This group is a fast-growing team of researchers working at the intersection of climate science and technology with a focus on the science and public policy of solar geoengineering under the leadership of David Keith, Professor of Applied Physics at Harvard’s School of Engineering and Applied Sciences and Professor of Public Policy at the Harvard Kennedy School.

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Recent Publications

Developing a Plume-in-Grid Model for Plume Evolution in the Stratosphere

Hongwei Sun, Sebastian Eastham, and David Keith. 3/21/2022. “Developing a Plume-in-Grid Model for Plume Evolution in the Stratosphere.” Journal of Advances in Modeling Earth Systems, 14, 4. Publisher's VersionAbstract
Stratospheric emissions from aircraft or rockets are important sources of chemical perturbations. Small-radius high-aspect-ratio plumes from stratospheric emissions are smaller than global Eulerian models' grid cells. To help global Eulerian models resolve subgrid plumes in the stratosphere, a Lagrangian plume model, comprising a Lagrangian trajectory model and an adaptive-grid plume model with a sequence of plume cross-section representations (from a highly resolved 2-D grid to a simplified 1-D grid based on a tradeoff between the accuracy and computational cost), is created and embedded into a global Eulerian (i.e., GEOS-Chem) model to establish a multiscale Plume-in-Grid (PiG) model. We compare this PiG model to the GEOS-Chem model based on a 1-month simulation of continuous inert tracer emissions by aircraft in the stratosphere. In the PiG results, the final injected tracer is more concentrated and approximately 1/3 of the tracer is at concentrations 2–4 orders of magnitude larger compared to the GEOS-Chem results. The entropy of injected tracer in the PiG results is 6% lower than the GEOS-Chem results, indicating less tracer mixing. The total product mass from a hypothetical second-order process (applied to the injected tracer) in the PiG results is 2 orders of magnitude larger than the GEOS-Chem results. Increasing the GEOS-Chem model's horizontal resolution 4-fold is insufficient to resolve this product difference, while requiring over seven times the computational resources of the PiG model. This paper describes the PiG model framework and parameterization of plume physical processes. Chemical and aerosol processes will be introduced in the future.
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Elicitation of US and Chinese expert judgments show consistent views on solar geoengineering

Zhen Dai, Elizabeth T. Burns, Peter J. Irvine, Dustin H. Tingley, Jianhua Xu, and David W. Keith. 2021. “Elicitation of US and Chinese expert judgments show consistent views on solar geoengineering.” Humanities and Social Sciences Communications, 8, 1, Pp. 1–9. Publisher's VersionAbstract
Expert judgments on solar geoengineering (SG) inform policy decisions and influence public opinions. We performed face-to-face interviews using formal expert elicitation methods with 13 US and 13 Chinese climate experts randomly selected from IPCC authors or supplemented by snowball sampling. We compare their judgments on climate change, SG research, governance, and deployment. In contrast to existing literature that often stress factors that might differentiate China from western democracies on SG, we found few significant differences between quantitative judgments of US and Chinese experts. US and Chinese experts differed on topics, such as desired climate scenario and the preferred venue for international regulation of SG, providing some insight into divergent judgments that might shape future negotiations about SG policy. We also gathered closed-form survey results from 19 experts with \textgreater10 publications on SG. Both expert groups supported greatly increased research, recommending SG research funding of \textasciitilde5% on average (10th–90th percentile range was 1–10%) of climate science budgets compared to actual budgets of \textless0.3% in 2018. Climate experts chose far less SG deployment in future climate policies than did SG experts.
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Solar geoengineering research on the U.S. policy agenda: when might its time come?

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.
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