The most prominent and most-studied approach to SRM is stratospheric aerosol injection (SAI). This entails injecting aerosols into the lower stratosphere to reflect back some incoming sunlight, reducing the amount of solar radiation that the Earth absorbs.

Future Horizons:

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5-yearhorizon

SAI conversations begin

An increase in research funding begins to establish a much-needed evidence base to inform discussion. The report of the Climate Overshoot Commission, COP28’s global stocktake, UN Environment Assembly and General Assembly considerations, and a special IPCC report on SRM increases the sense of climate urgency, and informed global conversations about SAI to begin. Moreover, they encourage internationally coordinated outdoor SRM research programmes to take place and to better understand the risks, benefits and governance challenges of SRM.

10-yearhorizon

Modelling informs decision-making

Continued indoor modelling research, particularly with advanced machine-learning techniques, as well as outdoor field experiments, result in sufficient information to begin to allow evidence-based decision-making on whether or not to consider SAI as a supplemental option to mitigate and adapt to climate change. Governance frameworks that had been put in place to guide international coordinated research on SAI, as well as further research on governance needs of SAI and the available evidence base, result in beginning work toward an international treaty for the long-term governance of SAI.

25-yearhorizon

Governance of SAI deployment begins

Advances in high-resolution modelling capabilities give better understanding of SAI’s impacts at local and regional scale. A global treaty provides a binding framework for long-term governance of SAI deployment as one of many climate-change-mitigation techniques. Its provisions also provide for a global authority to implement AI on behalf of the global community.

There is evidence that SAI can offset some of the impacts of climate change, but will come with ancillary risks of its own. Crucially, it would be possible to restore the average global temperature to pre-industrial levels if sufficient quantities of aerosols were injected in a sustained fashion.⁹ However, modelling studies suggest that it is not possible to reset temperatures in every region. The same applies to precipitation, wind patterns and other aspects of climate. So, while SAI could lead to a more favourable outcome overall, there would inevitably be some winners and some losers.¹⁰

Sulphate aerosols are the most commonly proposed substance for SAI. However, sulphur’s potential to damage the ozone layer or lead to acid rain is a significant concern and this is driving research into alternative materials, such as calcites or chalk powder. A better understanding of the way all these materials interact with the upper atmosphere is much needed.

The overwhelming majority of studies of the effectiveness and consequences of SAI have been carried out through computer modelling. Most of the field tests that have been proposed have been called off after facing opposition.¹¹ But a small number have taken place, carried out by independent researchers and funded by entrepreneurs, raising concern over the possibility of unilateral action.¹² ¹³

Stratospheric aerosol injection - Anticipation Scores

The Anticipation Potential of a research field is determined by the capacity for impactful action in the present, considering possible future transformative breakthroughs in a field over a 25-year outlook. A field with a high Anticipation Potential, therefore, combines the potential range of future transformative possibilities engendered by a research area with a wide field of opportunities for action in the present. We asked researchers in the field to anticipate:

The uncertainty related to future science breakthroughs in the field
The transformative effect anticipated breakthroughs may have on research and society
The scope for action in the present in relation to anticipated breakthroughs.

This chart represents a summary of their responses to each of these elements, which when combined, provide the Anticipation Potential for the topic. See methodology for more information.