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Cited by 119Climate Change and GeoengineeringAtmospheric aerosols and cloudsClimate Change and Environmental Impact

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Potential ecological impacts of climate intervention by reflecting sunlight to cool Earth

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Zarnetske, Phoebe L., Gurevitch, Jessica, Franklin, Janet, Groffman, Peter M., Harrison, Cheryl S., Hellmann, Jessica J., Hoffman, Forrest M., Kothari, Shan, Robock, Alan, Tilmes, Simone, Visioni, Daniele, Wu, Jin, Xia, Lili, Yang, Cheng-En·2021·Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.1921854118PMC PMC8053992
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Abstract

As the effects of anthropogenic climate change become more severe, several approaches for deliberate climate intervention to reduce or stabilize Earth's surface temperature have been proposed. Solar radiation modification (SRM) is one potential approach to partially counteract anthropogenic warming by reflecting a small proportion of the incoming solar radiation to increase Earth's albedo. While climate science research has focused on the predicted climate effects of SRM, almost no studies have investigated the impacts that SRM would have on ecological systems. The impacts and risks posed by SRM would vary by implementation scenario, anthropogenic climate effects, geographic region, and by ecosystem, community, population, and organism. Complex interactions among Earth's climate system and living systems would further affect SRM impacts and risks. We focus here on stratospheric aerosol intervention (SAI), a well-studied and relatively feasible SRM scheme that is likely to have a large impact on Earth's surface temperature. We outline current gaps in knowledge about both helpful and harmful predicted effects of SAI on ecological systems. Desired ecological outcomes might also inform development of future SAI implementation scenarios. In addition to filling these knowledge gaps, increased collaboration between ecologists and climate scientists would identify a common set of SAI research goals and improve the communication about potential SAI impacts and risks with the public. Without this collaboration, forecasts of SAI impacts will overlook potential effects on biodiversity and ecosystem services for humanity.

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Fig. 1. Although some effects of SRM with SAI on the climate are known from certain SAI scenarios (indicated with + for likely increases, − for decreases, Δ to indicate change), the effects of SAI on ecological systems are largely unknown. Such biotic and abiotic changes would vary across Earth and depend on the SAI scenario. Stratospheric aerosols from SAI would reflect more sunlight—including UV radiation—to space, reducing surface UV. SAI could also destroy stratospheric ozone, increasing surface UV (Fig. 2A). The net effects of SAI on UV and ozone depend on the amount and distribution of aerosols in the stratosphere, the type of aerosols used, and how the aerosols interact with the chemistry and radiation of the atmosphere (e.g., refs. 23 and 141). Potential changes in ocean temperature and ocean pH in different regions are illustrated below (Fig. 3). Symbols courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science (https://ian.umces.edu/symbols/).
Fig. 1. Although some effects of SRM with SAI on the climate are known from certain SAI scenarios (indicated with + for likely increases, − for decreases, Δ to indicate change), the effects of SAI on ecological systems are largely unknown. Such biotic and abiotic changes would vary across Earth and depend on the SAI scenario. Stratospheric aerosols from SAI would reflect more sunlight—including UV radiation—to space, reducing surface UV. SAI could also destroy stratospheric ozone, increasing surface UV (Fig. 2A). The net effects of SAI on UV and ozone depend on the amount and distribution of aerosols in the stratosphere, the type of aerosols used, and how the aerosols interact with the chemistry and radiation of the atmosphere (e.g., refs. 23 and 141). Potential changes in ocean temperature and ocean pH in different regions are illustrated below (Fig. 3). Symbols courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science (https://ian.umces.edu/symbols/).CC BY-NC-ND · PubMed Central
Fig. 2. Potential temperature change over time for two different SAI scenarios. (A) In a future with no climate change mitigation and with SAI deployment, high emissions result in rising temperatures (red line). Increasing amounts of SAI would have to be deployed to reduce temperature (blue arrows) to a specific temperature target (blue line). The risk of sudden SAI termination also increases (red arrow). (B) In a future with climate change mitigation and SAI “peak shaving,” temperature changes are first reduced by a combination of emission reduction (black line) and CDR (CO2 removal, gray line), then further reduced by SAI (blue arrows). The red shaded areas below the two curves indicate the potential overall risk for ecological systems from increased temperature and SAI deployment; carbon emissions alone would not create the same degree of risk reduction as shown in B. We note that SAI is not akin to a global thermostat that would only control global temperatures to remediate GHG-induced warming. GHGs add energy to the system at the surface and throughout the atmosphere, whereas reducing sunlight with SAI only changes the energy balance at Earth’s surface. Furthermore, GHGs operate 24 h a day and all year long, whereas reducing sunlight primarily has a direct impact during the daytime and more so in summer than winter. Data from refs. 142 and 143.
Fig. 2. Potential temperature change over time for two different SAI scenarios. (A) In a future with no climate change mitigation and with SAI deployment, high emissions result in rising temperatures (red line). Increasing amounts of SAI would have to be deployed to reduce temperature (blue arrows) to a specific temperature target (blue line). The risk of sudden SAI termination also increases (red arrow). (B) In a future with climate change mitigation and SAI “peak shaving,” temperature changes are first reduced by a combination of emission reduction (black line) and CDR (CO2 removal, gray line), then further reduced by SAI (blue arrows). The red shaded areas below the two curves indicate the potential overall risk for ecological systems from increased temperature and SAI deployment; carbon emissions alone would not create the same degree of risk reduction as shown in B. We note that SAI is not akin to a global thermostat that would only control global temperatures to remediate GHG-induced warming. GHGs add energy to the system at the surface and throughout the atmosphere, whereas reducing sunlight with SAI only changes the energy balance at Earth’s surface. Furthermore, GHGs operate 24 h a day and all year long, whereas reducing sunlight primarily has a direct impact during the daytime and more so in summer than winter. Data from refs. 142 and 143.CC BY-NC-ND · PubMed Central
Fig. 3. SAI alone would not reduce OA, which strongly impacts marine ecosystems. 1) Historical time series of CO2 and OA at station ALOHA (figure from https://www.pmel.noaa.gov/co2/file/Hawaii+Carbon+Dioxide+Time-Series). Anthropogenic carbon emissions (red line) have been absorbed by the ocean (green line), reducing pH and creating more acidic conditions that harm calcifying marine organisms at the base of the marine food web (blue line). 2) Shells of calcifying marine plankton (pteropods) are negatively affected by OA (figure from ref. 144). 3) Stratospheric aerosol intervention applied to a “peak shaving” future climate scenario as in Fig. 2B reduces sea surface temperature anomalies (ΔSST) (A and C) but would not ameliorate OA (ΔpH) (B and D). Scenario shown is SSP5-3.4-OS (see ref. 24 for simulation details) 2060s mean relative to preindustrial.
Fig. 3. SAI alone would not reduce OA, which strongly impacts marine ecosystems. 1) Historical time series of CO2 and OA at station ALOHA (figure from https://www.pmel.noaa.gov/co2/file/Hawaii+Carbon+Dioxide+Time-Series). Anthropogenic carbon emissions (red line) have been absorbed by the ocean (green line), reducing pH and creating more acidic conditions that harm calcifying marine organisms at the base of the marine food web (blue line). 2) Shells of calcifying marine plankton (pteropods) are negatively affected by OA (figure from ref. 144). 3) Stratospheric aerosol intervention applied to a “peak shaving” future climate scenario as in Fig. 2B reduces sea surface temperature anomalies (ΔSST) (A and C) but would not ameliorate OA (ΔpH) (B and D). Scenario shown is SSP5-3.4-OS (see ref. 24 for simulation details) 2060s mean relative to preindustrial.CC BY-NC-ND · PubMed Central

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  1. M. I. Budyko, Climate modification techniques. Meteorologiya i Gidrologiya 2, 91–97 (1974).

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Metadata

Authors
Zarnetske, P. L., Gurevitch, J., Franklin, J., Groffman, P. M., Harrison, C. S., Hellmann, J. J., Hoffman, F. M., Kothari, S., Robock, A., Tilmes, S., Visioni, D., Wu, J., Xia, L., & Yang, C.-E.
Affiliations
  • Michigan State University (US)
  • Stony Brook University (US)
  • University of California, Riverside (US)
  • The Graduate Center, CUNY (US)
  • The University of Texas Rio Grande Valley (US)
  • University of Minnesota (US)
  • Oak Ridge National Laboratory (US)
  • Rutgers, The State University of New Jersey (US)
  • NSF National Center for Atmospheric Research (US)
  • Cornell University (US)
  • University of Hong Kong (HK)
  • University of Tennessee at Knoxville (US)
Corresponding author
Franklin, Janet
ORCID
Venue
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences
Published
2021-04-05
Volume
118
Issue
15
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
DOI
10.1073/pnas.1921854118
PMC
PMC8053992
OpenAlex
W3145236039
Cited by
119
References
150
Citations by year
2026: 12 · 2025: 20 · 2024: 24 · 2023: 28 · 2022: 21 · 2021: 12
FWCI
8.71
Type
journal article
Language
en
Open access
Licence
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
  • CUNY Academic Works (City University of New York) (submittedVersion, cc-by-nc-nd)
  • Civil War Book Review (submittedVersion)
  • ScholarWorks @ UTRGV (The University of Texas Rio Grande Valley) (submittedVersion, cc-by-nc-nd)
  • eScholarship (California Digital Library) (submittedVersion, cc-by-nc-nd)
  • OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) (submittedVersion)
Funders
  • National Science Foundation (1937619, 1937699, 1617844, 1853697)
  • U.S. Department of Energy (SC-23 - RUBISCO SFA, TES SFA)
Topics
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
  • Physical Sciences › Environmental Science › Global and Planetary Change › Atmospheric aerosols and clouds
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Environmental Impact
Keywords
solar geoengineering, stratospheric aerosol injection, geoengineering, ecological impacts, climate intervention, Earth albedo, anthropogenic climate change, biodiversity, ecosystem services, ecological risk, climate-ecosystem interactions

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