Hazards of Geoengineering
Climate change has far-reaching and severe consequences for both humans and nature and is clearly visible through rising mean air temperatures as well as more frequent extreme weather events such as heavy rains, droughts, forest fires, or hot summers. While efforts to reduce greenhouse gas emissions and adapt to climate impacts are the only sustainable solution to climate change, researchers around the world are also investigating additional options to reduce global warming.
One of these options, called solar geoengineering, arose from the thinking of Nobel laureate Paul Crutzen. He postulated that introducing large amounts of sulfates at atmospheric altitudes of 10 to 25 kilometers (the lowest stratosphere) would lead to a cooling of the Earth and thus could counteract climate change. While these and other solar geoengineering strategies (e.g., influencing cloud characteristics) have the potential to lower global temperatures, they could also have a number of unknown or negative consequences.
IEK-7 scientists and U.S. colleagues have warned of the consequences of such solar geoengineering because the sulfates would seriously damage the ozone layer at the poles, which protects life on earth against UV radiation. Early results were published in the journal Science (Tilmes et al., 2008). The sulfate particles chemically alter stratospheric chlorine in such a way that it causes rapid ozone depletion. Thus, between one-third and one-half of the ozone layer over the Arctic could be destroyed. It would be particularly risky if a major natural volcanic eruption were to follow an artificial input of sulfates. Then even greater, extremely serious ozone depletion in the stratosphere could be expected.
It has been suggested that chemical ozone depletion cycles, which occur each year in polar winter, could also play a role in mid-latitudes in connection with sulfate geoengineering. Taking climate change into account, this might lead to increased UV exposure at the Earth's surface in the densely populated northern hemisphere. IEK-7 scientists showed that this risk of sulfate geoengineering can be considered low under current conditions but also under various future climate change scenarios (Robrecht et al., 2019, 2021).
A current research topic, in which IEK-7 scientists are also involved, is the strategy of (possible) injection of sulfate aerosol into the stratosphere. The injection strategy has a strong influence on the effectiveness of sulfate geoengineering as well as on undesirable side effects, such as stratospheric ozone loss (Tilmes et al., 2021).
Other consequences arising from chemistry-climate feedbacks, such as the influence on upper tropospheric jet stream dynamics and its interactions with ground weather, will become the continued focus of IEK-7 research.
Tilmes, S., Müller, R.; Salawitch, R.: The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes, SCIENCE, 320, 1201 – 1204, 2008.
Robrecht, S., Vogel, B., Grooß, J.-U., Rosenlof, K., Thornberry, T., Rollins, A., Krämer, M., Christensen, L., and Müller, R.: Mechanism of ozone loss under enhanced water vapour conditions in the mid-latitude lower stratosphere in summer, Atmos. Chem. Phys., 19, 5805–5833, https://doi.org/10.5194/acp-19-5805-2019, 2019.
Robrecht, S., Vogel, B., Tilmes, S., and Müller, R.: Potential of future stratospheric ozone loss in the midlatitudes under global warming and sulfate geoengineering, Atmos. Chem. Phys., 21, 2427–2455, https://doi.org/10.5194/acp-21-2427-2021, 2021.
Tilmes, S., J. H. Richter, B. Kravitz, D. G. MacMartin, A. S. Glanville, D. Visioni, D. E. Kinnison, and R. Mülller (2021) Sensitivity of total column ozone to stratospheric sulfur injection strategies, Geophys. Res. Lett., 48, e2021GL094058, https://doi.org/10.1029/2021GL094058.