Modification of solar radiation: an answer to the climate crisis?

Solar Radiation Modification (SRM) – a speculative group of technologies to cool the Earth is being explored as climate action lags – requires far more research into its risks and benefits before any consideration for potential deployment, according to an Expert Panel convened by the United Nations Environment Programme (UNEP).

The report by the panel finds that SRM is not yet ready for large-scale deployment to cool the Earth. The Panel says it is no substitute for a rapid reduction in greenhouse gas emissions, which must remain the global priority.

Emergency temporary measures such as SRM are being raised in scientific and public discourse since global efforts to reduce greenhouse gas emissions are not on track to meet the 1.5°C Paris Agreement goal. Climate change continues to worsen, with some of its impacts already irreversible.

SRM aims to cool the Earth rapidly by reflecting a small percentage of sunlight back into space. While some SRM technologies, like Stratospheric Aerosol Injection (SAI), are more mature and outdoor experiments are being actively pursued, the review finds critical unresolved issues overall.

There are significant uncertainties on the social and environmental impacts of SRM, and its safety and viability, according to a review of the scientific research by the multidisciplinary expert panel. SRM does not address the causes of climate change, so it will not fix or change the impacts we are already experiencing, the panel finds.

“Climate change is taking the world into unchartered lands, and the search is on for all viable solutions,” said Andrea Hinwood, UNEP Chief Scientist. “However, all new technologies must be clearly understood, and potential risks or impacts identified before being put into use.

“The private sector and regulators need to address the basic uncertainties surrounding these technologies, answer some fundamental questions about safety and employ the precautionary principle before SRM can even be contemplated.”

The impacts of SRM technologies on low- and middle-income countries remain understudied, even though these countries are often on the frontlines of climate change and would face the potential impacts of SRM technologies should they be deployed.

Other issues include the governance of small-scale outdoor experiments and operational deployment, technology development, and financing, as well as equity, and ethical concerns around consent.

The Expert Panel considers that near and mid-term large-scale SRM deployment is not warranted and would be unwise at this time. However, this view may change should climate action remain insufficient.

“There’s been a great deal of headway in SRM research and important advances in modeling, but we need far more empirical evidence on the risks and potential consequences before exposing our only atmosphere to SRM technologies,” said Hinwood. “There are no shortcuts or substitutes for slashing harmful emissions and there is no better alternative for our peace, health and well-being than a shift to a circular economy, in harmony with nature.”