Nations meeting to advance action on climate change at COP27 in Egypt know we’re headed for dangerous climate impacts. The UN Environment Programme confirmed in its 2022 emissions gap report ^[1] that there is no longer a ‘credible pathway’ to keep global warming below 1.5°C based on 2030 commitments. The report, titled The closing window, suggests that we may still have a shot at keeping warming to 2.0°C, but only if all countries fully meet their net-zero pledges. That’s far from guaranteed or likely given the lack of detail in those pledges. We’re already seeing extreme climate events annually—but even more dangerous impacts are locked in.

The good news is that our efforts to deploy clean energy have succeeded enough to rule out the worst-case projected emissions scenarios and it’s now unlikely that we’ll reach catastrophic warming beyond 4.0°C. There’s one important caveat: modelling suggests that any warming over 1.5°C ^[2] will increase the risk of self-reinforcing tipping points in the global climate system. Tipping points are temperature thresholds at which significant greenhouse gases can be released suddenly, greatly amplifying global warming—for example, a release of frozen stores of carbon dioxide and methane gas from thawing Arctic permafrost.

Because a climate-disrupted future remains possible, another danger needs our attention. As the impacts of warming become more extreme, countries are more likely to turn to riskier measures to combat them, including geoengineering.

Geoengineering can entail modifying local weather conditions (such as seeding clouds to change rainfall ^[3]), removing carbon dioxide from the atmosphere (separating it out and storing it) or managing solar radiation (reducing the amount of sunlight that can get trapped as heat in the atmosphere). These options have been discussed in climate circles for many years—at various times considered a last resort, a moral hazard that could delay decarbonisation of economies ^[4], or generally a dystopian nightmare.

Solar radiation management is the most troubling geoengineering idea. The objective is to block sunlight entirely by deploying satellite sunshades between the earth and the sun, to dim the skies by dispersing reflective sulphate aerosols in the stratosphere, or to increase the reflectivity of clouds (cloud whitening) or surface objects like rooftops (or, in an extreme case, glass beads scattered across the Arctic ^[5]).

In theory, these approaches could rapidly cool global temperatures—especially the dispersal of sulphate aerosols, whose effect would be somewhat like what happens naturally from massive volcanic plumes ^[6]. The eruption of Mount Pinatubo in mid-1991, for example, is estimated to have cooled global temperatures by 0.5°C for two years ^[7]. Some geoengineering proponents believe that releasing sulphate aerosols into the atmosphere could achieve a similar result and help blunt the threat posed by climate change in the near term.

The danger with these approaches is that deep uncertainty exists about their impacts. They could drive severe consequences that—like global warming itself—don’t respect borders. Dimming sunlight with sulphate aerosols could diminish crop productivity ^[8] while altering precipitation patterns and increasing the acidity of rainfall, all of which would further stress climate-change-affected regions and the global food system. The massive and rapid changes in atmospheric conditions from such cooling could have simultaneous and devastating consequences for food-insecure communities globally.

Other geoengineering approaches could backfire in other ways. For example, deploying a massive number of glass beads to enable the Arctic to reflect more sunlight could instead trap more sunlight ^[9] as heat, likely resulting in faster melting of sea ice.

Scientific uncertainty about the use and consequences of geoengineering is a legitimate concern, but there are barriers even to studying it (particularly in the case of solar radiation management). The UN Convention on Biological Diversity has banned all but small-scale geoengineering experiments for over a decade. Earlier this year, a group of concerned scientists and governance experts ^[10] published an open letter calling for a total ban on solar geoengineering on the grounds that its impacts can never be fully understood or equitably governed in the international system. The main international body that helps coordinate and prioritise climate science research, the World Climate Research Programme, is still determining what role it should play in research on geoengineering.

In response to a recommendation by the National Academies of Science, Engineering and Medicine ^[11] in 2021 to help address uncertainties, the US began developing ^[12] a research plan on solar geoengineering in mid-2022. Readiness to develop research isn’t matched with an eagerness to address governance issues, however. Under a different US administration, a 2019 proposal led by Switzerland asking the UNEP to produce a report on geoengineering was blocked by the US and Saudi Arabia.

What makes governance of these approaches difficult is that they may be cheap enough to be deployed by many state and non-state actors. The incremental cost of avoiding 1.0°C of warming ^[13] with sulphate aerosol dispersion may be only US$18 billion a year, a significant but achievable budget allocation for many advanced and emerging economies, high-net worth individuals or companies.

In addition, it’s difficult to know when techniques like solar radiation management should be used because global average temperature rises will result in variable impacts. For example, 2°C of warming will be difficult for all countries but will threaten the existence of some. The cross-border and likely uneven impacts of geoengineering make it difficult to know who would benefit or suffer, further complicating a consensus decision on when the risks of something like sulphate aerosol dispersion would justify its use.

These dynamics mean it’s time to establish multilateral institutions and global norms for geoengineering research and use. We need to do that now. A fence needs to be set around geoengineering so that it can’t be used to justify backsliding among advanced economies to delay decarbonisation. Instead, the principles of its use and study must be informed explicitly by the countries that are the most exposed to climate impacts at any level of warming above 1.5°C and the least able to adapt.

Multilateral institutions are our best hope for governing geoengineering. As ineffective as they may seem at managing our shared atmosphere, particularly as we return to a multipolar world, they’re the reason we’ve avoided the worst-case emissions scenario—and are recovering our ozone layer. Energy markets and economic self-interest may drive the transition, but it was global scientific consensus and the UN that established the knowledge, imperative and targets driving global efforts.

There should be no doubt that geoengineering is an absolute last resort we should fear—for a worst-case scenario we can still avoid. Of course, we need to rapidly reduce emissions to avoid dangerous warming in the first place and redouble investments in adaptation. But as the UNEP emissions gap report suggests, we still need to prepare for dangerous climate impacts—including the possibility of disruptive tipping points. That planning process must include getting a better understanding of geoengineering and deciding what part it will play in our response.

We’re running out of time and can’t keep kicking the can down the road. With everything else climate change brings, in an era of renewed strategic competition, Australia cannot afford to sit this issue out.