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  1. Home
  2. Geoengineering

Frequent Questions

On this page: 

  • Does solar geoengineering cool the earth?
  • Has large-scale solar geoengineering deployment already happened?
  • Are there any state level laws or regulations regarding solar geoengineering and weather modification?
  • Are there international regulations governing solar geoengineering?
  • How is solar geoengineering distinct from/related to weather modification?
  • Are contrails related to geoengineering or weather modification?
  • Have any additional concerns been expressed about solar radiation modification?

Does solar geoengineering cool the earth? 

Much of our understanding of the temperature impacts of stratospheric aerosol injection (SAI) comes from observations and modeling of natural analogs. For example, like SAI, volcanic eruptions also inject sulfur dioxide (SO2) into the stratosphere that forms reflective sulfate particles. In 1991, the eruption of Mt. Pinatubo injected about 20 million tons of SO2 into the stratosphere, which is estimated to have cooled the planet for a couple of years by about 0.3 degrees Celsius (0.5 degrees Fahrenheit). [1] 

Has large-scale solar geoengineering deployment already happened? 

No. The U.S. government is not engaged in any form of outdoor solar geoengineering testing (e.g., small-scale experiments designed to study injection technologies) or large-scale deployment (e.g., intentional use of SRM to cool the Earth). Solar geoengineering is not occurring via direct delivery by commercial aircraft and is not associated with aviation contrails. As of July 2025, EPA is aware of only one private sector actor, Make Sunsets, that has actively deployed SAI or MCB in the United States. While there are a few private actors focused on developing different solar geoengineering technologies, the amount of material that has been intentionally released into the atmosphere to date is very small relative to natural events like volcanic eruptions. 

Are there any state level laws or regulations regarding solar geoengineering and weather modification? 

Yes. In June 2025, Florida passed a law “prohibiting certain acts intended to affect the temperature, the weather, or the intensity of sunlight within the atmosphere of this state”, which encompasses both solar geoengineering and traditional weather modification. In 2024, Tennessee passed a similar law banning the intentional modification of sunlight, weather, or temperature. Related bills banning solar geoengineering and weather modification have been recently introduced in many other states, including Texas, Pennsylvania, North Carolina, and Vermont, though not all bills have passed out of their respective committees. Some states have alternatively adopted a narrower scope focused on intentional solar geoengineering, but excluding traditional weather modification techniques like cloud seeding. For example, the Arizona Senate recently passed a bill banning solar radiation management (and not weather modification), and the Montana Senate passed a similar bill that explicitly allowed cloud seeding, but this bill did not advanced past the House.  

Are there international regulations governing solar geoengineering?

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.  

  • In 2023, the Scientific Groups of the London Convention and London Protocol issued a statement that recognized the “potential for deleterious effects” of emerging solar radiation modification techniques. Learn about about marine geoengineering and the London Convention and London Protocol.  

  • The Convention on Biological Diversity issued a moratorium in 2010 (decision X/33), which was reaffirmed in 2024 (decision XI/20) on deployment of geoengineering activities that may affect biodiversity. 

  • Parties to the Montreal Protocol on Substances that Deplete the Ozone Layer have expressed concern over solar geoengineering and are tracking relevant research. A 2022 report (pdf) (35.9 MB) by the World Meteorological Organization discussed the potential effects of solar geoengineering on stratospheric ozone; the Montreal Protocol’s Scientific Assessment Panel provides regular updates on geoengineering techniques for consideration by the parties.  

  • A panel of scientific advisors to the European Union published policy recommendations in December 2024, including an “EU-wide moratorium on the use of SRM” and a call for research on the “full range of direct and indirect effects and unintended impacts of SRM”. 

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. 

How is solar geoengineering distinct from/related to weather modification? 

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]

Federal agencies have more recently supported cloud seeding efforts at the state and regional level to combat droughts and megadroughts. The research efforts being conducted at the federal and state levels are for the purpose of more fully understanding cloud seeding and cloud physics.    

A December 2024 Government Accountability Office (GAO) report notes two recent examples: “[I]n 2023 the Bureau of Reclamation provided a $2.4 million grant to the Southern Nevada Water Authority for cloud seeding operations in Colorado, Utah, and Wyoming intended to benefit the Colorado River and to better understand efficacy of cloud seeding... [and] [t]he National Science Foundation (NSF) awarded nearly $3.5 million to a 2017 Idaho field experiment to observe and model cold season cloud seeding. USDA awarded $100,000 in 2021 to fund research examining seeding using electrostatically-charged water.”  [8]

Today, according to the same GAO report, cloud seeding activities in the U.S. are "primarily funded at the state or local level." [9] As of July 2024, cloud seeding programs were active in nine states: California, Colorado, Idaho, Nevada, New Mexico, North Dakota, Texas, Utah, and Wyoming. Depending on the state, these programs have either been directly supported by state funds, indirectly by state grants to local agencies, or by local revenue or sponsors. Historically, state-sponsored cloud seeding programs were also active in Kansas and South Dakota in the 1970s, but have since been suspended. Ongoing research into the feasibility of cloud seeding is also occurring in other U.S. states, including Arizona and Montana.  

While NOAA does not regulate weather modification activities, it does track them through WMRA reporting requirements. Failure to report under terms of the WMRA can result in fines of up to $10,000. A public database of NOAA weather modification activity reports can be viewed here: Weather Modification Project Reports. 

There are potential negative consequences to weather modification and cloud seeding. For instance, some studies have focused on the extent to which precipitation could increase or decrease outside of the intended area. There are some public health and environmental concerns as well. The 2024 GAO report notes that “[e]xisting research we reviewed, while limited to a handful of recent studies, suggests that silver iodide does not pose an environmental or health concern at current levels,” adding “it is not known whether more widespread use of silver iodide would have an effect on public health or be a risk to the environment.” [10] While silver iodide is nearly insoluble, when it dissolves it releases a small number of silver ions, which, if released at high enough levels, could harm beneficial bacteria in the environment and water resources. There are other, less widely used cloud-seeding agents, and any new agents may be subject to EPA approval. 

Are contrails related to geoengineering or weather modification? 

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.   

Have any additional concerns been expressed about solar radiation modification? 

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

  • The scalability of the platforms and materials required for large-scale deployment

  • The long-term commitment of SRM – material would need to be continually injected into the atmosphere to maintain cooling, since aerosols are naturally removed from the stratosphere within a few years and from the troposphere within days. As a result, stopping SRM could lead to a sudden increase in global temperature

  • Unforeseen, or undesirable changes to weather, such as rainfall, and to the composition of the atmosphere, such as the stratospheric ozone layer

  • Societal impacts and the potential for geopolitical risks 

References

1  Congressional Research Service. (May 9, 2023). Solar Geoengineering and Climate Change.  CRS Report No. R47551.

2 United States Government Accountability Office. (December 2024). Cloud Seeding Technology Assessing Effectiveness and Other Challenges. GAO-25-107328. p. 5

3  United States Government Accountability Office. (November 1, 1979). Federal Weather Modification Efforts Need Congressional Attention. CED-80-5 

4   Atlantic Oceanic and Meteorological Laboratory. (October 12, 2017). 70th Anniversary of the first hurricane seeding experiment. Retrieved July 8, 2025 from: https://www.aoml.noaa.gov/hurricane_blog/70th-anniversary-of-the-first-hurricane-seeding-experiment/ 

5 National Oceanic and Atmospheric Administration. (October 23, 2024). Fact check: Debunking weather modification claims. Retrieved July 8, 2025 from https://www.noaa.gov/news/fact-check-debunking-weather-modification-claims 

6 U.S. Government Printing Office. 1974. 93rd Congress Senate Hearing on Weather Modification, S. Hrg. 93. pg. 87. 

7 National Oceanic and Atmospheric Administration. (October 23, 2024). Fact check: Debunking weather modification claims. Retrieved July 8, 2025 from https://www.noaa.gov/news/fact-check-debunking-weather-modification-claims 

8 United States Government Accountability Office. (December 2024). Cloud Seeding Technology Assessing Effectiveness and Other Challenges. GAO-25-107328. p. 8

9 United States Government Accountability Office. (December 2024). Cloud Seeding Technology Assessing Effectiveness and Other Challenges. GAO-25-107328. p. 6 

10 United States Government Accountability Office. (December 2024).  Cloud Seeding Technology Assessing Effectiveness and Other Challenges.  GAO-25-107328.  p. 18. 

Contact Us About Geoengineering to ask a question, provide feedback, or report a problem.
Last updated on July 10, 2025
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