Navigating Plan C

The governance gap

No international body currently has the authority to approve, regulate, or prevent solar geoengineering. Existing treaties don’t cover it – the closest is the 1977 ENMOD convention, which only prohibits hostile environmental modification. A 2010 decision by the Convention on Biological Diversity urged caution, but is non-binding and has not been actioned. More recently, a Swiss proposal to create a UN scientific expert group on SRM was pulled in 2024 after opposition from the African Group and others. The result is a patchwork of informal norms – with no clear rules for a set of technologies that would affect everyone, and no established framework for ensuring transparency, public participation, or equitable decision-making.

Could a single country act alone?

Solar geoengineering could, in theory, be deployed by one country without international consent. The financial costs – estimated in the tens of billions of dollars per year – are within reach of many governments. However, only about ten countries possess the aerospace and logistical capacity for large-scale deployment, and any that tried would likely face significant pushback: economic sanctions, diplomatic isolation, or worse.

These constraints make unilateral deployment less likely than is sometimes claimed. A country wanting to pursue SRM would probably seek a coalition or agreement. But the absence of any framework for doing so is the core problem. There is currently no institution or process through which countries could negotiate, agree on, or object to a deployment – which is why governance is considered at least as urgent as the science itself.

A divided landscape

In the United States, legislation to ban or restrict SRM activities has been proposed in 37 states and at the federal level, with three states already approving such measures. Internationally, African environment ministers have called for a formal non-use agreement. These movements reflect concerns not only about the technology, but about power, trust, and historical inequity.

At the same time, governments – notably the UK – are increasing their investment in SRM research, and the topic is appearing on intergovernmental agendas more frequently. The result is a governance landscape defined by tension rather than consensus.