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  2. Geoengineering

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  • Glossary
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Glossary

Carbon Dioxide Removal (CDR): a subset of geoengineering activities intended to cool the Earth by removing carbon dioxide from the atmosphere and sequestering it deep underground or in the ocean for long periods. CDR techniques can include approaches like direct air capture and ocean-based methods.

Chemtrails: short for “chemical trails," this is a term some people use to inaccurately claim that contrails resulting from routine air traffic are actually an intentional release of dangerous chemicals or biological agents at high altitudes for a variety of nefarious purposes, including population, mind control, or attempts to geoengineer Earth or modify the weather. It should be noted that chemicals are sometimes intentionally sprayed from aircraft for legitimate purposes like firefighting or farming, but these are well-documented occurrences, regulated, and used for specific legitimate purposes. Releases of this type are from low-flying propeller aircraft, not high-altitude jets. EPA proactively works with other federal agencies to monitor air traffic for any and all potential, dangerous activities and will continue to do so. 

Cirrus Cloud Thinning (CCT): a solar geoengineering technique that involves adding small particles to the upper atmosphere to reduce the thickness and lifespan of cirrus clouds, which are high altitude clouds that trap outgoing radiation (heat), similar to the greenhouse effect. Reducing cirrus clouds therefore cools the Earth by trapping less heat.

Cloud Seeding:  a weather modification approach that often involves adding small particles to the lower atmosphere to increase precipitation or decrease hail.

Contrails: short for condensation trails, these line-shaped clouds are sometimes produced by aircraft as hot engine exhaust causes water in the atmosphere to condense and freeze. Most contrails are short-lived, but under high humidity conditions, some contrails can persist for hours and sometimes spread into cirrus clouds. 

DOE: U.S. Department of Energy

Earth's Radiation Budget: a term used to describe the balance of incoming and outgoing radiation (e.g., sunlight and heat) at the top of the atmosphere, which impacts Earth’s climate.

EPA: U.S. Environmental Protection Agency 

Geoengineering: a broad range of activities that intentionally attempt to cool the Earth or remove certain gases from the atmosphere.

Marine Cloud Brightening: a solar geoengineering technique that involves adding small particles to the lower atmosphere to increase the reflectivity of clouds over the ocean.

Marine Protection, Research and Sanctuaries Act (MPRSA) (33 U.S.C. 1401 et seq): regulates the transportation and disposition of material into the ocean and prohibits the dumping of material into the ocean that would unreasonably degrade or endanger human health, welfare, or amenities, or the marine environment, ecological systems, or economic potentialities.

NASA: National Aeronautics and Space Administration 

NOAA: National Oceanic and Atmospheric Administration 

OSTP: U.S. Office of Science and Technology Policy

Solar Geoengineering: A subset of geoengineering activities intended to cool the Earth by intentionally modifying the amount of sunlight reaching Earth’s surface.

Solar Radiation Modification (SRM): see Solar Geoengineering 

SRM Deployment: the intentional use of solar geoengineering to cool the Earth. 

SRM Testing or Outdoor Experiments: small-scale experiments designed to release a small amount of material to the atmosphere over short periods of time. These experiments could be used to validate laboratory or modeling results, test injections technologies, or inform potential deployment strategies.

Stratosphere: the second-lowest layer of Earth’s atmosphere, that extends from roughly 6-50 kilometers (or 4-31 miles) above Earth’s surface.

Stratospheric Aerosol Injection: a solar geoengineering technique that involves adding small reflective particles to the stratosphere to reflect incoming sunlight.

Tropopause: the boundary between the two lowest layers of the atmosphere, the troposphere and the stratosphere. This boundary occurs at roughly 10-15 kilometers (or 6-11 miles) above Earth’s surface.

Troposphere: the lowest layer of Earth’s atmosphere, that extends from roughly 0-10 kilometers (or 0-6 miles) above Earth’s surface.

Weather modification: activities that intentionally attempt to modify regional or local weather patterns. 

Weather modification reporting Act of 1972: (15 U.S.C. § 330 et seq.) – requires all persons intending to engage in weather modification activities in the United States to provide a report to NOAA at least 10 days prior to undertaking the activity. Under the 15 CFR § 908.3, reporting requirements for weather modification encompass solar geoengineering activities “modifying the solar radiation exchange of the earth or clouds, through the release of gases, dusts, liquids, or aerosols into the atmosphere.”

For more information on contrails and chemtrails, visit Information on Contrails from Aircraft.   

Resources to Learn More

DOE-NOAA. (November 2022) Marine Cloud Brightening Workshop Report (pdf) (5.2 mb)

National Academies of Sciences, Engineering, and Medicine (NAS). Considering Climate Interventions. 

U.S. Congressional Research Service (CRS). (May 2023) Solar Geoengineering and Climate Change, CRS Report-R47551. 

U.S. Government Accountability Office (GAO). (September 2010) A Coordinated Strategy Could Focus Federal Geoengineering Research and Inform Governance Efforts. GAO-10-903 

U.S. Government Accountability Office (GAO). (December 2024) Cloud Seeding Technology: Assessing Effectiveness and Other Challenges. GAO-25-107328

U.S. Office of Science and Technology Policy (OSTP). (June 2023) Congressionally Mandated Research Plan and an Initial Research Governance Framework Related to Solar Radiation Modification (pdf) (923 kb) 

Geoengineering

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