Understanding and managing temperature overshoot risks

Cynthia ScharfBy Nicholas Harrison and Cynthia Scharf1

As recent experience shows us, emergent crises such as pandemics or military conflicts demand immediate responses that can not only pose rapid and strenuous challenges for multilateralism but also, necessarily, divert attention from other urgent risks such as climate change.

While climate change has in the past been framed as a longer-term risk to be responded to over decades (rather than the days, weeks, or months-scale response times demanded by disasters, pandemics, or conflicts), its near-term hazards (and our exposure to them) are becoming increasingly evident from observed impacts on human and ecological systems globally.

It is in this context that the latest Intergovernmental Panel on Climate Change (IPCC) Working Group II (WGII) report was published last month.2 This is the second of three Working Group reports produced by the Intergovernmental Panel on Climate Change (IPCC) as part of its sixth assessment cycle. The third, WGIII report is expected in early April, followed by a Synthesis Report in September 2022.

This latest assessment undertaken by hundreds of leading scientists from all over the world has massive implications for life on earth and should ring alarm bells in every country and every sector of society.3

UN Secretary-General Antonio Guterres referred to the report as “an atlas of human suffering and a damning indictment of failed climate leadership.” With very high confidence, the report summary (approved by the IPCC’s 195 member governments) concluded that “Any further delay in concerted anticipatory global action on mitigation and adaptation will miss a brief and rapidly closing window of opportunity to secure a livable and sustainable future for all.”

That window is closing very rapidly indeed. As highlighted in the IPCC’s WGI report last August, only two of the five scenarios for addressing the climate crisis would deliver the Paris Agreement temperature goals4 and would require transformational levels of emissions reductions and carbon dioxide removal (CDR). However, such emissions reductions remain persistently elusive and CDR at the scale implied in such scenarios would take many years, if not decades, to put in place. Furthermore, even in the scenario with net-zero emissions around or after 2050 and the greatest use of CDR, the IPCC assessed it is still more likely than not that global warming would overshoot 1.5°C.5

According to several analyses, even if all the mitigation pledges made in Glasgow at COP26 are fulfilled, the world will still be on course for average temperature increase overshooting 2°C, threatening increasingly widespread – and in some cases irreversible – adverse impacts and losses for human and ecological systems globally.

The WGII report released last month focuses on climate impacts, adaptation and vulnerability and unpacks many of the changes already observed, and what more the world might expect to face. Extreme heat is one of them. If heating levels overshoot the agreed Paris temperature goals, massive consequences can be expected for, among other things, human health, food security, migration, and the global economy.6

We mention this one example for a reason, namely, because beyond existing mitigation and adaptation response options, additional approaches known as solar radiation modification (SRM) if ever deployed, would primarily seek to address this specific climate hazard.

Policymakers may therefore need to weigh the risks of using approaches such as SRM to avoid average global temperature increase rising beyond agreed limits against the risks of not using them, thereby facing a world of extreme heat that exceeds the Paris goals.

Put simply, if global average temperature increase overshoots 1.5°C, as the IPCC assesses is very likely unless deep reductions occur in greenhouse gases in the coming decades, how do we assess if the world will be better off with – or without – deploying additional response options, such as SRM?

if global average temperature increase overshoots 1.5°C, how do we assess if the world will be better off with – or without – deploying additional response options, such as SRM?

SRM in the IPCC WGII report: risks and governance challenges

As the IPCC’s assessments make clear, SRM could not be a substitute for emissions reductions, removals or adaptation, all of which are necessary to avoid the risks of overshooting the Paris temperature goals. According to the WGII report, “There is high agreement in the literature that for addressing climate change risks, SRM is, at best, a supplement to achieving sustained net zero or net negative CO2 emission levels globally.”7

The report’s Summary for Policymakers notes that SRM has the potential to offset warming and reduce climate risks as a supplementary option that augments existing efforts. But even if it proves effective, SRM could also introduce a widespread range of new risks to people and ecosystems, which are not well understood.8

The report also notes that, “Large uncertainties and knowledge gaps are associated with the potential of SRM approaches to reduce climate change risks.”  This includes governance, about which the report highlights: “Currently, there is no dedicated, formal international SRM governance for research, development, demonstration, or deployment…” and “…the lack of robust and formal SRM governance poses risks.”

For further detail on how SRM is addressed in the WGII report, you can read C2G’s Briefing Note, which summarizes key findings and provides an analysis of potential policy implications.

Risk-Risk analysis

Climate change poses fundamental challenges for sustainable development as temperature increases and other hazards put past and future development achievements increasingly at risk. Understanding such risk as well as those triggered by response measures is therefore central to assessing the pros and cons of any set of options for responding to climate change.

As the WGII report notes, “Across all three IPCC working groups, risk provides a framework for understanding the increasingly severe, interconnected and often irreversible impacts of climate change on ecosystems, biodiversity, and human systems…The risk that can be introduced by human responses to climate change is a new aspect considered in the risk concept.”9

To further explore this new aspect in relation to SRM, C2G recently commissioned a report on Solar Radiation Modification: A Risk-Risk Analysis with expert contributions from authors across a diverse range of disciplines and backgrounds. The report examines how the relative risks of SRM might be considered in relation to existing response options for reducing climate risk.

The authors found that “employing a risk-risk framework in policy analysis and decision-making concerning SRM would enable a more comprehensive assessment, comparison, and management of risks associated with climate change, emissions reductions, CDR, adaptation, and SRM.” They also noted that “risk-risk analysis can also help focus climate change risk management on broader societal objectives – such as the SDGs – rather than on temperature goals alone.”

Indeed, many government representatives C2G has spoken with say that discussing SRM in the context of sustainable development is more helpful than a purely climate, technology or security framing. After all, the impacts and implications of SRM, if it were ever to be used, go far beyond any one government ministry, and would reverberate throughout all aspects of society. To that end, the report authors also note that “New governance institutions or mechanisms may be needed to restrain harmful or unjust use of SRM, ensure that any deployment is beneficial and just, and assess and minimize any countervailing harms.”

The world faces mounting challenges when it comes to climate change. The IPCC has shown us the gravity of the situation we now face and the fast-closing window for climate action that remains. While intensifying the scale and pace of mitigation and adaptation must firmly remain the focus, concern about the risk of climate action failure is growing.10 More serious conversations about the likelihood and risks of overshooting the Paris goals, and whether additional response options such as SRM should or should not have a role in managing those risks, could help to ensure societies and decision-makers are better informed and thus better prepared to address whatever lies ahead. Risk-risk analysis may potentially provide important inputs to such conversations, helping to build understanding, navigate the risks of different options, and develop any new governance that may be needed.

1 The authors are grateful to Janos Pasztor and Kai-Uwe Barani Schmidt for their review and inputs.

2 This is the second of three Working Group reports produced by the Intergovernmental Panel on Climate Change (IPCC) as part of its sixth assessment cycle. The third, WGIII report is expected in early April, followed by a Synthesis Report in September 2022.

3 Note: “The report recognizes the interdependence of climate, ecosystems and biodiversity, and human societies (Figure SPM.1) and integrates knowledge more strongly across the natural, ecological, social and economic sciences than earlier IPCC assessments.” IPCC (2022) AR6 WG2 Summary for Policymakers, SPM.A

4 The temperature goals presented in the Paris Agreement (2015) are to limit global warming to well below 2, preferably to 1.5 degrees Celsius, compared to pre-industrial levels.

5 IPCC (2021) AR6 WG1 Summary for Policymakers, B1.3.

6 For more details more detail on impacts of increased heat, see the IPCC’s factsheets on regional impacts, adaptation, and vulnerability See also, IPCC (2022) AR6 WGII Ch.16

7 IPCC (2022) AR6 WGII Technical Summary, C.13.4

8 IPCC (2022) AR6 WGII Summary for Policymakers, B.5.5. The report also states that risks arise from various responses that are intended to reduce the risks of climate change, including risks from maladaptation and adverse side effects of some emission reduction and carbon dioxide removal measures. {B5.4}

9 IPCC (2022) AR6 WGII Summary for Policymakers, SPM.A.

10 The World Economic Forum Global Risks Report 2022 identified Climate action failure as the most severe global risk over the next decade https://www.weforum.org/reports/global-risks-report-2022


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