Solar radiation management (SRM) is a set of geoengineering techniques that aim to counter climate change by reflecting inbound sunlight back out into space. SRM is still in an early stage of research, although a field study is being planned for next year. This study will involve spraying reflective particles into the stratosphere and then measuring their behavior, interactions, and effects.
We already know from past volcanic eruptions that an influx of particles into the upper atmosphere can lower temperatures on the ground. But we’re not that clear on how the process works or how we could control it enough to avoid adverse side effects, such as changes in global precipitation patterns. SRM should be explored to resolve uncertainties such as these and reduce the risks, because models of stratospheric aerosols and other SRM schemes have consistently shown they would reduce surface temperatures. Plus, initial calculations indicate they could be deployed relatively quickly and cheaply.
Since SRM effects would likely cross national boundaries, there are all sorts of political issues to be addressed before the technology could be scaled up. Here's a nice summary of the political issues at each stage of research:
Source: https://www.publications.parliament.uk/pa/cm200910/cmselect/cmsctech/221/10011302.htm
Some critics are against SRM research (much less implementation) on the principle that climate systems are just too complex to meddle with. This objection draws its strength from two related tropes: the delicate balance of nature and the “butterfly effect" - variations on the idea that small changes can wreak large havoc. Such tropes may shed light on particular cases but they're not falsifiable as general rules. There's always an out: absence of predicted havoc just means we have to wait longer. So these critics will never be satisfied that SRM isn't inherently dangerous, no matter what the evidence.
Others don’t want to move forward with SRM research because they consider it a distraction from what our main focus should be: cutting greenhouse gas emissions. These critics want us to embrace the necessity of sacrifice, not rely on the hope that technology will save the planet before disaster strikes. Such hope would reduce the sense of urgency to act now, so we mustn’t feed that particular wolf. Or so they say.
There's actually no evidence the public would respond to the prospect of SRM with a general slackening of resolve to reduce emissions. In fact, some research has suggested people would have the opposite reaction - becoming even more serious about bringing down emissions because the idea of SRM seems a bit scary.
Scary or not, it's time to move beyond computer modeling and find out if solar radiation management is viable and safe in the real world. One field study at a time.