Publications

    Anthony R. Harding, Mariia Belaia, and David W. Keith. 6/14/2022. “The Value of Information About Geoengineering and the Two-Sided Cost of Bias.” Climate Policy, Pp. 1-11. Publisher's VersionAbstract
    Solar geoengineering (SG) might be able to reduce climate risks if used to supplement emissions cuts and carbon removal. Yet, the wisdom of proceeding with research to reduce its uncertainties is disputed. Here, we use an integrated assessment model to estimate that the value of information that reduces uncertainty about SG efficacy. We find the value of reducing uncertainty by one-third by 2030 is around $4.5 trillion, most of which comes from reduced climate damages rather than reduced mitigation costs. Reducing uncertainty about SG efficacy is similar in value to reducing uncertainty about climate sensitivity. We analyse the cost of over-confidence about SG that causes too little emissions cuts and too much SG. Consistent with concerns about SG’s moral hazard problem, we find an over-confident bias is a serious and costly concern; but, we also find under-confidence that prematurely rules out SG can be roughly as costly. Biased judgments are costly in both directions. A coin has two sides. Our analysis quantitatively demonstrates the risk-risk trade-off around SG and reinforces the value of research that can reduce uncertainty.
    A. P. Behrer, R. J. Park, C. M. Golja, D. W. Keith, and G. Wagner. 9/15/2021. “Heat has larger impacts on labor in poorer areas.” Environmental Research Communications, 3, 095001. Publisher's VersionAbstract
    Hotter temperature can reduce labor productivity, work hours, and labor income. The effects of heat are likely to be a joint consequence of both exposure and vulnerability. Here we explore the impacts of heat on labor income in the US, using regional wealth as a proxy for vulnerability. We find that one additional day >32 °C (90 °F) lowers annual payroll by 0.04%, equal to 2.1% of average weekly earnings. Accounting for humidity results in slightly more precise estimates. Proxying for wealth with dividend payments we find smaller impacts of heat in counties with higher average wealth. Temperature projections for 204050 suggest that earnings impacts may be 95% smaller for US counties in the richest decile relative to the poorest. Considering the within country distribution of vulnerability, in addition to exposure, to climate change could substantially change estimated within-country differences between the rich and poor in income losses from climate change.
    Tyler Felgenhauer, Joshua Horton, and David Keith. 2021. “Solar geoengineering research on the U.S. policy agenda: when might its time come?” Environmental Politics, Pp. 1–21. Publisher's VersionAbstract
    Solar geoengineering (SG) may be a helpful tool to reduce harms from climate change, yet further research into its potential benefits and risks must occur prior to any implementation. So far, however, organized research on SG has been absent from the U.S. national policy agenda. We apply the Multiple Streams Approach analytical framework to explain why a U.S. federal SG research program has failed to materialize up to now, and to consider how one might emerge in the future. We argue that establishing a federal program will require the formation of an advocacy coalition within the political arena that is prepared to support such a policy objective. A coalition favoring federal research on SG does not presently exist, yet the potential nucleus of a future political grouping is evident in the handful of ‘pragmatist’ environmental organizations that have expressed conditional support for expanded research.
    Peter Irvine, Elizabeth Burns, Ken Caldeira, Frank Keutsch, Dustin Tingley, and David Keith. 2021. “Expert judgments on solar geoengineering research priorities and challenges.” EarthArXiv. Publisher's VersionAbstract
    Solar geoengineering describes a set of proposals to deliberately alter the earth’s radiative balance to reduce climate risks. We elicit judgements on natural science research priorities for solar geoengineering through a survey and in-person discussion with 72 subject matter experts, including two thirds of all scientists with ≥10 publications on the topic. Experts prioritized Earth system response (33%) and impacts on society and ecosystems (27%) over the human and social dimensions (17%) and developing or improving solar geoengineering methods (15%), with most allocating no effort to weather control or counter-geoengineering. While almost all funding to date has focused on geophysical modeling and social sciences, our experts recommended substantial funding for observations (26%), perturbative field experiments (16%), laboratory research (11%) and engineering for deployment (11%). Of the specific proposals, stratospheric aerosols received the highest average priority (34%) then marine cloud brightening (17%) and cirrus cloud thinning (10%). The views of experts with ≥10 publications were generally consistent with experts with <10 publications, though when asked to choose the radiative forcing for their ideal climate scenario only 40% included solar geoengineering compared to 70% of experts with <10 publications. This suggests that those who have done more solar geoengineering research are less supportive of its use in climate policy. We summarize specific research recommendations and challenges that our experts identified, the most salient of which were fundamental uncertainties around key climate processes, novel challenges related to solar geoengineering as a design problem, and the challenges of public and policymaker engagement.
    Joshua B. Horton, Penehuro Lefale, and David Keith. 10/10/2020. “Parametric Insurance for Solar Geoengineering: Insights from the Pacific Catastrophe Risk Assessment and Financing Initiative.” Global Policy, Special Issue. Publisher's VersionAbstract
    Solar geoengineering (SG) entails using technology to modify the Earth's radiative balance to offset some of the climate changes caused by long‐lived greenhouse gases. Parametric insurance, which delivers payouts when specific physical indices (such as wind speed) cross predefined thresholds, was recently proposed by two of us as a compensation mechanism for SG with the potential to ease disagreements about the technology and to facilitate cooperative deployment; we refer to this proposal as reduced‐rate climate risk insurance for solar geoengineering, or ‘RCG’. Here we probe the plausibility of RCG by exploring the Pacific Catastrophe Risk Assessment and Financing Initiative (PCRAFI), a sovereign risk pool providing parametric insurance coverage against tropical cyclones and earthquakes/tsunamis to Pacific island countries since 2013. Tracing the history of PCRAFI and considering regional views on insurance as compensation necessitates reconfiguring RCG in a way that shifts the focus away from bargaining between developed and developing countries toward bargaining among developed countries. This revised version of RCG is challenged by an assumption of broad developed country support for sovereign climate insurance in the developing world, but it also better reflects the underlying incentive structure and distribution of power.
    Joshua B. Horton and Barbara Koremenos. 8/31/2020. “Steering and Influence in Transnational Climate Governance: Nonstate Engagement in Solar Geoengineering Research.” Global Environmental Politics, 20, 3, Pp. 93-111. Publisher's VersionAbstract
    Theorists of transnational climate governance (TCG) seek to account for the increasing involvement of nonstate and substate actors in global climate policy. While transnational actors have been present in the emerging field of solar geoengineering—a novel technology intended to reflect a fraction of sunlight back to space to reduce climate impacts—many of their most significant activities, including knowledge dissemination, scientific capacity building, and conventional lobbying, are not captured by the TCG framework. Insofar as TCG is identified with transnational governance and transnational governance is important to reducing climate risks, an incomplete TCG framework is problematic for effective policy making. We attribute this shortcoming on the part of TCG to its exclusive focus on steering and corollary exclusion of influence as a critical component of governance. Exercising influence, for example, through inside and outside lobbying, is an important part of transnational governance—it complements direct governing with indirect efforts to inform, persuade, pressure, or otherwise influence both governor and governed. Based on an empirical analysis of solar geoengineering research governance and a theoretical consideration of alternative literatures, including research on interest groups and nonstate advocacy, we call for a broader theory of transnational governance that integrates steering and influence in a way that accounts for the full array of nonstate and substate engagements beyond the state.
    Jesse L. Reynolds and Joshua B. Horton. 2/2020. “An earth system governance perspective on solar geoengineering.” Earth System Governance, 3.Abstract
    Solar geoengineering appears capable of reducing climate change and the associated risks. In part because it would be global in effect, the governance of solar geoengineering is a central concern. The Earth System Governance (ESG) Project includes many researchers who, to varying degrees, utilize a common vocabulary and research framework. Despite the clear mutual relevance of solar geoengineering and ESG, few ESG researchers have considered the topic in substantial depth. To stimulate its sustained uptake as a subject within the ESG research program, we identify significant contributions thus far by ESG scholars on the subject of solar geoengineering governance and survey the wider solar geoengineering governance literature from the perspective of the new ESG research framework. Based on this analysis, we also suggest specific potential lines of inquiry that we believe are ripe for research by ESG scholars: nonstate actors’ roles, polycentricity, public engagement and participation, and the Anthropocene.
    Douglas MacMartin, Peter Irvine, Ben Kravitz, and Joshua Horton. 9/23/2019. “Technical characteristics of a solar geoengineering deployment and implications for governance.” Climate Policy, 19, 10, Pp. 1325-1339. Publisher's VersionAbstract
    Consideration of solar geoengineering as a potential response to climate change will demand complex decisions. These include not only the choice of whether to deploy solar engineering, but decisions regarding how to deploy, and ongoing decisionmaking throughout deployment. Research on the governance of solar geoengineering to date has primarily engaged only with the question of whether to deploy. We examine the science of solar geoengineering in order to clarify the technical dimensions of decisions about deployment – both strategic and operational – and how these might influence governance considerations, while consciously refraining from making specific recommendations. The focus here is on a hypothetical deployment rather than governance of the research itself. We first consider the complexity surrounding the design of a deployment scheme, in particular the complicated and difficult decision of what its objective(s) would be, given that different choices for how to deploy will lead to different climate outcomes. Next, we discuss the on-going decisions across multiple timescales, from the sub-annual to the multi-decadal. For example, feedback approaches might effectively manage some uncertainties, but would require frequent adjustments to the solar geoengineering deployment in response to observations. Other decisions would be tied to the inherently slow process of detection and attribution of climate effects in the presence of natural variability. Both of these present challenges to decision-making. These considerations point toward particular governance requirements, including an important role for technical experts – with all the challenges that entails.
    David Keith and Joshua Horton. 4/23/2019. “Multilateral parametric climate risk insurance: a tool to facilitate agreement about deployment of solar geoengineering?” Climate Policy. Publisher's VersionAbstract
    States will disagree about deployment of solar geoengineering, technologies that would reflect a small portion of incoming sunlight to reduce risks of climate change, and most disagreements will be grounded in conflicting interests. States that object to deployment will have many options to oppose it, so states favouring deployment will have a powerful incentive to meet their objections. Objections rooted in opposition to the anticipated unequal consequences of deployment may be met through compensation, yet climate policy is inhospitable to compensation via liability. We propose that multilateral parametric climate risk insurance might be a useful tool to facilitate agreement on solar geoengineering deployment. With parametric insurance, predetermined payouts are triggered when climate indices deviate from set ranges. We suggest that states favouring deployment could underwrite reduced-rate parametric climate insurance. This mechanism would be particularly suited to resolving disagreements based on divergent judgments about the outcomes of proposed implementation. This would be especially relevant in cases where disagreements are rooted in varying levels of trust in climate model predictions of solar geoengineering effectiveness and risks. Negotiations over the pricing and terms of a parametric risk pool would make divergent judgments explicit and quantitative. Reduced-rate insurance would provide a way for states that favour implementation to demonstrate their confidence in solar geoengineering by underwriting risk transfer and ensuring compensation without the need for attribution. This would offer a powerful incentive for states opposing implementation to moderate their opposition.
    Gernot Wagner and Martin L. Weitzman. 7/2018. “Potentially large equilibrium climate sensitivity tail uncertainty.” Economics Letters, 168, Pp. 144-6. Publisher's VersionAbstract
    Equilibrium climate sensitivity (ECS), the link between concentrations of greenhouse gases in the atmosphere and eventual global average temperatures, has been persistently and perhaps deeply uncertain. Its ‘likely’ range has been approximately between 1.5 and 4.5 degrees Centigrade for almost 40 years (Wagner and Weitzman, 2015). Moreover, Roe and Baker (2007), Weitzman (2009), and others have argued that its right-hand tail may be long, ‘fat’ even. Enter Cox et al. (2018), who use an ’emergent constraint’ approach to characterize the probability distribution of ECS as having a central or best estimate of 2.8℃ with a 66% confidence interval of 2.2-3.4℃. This implies, by their calculations, that the probability of ECS exceeding 4.5℃ is less than 1%. They characterize such kind of result as “renewing hope that we may yet be able to avoid global warming exceeding 2[℃]”. We share the desire for less uncertainty around ECS (Weitzman, 2011; Wagner and Weitzman, 2015). However, we are afraid that the upper-tail emergent constraint on ECS is largely a function of the assumed normal error terms in the regression analysis. We do not attempt to evaluate Cox et al. (2018)’s physical modeling (aside from the normality assumption), leaving that task to physical scientists. We take Cox et al. (2018)’s 66% confidence interval as given and explore the implications of applying alternative probability distributions. We find, for example, that moving from a normal to a log-normal distribution, while giving identical probabilities for being in the 2.2-3.4℃ range, increases the probability of exceeding 4.5℃ by over five times. Using instead a fat-tailed Pareto distribution, an admittedly extreme case, increases the probability by over forty times.
    Thomas Stoerk, Gernot Wagner, and Robert ET Ward. 6/4/2018. “Recommendations for Improving the Treatment of Risk and Uncertainty in Economic Estimates of Climate Impacts in the Sixth Intergovernmental Panel on Climate Change Assessment Report.” Review of Environmental Economics and Policy. Publisher's VersionAbstract
    Large discrepancies persist between projections of the physical impacts of climate change and economic damage estimates. These discrepancies increase with increasing global average temperature projections. Based on this observation, we recommend that in its Sixth Assessment Report (AR6), the Intergovernmental Panel on Climate Change (IPCC) improve its approach to the management of the uncertainties inherent in climate policy decisions. In particular, we suggest that the IPCC (1) strengthen its focus on applications of decision making under risk, uncertainty, and outright ambiguity and (2) estimate how the uncertainty itself affects its economic and financial cost estimates of climate damage and, ultimately, the optimal price for each ton of carbon dioxide released. Our hope is that by adopting these recommendations, AR6 will be able to resolve some of the documented inconsistencies in estimates of the physical and economic impacts of climate change and more effectively fulfill the IPCC’s mission to provide policymakers with a robust and rigorous approach for assessing the potential future risks of climate change.
    Sebastian D. Eastham, Debra K. Weisenstein, David W. Keith, and Steven R. H. Barrett. 5/25/2018. “Quantifying the impact of sulfate geoengineering on mortality from air quality and UV-B exposure.” Atmospheric Environment. Publisher's VersionAbstract
    Sulfate geoengineering is a proposed method to partially counteract the global radiative forcing from accumulated greenhouse gases, potentially mitigating some impacts of climate change. While likely to be effective in slowing increases in average temperatures and extreme precipitation, there are known side-effects and potential unintended consequences which have not been quantified. One such consequence is the direct human health impact. Given the significant uncertainties, we take a sensitivity approach to explore the mechanisms and range of potential impacts. Using a chemistry-transport model, we quantify the steady-state response of three public health risks to 1 °C global mean surface cooling. We separate impacts into those which are “radiative forcing-driven”, associated with climate change “reversal” through modification of global radiative forcing, and those “direct impacts” associated uniquely with using sulfate geoengineering to achieve this. We find that the direct (non-radiative forcing driven) impact is a decrease in global mortality of ∼13,000 annually. Here the benefits of reduced ozone exposure exceed increases in mortality due to UV and particulate matter, as each unit of injected sulfur incurs 1/25th the particulate matter exposure of a unit of sulfur emitted from surface sources. This reduction is exceeded by radiative forcing-driven health impacts resulting from using sulfate geoengineering to offset 1 °C of surface temperature rise. Increased particulate matter formation at these lower temperatures results in ∼39,000 mortalities which would have been avoided at higher temperatures. As such we estimate that sulfate geoengineering in 2040 would cause ∼26,000 (95% interval: −30,000 to +79,000) early deaths annually relative to the same year without geoengineering, largely due to the loss of health benefits associated with CO2-induced warming. These results account only for impacts due to changes in air quality and UV-B flux. They do not account for non-mortality impacts or changes in atmospheric dynamics, and must be considered in the wider context of other climate change impacts such as heatwave frequency and sea level rise.
    Sebastian D. Eastham, David W. Keith, and Steven R. H. Barrett. 3/9/2018. “Mortality tradeoff between air quality and skin cancer from changes in stratospheric ozone.” Environmental Research Letters, 13, 3. Publisher's VersionAbstract
    Skin cancer mortality resulting from stratospheric ozone depletion has been widely studied. Similarly, there is a deep body of literature on surface ozone and its health impacts, with modeling and observational studies demonstrating that surface ozone concentrations can be increased when stratospheric air mixes to the Earth's surface. We offer the first quantitative estimate of the trade-off between these two effects, comparing surface air quality benefits and UV-related harms from stratospheric ozone depletion. Applying an idealized ozone loss term in the stratosphere of a chemistry-transport model for modern-day conditions, we find that each Dobson unit of stratospheric ozone depletion results in a net decrease in the global annual mortality rate of ~40 premature deaths per billion population (d/bn/DU). The impacts are spatially heterogeneous in sign and magnitude, composed of a reduction in premature mortality rate due to ozone exposure of ~80 d/bn/DU concentrated in Southeast Asia, and an increase in skin cancer mortality rate of ~40 d/bn/DU, mostly in Western Europe. This is the first study to quantify air quality benefits of stratospheric ozone depletion, and the first to find that marginal decreases in stratospheric ozone around modern-day values could result in a net reduction in global mortality due to competing health impact pathways. This result, which is subject to significant methodological uncertainty, highlights the need to understand the health and environmental trade-offs involved in policy decisions regarding anthropogenic influences on ozone chemistry over the 21st century.
    Kristina Mohlin, Jonathan R. Camuzeaux, Adrian Muller, Marius Schneider, and Gernot Wagner. 2/12/2018. “Factoring in the forgotten role of renewables in CO2 emission trends using decomposition analysis.” Energy Policy, 116, Pp. 290–296. Publisher's VersionAbstract
    This paper introduces an approach for separately quantifying the contributions from renewables in decomposition analysis. So far, decomposition analyses of the drivers of national CO2 emissions have typically considered the combined energy mix as an explanatory factor without an explicit consideration or separation of renewables. As the cost of renewables continues to decrease, it becomes increasingly relevant to track their role in CO2 emission trends. Index decomposition analysis, in particular, provides a simple approach for doing so using publicly available data. We look to the U.S. as a case study, highlighting differences with the more detailed but also more complex structural decomposition analysis. Between 2007 and 2013, U.S. CO2 emissions decreased by around 10%—a decline not seen since the oil crisis of 1979. Prior analyses have identified the shale gas boom and the economic recession as the main explanatory factors. However, by decomposing the fuel mix effect, we conclude that renewables played an equally important role as natural gas in reducing CO2 emissions between 2007 and 2013: renewables decreased total emissions by 2.3–3.3%, roughly matching the 2.5–3.6% contribution from the shift to natural gas, compared with 0.6–1.5% for nuclear energy.
    J. Paul Kelleher and Gernot Wagner. 2/2018. “Ramsey discounting calls for subtracting climate damages from economic growth rates.” Applied Economics Letters. Publisher's VersionAbstract
    The Ramsey equation ties the utility discount rate and the elasticity of marginal utility of consumption together with per capita consumption growth rates to calculate consumption discount rates. For many applications, per capita consumption growth rates can be approximated with per capita output growth rates. That approximation does not work for climate change, which drives an ever-increasing and increasingly uncertain wedge between output and consumption growth. NAS (2017), in a central recommendation and illustrative example, conflates the two. The correct, consumption-based discounting method generally decreases consumption discount rates and, thus, increases the resulting Social Cost of Carbon Dioxide (SC-CO2).
    Paul Bodnar, Caroline Ott, Rupert Edwards, Stephan Hoch, Emily F. McGlynn, and Gernot Wagner. 12/4/2017. “Underwriting 1.5°C: competitive approaches to financing accelerated climate change mitigation.” Climate Policy. Publisher's VersionAbstract

    Delivering emission reductions consistent with a 1.5°C trajectory will require innovative public financial instruments designed to mobilize trillions of dollars of low-carbon private investment. Traditional public subsidy instruments such as grants and concessional loans, while critical to supporting nascent technologies or high-capital-cost projects, do not provide the price signals required to shift private investments towards low-carbon alternatives at a scale. Programmes that underwrite the value of emission reductions using auctioned price floors provide price certainty over long time horizons, thus improving the cost-effectiveness of limited public funds while also catalysing private investment.

    Taking lessons from the World Bank’s Pilot Auction Facility, which supports methane and nitrous oxide mitigation projects, and the United Kingdom’s Contracts for Difference programme, which supports renewable energy deployment, we show that auctioned price floors can be applied to a variety of sectors with greater efficiency and scalability than traditional subsidy instruments. We explore how this new class of instrument can enhance the cost-effectiveness of carbon pricing and complementary policies needed to achieve a 1.5°C outcome, including through large-scale adoption by the Green Climate Fund and other international and domestic climate finance vehicles.

    Key policy insights

    • Traditional public climate finance interventions such as grants and concessional loans have not mobilized private capital at the scale needed to decarbonize the world economy consistent with the 2°C target, much less 1.5°C, and will likely face ongoing constraints in the future.
    • Auctioned price floors – subsidies that offer a guaranteed price for future emission reductions – maximize climate impact per public dollar while incentivizing private investment in low-carbon technologies.
    • This new subsidy instrument, if applied at scale via the Green Climate Fund and other domestic and international climate finance vehicles, can promote private sector competition to bring down technology costs and drive innovation, thereby supporting a longer term transition to regulation and sector- or economy-wide carbon markets.
    • To facilitate the transition from public subsidy to the market-based support of climate mitigation, auctioned price floors should work in tandem with carbon pricing and complementary policies, using the same accounting and monitoring, reporting and verification toolkits.
    Jonas Meckling, Thomas Sterner, and Gernot Wagner. 11/13/2017. “Policy sequencing toward decarbonization.” Nature Energy. Publisher's VersionAbstract
    Many economists have long held that carbon pricing—either through a carbon tax or cap-and-trade—is the most cost-effective way to decarbonize energy systems, along with subsidies for basic research and development. Meanwhile, green innovation and industrial policies aimed at fostering low-carbon energy technologies have proliferated widely. Most of these predate direct carbon pricing. Low-carbon leaders such as California and the European Union (EU) have followed a distinct policy sequence that helps overcome some of the political challenges facing low-carbon policy by building economic interest groups in support of decarbonization and reducing the cost of technologies required for emissions reductions. However, while politically effective, this policy pathway faces significant challenges to environmental and cost effectiveness, including excess rent capture and lock-in. Here we discuss options for addressing these challenges under political constraints. As countries move toward deeper emissions cuts, combining and sequencing policies will prove critical to avoid environmental, economic, and political dead-ends in decarbonizing energy systems.

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