What is SRM?
SRM stands for 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.
This would create a cooling effect, offsetting some human-caused global warming. However, it would not replace the need for cutting carbon emissions or other climate policies.
Solar radiation modification is also known as solar radiation management, sunlight reflection methods, or solar geoengineering, and can come under the umbrella of ‘climate interventions’.
Why is SRM being considered?
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 2.5°C.
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 over the next couple of decades.
Scientists are therefore trying to understand whether SRM could help reduce the impacts of warming while humanity is eliminating greenhouse gas emissions.
What are the main SRM methods?
SRM approaches remain theoretical – no one is deploying the technology and there have only been a few small outdoors experiments. But there are several approaches being studied.
Stratospheric aerosol injection (SAI) proposes injecting tiny reflective aerosols into the upper atmosphere to replicate the cooling effect of major volcanic eruptions. Any impacts would be global, as the particles would spread throughout the stratosphere. Most SRM modelling studies investigate how SAI could change the climate and assess its potential environmental impacts.
Marine cloud brightening (MCB) would involve spraying sea water from ships to encourage droplet formation and make marine clouds more reflective. This could produce more local effects, and is being increasingly studied in modelling scenarios.
There are several other methods proposed, with varying degrees of study and predicted effectiveness, including cirrus cloud thinning (CCT), space-based reflection and surface albedo modification.
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.
Explainer videos
What is Stratospheric Aerosol Injection?
What is SRM?
