Geoengineering Climate: Technical Evaluation of Selected Approaches

Two reports will be released on Tuesday, February 10, 2015 as a result of this study: Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, and Climate Intervention: Reflecting Sunlight to Cool Earth. Find more information on the release event here.

The term “geoengineering” is used to describe deliberate, large-scale manipulations of Earth’s environment that might be used to potentially offset some of the consequences of climate change. Learn more about geoengineering. The concept has gained recent attention as a possible backstop measure if other emissions reduction strategies to are not successful or if climate trends become disruptive enough to warrant extreme measures.

Because geoengineering involves manipulating the climate, it raises some societal and ethical controversies. It also poses potential environmental, economic, and national security concerns. Future decisions should be informed by a through scientific understanding of the techniques being discussed, including what they are, how they would work, the expected risks, and possible consequences (intended and unintended).

Frequently Asked Questions About This Study

What is the U.S. National Academy of Sciences?

The National Academy of Sciences is a private, nonprofit institution chartered by Congress in 1863 to provide science, technology, and health policy advice to the government.  It is not part of the U.S. government.  Through its operating arm, the National Research Council, the National Academy of Sciences enlists leading scientists, engineers, and other experts to answer scientific and technical issues facing the United States.  Members of study committees serve as volunteers and are not paid for their service.

What is geoengineering?

Geoengineering is a broad term for deliberate, large-scale manipulations of Earth’s environment that have been proposed as methods to potentially offset some of the consequences of climate change. Climate change is caused by increasing amounts of carbon dioxide and other greenhouse gases in the atmosphere. In general, proposed geoengineering techniques fall into two categories: solar radiation management approaches that aim to change the incoming solar radiation balance, and carbon dioxide removal approaches that would reduce the amount of carbon dioxide in the atmosphere.

Why is the National Academy of Sciences studying geoengineering?

Discussions of geoengineering are often controversial because of the societal, economic, and ethical implications. Those dimensions are critically important, but a first requirement to support informed discussions and decisions is a sound scientific understanding of the proposed techniques, including what they are, how they would work, the expected risks, and the possible consequences (intended and unintended). In particular, there is a need for improved understanding of the physical potential and technical feasibility of geoengineering approaches, as well as an evaluation of the potential consequences of various techniques on other aspects of the Earth system, including ecosystems on land and in the oceans.

Why is the U.S. government interested in geoengineering?

Geoengineering has become a part of the overall public conversation on how society can address the threats posed by climate change.  There has been speculation that geoengineering may possibly be needed if the impacts of climate change were to shift abruptly and result in a “climate emergency.”  There has also been discussion of whether geoengineering should be included as part of an overall portfolio of activities to combat the effects of climate change.

The concept of geoengineering raises a wide array of ethical, legal, and political concerns, including questions on transparent governance of geoengineering research and legal structures that pertain to geoengineering. Several U.S. science agencies have provided support for this study to better inform these various discussions and provide an assessment of the state of the science of geoengineering and its potential consequences, both intended and unintended.

Geoengineering also involves a wide array of national security concerns, including concerns should an independent actor decide to unilaterally deploy a geoengineering technology.  The U.S. government has provided funding for this study to help provide an understanding of the state of the science of geoengineering to inform these various discussions.

What is the goal of the study?

This study is intended to provide a careful, clear scientific foundation that informs ethical, legal, and political discussions surrounding geoengineering.  It will discuss what is known about the science of selected geoengineering techniques, what resources would be required to implement them, the potential risks associated with the technologies, and the potential impacts in general should geoengineering approaches be deployed, including possible environmental, economic, and national security concerns.

The study will also discuss historical examples of related technologies (e.g., cloud seeding and other weather modification) for lessons that might be learned about societal reactions, examine international agreements that may be relevant to the experimental testing or deployment of geoengineering technologies, and identify research needed to provide a credible scientific underpinning for future discussions.

Will NAS develop any geoengineering technologies?

No.  The study is a technical evaluation of proposed geoengineering techniques and general discussion of potential impacts.  This assessment will primarily be based on the peer-reviewed literature, and will not involve any classified information nor any substantial new research.  The study committee will not conduct experiments with proposed geoengineering techniques or develop new technologies.

How will the results of the NAS report be used?

The committee will produce a consensus report with findings and recommendations that will be available to the public upon its release (expected completion date is early 2015) after undergoing a rigorous external peer-review process.  The committee has not been asked to make any recommendations about the adoption or deployment of geoengineering technologies by the United States.  The final report will be delivered to various parts of the U.S. government, including the study sponsors, the U.S. Congress, and the executive branch.

Will the results of the study be available to the public?

Yes.  An electronic version of the final report will be available to download for free at upon completion of the study (early 2015).  In addition, information provided to the committee during the study process is available through the National Academy of Sciences’ Public Access Records Office.  No parts of the final report will be classified.

Where can I get more information?

Click here for details about the study’s scope, full committee membership, and public meetings.

Find background on geoengineering and climate change here.

Please direct any inquiries to the Office of News and Public Information; tel. 202-334-2138 or e-mail

About Geoengineering

Geoengineering encompasses two different classes of approaches: carbon dioxide removal (CDR) and solar radiation management (SRM).  Potential SRM approaches that have been suggested include the deliberate introduction of sulfate aerosols into the stratosphere (e.g., by injection of sulfur dioxide), the enhancement of cloud reflectivity through increasing the number of water droplets in clouds (e.g., by …

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