The Paris Agreement’s goal of limiting global warming to 1.5 C or well below 2 C above pre-industrial levels is critical to achieving the Sustainable Development Goals (SDGs). But achieving the 1.5 degree target would require an immediate fivefold increase in current national mitigation commitments; limiting warming to two degrees would require a threefold increase. As both seem uncertain, technologies for solar radiation modification (SRM) have been floated – at least as a theoretical option – alongside measures that reduce greenhouse gas emissions and remove carbon dioxide from the atmosphere.
One approach – stratospheric aerosol injection (SAI) – has been most widely discussed because the technology potentially offers a pathway to limit the effects of climate change, even if global emissions are not reduced to (net) zero before 2050. Stratospheric aerosol injection involves the introduction of certain aerosols into the stratosphere, for example sulphur or calcite-based aerosols, to scatter or dim a small percentage of the incoming sunlight and thereby deflect some heat energy away from the Earth.
SRM in general differs from greenhouse gas mitigation: The deployment costs appear to be relatively low and the technologies take effect rapidly. This suggests that SRM could support efforts to achieve the UN Sustainable Development Goals (SDGs) and maintain these gains over the longer term despite the serious threats posed by climate change.
However, it is important to note that SRM does not address the root cause of climate change, which is the increasing concentration of greenhouse gases in the atmosphere due to human emissions. Moreover, the use of SRM would also entail risks – some might be significant – which would have to be considered in a holistic assessment of the threats posed by climate change and their possible attenuation through SRM.
Transdisciplinary approach offers overview and generates criteria to support decision-making
Prepared with the support of the Carnegie Climate Governance Initiative, this study makes a further contribution to broad-based assessment. In order to gain a holistic overview of the current understanding of SRM, a group of individuals were invited to critically appraise and add to the authors’ initial review of the literature. This expert elicitation comprised 30 individuals from 20 countries with complementary expertise and field experience in governance institutions relevant to all 17 Sustainable Development Goals. A particular focus was placed on combining bio-physical, ecological, social, economic, political and institutional perspectives in this analysis.
This transdisciplinary approach was pursued in an attempt to mitigate the shortfalls of conventional analyses of climate change, which usually draw on models based on physical parameters. Second-order climate effects are often considered in climate impact models, where physical variables are translated into economic costs and benefits. However, this simplification fails to consider the interconnections between physical and non-physical impact pathways. Regional knowledge is also frequently disregarded in this context. Therefore, particular attention was paid to ensuring that the contributors represented a diverse range of countries in order to better identify the possible implications of SRM with global relevance.
Conclusion: Policy-dependent impacts on SDGs
The analysis of current modelling studies consistently indicates that limiting global warming to, for example, 1.5 degrees instead of three degrees Celsius through a broadly uniform deployment of SRM could contribute to efforts to achieve the SDGs. In contrast, warming of three degrees Celsius in the absence of SRM would massively jeopardize these efforts.
In light of this, the team of authors considers its possible that a broad-based, successful deployment of SRM could significantly help limit the impacts of climate change on the achievement of the 17 Sustainable Development Goals and the associated risk of failing to achieve them. At the same time, however, the possibility of negative impacts could not be discounted due to SRM’s diverse physical, socioeconomic, political, and cultural effects, the authors said. The deployment of SRM could therefore also have a negative impact on at least nine of the 17 SDGs, including, for example, Goal 6 on “Clean water and sanitation”, Goal 3 on “Good health and well-being” or Goal 16 on “Peace, justice and strong institutions”. The latter in particular highlights the need for robust international decision-making and implementation processes and institutions. The team also see further risks for efforts to implement Goal 2 “No hunger” and Goal 7 “Affordable and clean energy” and in air pollution resulting from the introduction of aerosol particles into the atmosphere. However, these risks are contrasted by the potential gains that could be achieved through SRM.
One critical insight of this study is that our current knowledge is not sufficient to properly weigh the possible positive and negative effects of SRM deployment. In their conclusion, the authors recommend the development of broad-based assessment metrics that span the dimensions of the SDGs so that linkages can be better explored and discussed. This would include both qualitative and quantitative analyses of the potential risks and benefits of SRM in order to avoid under- or overestimating its potential impacts on climate and sustainable development.
Honegger, M. et al.: Potential implications of Solar Radiation Modification for Achievement of the Sustainable Development Goals, Mitigation and Adaptation Strategies for Global Change. DOI:10.1111/reel.12401