Use the future to build the present
Managing Solar Radiation
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Invited Contribution:

Managing Solar Radiation

Even to an audience that has grown numb to climate warnings, a working group report published in August as part of the IPCC’s latest assessment report (AR6) was alarming. The threat of catastrophic impacts felt grimly familiar, but what hit hardest was the rapidly dwindling time left to avoid them, and the woeful, continued shortfall — even after so much discussion and effort — of the world’s emergency response.

Following a year of headline-grabbing floods, fires and storms, there is no more room for scepticism. The UN Secretary General called it “code red for humanity”. Linda Mearns, an IPCC co-author, of the US National Center for Atmospheric Research memorably was quoted: there is “nowhere to run, nowhere to hide”.

The fiendish conundrum facing societies around the world is how to rapidly wean themselves off fossil fuels whilst avoiding too much pain or disruption. As governments do the maths on net zero emissions by 2050, realisation is growing as to how challenging this will be, and how difficult it is to bring everyone along. And that is only the first half of the challenge; then comes the task of cleaning up excess carbon dioxide already in the atmosphere.

That is why an additional pillar of action is rapidly rising up the agenda: large-scale carbon dioxide removal (CDR). The IPCC’s report outlines two scenarios in which humanity has a theoretical chance of limiting warming to either 1.5 or 2°C, and thereby not overshooting the temperature goals of the Paris Agreement. Both scenarios require removing billions of tons of carbon dioxide directly from the atmosphere and storing it in perpetuity.

This idea, until recently, was often dismissed as a distraction. There remain also concerns of “moral hazard” in that CDR could be used by some to avoid cutting emissions. But society is coming to realise that it needs every tool in the toolbox. It is not a question of either emissions cuts or removals, but how to ensure both can work in concert. Not considering and planning for the carbon dioxide removal needed is considered by some as overoptimistic or magical thinking — another side of moral hazard.

But large-scale removal of carbon dioxide from the atmosphere is not easy. All approaches have limits — related to scaling, permanence, maturity, monitoring and costs — and there is no silver bullet. Nature-based approaches give rise to land use and water issues, and can be fragile, as shown by this year’s forest wildfires. Technology-based approaches are immature and expensive, and there is insufficient political and therefore market support for their development.

In practice, even with substantial mitigation efforts, including a combination of emissions cuts on all gases and CDR, it’s far from certain the world will achieve net zero in the next 20-30 years — let alone achieve the required net removal thereafter.

Yet not limiting temperature rise to 1.5 or 2°C will lead to massive global suffering and the breaching of multiple planetary boundaries and potentially global tipping points, with devastating consequences for all humanity.

Faced with this stark situation, it may be time to start thinking about the unthinkable.

Solar radiation modification (SRM) is a theoretical set of approaches that seek to limit warming by deflecting more sunlight back into space. They would not be a substitute for cutting greenhouse gas emissions and removing excess carbon dioxide from the atmosphere, but could potentially help reduce climate impacts and avert tipping points while the essential work of decarbonisation is completed.

The IPCC cites several ideas: surface albedo enhancement, cirrus cloud thinning, marine cloud brightening, and — most controversially — stratospheric aerosol injection (SAI), which would “inject highly reflective aerosols such as sulphates into the lower stratosphere … resulting in a planetary cooling.”

But these techniques are uncertain and bring new risks. The IPCC says it is “conceptually possible for optimally designed SRM strategies to achieve multiple climate policy goals”, but notes that there is limited understanding of their effects, and that the direct and indirect effects of deployment would not be equal globally.

A sudden and sustained cessation of SRM, the IPCC adds, would drive a rapid increase in global temperature, endangering biodiversity, weakening carbon sinks, increasing precipitation and changing water cycles. At the same time, the IPCC says a gradual phase-out of SRM with concurrent emission reductions could reduce that termination shock. Could the world create governance robust enough to safeguard against such risks? Could countries find consensus on how and at what level deployment should take place?

The IPCC will address the potential risks, the ethics, the public perceptions of SRM, and other governance issues as part of its second and third working group reports in 2022. But it’s already clear that SRM creates an unusually big and complicated governance challenge, which needs to be addressed.

SRM opponents believe the risks — known and unknown — as well as the governance challenges are simply too high to explore it any further. Furthermore, they believe that SRM would create a moral hazard by deterring other efforts to address the cause of the climate crisis via mitigation, by reducing emissions and removing excess carbon from the atmosphere.

But others see risks in pinning humanity’s hopes on current strategies alone and not exploring whether or not SRM could help avoid the impacts of overshooting temperature goals beyond what is possible through adaptation and resilience measures. They think the time has now come to learn more.

Addressing the causes of climate change is the priority. But should the world not also examine what potential insurance strategies might or might not exist? Should we not explore how to develop them, or how to prepare new possibilities if current implementation strategies prove insufficient?

If we decide to do so, addressing the moral hazard issue through effective governance will be crucial. We would need to build governance structures to avoid any deterrence of mitigation. But we also need to avoid falling into the trap of false optimism in other existing and emerging approaches, and to be prepared for unexpected developments.

The situation is certainly tricky: not building systems to learn more about and better understand the feasibility and viability of SRM is a decision in itself, and increasingly a risky one. It could deny future generations an option to reduce the impacts of soaring temperatures if SRM is found to be viable and the potential risks it poses are found to be acceptable compared to the benefit of reducing climate impacts. It could also increase the risk of ungoverned SRM deployment in the future. What governance would then be required? If we decide to duck this debate, are we accepting those risks?

The reality is that we don’t know enough about the risks, benefits and governance challenges and opportunities to take decisions about SRM today, including whether to reject them.

Understanding more about the availability, feasibility and use of SRM — or indeed the implications of a decision not to use it — could also have important ramifications for other important decisions relating to resilience and adaptation.

We need to learn more. Building a global information platform could be a crucial first step to creating more inclusive and responsible discussions. But these things take time, something we are fast running out of. Finding broad-based agreement on the best way forward needs to start now.

One thing we already know: decisions and actions on SRM governance need to be global — including any decision not to use it. If the world went ahead with SRM, and in particular stratospheric aerosol injection, it would be the most global endeavour undertaken by humanity.

In practice, the United Nations is the only organisation where governments can address this issue with the rigour it demands. Ideally, governments would put different parts of the SRM governance challenge on the agenda of various UN bodies – including reviewing the potential risks and benefits; how the use or not of SRM may impact the sustainable development goals worldwide, and what may come after their expiration in 2030; and make available transparent information on who is doing what in this area world-wide.

We need to face the sobering reality: there are no risk-free pathways ahead. The best we can hope for is to lessen those risks through better understanding and better preparation. In that light, to defer debate about SRM looks increasingly irresponsible.

Janos Pasztor is Executive Director of the Carnegie Climate Governance Initiative (C2G), and would like to thank his colleagues, in particular Cynthia Scharf, Nick Harrison, Kai-Uwe Schmidt and Mark Turner for their contributions to this article.