Global heating could become “catastrophic” for humanity if temperature rises are worse than many predict or cause cascades of events we have yet to consider, or indeed both. The world needs to start preparing for the possibility of a “climate endgame.”
This is according to an international team of researchers led by the University of Cambridge, who propose a research agenda for facing up to bad-to-worst-case scenarios. These include outcomes ranging from a loss of 10% of the global population to eventual human extinction.
“There are plenty of reasons to believe climate change could become catastrophic, even at modest levels of warming,” said lead author Dr. Luke Kemp from Cambridge’s Center for the Study of Existential Risk.
“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.”
Kemp and colleagues argue that the consequences of 3˚C (5.4˚F) warming and beyond, and related extreme risks, have been under-examined.
“Average annual temperatures of 29˚C (84˚F) currently affect around 30 million people in the Sahara and Gulf Coast,” said 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.
Last year’s IPCC report suggested that if atmospheric CO2 doubles from pre-industrial levels—something the planet is halfway towards—then there is an roughly 18% chance temperatures will rise beyond 4.5˚C (8.1˚F).
Added Kemp: “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.”
“If we don’t look at the intersecting risks, we’ll be painfully surprised,” said University of Washington public health and climate professor Kristie Ebi, a co-author who like Lenton has been part of United Nations global climate assessments.
It was a mistake health professionals made before COVID-19 when assessing possible pandemics, Ebi said. They talked about disease spread, but not lockdowns, supply chain problems and spiralling economies.
Study authors said they worry about societal collapse—war, famine, economic crises—linked to climate change more than the physical changes to Earth itself.
“I do not believe civilization as we know it will make it out of this century,” University of Victoria climate scientist Andrew Weaver, a former British Columbia legislator for the Green Party, said in an email. “Resilient humans will survive, but our societies that have urbanized and are supported by rural agriculture will not.”