2013 Keith_A Case for Climate Engineering

Briefing Document: A Case for Climate Engineering by David Keith

Overview

"A Case for Climate Engineering" by David Keith (2013) presents a detailed argument for the consideration and potential implementation of solar geoengineering, specifically stratospheric aerosol injection, as a tool to manage climate risk. Keith, an "oddball environmentalist" and "tinkerer and technophile," approaches the topic from a background in physics and a long-standing interest in climate and energy. He advocates for a nuanced discussion of geoengineering, separating it from carbon removal technologies due to their distinct scientific, technological, cost, and risk profiles. The book explores the technical feasibility, potential benefits, risks, economic implications, and ethical/political challenges associated with deploying solar geoengineering. Keith emphasizes that while geoengineering is not a perfect solution and should not replace emission cuts, it offers a "plausible scenario for managing the human and ecological risks of climate change in a world without politics."

Main Themes and Key Ideas

1. Technical Feasibility and Low Cost of Solar Geoengineering

• Simplicity and Affordability: Keith asserts that cooling the planet by injecting reflective sulfuric acid particles into the upper atmosphere is "cheap and technically easy." The initial deployment could be achieved in a few years for the cost of a "Hollywood blockbuster."
• Mechanism: The process involves injecting tiny watery droplets of sulfuric acid (about a thousand times smaller than a human hair) into the stratosphere, approximately 20 kilometers above Earth's surface. These droplets scatter sunlight back into space, creating a "thin sunshade" that partially offsets the warming effect of greenhouse gases. Sulfuric acid is used to prevent the droplets from evaporating in the dry stratosphere; they persist for about a year and must be continuously replenished.
• Scaling Up: To offset half of the annual growth in warming, approximately 25 thousand tons of sulfur would be needed per year initially, rising to 250 thousand tons per year after a decade (by 2030) and over a million tons per year by 2070.
• Deployment Hardware: While specialized hardware does not currently exist, the capability to engineer and build the necessary aircraft and dispersal technology within a few years is present. Retrofitted business jets like the Gulfstream G650 could be used initially, with purpose-built aircraft later reducing costs. The direct cost of a large-scale program, even after half a century, would be "less than one percent of what we now spend on clean energy development" (around $1 billion per year for one million tons of material).
• Comparison to Natural Events: Our understanding of risks is informed by real-world events. For instance, the 1991 Mount Pinatubo eruption injected eight million tons of sulfur into the stratosphere, and humans annually pump approximately fifty million tons of sulfur into the atmosphere as air pollution. This provides "strong empirical basis on which to assess these risks."
• Reversibility: Unlike releasing genetically engineered species, sulfate injections are not irreversible; if stopped, the sulfates would disappear from the stratosphere in a few years.
• "Big Droplet Problem" and Solutions: Continuous injection of sulfur dioxide can lead to larger, less effective aerosol particles. A potential solution is the "direct aerosol" sulfuric acid method, releasing sulfuric acid vapor from aircraft, which encourages the formation of new, smaller, more efficient droplets. This method could require less than half the sulfur of the sulfur dioxide method for the same radiative forcing, meaning "less sulfur should mean less environmental risk."
• Advanced Technologies: Keith discusses speculative future technologies such as "nano-structured particles" that could scatter more sunlight per unit mass, or "photophoretic effect" particles that levitate in the upper atmosphere, potentially avoiding direct impact on the ozone layer. However, these are not ready for immediate implementation.

2. Climate Risk and Inevitable Warming

• Serious, Not Catastrophic (Yet): While acknowledging climate change as a serious risk, Keith pushes back against "claims of imminent doom" or "game over for the planet" rhetoric, which he views as lacking scientific basis and appealing to "millennial fears."
• Unprecedented Rate of Change: Industrial humanity is a "geological force driving change at unprecedented rates." Half of all human carbon dioxide emissions occurred in the last quarter century, pushing CO2 concentrations to levels not seen since the Eocene era (35 million years ago), when crocodilians inhabited the Canadian Arctic.
• Inertia in Climate and Economy: Even with dramatic efforts to decarbonize the energy system today, "we would not see most the benefits of reduced climate change until late this century" due to the combined inertia of the carbon cycle and the human economy (e.g., long lifetimes of industrial capital stock).
• Climate Sensitivity Uncertainty: There is significant uncertainty in predicting the exact amount of warming for a given amount of emissions ("climate sensitivity"). A thousand billion tons of carbon emissions this century (keeping current rates) could lead to warming anywhere from below 1 degree Celsius to above 4 degrees Celsius, with the "most likely outcome is somewhat above the 2 degree mark."

3. Benefits and Limitations of Solar Geoengineering

• Substantial Risk Reduction: Geoengineering can "substantially reduce many of the most important climatic changes and their associated risks." It can moderate global average temperature, reduce regional changes in precipitation and temperature, and even "halt or even reverse the loss of Arctic sea ice."
• Partial Solution: Geoengineering "does nothing to stop ocean acidification and cannot perfectly compensate for the multidimensional climate changes produced by greenhouse gases." It's an imperfect fix.
• Proposed Usage: Keith suggests a "slow ramp scenario" that would aim to "offset only half the warming." This approach "tips the scales away from risks and toward benefits" and "has the advantage of preserving a direct incentive to cut emissions."
• Addressing Monsoon Concerns: Keith refutes criticisms that geoengineering would disrupt the Asian and African monsoons. He argues that many models show "harmful precipitation increases" in the Asian monsoon region due to climate change, and if geoengineering can slow or stop this, "then it is delivering a benefit, not a harm." The claim that geoengineering reduces precipitation is often based on the assumption it would be used to stop all warming.

4. Risks and Unintended Consequences

• Ozone Layer Damage: Injecting sulfates into the stratosphere will "likely increase the damage to the ozone layer."
• Air Pollution: Descending sulfate particles will "contribute to air pollution." While less concentrated than industrial pollution, "if we begin putting a million tons of sulfur into the stratosphere each year, it will probably contribute to thousands of air pollution deaths a year." Keith suggests geoengineering "presumably would save more lives than it would take because it would reduce climate risks that kill by heat stress, floods, or famine," but acknowledges the "moral concerns as different people will die."
• Regional Disparities: While geoengineering will likely reduce damage in most regions, "even in the best case geoengineering will make some regions worse off, perhaps by increasing drought."
• Unknown Unknowns: The "largest concern is not the risks we know but rather a sensible fear of the unknown-unknowns that may surprise us."
• Impact on Solar Power: Sulfates create a "high layer of haze," increasing diffuse light. This could "decrease the effectiveness of concentrating solar power plants."
• Extreme Leverage: These technologies give humanity "unprecedented leverage over global climate, and that leverage can be used for good or ill." In a "theoretical worst-case," advanced geoengineering could "create a worldwide Ice Age, a snowball earth." This potential disruption is "greater than the environmental disruption that could be achieved with the world’s nuclear weapons."

5. Ethical, Political, and Social Considerations

• Social Readiness vs. Technical Readiness: Technology advances faster than "our ability to absorb it." The hardware could be ready by 2020, but we lack "the social tools to make sound collective decisions about planetary management." Meaningful deployment likely won't begin until 2025, "and, more realistically, 2035 with missteps and surprises."
• The "Geo-clique" and Groupthink: Keith acknowledges the "thin record of serious analysis of geoengineering" and the "danger of group-think" among the small group of scientists (including himself) who have been involved, dubbed the "geo-clique."
• Moral Hazard (Risk Compensation): Keith clarifies that the concern that geoengineering will reduce incentives for emissions cuts is more accurately described as "risk compensation," not "moral hazard." He argues that "it would be perverse in the extreme to argue that risk compensation justifies withholding condoms or seatbelts." If climate risk is reduced, it is "sensible" from a utilitarian perspective for policy to reflect that by slowing emissions cuts, as "less risk means less resources expended to insure against the risk."
• Legitimacy and Governance: Keith argues that concerns about equity arise "more sharply from questions about the legitimacy of decision making in the use of solar geoengineering, rather than the inherent limits of the technique itself."
• Centralized Control vs. Regional Autonomy: Geoengineering "seems to demand centralized control. But whose hand will be on the thermostat?" Regional climates are highly interconnected, making independent regional control "impossible." Technologies allowing regional control, like cloud brightening, "might be more curse than blessing" in a world without strong international governance. For example, efforts by China to boost its monsoon might weaken India's, leading to conflict between nuclear powers.
• Power Dynamics and "Leveling Technology": The low cost of geoengineering makes it accessible to "most nations." This makes it a "leveling technology in the same ambiguous sense as the internet or nuclear weapons," potentially diffusing power away from the wealthiest nations. This "is disturbing in its potential to lead to international conflict."
• Motivation Beyond Environmental Limits: Keith suggests that humanity's historical tendency is to use technology not just to limit environmental impact, but to "increase what an ecologist might call the planet’s carrying capacity for our species enabling an expansion in global consumption." He quotes Nobel Laureate Tom Schelling, who noted in 1982 that interest in geoengineering might "flourish independent of whatever is done about CO2."
• Value-Driven Decisions: Keith emphasizes that "knowledge alone does not tell us what we should do about climate change." Scientists who present recommendations as purely objective are "abusing public trust," as their "value judgments have at least as large a role as facts." He expresses personal skepticism about the utilitarian economic framing of climate policy that underpins much of the mainstream debate, finding it "utterly unconvincing" as a sole justification. He believes decisions about managing the natural world "will influence the values of future generations, perhaps profoundly."

Conclusion

Keith concludes that solar geoengineering, while a "joyless choice between unpleasant alternatives," represents a powerful new capacity for humanity. He urges serious research into the technology now to be prepared for "unpleasant surprises in the greenhouse." Despite the significant risks and complex political challenges, he maintains that the technical ease and low cost of stratospheric aerosol injection make it a tool that deserves serious consideration as part of a broader climate risk management strategy, not as a substitute for emissions reductions, but as a potential means to reduce the severity of climate impacts.

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