Frequent Questions

As of July 2025, there is no international framework for governing solar geoengineering research or outdoor experiments and deployment. However, EPA is aware of multiple international agreements that may be relevant to solar geoengineering research and possible deployment.  

Outside of these agreements and recommendations, EPA is not aware of any individual countries that have explicitly banned the deployment of solar geoengineering. Following a release of SO₂-filled balloons by the company Make Sunsets in Mexico in 2022, the Mexican government stated in January 2023 that they plan to develop a strategy to ban outdoor solar geoengineering experimentation but have not finalized new regulations. In addition, the Australian government is supporting research and deployment of Marine Cloud Brightening (MCB) to better shade and cool the ocean water over the Great Barrier Reef.  In addition, the UK recently announced a £50 million government-funded research program focused on geoengineering. 

Weather modification is the intentional modification of regional or local weather patterns. The most common example is cloud seeding, which involves introducing artificial particles into clouds with the objective of increasing rain or snow or modifying regional and local weather patterns. [2] The main difference between weather modification and solar geoengineering is that weather modification is intended to have local, short-term effects, whereas solar geoengineering is intended to have larger regional or global effects that persist. Despite the different intended impacts, there can be overlap between the two definitions in regulatory statutes. For example, weather modification activities reported under the Weather Modification Reporting Act (WMRA) also include the intentional modification of solar radiation, and multiple states are considering bans to both intentional weather and sunlight modification. 

Unlike solar geoengineering, the U.S. federal government and various state governments have historically been involved in weather modification, mainly through cloud seeding activities. Scientists at the General Electric Research Laboratory first demonstrated the basis of cloud seeding in a laboratory setting in the 1940s. After this discovery, the U.S. federal government spent the following decades supporting cloud seeding research and field experiments until funding was cut in the 1980s. [3]

For example, the U.S. government engaged in several weather modification programs that have long-since been discontinued, including:

• Project Cirrus: GE Labs, the Naval Research Laboratory, and Army Signal Corps used Air Force aircraft to conduct the first hurricane cloud seeding experiment with dry ice. In October 1947, the project had two military aircraft dump dry ice into a hurricane off Florida’s coast. [4] While results of that experiment were inconclusive, current science indicates that no existing technology can modify hurricanes. [5]
• Operation Popeye: A classified military weather modification program carried out during the Vietnam War that attempted to extend monsoon season to disrupt select supply routes in North Vietnam and Laos. [6]
• Project Stormfury: Led by NOAA and the U.S. Navy, this program sought to modify hurricane strength through seeding with silver iodide to reduce the most destructive wind speeds. Experiments were carried out on four hurricanes on eight different days between 1961 and 1971. Although the results were considered "positive" at the time, the observed changes were within the expected natural variability of hurricanes. Current science indicates that no existing technology can modify hurricanes. [7]

No. Contrails are line-shaped exhaust clouds or “condensation trails” that are visible behind jet aircraft.  Since aircraft typically fly at high altitudes where it is very cold, the very hot exhaust coming out of the jet engine reacts with the very cold air, sometimes causing an exhaust cloud to form that you can see under certain atmospheric conditions. Jet aircraft form contrails under these atmospheric conditions for the same reason that you can see the exhaust from your vehicle or your own breath on a cold day. The federal government is not aware of there ever being a contrail intentionally formed over the United States for the purpose of geoengineering/weather modification. 

For more information about contrails, the potential impact on climate, and the distinction from “chemtrails”, visit Information on Contrails from Aircraft.   

Yes. While SAI and MCB are approaches discussed by some for large scale SRM, there are considerable challenges and considerations, including: