Solar radiation management (SRM) sparks perhaps the greatest controversy of all proposed climate change prevention strategies. However, as the most recent report by the Intergovernmental Panel on Climate Change (IPCC) highlights, the effects of global warming continue to become ever more radical, and hence so too must become our efforts to impede them.
The 2021 Climate Change Summary for Policy Makers released by the IPCC details the current state of our climate, bringing with it a clear sense of urgency to reconsider our approach as a human race. It is estimated that there has been a 1.09 °C human-induced global surface temperature increase from 1850-1900 to 2010-2019, to which a near-linear relationship with cumulative anthropogenic CO2 emissions can be made.
At the current rate of increase, it has become apparent that emission reduction strategies alone will not be sufficient to prevent the severe climate change impacts we are facing. The scientific community is now turning to geoengineering techniques, including solar radiation management, as a potential supplementary avenue to global warming reduction.
What is Solar Radiation Management?
The concept of geoengineering encompasses any technological, large-scale manipulation of the Earth's ecosystems with the purpose of climate change prevention. Within this umbrella falls solar radiation management.
Every day, a constant stream of short-wavelength UV rays enters the Earth's atmosphere. A small proportion of these rays are reflected back into space by clouds and atmospheric particles. The remainder penetrates through to the Earth's surface, where it is absorbed and subsequently re-radiated as long-wave radiation. This significant change in wavelength causes entrapment by greenhouse gases within the lower atmosphere, leading to the startling temperature increases found by the IPCC. The theory of SRM is quite simple; reflect these UV rays back into space before they are transformed into long-wave absorbable radiation.
According to research undertaken by the Solar Radiation Management Governance Initiative, current computer models have indicated that such solar engineering technologies could be relatively cheap to deploy compared to other mitigation approaches. The effects would also be immediate, with the potential to reduce temperatures to pre-industrial levels within just a few years of deployment, giving every impression SRM could be a cheap express ticket to climate change prevention.
Proposed SRM Strategies
At present, SRM remains in the concept stage. On a small scale, these proposals include amplifying the reflective properties of ground-level bodies. Examples include the genetic engineering of crops to yield shinier leaves, the ejection of microbubble trails from ships to achieve "ocean mirroring", or the use of white paint on roofs.
These ground-level SRM options if implemented at a large enough scale across multiple locations, could even have a modest impact on global heating.
Simon Nicholson, Professor, Co-Director, Institute for Carbon Removal Law and Policy
However, the two most discussed strategies, marine cloud brightening, and stratospheric aerosol injection would both operate in the atmosphere as a means of increasing the Earth's outer "albedo".
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Marine Cloud Brightening
Marine cloud brightening would operate by installing powerful salt spray systems on ships to propel saltwater towards the clouds, facilitating the condensation of any water vapor into water droplets, swelling, and brightening the clouds to enhance UV ray reflection.
Australia has already trialed its own saltwater delivery system in 2020, employing a modified turbine equipped with hundreds of nozzles to eject the spray towards ocean clouds. With government funding obtained as part of a more comprehensive AU $150 million research enterprise focused on reducing heat-induced damage to the Great Barrier Reef, further tests will assess the spray system's atmospheric and ocean surface impacts.
Stratospheric Aerosol Injection
The second of the most considered SRM technologies, stratospheric aerosol injection (SAI), consists of the direct ejection of reflective particles into the upper atmosphere. This seemingly radical intervention into the planet's ecosystem takes inspiration from nature itself; the eruption of Mount Pinatubo in 1991 released a powerful plume of 20 million tons of solar-reflective sulfur dioxide, ensuing an average global temperature decrease of 0.5 °C for the following 18 months. Still, SAI will most likely be delivered instead by a fleet of high-altitude aircraft with calcium carbonate or engineered nanoparticles as possible alternatives to sulfur dioxide.
Harvard University is currently conducting a physical study aiming to provide quantitative measurements regarding the interactions of particles and radiation within the stratosphere. The hope is to improve understanding around the feasibility of replicating the dramatic cooling effect of Mount Pinatubo.
Why is SRM Not Already Implemented?
Despite this promise of a quick and cost-effective means to global warming reduction, significant controversy surrounds solar engineering. As such, it is not included as an available pathway to climate change by the 2018 IPCC summary for policymakers.
Foremost, the deliberate manipulation of the Earth's climate, even preliminary testing, has a strong likelihood of tipping its already fragile balance. Disrupted rain patterns, amplified seasonal cycles, and depleted stratospheric ozone are all risks associated with SAI. Even the seemingly simple ocean mirrors could initiate a snowball effect of ecological disharmony; less sunlight would penetrate deep into the water, reducing the growth of marine vegetation, transmitting adverse effects along the entire food chain.
Fundamentally, it must be acknowledged that SRM does not tackle the increasing greenhouse gas emissions reported by the IPCC as the root cause of global warming, but instead offsets its impacts. The phrase "prevention not cure" is a well-founded argument against geoengineering as the sole climate change solution.
Yet, perhaps the most heated debate revolves around the social and political ramifications. As highlighted by the Forum for Climate Engineering Assessment:
- "SRM could be sold by fossil fuel interests and others as a kind of get-out-of-jail-free card;
- SRM might distract elites or society from the essential work of emissions abatement;
- Even medium to large-scale testing of some forms of SRM would amount to messing with ecosystems, with very limited knowledge and ability to control and account for the impacts of such interventions."
Opinions regarding SRM are based on the minimal computer-aided analysis currently available and differing global environmental politics and ethics. What can therefore be agreed is that efforts must first be focused on achieving global solar engineering governance.
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Could Solar Radiation Management be the Future of Fighting Climate Change?
As the Council of Councils concluded in their 2019 Global Governance Working Paper, the safe presence of solar radiation management in future climate change action "revolves around establishing a clear path towards agreed governance".
Their recommendation is to advance in a step-by-step manner, addressing uncertainties and risks at each level. Continuous collaboration from researchers, institutions, and non-state organizations is fundamental to ensure conversations are not purely fueled by political agendas.
The question does remain, however, as to how these discussions are to be conducted, with the UN convention for climate change already flooded with environmental debates.
As proposed by Susan Biniaz and Daniel Bodanksy in their 2020 International Solar Climate Intervention paper, a polycentric governance approach will be the most feasible at present; suggesting the Intergovernmental Panel on Climate Change and World Meteorological Organization to provide scientific standpoints, and the UN Security Council or G7/G20 responsible for policy decisions.
If one thing is clear about the future of SRM, it is that, if employed, it must be done so in unison with emissions abatement pathways as detailed by the IPCC. Time could then be allowed for the development of large-scale carbon reduction technologies, hence tackling climate change at its anthropogenic route.
Industrial Response to Climate Change
This article is a part of the IPCC Editorial Series: Industrial Response to Climate Change, a collection of content exploring how different sectors are responding to issues highlighted within the IPCC 2018 and 2021 reports. Here, Cleantech showcases the research institutions, industrial organizations, and innovative technologies driving adaptive solutions to mitigate climate change.
References and Further Reading
Biniaz, S. Bodanksy, D. (2020) Solar Climate Intervention: options for International Assessment and Decision-Making. Center for Climate and Energy Solutions & SilverLining. [Online]. Available at: https://www.c2es.org/wp-content/uploads/2020/07/solar-climate-intervention-options-for-international-assessment-and-decision-making.pdf
Coninck, H., A. Revi, M. Babiker, P. et al. (2018) Strengthening and Implementing the Global Response. Global Warming of 1.5°C. An IPCC Special Report on the impacts of global Warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Available at: https://www.ipcc.ch/sr15/chapter/chapter-4/
EDF, The Royal Society, TWAS. (2011) Solar Radiation Management: The Governance of Research. [Online]. Available at: https://royalsociety.org/topics-policy/projects/solar-radiation-governance/report/
Chhetri, et al. (2018) Governing Solar Radiation Management. Washington, DC: Forum for Climate Engineering Assessment, American University. [Online]. Available at: https://doi.org/10.17606/M6SM17
Geden, O. and Dröge, S., (2019) The Anticipatory Governance of Solar Radiation Management. [online] Council on Foreign Relations. Available at: https://www.cfr.org/report/anticipatory-governance-solar-radiation-management
IPCC. (2018) Summary for Policymakers. Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Available at: https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15_SPM_version_report_LR.pdf
IPCC. (2021) Summary for Policymakers. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate. Available at: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf
Keutschgroup.com. (2021) Keutsch Group at Harvard - SCoPEx. [online] Available at: https://www.keutschgroup.com/scopex
Nicholson, S. (2020) Solar Radiation Management. [online] Wilson Centre. Available at: https://www.wilsoncenter.org/article/solar-radiation-management
Samarco, G. (2021) Futuristic Solar Radiation Management. [online] Eni. Available at: https://www.eni.com/en-IT/low-carbon/futuristic-solar-radiation.html