Geoengineering (deliberate, temporary modification of the climate system; also called climate intervention or climate engineering) is increasingly receiving attention as a field of study and a potential method of reducing the most severe negative effects of climate change. If decision-makers are going to seriously consider geoengineering as an option, they need to understand the risks of deploying geoengineering, as well as the risks of not doing so.
Because large-scale outdoor climate-perturbing field experiments of geoengineering methods, such as injecting several megatons of sulfur compounds into the stratosphere, are not viable, the best tools available to understand this topic are global climate models. By comparing the results from multiple global climate models, scientists can understand—and potentially reduce—key uncertainties in the expected effects of geoengineering on climate and society.
In April, some 40 scientists attended the eighth annual meeting of the Geoengineering Model Intercomparison Project (GeoMIP) at ETH Zürich. The U.S. National Science Foundation supported the meeting and provided travel support for some of the participants. This project, an official part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) of the World Climate Research Programme, is designed to understand robust climate model responses to several standardized scenarios of geoengineering.
Attendees presented results on climate modeling and climate effects, and they engaged in discussions on new analyses to conduct, new computer experiments to pursue, and potential future directions for GeoMIP to investigate. In keeping with the inclusive aims of the project, approximately one third of the attendees had never before participated in a GeoMIP meeting, and the meeting included several participants from developing countries.
Discussions at the meeting included a wide variety of topics on the effects of geoengineering, largely focusing on two of the most commonly discussed solar geoengineering methods: stratospheric sulfate aerosol geoengineering and marine cloud brightening. Of key importance was the inclusion of presentations on potential effects of geoengineering, such as flooding, and potential consequences for water security, ecosystems, and human health.
In addition, attendees proposed novel approaches to geoengineering, consistent with the idea of the GeoMIP Testbed, a platform that allows for simulation designs to be tested by single models before adoption by the larger group. These novel approaches included direct injection of sulfuric acid droplets instead of sulfur dioxide into the atmosphere, simulations that provide feedback to meet specified objectives instead of specifying the forcing, and Arctic ice restoration.
Notably, the meeting reinforced the idea that at the present state of development, state-of-the-art Earth system models are incapable of properly representing the processes involved in cirrus cloud thinning (one proposed type of geoengineering). The discussions included replacements for the standardized cirrus thinning experiment G7cirrus that was proposed for inclusion in the next phase of GeoMIP. No conclusions were reached at the meeting, and discussions are ongoing.
Overall, GeoMIP continues to meet its objectives of expansion, bringing in new people and perspectives, and increasing its focus on geoengineering’s effects. We are excited that GeoMIP continues to serve a role in the community to advance research on geoengineering.
—Ben Kravitz (email: [email protected]), Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Wash.; Alan Robock, Department of Environmental Sciences, Rutgers University, New Brunswick, N.J.; and Ulrike Lohmann, ETH Zürich, Switzerland