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Spring/Summer 2015 Vol. 15 Number 1

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Climate Intervention

Manipulating the Climate Through Certain Technologies Not Viable at Present

The mounting evidence indicating that our climate is changing rapidly -- and pointing to human activity as the culprit -- has prompted scientists to begin asking whether humans can also prevent its worst impacts.

One set of options that has recently gained traction is known as "geoengineering," or purposefully manipulating the climate to halt certain effects of climate change. Two proposed classes of techniques in particular have received the most attention: removing carbon dioxide from the atmosphere -- which addresses the root cause of climate change -- and reflecting sunlight back to space to cool the Earth.

After reviewing these methods for technological readiness, cost, and risk, an Academies committee concluded that neither is currently ready for large-scale deployment, and that mitigation by reducing carbon emissions together with adaptation is still the safest, most effective way to ease the impacts of climate change.

The committee also said that the term "geoengineering" implies having precise control over the climate and instead preferred the term "climate intervention" to more accurately convey that these technologies could modify the climate in different ways to lessen the impacts of climate change.

The two types of intervention strategies differ in almost every aspect. Carbon dioxide removal is currently prohibitively expensive and would only produce modest effects on the climate over decades; using aerosols to block sunlight -- known as albedo modification -- is relatively inexpensive and could have a substantial impact within a short time. Carbon dioxide removal would likely require cooperation among many countries, and its risks are minimal and generally well-characterized, while albedo modification could be implemented suddenly and unilaterally, but it likely presents serious risks, known and unknown. These differences led the committee to evaluate the strategies separately and recommend different paths forward for each set of techniques.

Because cost and technological immaturity are the major obstacles facing carbon dioxide removal, increased investment in research and development could help develop techniques that are efficient and affordable, as well as enable better understanding of the risks that do exist, such as how ocean iron fertilization, which raises the rate of CO2 absorption by ocean plant life, could affect marine ecology.

Albedo modification, on the other hand, raises serious social, political, and ethical concerns. Many of the natural processes most relevant to albedo modification, such as the formation of clouds and aerosols in the atmosphere, are among the most difficult components of the climate system to model and monitor, making it challenging to predict the effects of this intervention on weather, climate, or other Earth systems. Furthermore, albedo modification doesn't counteract the rising concentration of greenhouse gases in the atmosphere, so it wouldn't resolve related climate change issues such as ocean acidification. If deployed in the absence of efforts to reduce carbon emissions, albedo modification would have to continue perpetually; a sudden termination would reintroduce all of the problems associated with a warming climate.

The committee recommended against using albedo modification at this time, but additional research to better understand these uncertainties is needed in the event that deployment becomes a necessary climate response in the future or if a lone actor pursues the technology. Much of the required research overlaps with basic climate research.

Any research, including potential small-scale field experiments, should be subject to a deliberative process, which should involve a broad set of stakeholders to examine what types of governance models are needed beyond those already in place, and what research would require such oversight based on its expected environmental impact and other potential direct and indirect effects.

-- Lauren Rugani

Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration.

Climate Intervention: Reflecting Sunlight to Cool Earth.

Committee on Geoengineering Climate: Technical Evaluation and Discussion of Impacts, Board on Atmospheric Sciences and Climate and Ocean Studies Board, Division on Earth and Life Studies. The committee was chaired by Marcia McNutt, editor-in-chief at Science and former director of the U.S. Geological Survey. The study was funded by the National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, U.S. Department of Energy, the intelligence community, and the National Academy of Sciences.

Both reports are available from the National Academies Press, tel. 1-800-624-6242 or on the Internet at <>.

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