Research focuses primarily on the interdisciplinary application of engineering feedback analysis, dynamics, and control tools to problems in climate; principally solar climate engineering or geoengineering (and climate dynamics/variability, but there is no ongoing activity in this area). Additional interests include control of fluid dynamics, vibration and noise, and telescope control.
Climate Engineering refers to large-scale intentional intervention in the climate system as a possible additional tool to help manage some impacts of climate change; an example would be adding aerosols to the stratosphere to reflect some sunlight. This doesn’t reduce the need to cut greenhouse gas emissions, nonetheless deploying some amount of Climate Engineering might reduce climate damages, and more research is needed to evaluate it.
Research is funded by NSF and by the Cornell University Atkinson Center.
Main research questions:
- How can one “design” stratospheric-aerosol climate engineering, using available degrees of freedom (e.g., latitudes, times of year to inject material) to achieve desired objectives?
- What would the climate impacts be for different deployment choices?
- How uncertain are our predictions and what are the dominant uncertainties?
I am also interested in collaborations in social-science and governance of these technologies.
A few potential research opportunities are listed below; come talk to me if any of these sound interesting or you’d like more than the terse description below!
- What is the best way to get material up to the stratosphere at 23-25km? How much does this cost?
- Would electrically-powered aircraft be better than conventional? (Note that mission duration/range requirements are short!)
- Would a railgun be a better option?
- If you choose available degrees of freedom (latitude, altitude, time of year) to optimize for one set of climate metrics, what happens to other metrics?
- Improve the feedback control algorithms used in simulations:
- Current simulations use feedback to manage surface temperature goals. Design and demonstrate feedback control of aerosol optical depth instead, and then demonstrate an inner/outer loop structure to control surface temperature using desired AOD as the input.
- How robust are the feedback algorithms used to date in Climate Engineering? Do they still work when the aerosol properties are changed? One option is to change the properties by injecting sulfate directly, another would be to change the parameters of the aerosol model.
- How can we design multivariable feedback algorithms to simultaneously manage multiple metrics?
- How sensitive are predictions to uncertainty? What happens if we change parameters influencing aerosol size distribution, for example?
- What would happen if there was a volcanic eruption during a stratospheric aerosol deployment?
- What is the smallest useful global experiment to measure stratospheric aerosol properties? (This isn’t quite my expertise.) What is the signal-to-noise for detecting aerosol optical depth or aerosol size parameters from satellite measurements or balloons; or more generally, what observations are required? A related question would be, what would the first years of a stratospheric aerosol deployment look like?
- Using an emulator (reduced-order dynamic model), predict the response for different scenarios, including for example predicting the rate-of-change of temperature and precipitation to understand stressors on ecosystems, or predicting the impact of a 1-, 2-, or 3-year interruption in deployment.
- Using System identification to assess regional climate response to Marine Cloud Brightening (geoengineering by “brightening” clouds in particular regions and seasons). Some preliminary simulations and analysis have been conducted, see paper here, but analysis so far has only scratching the surface. Nothing like this has yet been done in climate science!
Some old ideas:
- “Big data” and climate science: can we use ARGO float data to understand ocean eddies? The ARGO float trajectories provide massive (though sparse in space and time) data on currents, but most researchers have only looked at temperature/salinity profiles – can we build some spatiotemporal estimate of ocean eddies?
- Application of Engineering System identification tools to understand dynamics underlying ENSO or AMOC (requires funding for computational resources); a useful starting point is here.
- Efficacy – how do we compare different forcing agents in the climate system, such as comparing CO2 versus methane? One metric is how much of each cause the same change in global mean temperature; this can be efficiently computed with a feedback loop. The concept has been written down here, but there’s a lot of different forcing to consider, and different metrics that could be evaluated.
- If we sprayed sea water on top of existing sea ice in late fall and early winter to generate a thicker layer of ice, would this extend the life of the ice through the following summer?
- Holistic Assessment of SO2 injections into the stratosphere: can we combine aerosol injection at different latitudes to improve climate outcomes or meet specific goals? (A start towards “well-designed” geoengineering!) Joint with PNNL and NCAR.
- Geoengineering on a Regional Scale: With significant impacts projected from global warming and melting ice, the Arctic is a critical region for evaluating possible future global cooling techniques, such as injecting aerosols into the stratosphere to boost “albedo” and reflect some of the sun’s energy. Combining social science, engineering, and communication, this team will engage Arctic communities in a participatory discussion about these emerging technologies, identify public concerns, and evaluate regionally specific geoengineering strategies that address them. (Atkinson Center for a Sustainable Future, Academic Venture Fund, 2015, with Bruce Lewenstein and Holly Buck)
- How Do You Construct a Strategic Approach to Climate Change by Coupling Geoengineering to Mitigation and Adaptation? (Atkinson Center Impact through Innovation Fund, with Environmental Defense Fund)