What is Solar Geoengineering?

Also known as Solar Radiation Modification (SRM), solar geoengineering refers to technologies that would reflect a portion of the sun’s rays back into space, with the goal of limiting or reversing global warming. These technologies would have to be deployed at a very large scale, and would create major side effects on the earth’s weather systems, ecology, agriculture, and public health. All SRM technologies are currently speculative and unproven, but a growing number of researchers and entrepreneurs are rushing towards the development of deployment technologies – regardless of the risks.

The most common types of solar geoengineering proposed are:

1. Stratospheric Aerosol Injection (SAI) – designed to mimic the largest volcanic eruptions by injecting more than 38 million metric tons of sulfur dioxide into the stratosphere every year by spraying from the back of dedicated airplanes flying up to 6,000 flights per day.
2. Marine Cloud Brightening (MCB) – would require a fleet of 1,500 customized ships deployed around the globe, pumping 12,000 gallons of seawater per second into the air to make marine clouds reflect more sunlight.
3. Surface Albedo Modification (SAM) – a broad category of proposals to reflect more sunlight from Earth’s surface. These schemes include covering Arctic ice sheets with billions of hollow glass microspheres; painting roofs and urban surfaces white; or even genetically modifying crops to have a lighter/whiter color.
4. Space Sunshades or Space Mirrors – propose launching very large (or large quantities of) mirrors, lenses, or metallic discs into space between the sun and the earth.

Solar geoengineering attempts to address one symptom of climate change – rising global temperatures – but doesn’t treat the cause, which is human-driven greenhouse gas emissions. Many serious impacts of climate change such as ocean acidification and glacial ice loss would be unaffected.

Is solar geoengineering dangerous?

Some solar geoengineering proposals, such as painting roofs white or genetically altering food crops to have a lighter color, would have little to no impact on the climate according to modeling. SAI or MCB, however, if deployed at levels that could restore atmospheric temperatures to pre-industrial levels, could create potentially catastrophic side effects on the planet, particularly by altering global weather patterns. For example, studies have shown that Stratospheric Aerosol Injection could:

• Reduce monsoon rainfall over Asia and Africa threatening the food supply of two billion people.
• Further erode the ozone layer.
• Increase the risk of malaria for over one billion people.

Marine Cloud Brightening could reduce rainfall over the Amazon, create dangerous air quality at ground levels with ozone pollution, or if it was used at smaller scales to cool California, increase heat levels in Europe.

One unique problem with all geoengineering technologies is that even at fairly large scales their impacts are impossible to distinguish from the large natural fluctuations in weather and temperature. The only way to learn whether solar geoengineering works, and what the side-effects may be, is to deploy at full scale. For this reason, there is no safe or humane scientific pathway for the development of these technologies.

One of the greatest risks from solar geoengineering arises if a technology is used, then suddenly stopped or paused. Known as “termination shock,” earth’s temperatures could rise very rapidly over a very short period of time – leading to even more extreme weather events than we would see under gradual climate warming, and leaving humanity with even less time to adapt.

Finally, SRM represents a major threat to international peace and security. The U.S. National Intelligence Council has assessed that the lack of national or global regulation of SRM “increases the possibility that state or nonstate actors will independently develop or deploy the technology— possibly covertly—in a manner that risks conflict if other nations blame them for a weather disaster they believe was caused by geoengineering.” Recent interviews with 125 experts from 21 countries identified an even larger range of peace and security risks associated with geoengineering, such as nations using the threat of deployment as a negotiating tactic to force concessions from other countries, or even military conflict leading to unexpected stops in geoengineering and termination shock.

Who’s behind the growth in geoengineering experiments?

Funding for geoengineering projects has surged, and is coming largely from Global North-based tech and hedge-fund billionaires focused on finding magical techno-fixes to the climate crisis. They include Bill Gates of Microsoft, Mark Zuckerberg and Dustin Moskowitz of Facebook, Greg Skinner and Suneil Setiya of the hedge fund Quadrature Capital, Rachel and Roland Pritzker of the Hyatt Hotels fortune, and Jim Simons of the hedge fund Renaissance Technologies. Some solar geoengineering companies are already selling “cooling credits” to individuals and corporations to allegedly offset their own emissions.

Who bears the risks of geoengineering?

Most models find that the negative side effects of geoengineering would disproportionately impact the Global South and coastal communities – the same communities suffering the worst impacts of climate change but who are the least responsible for causing it. These effects include reduced monsoon rainfall in Asia and Africa, reduced rainfall over the Amazon, or in the case of artificially-created salt-water marine clouds, damage to the agriculture of coastal communities when salt water falls to the ground.  Geoengineering experiments have also frequently targeted Indigenous communities and their lands. Resistance to geoengineering has come primarily from the Global South and Indigenous Peoples. Every country in Africa (called the “Africa Group” at the United Nations) has called for a “Non-Use Agreement” on solar geoengineering at the U.N. Environment Assembly, echoed by a petition of more than 500 academics who have called for an international Non-Use Agreement. Multiple geoengineering experiments have been blocked by resistance from Indigenous Peoples, including Saami opposition to a Stratospheric Aerosol Injection experiment in Northern Sweden, and Alaska native organizations resisting the deployment of microspheres on the Arctic ice sheet in Alaska.

Is solar geoengineering already being conducted by spraying chemicals in the wake of airplanes (chemtrails)?

No. Concern about chemtrails is common and a frequent topic on social media, but there is no evidence that the airline industry or governments are already deploying solar geoengineering technologies. The long cloud-like trails that often form behind airplanes are actually condensation trails, or “contrails” for short. Contrails form because airplane engines emit water vapor that condenses around soot particles and, due to the heights at which commercial airlines fly, these can freeze into ice crystals and form cirrus clouds. Contrails do not fall to the ground, but they are dangerous for the planet because they trap heat near the surface and contribute to global warming. Contrails particularly contribute to warming the planet at night, and may have an impact on warming similar to or greater than the greenhouse gas emissions from airplanes. Note: this is the opposite effect as that intended by solar geoengineering, which aims to cool the planet by reflecting solar radiation back into space.

Is solar geoengineering legal?

The U.N. Convention on Biological Diversity (CBD) has established a moratorium on geoengineering for most of the world, making exceptions only for small-scale scientific research “conducted in a controlled setting.” The U.S. is one of the only countries that has not ratified the CBD, and no federal law explicitly prohibits or regulates the deployment of solar geoengineering technologies, making the U.S. one of the most exposed countries in the world for private actors to attempt solar geoengineering.

The Environmental Protection Act has extended water pollution laws to regulate “marine solar radiation modification” technologies if they involve dumping any substance into public waters (such as micro-bubbles intended to reflect sun back from the ocean’s surface, or salt-water sprayed to brighten clouds). Attempts to release sulfur dioxide into the stratosphere may trigger Clean Air Act regulations on sulfur pollution, but these existing laws were designed to regulate dumping and pollution, not climate modification technologies.

Is the federal government in the U.S. funding research into solar geoengineering?

Yes. Since 2020 Congress has allocated funds to the National Oceanic and Atmospheric Administration (NOAA) under its Earth’s Radiation Budget (ERB) initiative to develop modeling and measurement tools for solar geoengineering, but the program does not fund open-air experiments currently.

What’s the real solution to the climate crisis?

The idea of engineering our way out of the climate crisis may seem alluring, but it is ultimately a false promise. Geoengineering diverts attention and resources away from renewable energy futures. It is the ultimate dangerous distraction from doing what is unambiguously necessary – a just and equitable fossil fuel phaseout and the radical transformation of our industrial agriculture and land use practices. Learn how to support real climate action.