” global heating, according to University of Cambridge researchers, including a worst-case scenario of eventual human extinction.

Arguing the risks have so far been “dangerously unexplored”, they call for more study of a “climate endgame”.

They warn that high temperatures themselves are just one of the potential risks we face - and say there is “serious potential for disastrous knock-on effects”.

They propose a research agenda focusing on what they call the “four horsemen” of the climate endgame: famine and malnutrition, extreme weather, conflict and vector-borne diseases.

Dr Luke Kemp, from Cambridge’s Centre for the Study of Existential Risk, said: “There are plenty of reasons to believe climate change could become catastrophic, even at modest levels of warming.

“Climate change has played a role in every mass extinction event. It has helped fell empires and shaped history. Even the modern world seems adapted to a particular climate niche.

“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, and impede recovery from potential disasters such as nuclear war. The catastrophic risk is there, but we need a more detailed picture.”

The international team of researchers, led by those in Cambridge, call on the Intergovernmental Panel on Climate Change (IPCC) to dedicate a future report to catastrophic climate change to galvanise research and inform the public.

They suggest the consequences of the planet warming by 3°C or more, the related extreme risks, are under-examined.

“A greater appreciation of catastrophic climate scenarios can help compel public action,” argued Dr Kemp. “Understanding nuclear winter performed a similar function for debates over nuclear disarmament.”

These scenarios should range from bad to worst - from the loss of 10 per cent of the global population to eventual human extinction.

“We know least about the scenarios that matter most,” said Dr Kemp.

In a paper published just weeks after the UK recorded its record temperature, the researchers say the warming climate poses a major threat to global food supply, with growing probability of “breadbasket failures” as the world’s most agriculturally productive areas suffer collective meltdowns.

Hotter and more extreme weather could also create the conditions for new disease outbreaks, with habitats for humans and wildlife alike changing and shrinking.

Climate breakdown could also exacerbate other “interacting threats”, they argue, from rising inequality and misinformation to democratic collapse.

Even destructive new forms of AI weaponry are proposed in one Doomsday scenario..

The paper, published in the journal Proceedings of the National Academy of Sciences, highlights the possibility of “warm wars”, in which technologically enhanced superpowers fight over both dwindling carbon space and giant experiments designed to deflect sunlight and reduce global temperatures.

The team’s modelling shows areas of extreme heat - meaning annual average temperatures of more than 29 °C - could stretch to cover two billion people by 2070.

The areas involved are some of the most densely populated and politically fragile.

“Average annual temperatures of 29 degrees currently affect around 30 million people in the Sahara and Gulf Coast,” said the paper’s co-author Chi Xu, of Nanjing University.

“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,” he said.

A report from the IPCC last year warned that if atmospheric carbon dioxide doubles from pre-industrial levels - and we are halfway there already - there is about an 18 per cent change that temperatures will rise beyond 4.5C.

A study that used text mining technology, published earlier this year, found IPPC assessments have shifted away from high-end warming to focus instead on lower temperature rises.

These may be more likely, but the extreme scenarios are “underexplored relative to their likelihood”, Dr Kemp argued.

In particular, we must study potential tipping points within “Hothouse Earth”. These could include methane released by permafrost melts, the loss of forests that act as “carbon sinks”, and the potential for vanishing cloud cover.

Co-author Prof Johan Rockström, director of the Potsdam Institute for Climate Impact Research said: “The more we learn about how our planet functions, the greater the reason for concern.

“We increasingly understand that our planet is a more sophisticated and fragile organism. We must do the math of disaster in order to avoid it,” he said.

Fellow co-author Prof Kristie Ebi, from the University of Washington, said: “We need an interdisciplinary endeavour to understand how climate change could trigger human mass morbidity and mortality.”

Dr Kemp concluded: “We know that temperature rise has a ‘fat tail’, which means a wide range of lower probability but potentially extreme outcomes..

“Facing a future of accelerating climate change while remaining blind to worst-case scenarios is naive risk-management at best and fatally foolish at worst.”