An analysis of climate engineering as a response to climate change.

PREFACE COPENHAGEN CONSENSUS ON CLIMATE The Copenhagen Consensus Center has commissioned 21 papers to examine the costs and benefits of different solutions to global warming. The project’s goal is to answer the question: “If the global community wants to spend up to, say $250 billion per year over the next 10 years to diminish the adverse effects of climate changes, and to do most good for the world, which solutions would yield the greatest net benefits? ” The series of papers is divided into Assessment Papers and Perspective Papers. Each Assessment Paper outlines the costs and benefits of one way to respond to global warming. Each Perspective Paper reviews the assumptions and analyses made within an Assessment Paper. It is hoped that, as a body of work, this research will provide a foundation for an informed debate about the best way to respond to this threat. This paper offers a preliminary and exploratory assessment of the potential benefits and costs of climate engineering (CE). We examine two families of CE technologies, solar radiation management (SRM) and air capture (AC), under three emissions control environments: no controls, optimal abatement, and limiting temperature change to 2°C. Our analysis suggests that SRM offers potentially large net benefits, but that many important uncertainties remain. The near-term net benefits of AC appear to be much lower than those of SRM. However, we argue that both deserve to be investigated further. In the case of SRM, we focus on two specific technologies: the injection of aerosols into the stratosphere and the increase of marine cloud albedo. We estimate direct benefit-cost (B/C) ratios of around 25 to 1 for aerosols and around 5000 to 1 for cloud albedo enhancement. Technological progress might significantly lower direct cost estimates of stratospheric aerosols and thus raise the expected benefits. Yet, large uncertainties remain about the science and engineering of actually deploying SRM. Only a substantial research program could resolve these uncertainties, but the very large potential net benefits of SRM offer strong prima facie evidence for including R&D on SRM as a part of any portfolio of climate policies during the next decade. Therefore, we suggest that the Copenhagen Consensus allocate an average of approximately 0.3% of its $250 billion annual climate-change budget ($750 million per year) to SRM and AC research over the next decade. SRM is the higher priority, owing to its larger and earlier net benefit potential. This research program should explicitly focus on identifying possible side effects, especially those which might imply non-trivial costs. We estimate that the benefit of a single watt per square meter of SRM results in almost a 35% decrease in climate damages and abatement costs (over $6 trillion) under an emissions control regime of optimal abatement. Furthermore, when considering only the impact on temperature, we show that a single watt per square meter of SRM has the same economic benefit as capturing and sequestering almost 65% of yearly CO2 emissions, which, in conjunction with AC’s significant costs, argues in favor of SRM in the near term. In addition to quantitative benefit and cost estimates, we stress the potential importance of transaction costs and “political market failures. ” Some of these costs could be significant, but may be less so than with other strategies for coping with climate change.