Solar radiation modification (SRM) is a controversial proposal for reducing some of the impacts of climate change by reflecting a small fraction of sunlight away from the Earth.
While there are a number of proposed techniques for reflecting sunlight through SRM, Degrees primarily focuses on Stratospheric Aerosol Injection (SAI). This form of SRM proposes injecting tiny reflective aerosols into the upper atmosphere to replicate the cooling effect of major volcanic eruptions.
SRM approaches remain theoretical—no one is deploying the technology and there have only been a few small outdoors experiments. In general the evidence that we have on SRM’s impacts comes from observing the climate effects of volcanic eruptions, and from computer modelling research, where scientists use climate models to evaluate how SRM might reduce, increase, or alter the impacts of global warming.
Why is SRM being considered?
SRM is no one’s preferred way to deal with the risks of climate change. It would involve directly intervening in the Earth’s climate system and it has some serious risks and large unknowns. But it’s being considered because it’s the only known way to quickly slow or reverse the rise in global temperatures, and it therefore might prove a useful complement to controlling greenhouse gases and adapting to the effects of warming.
The climate challenge
The world is not on track to meet its international climate change goals and impacts are rising. With current climate policies, warming is projected to rise beyond 2.5C and the climate-vulnerable countries of the Global South are going to suffer most.
Ending greenhouse gas emissions is the primary strategy to limit global warming. Adaptation can help limit risks from increasing warming. Carbon dioxide removal will also play an increasing role. However, collectively, these forms of action may not be enough to sufficiently limit risks.
Scientists are therefore trying to understand whether SRM could help reduce the impacts of warming while humanity is eliminating greenhouse gas emissions.
Evaluating SRM as a response to climate change
SRM could be very helpful or very harmful. It is the only known way to quickly stop or reverse the rise in global temperatures, and could be the only way to keep warming below 2°C if mitigation proves insufficient.
But it could also have damaging side effects, could cause political tensions, and could distract politicians from cutting emissions. The stakes are high and nowhere are they higher than in developing countries, which are on the front lines of climate change. If SRM could work to reduce climate impacts, they stand to gain the most. But if SRM goes wrong—or is rejected prematurely—they stand to lose the most.
Historically, most SRM research has taken place in the Global North. A laissez-faire approach would mean the gulf will continue to widen. It is therefore critical that the countries of the Global South play a more central role in the evaluation of SRM.
The more Global South experts understand SRM and its implications, the better placed they will be to stand up for their interests, and to resist any bad-faith attempts to persuade them to support or oppose SRM.
Is there a moral hazard in researching SRM?
Some believe that the very act of researching and discussing SRM could weaken a country’s commitment to reduce greenhouse gas emissions. This is sometimes called the moral hazard effect, or mitigation displacement.
The moral hazard effect is a real concern, but to date there is little evidence that researching SRM weakens commitments to cutting emissions. Conversely, a number of studies have concluded that learning about SRM makes people feel more concerned about the risks of climate change.