Blocking The Sun Could Help Prevent Climate Change But May Be Risky, Says New Report

More research is needed to determine the feasibility of solar geoengineering. Image: Ed Conno/

The US National Academy of Sciences, Engineering, and Medicine (NASEM) has called for the establishment of a research program to investigate the potential of solar geoengineering solutions to the climate crisis. While the academy insists that curbing emissions should still be considered the “first line of defense” against climate change, it says that failure to achieve this goal may necessitate more extreme measures to reduce the sun’s heat.

In a newly published report, the NASEM explains that solar geoengineering “refers to attempts to moderate warming by increasing the amount of sunlight that the atmosphere reflects back to space or by reducing the trapping of outgoing thermal radiation.” However, because such an approach is likely to generate an array of as-yet-unknown side effects, the academy has urged the US to set up a research program in order to assess the wider impact of solar geoengineering technologies.

It’s therefore important to recognize that the NASEM is not, at this stage, recommending that such interventions be deployed as a solution to climate change. Rather, it has asked for an initial investment of $100 to $200 million to investigate the pros and cons of solar geoengineering, with the aim of helping policymakers determine whether or not to consider the technology when devising future climate strategies.

The report has identified three specific techniques that it believes are worthy of study. The first of these is stratospheric aerosol injection, which involves the release of tiny reflective particles into the stratosphere in order to reflect incoming sunlight back into space.

Previous research has indicated that volcanic eruptions cool the climate by spewing particles high into the atmosphere, thereby suggesting that such an approach may be effective. However, uncertainties remain over how this effect can be artificially reproduced.

The second technique is known as marine cloud brightening and involves the injection of particles into the lower atmosphere in order to increase the reflectivity of low-lying clouds over the ocean.

Finally, the report highlights the potential of cirrus cloud thinning, whereby high-altitude cirrus clouds are disrupted in order to prevent them from trapping heat. However, the report authors point out that such an approach is likely to be hindered by “very limited understanding of cirrus cloud properties and the microphysical processes determining how cirrus may be altered.”

Solar geoengineering
Illustration of stratospheric aerosol injection, marine cloud brightening, and cirrus cloud thinning – the three solar geoengineering interventions considered in the report. Image: National Academy of Sciences.

While the authors believe that these methods may prove effective at easing some of the risks associated with climate change, they insist that “these interventions could also introduce an array of potential new risks.” Among these are a loss of stratospheric ozone and the disruption of regional climate features like monsoons.

The report also highlights the “social, political, and economic” instability that may ensue if solar geoengineering techniques are deployed, and therefore urges that research proceed with extreme caution in order to ensure the technology is not abused.

For instance, the NASEM says that a strict code of conduct should be created and that all research should be cataloged in a public registry. It also says that outdoor experiments should be limited, and that only small amounts of substances should be released into the atmosphere in order to prevent “detectable changes in global mean temperature or adverse environmental effects.”

“Given the urgency of the climate crisis, solar geoengineering needs to be studied further,” explained NAS president Marcia McNutt in a statement. “But just as with advances in fields such as artificial intelligence or gene editing, science needs to engage the public to ask not just can we, but should we?”


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