Geoengineering—large-scale interventions designed to modify the climate—could take many forms. A team of scientists from Pacific Northwest National Laboratory, the National Center for Atmospheric Research, and Cornell University developed a specialized algorithm for an Earth system model that varies the amount and location of one type of geoengineering—sulfur dioxide injections into the upper atmosphere—and found that the approach could potentially be used to limit Earth's warming.
Previous studies looking at simulated effects of geoengineering on Earth's climate have raised concerns about the potential side effects. One of the common features of those simulations is uneven cooling of the globe. In this study, scientists found that a specific approach to geoengineering could avoid that uneven cooling, limiting warming in multiple areas simultaneously. They caution, however, that there are other potential side effects and more research is needed to determine if this approach would be practical, or even possible, in the real world. The possibility of a global geoengineering effort to combat warming also raises serious governance and ethical concerns.
The team studied one much-discussed geoengineering approach: mimicking volcanic eruptions by creating reflective particles in the upper atmosphere that cool the planet. The scientists used the Whole Atmosphere Community Climate Model (WACCM), a state-of-the-art extension of the Community Earth System Model. The team recently updated the model to include particle growth and stratospheric wind variability. They successfully tested the model to see how well it could simulate the massive 1991 eruption of Mount Pinatubo, including the amount and rate of aerosol formation, as well as how those aerosols were transported around the globe and how long they stayed in the atmosphere. Then the scientists explored effects like cooling and precipitation after injecting sulfur dioxide at seven different latitudes and two different altitudes.
A team of scientists, including PNNL climate scientist Ben Kravitz, created a single model simulation with specific objectives: to limit average global warming to 2020 levels through the end of the century and to minimize the difference in cooling between the equator and the poles, as well as between the northern and southern hemispheres. The model successfully kept surface temperatures near 2020 levels against a background of increasing greenhouse gas emissions, and did so more evenly than in previous studies.
The research was funded in part by the Defense Advanced Research Projects Agency and the National Science Foundation, NCAR's sponsor.
B. Kravitz, D. MacMartin, M.J. Mills, J.H. Richter, and S. Tilmes, Journal of Geophysical Research: Atmospheres:
- "Radiative and chemical response to interactive stratospheric sulfate aerosols in fully coupled CESM1(WACCM)" [DOI: 10.1002/2017JD027006]
- "Sensitivity of aerosol distribution and climate response to stratospheric SO2 injection locations" [DOI: 10.1002/2017JD026888]
- "Stratospheric Dynamical Response and Ozone Feedbacks in the Presence of SO2 Injections"[DOI: 10.1002/2017JD026912]
- "The climate response to stratospheric aerosol geoengineering can be tailored using multiple injection locations" [DOI: 10.1002/2017JD026868]
- "First simulations of designing stratospheric sulfate aerosol geoengineering to meet multiple simultaneous climate objectives" [DOI: 10.1002/2017JD026874].
All the data from the experiments are available on the Earth System Grid at https://www.earthsystemgrid.org/dataset/ucar.cgd.ccsm4.so2_geoeng.html or http://dx.doi.org/10.5065/D6X63KMM
For more information, see the NCAR news release at https://www2.ucar.edu/atmosnews/news/129835/new-approach-geoengineering-simulations-significant-step-forward.