Introduction to Solar Radiation Modification
Reducing the amount of sunlight reaching Earth could halt global warming and limit the damage caused by climate change. The Royal Society has suggested that bold new technology to reflect sunlight back into space could "buy time" for cuts in fossil fuel emissions to take effect.
Strategies for Solar Radiation Modification
Two strategies – pumping reflective particles high into the atmosphere and spraying salt into clouds over the sea to make them whiter – were identified as likely effective and technically feasible. However, the report’s authors warn that a rogue state acting alone and attempting to dim sunlight in one region could lead to extreme droughts and other weather disruptions elsewhere in the world.
Risks and Limitations
Professor Keith Shine, chair of the report’s working group, noted that there may come a time when world leaders agree that solar radiation modification (SRM) is the least-worst option. He emphasized that SRM is not without risks, but these risks may be viewed as less serious than the risks of inadequately contained climate change.
Current Climate Situation
Global efforts to reduce greenhouse gas emissions are becoming increasingly unlikely to stop global temperatures rising above 1.5C, seen by many scientists as a "safe" limit. Under current policies, temperatures are expected to be at least 3°C warmer by 2100 than in pre-industrial times.
Aerosol Injection into the Stratosphere
The working group evaluated aerosol injection into the stratosphere as the most promising option for reducing the amount of sunlight reaching the Earth’s surface. Planes would fly at high altitudes and release sulfur dioxide gas, which would form particles that reflect a small amount of sunlight. There is evidence that this could work, as the 1991 eruption of Mount Pinatubo reduced temperatures by 0.5°C for one to two years.
Cost and Effectiveness
Computer models suggest that releasing eight to 16 million tonnes of sulfur dioxide from aircraft each year in both the northern and southern hemispheres could reduce global temperatures by 1°C. The likely cost would be “in the low tens of billions of dollars per year,” which is far less than the global cost of more extreme weather events, wildfires, and other climate impacts.
Limitations and Alternatives
The Royal Society report warns that SRM would not address the root cause of climate change and is not an alternative to reducing emissions. However, it could lower temperatures as carbon dioxide levels in the atmosphere peak and then begin to fall. This could mean that SRM would have to be used for 100 years or longer.
