The Climate Trade-Offs of Geoengineering


Climate Change
Faculty ResearcherDavid Keith, Professor of Public Policy, Harvard Kennedy School; McKay Professor of Applied Physics, School of Engineering and Applied Sciences, Harvard UniversityPaper Title A Simple Model to Account for Regional Inequalities in the Effectiveness of Solar Radiation Management
CoauthorsJuan Moreno-Cruz, University of Calgary; Katharine Ricke, Carnegie Mellon University

Good intelligence can often prevent bad things from happening, but only if the dots are connected in the right ways.

Two concepts might be said to dominate the language of climate change policy: mitigation and adaptation. But somewhere between reducing the levels of greenhouse gases and learning how to cope with a changed climate lives another, very controversial concept: geoengineering. This is “planetary-scale environmental engineering, particularly engineering aimed at countering the undesired effects of other human activities,” according to a definition offered by David Keith, professor of public policy at Harvard Kennedy School and McKay Professor of Applied Physics at Harvard’s School of Engineering and Applied Sciences.

Geoengineering proposals for climate change range from fertilizing the sea with iron, which would allow increased numbers of microorganisms to capture carbon dioxide from the atmosphere, to afforestation, which would simply require planting enormous numbers of trees.

Perhaps the most important form of geoengineering involves increasing albedo, or the reflectivity, of the earth by introducing aerosols in the atmosphere, a technique known as Solar Radiation Management (srm). The idea may sound like science fiction, but scientists point to the eruption of Mount Pinatubo in the Philippines in the early 1990s, when 20 million tons of sulfur dioxide and ash particles were released into the evidence and had a measurable effect on the earth’s climate, as evidence of srm’s efficacy.

Moreover, Keith has argued, srm could reduce the rate of climate change far more cheaply than cutting emissions, but there are risks that grow as if emissions continue to accumulate carbon in the atmosphere.

But, in large part because of the moral hazard created by geoengineering (if there’s a cheap engineering solution to climate change, why bother with mitigation at all?), it has not been considered widely as a solution.

Keith, who has studied geoengineering for two decades, thinks that’s a mistake and argues that scientists and policymakers need to examine it closely for a number of reasons: Steps toward mitigation are being taken extremely slowly and greenhouse gases are increasing more quickly than predicted; even with all the political will in the world, the desired effect will lag behind the response because of how long emissions persist in the atmosphere; it’s impossible to accurately forecast the damage, economic or otherwise, created by climate change; and with the technology for geoengineering increasingly available, a single country could undertake its own program.

The fact that geoengineering, like climate change itself, would effect different regions in varying ways is examined in Keith’s research paper, “A Simple Model to Account for Regional Inequalities in the Effectiveness of Solar Radiation Management,” written with Juan Moreno-Cruz, of the University of Calgary, and Katharine Ricke, of Carnegie Mellon University.

The researchers created a model to examine the effects of srm on the temperature and precipitation of various regions. To further explore the regional impact, they added another analytic layer that weighted changes according to three social objectives: egalitarian, where each region is weighted by population; utilitarian, where regions are weighted by economic output; and ecocentric, where regions are weighted by their total area.

In other words, they created a model that would allow them to analyze the sort of trade-offs that would inevitably arise if geoengineering were considered as policy.

The researchers found that according to their model, srm worked surprisingly well at restoring overall temperatures and precipitation to their baselines (99 percent and 97 percent respectively). But the trade-offs become evident when regional and socioeconomic differences or combinations of temperature and precipitation were taken into account. For example, southern Asia would require a lower level of srm than northern Europe because it cools more quickly. “So, if changes were weighted by population — in which Southern Asia is dominant — less srm would be optimal than if changes are weighted by economic output in which Northern Europe is dominant.”

Keith and his coauthors concluded that although inequalities were important, they were not as severe as might be assumed. But their research also demonstrates the need to continue exploring the science and policy of geoengineering — both because of its overall effects and because it will inevitably create relative winners and losers.

— by Robert O'Neill

Keith and his coauthors concluded that although inequalities were important, they were not as severe as might be assumed.

John F. Kennedy School of Government 79 John F. Kennedy Street
Cambridge, MA 02138
617-495-1100 Get Directions Visit Contact Page