They argued that the world needs to start preparing for the possibility of the “climate endgame”, saying “Analysing the mechanisms for these extreme consequences could help galvanise action, improve resilience, and inform policy.”
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 proposed a research agenda, including what they called 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.
“Tipping points” were particularly concerning — where a small rise in global temperature resulted 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, or climate breakdown, which 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.
“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.
“There are warnings from history. Climate change has played a role in the collapse or transformation of numerous previous societies and in each of the five mass extinction events in Earth's history.”
The domino effect of climate events could move Earth into a “hothouse” state.
Extreme heat — defined as an annual average temperature of more than 29C — could affect 2 billion people by 2070 if carbon emissions continued.
Temperatures of more than 2C above pre-industrial levels have not been sustained on Earth for more than 2.6m years, far before the rise of human civilisation 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. “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.”
This from Nasa: “Humans have caused major climate changes . . . and we have set in motion more changes still. However, if we stopped emitting greenhouse gases today, the rise in global temperatures would begin to flatten within a few years. Temperatures would then plateau but remain well elevated for many, many centuries. There is a time lag between what we do and when we feel it, but that lag is less than a decade.”
