Scientists and policy experts around the world are exploring whether sunlight reflection methods (SRM) – also known as solar geoengineering – could be part of the toolkit for tackling climate change. But this work is controversial, and there are deep concerns about its potential consequences. Why are people turning to such a drastic idea? Could it help, and what are the challenges?
The climate crisis
The world is making progress on climate change but is not on track to meet its climate goals.
Around $2 trillion – roughly 2% of global GDP – went into clean energy investments in 2024, almost double what it was a decade ago. Enormous progress has been made, but global carbon dioxide emissions keep rising.
2024 was also the first calendar year to see the global average temperature breach 1.5°C above pre-industrial levels. Keeping this rise to 2°C – the goal of global climate agreements – may soon be slipping out of reach.
In fact, even if the countries of the world meet their emissions commitments, the world seems to be on track for more than 2.5°C warming by the end of the century. That could be devastating.
Global temperature change with and without human influence
Climate models show that observed warming can only be reproduced in climate model simulations if human actions, including greenhouse gas emissions, are included.
Change in global annual average temperature relative to 1850-1900
Observed
Simulated human and natural
Simulated natural
(solar and volcanic)
2.0°C
1.5
1.0
0.5
0
–0.5
1850
1900
1950
2000
Source: IPCC
Change in global annual average temperature relative to 1850-1900
2.0°C
1.5
Observed
Simulated human and natural
1.0
0.5
Simulated natural (solar and volcanic)
0
–0.5
1850
1900
1950
2000
Source: IPCC
The impacts of global warming
The impacts of global warming are being felt in every country and every community around the world, but especially in the Global South. Devastating wildfires stoked by hotter, drier conditions are burning out of control; droughts and floods are made more intense by rising temperatures; glaciers and sea ice are retreating, changing landscapes and livelihoods. Almost everyone has a story about how the changing climate is affecting their local area, undermining prosperity, increasing insecurity, and changing ecosystems.
Some key impacts of climate change
Food
Rising temperatures and intensified weather extremes will pressure food production systems, undermining food security.
Water
Climate change is impacting water security, increasing both extreme high and extreme low water flows in some regions.
Health
The health risks of extreme heat rise dramatically with warming – in Europe impacts at 3°C could be triple what they are at 1.5°C.
Climate change is changing how diseases like malaria spread, endangering new populations.
Ecosystems
Tropical Coral Reefs will decline substantially by 1.5°C of warming and could be virtually lost by 2°C warming.
At 2°C of warming, up to 18% of species on land could face a very high risk of extinction, and up to 29% at 3°C.
Extreme weather
The intensity of many weather extremes rises with temperatures, e.g., the intensity of extreme rainfall rises by ~7% for every degree Celsius of warming.
Economy
The economic impacts of climate change are expected to rise dramatically with warming.
Security
Climate change increases risks of violent conflict through climate extremes and impacts on water and food security.
Source: SRM360.org
Food
Rising temperatures and intensified weather extremes will pressure food production systems, undermining food security.
Water
Climate change is impacting water security, increasing both extreme high and extreme low water flows in some regions.
Health
The health risks of extreme heat rise dramatically with warming – in Europe impacts at 3°C could be triple what they are at 1.5°C.
Climate change is changing how diseases like malaria spread, endangering new populations.
Ecosystems
Tropical Coral Reefs will decline substantially by 1.5°C of warming and could be virtually lost by 2°C warming.
At 2°C of warming, up to 18% of species on land could face a very high risk of extinction, and up to 29% at 3°C.
Extreme weather
The intensity of many weather extremes rises with temperatures, e.g., the intensity of extreme rainfall rises by ~7% for every degree Celsius of warming.
Economy
The economic impacts of climate change are expected to rise dramatically with warming.
Security
Climate change increases risks of violent conflict through climate extremes and impacts on water and food security.
Source: SRM360.org
Food
Water
Health
Ecosystems
Extreme weather
Economy
Security
Rising temperatures and intensified weather extremes will pressure food production systems, undermining food security.
Climate change is impacting water security, increasing both extreme high and extreme low water flows in some regions.
The health risks of extreme heat rise dramatically with warming – in Europe impacts at 3°C could be triple what they are at 1.5°C.
Climate change is changing how diseases like malaria spread, endangering new populations.
Tropical Coral Reefs will decline substantially by 1.5°C of warming and could be virtually lost by 2°C warming.
At 2°C of warming, up to 18% of species on land could face a very high risk of extinction, and up to 29% at 3°C.
The intensity of many weather extremes rises with temperatures, e.g., the intensity of extreme rainfall rises by ~7% for every degree Celsius of warming.
The economic impacts of climate change are expected to rise dramatically with warming.
Climate change increases risks of violent conflict through climate extremes and impacts on water and food security.
Source: SRM360.org
Adding to those concerns, the world may be on the brink of multiple “tipping points”– such as the destabilisation of the ice sheets – that, if crossed, could prove irreversible and cause massive harm to people and ecosystems.
There is no cliff edge at 1.5°C or 2°C of warming, but every tenth of a degree of warming will make things worse. Every additional tenth of a degree will impact people and ecosystems and is worth fighting to prevent.
The current strategy and its limits
The primary strategy to prevent further warming is to stop burning fossil fuels and reduce other sources of greenhouse gas emissions.
However, eliminating emissions will only stop global warming getting worse, it will not reverse it. To return temperatures to safer levels, the world must also remove hundreds of billions of tonnes of carbon dioxide already in the atmosphere.
Significant progress has been made, and decarbonisation is underway. But the impacts of climate change are being felt today and will get worse over the coming decades.
That is why a growing number of scientists and policymakers are asking: are there additional approaches the world could use to reduce the impacts of climate change while emissions are driven down?
Emissions cuts, carbon removal, and SRM
Emissions cuts and carbon dioxide removal (CDR) tackle the root cause of climate change, and sunlight reflection methods (SRM) could limit warming while they work.
GLOBAL TEMPERATURE INCREASE
No emissions cuts
Temperatures would continue to rise.
Cut emissions
Eliminating CO2 emissions would stop global warming, but not reverse it.
4.0°C
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
2000
2100
2200
2300
2400
Reflect sunlight
SRM could offset global warming while emissions cuts and CDR work.
Remove carbon
CDR could then slowly lower temperatures.
Source: Based on Boselius et al. (2025), Oxford Open Climate Change
GLOBAL TEMPERATURE INCREASE
4.0°C
No emissions cuts
Temperatures would continue to rise.
CUT EMISSIONS
Eliminating CO2 emissions would stop global warming, but not reverse it.
3.5
3.0
2.5
2.0
REMOVE CARBON
CDR could then slowly lower temperatures.
1.5
REFLECT SUNLIGHT
SRM could offset global warming while emissions cuts and CDR work.
1.0
0.5
2000
2050
2100
2150
2200
2250
2300
2350
2400
Source: Based on Boselius et al. (2025), Oxford Open Climate Change
Learn More
SRM cannot solve climate change, but could it help?
Sunlight reflection methods (SRM) – also known as solar geoengineering or solar radiation modification – describe a set of ideas to reflect a small portion of incoming sunlight to reduce global temperatures.
SRM covers a range of approaches, but two stand out. One would involve adding a layer of tiny, reflective particles into the upper atmosphere, and the other would make ocean clouds more reflective.
Sunlight reflection methods
Sunlight reflection methods (SRM) are hypothetical approaches to lower global temperatures by increasing the amount of sunlight reflected to space.
Sunlight
Stratospheric aerosol
injection (SAI)
Tiny particles released in the stratosphere would directly reflect a small fraction of sunlight.
Marine cloud brightening (MCB)
Sea salt particles would be sprayed from ships to enhance the reflectivity of low-lying clouds
Source: SRM360.org
Sunlight reflection methods
Sunlight reflection methods (SRM) are hypothetical approaches to lower global temperatures by increasing the amount of sunlight reflected to space.
Stratospheric aerosol injection (SAI)
Tiny particles released in the stratosphere would directly reflect a small fraction of sunlight.
Marine cloud brightening (MCB)
Sea salt particles would be sprayed from ships to enhance the reflectivity of low-lying clouds
Sunlight
Source: SRM360.org
None of these approaches would be a solution to climate change, but scientists are exploring whether they could limit some of the risks caused by global warming while the root causes are being addressed.
None of these approaches are currently being deployed but they are being studied by scientists across the world, and a few small-scale field experiments have been conducted.
By changing the global climate, SRM would affect everyone. This raises many difficult ethical questions that need to be discussed. To inform those discussions, people need to understand what these approaches are, how their risks compare to the risks of climate change, and what could go wrong.
With that understanding, the world can work towards more effective governance of SRM: whether that is to block these ideas, or to develop them further.
