09 September 2022

Consider Catastrophic Climate Change

Welcome back. In the long history of warnings about climate change, June 1988 stands out.

On 23 June, James Hansen, then director of NASA’s Goddard Institute for Space Studies, testified to the Senate Committee on Energy and Natural Resources. He warned that it was 99% certain that the global warming trend was not a natural variation but the result of a buildup of CO2 and other artificial gases in the atmosphere.

A week later, at the conclusion of the 27-30 June Toronto Conference on the Changing Atmosphere: Implications for Global Security, the 300 policy makers, international scientists and representatives of non-governmental, governmental and UN organizations issued a stark declaration: Humans had triggered uncontrolled changes to the atmosphere that, if left unchecked, could lead to consequences second only to a global nuclear war.

Proceedings of 1988 Toronto Conference on The Changing Atmosphere (World Meteorological Organization report OMM-No.710, 1989).
Considering the Worst
Could climate change truly result in societal collapse or even human extinction? An international team of 11 climate scientists, led by a researcher with the UK’s University of Cambridge, addressed the topic in a recently published paper.

Noting that prudent risk management requires consideration of bad-to-worst-case scenarios, they discuss the likelihood of extreme climate change, why understanding bad-to-worst cases is vital and reasons for concern about catastrophic outcomes. They then define key terms and present a research agenda to direct exploration of the worst risks associated with anthropogenic (human-caused) climate change.

The Potential for Climate Catastrophe
The researchers’ concern about climate change per se is that greenhouse gas emissions are increasing at unprecedented geological speed, putting the world on track for a temperature rise between 2.1°C and 3.9°C by 2100.

Their key reasons for concern about a global climate catastrophe are that climate change (1) has played a role in the collapse or transformation of numerous societies and in the five mass extinction events in the current geologic eon; (2) could trigger other catastrophic risks, such as international conflict, or exacerbate disease spread; (3) could aggravate vulnerabilities and cause multiple indirect stresses; and (4) could irrevocably undermine humanity’s ability to recover from another cataclysm.

A Research Agenda
Setting global warming of 3°C or more by 2100 as a marker for extreme climate change, the researchers propose a research agenda for catastrophic climate change that focuses study on:
- Understanding extreme climate change dynamics and impacts in the long term.
- Exploring climate-triggered pathways to mass morbidity and mortality.
- Investigating social fragility: vulnerabilities, risk cascades and risk responses.
- Synthesizing research findings into integrated catastrophe assessments.

Extreme Earth System States
Understanding potential long-term states of the Earth system under extreme climate change will require mapping different “Hothouse Earth” scenarios or other extreme scenarios, such as alternative circulation regimes or large, irreversible changes in ice cover and sea level.

Mass Morbidity and Mortality
There are many potential contributors to climate-induced morbidity and mortality that require further study, but the “four horsemen” are likely to be famine and undernutrition, extreme weather events, conflict, and vector-borne diseases. These will be worsened by additional risks and impacts such as air pollution and sea level rise.

Societal Fragility

A complete risk assessment needs to consider climate impacts, differential exposure, systemic vulnerabilities, responses of societies and actors, and the knock-on effects across borders and sectors, potentially resulting in systemic crises. A domino effect or spiral could continuously worsen the initial risk.

A high-level, simplified depiction of how risk cascades could unfold (from www.pnas.org/doi/full/10.1073/pnas.2108146119).
Integrated Catastrophic Assessments
Climate change will unfold in a world of changing ecosystems, geopolitics and technology, as well as natural shocks. Such developments and scenarios need to be considered to build a full picture of climate dangers.

Wrap Up

There is ample evidence that climate change could become catastrophic. To galvanize research and inform the public, the researchers urge the Inter-governmental Panel on Climate Change (IPCC) to dedicate a future report to catastrophic climate change.

They warn that facing a future of accelerating climate change while blind to worst-case scenarios is naive risk management at best and fatally foolish at worst.

Thanks for stopping by.


James Hansen’s warning to US Senate: www.theguardian.com/environment/2018/jun/19/james-hansen-nasa-scientist-climate-change-warning
Toronto Conference on the Changing Atmosphere: en.wikipedia.org/wiki/Toronto_Conference_on_the_Changing_Atmosphere
Key aspects of the Paris Agreement: unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement/key-aspects-of-the-paris-agreement
IPCC climate report 2022 summary: climate.selectra.com/en/news/ipcc-report-2022
Paper on exploring catastrophic climate change in Proceedings of the National Academy of Sciences: www.pnas.org/doi/full/10.1073/pnas.2108146119
Articles on paper on EurekAlert! and Axios websites:

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