One Atmosphere: An Independent Expert Review on Solar Radiation Modification Research and Deployment by UNEP

[Geoengineering News]

https://wedocs.unep.org/handle/20.500.11822/41903

Date

2023-02

Author

United Nations Environment  

Description

The United Nations Environment Programme (UNEP) convened a multidisciplinary expert panel to undertake a rapid review of the state of scientific research on Solar Radiation Modification (SRM)

URI

https://wedocs.unep.org/20.500.11822/41903

Key findings

1. While international efforts must focus on rapid emissions mitigation and adapting to anthropogenically induced climate change, Solar Radiation Modification (SRM) is being discussed as an additional approach to offset some impacts and avoid global temperature exceeding the limits set in the Paris Agreement, while the global energy system is being transformed.  

• In current climate model simulations, well-designed SRM deployments offset some effects of greenhouse gases (GHG) on global and regional climate change by reflecting more sunlight into space.

• SRM is the only option that could cool the planet within years. To be effective at limiting global warming, SRM would need to be maintained for several decades to centuries, depending on the pace of emissions reductions and carbon removal. 

• The estimated direct costs for deploying SRM, without considering costs of possible adverse impacts, may be tens of billions of US dollars per year per 1°C of cooling.

• SRM is not a substitute for mitigation. Impacts from excess carbon dioxide (CO2), such as ocean acidification and ecological degradation, would continue.

2. An operational SRM deployment would introduce new risks to people and ecosystems. 

• Strong concerns around large-scale SRM deployment include damaging the ozone layer, overcompensating climate change at regional scales and increasing or redistributing climate change impacts on society and ecosystems.

• SRM deployment, if abruptly terminated, would lead to rapid climate change that would increase risks for humans and ecosystems.

• SRM research could reduce efforts to mitigate GHG emissions by drawing resources away from mitigation efforts.

• An SRM deployment could increase power imbalances between nations, spark conflicts and raise ethical, moral, legal, equity and justice issues.

3. With many unknowns and risks, there is a strong need to establish an international scientific review process to identify scenarios, consequences, uncertainties and knowledge gaps. 

• The possible consequences of an SRM deployment need to be understood and weighed against the consequences in a world without SRM. 

• An international assessment may reduce risks to society by identifying in advance the possible negative consequences of a proposed SRM deployment.  

• This expert panel considers that the scientific, technical, social and environmental aspects of a large-scale deployment of SRM have not been fully assessed and deployment is not warranted at present.

4. A governance process would be valuable to guide decisions around research activities, including indoor research, small-scale outdoor experiments and SRM deployments. 

• SRM indoor research, which is mostly theoretical analyses and climate modelling, has been going on for over 50 years. In the interests of academic freedom, it is suggested by this expert panel that norms, guidelines and voluntary codes of conduct for indoor research could help balance societal concerns with scientific inquiry.

• The views of the panel on the need to impose governance on small-scale outdoor experimentation and operational deployment diverge because of differences in perceived risk. Governance of small-scale outdoor experimentation could limit the potential of a ‘slippery slope’ from experimentation to large-scale deployment. Governance of large-scale deployment would be valuable given the inherent risks.

• This panel unanimously suggests a broader framework for the governance of the stratosphere, which would, amongst other things, address the changes that occur in this layer of the atmosphere from stratospheric aerosol injection (SAI) experiments or deployment. 

5. SRM research and deployment decisions require an equitable, transparent, diverse and inclusive discussion of the underpinning science, impacts, risks, uncertainties and governance.

• This process would need to involve discussion with, and more research from, all stakeholders as most from the global south are not sufficiently engaged in current SRM discussions. The UN is well-positioned to promote a globally inclusive conversation on SRM.

Executive summary

We have ‘One Atmosphere’. Everyone is a stakeholder. 

Since the beginning of the industrial era, carbon dioxide (CO2) and other greenhouse gases (GHGs) have been accumulating in the atmosphere due to fossil fuel burning and changes in land use such as deforestation. As a result, anthropogenic climate change is now affecting every region across the globe. 

The consequences of continued GHG emissions will be severe and long-lasting, including exceedance of temperature targets; increases in the frequency, intensity and persistence of extreme weather and climate events; reductions in sea and land ice, snow cover and permafrost; and sea level rise. Through the United Nations Framework Convention on Climate Change (UNFCCC) and other processes, the international community has been working to reduce GHG emissions. However, action and current commitments are not yet sufficient to meet the Paris Agreement’s temperature goals. 

This situation has led to increased interest in understanding whether an operational large-scale Solar Radiation Modification (SRM, or sometimes called ‘solar geoengineering’) deployment might be able to help protect humans and the ecosystems upon which humanity depends.

The expert panel considers that a near and mid-term large-scale SRM deployment is not currently warranted and would be unwise. 

This view may change if climate action remains insufficient. In most proposed SRM approaches (Figure 1; Annex 1), a small amount of sunlight is deliberately reflected to space to cool the planet. SRM is the only known approach that could be used to cool the Earth within a few years10,15,16. The most studied method involves the introduction of sub-micron-size reflective particles into the stratosphere (stratospheric aerosol injection – SAI – Figure 3). Other methods (Figure 1; Annex 1) have also been proposed, including approaches such as marine cloud brightening (MCB – brightening of low clouds over the ocean). Cirrus cloud thinning (CCT) is often categorized as an SRM method, although instead of altering the amount of sunlight that enters the Earth’s system, it allows more infrared radiation from Earth to escape into space. 

Climate model simulations consistently show that SRM could offset some of the effects of increasing GHGs on global and regional climate, including carbon and water cycles, but there could be substantial residual or overcompensating climate change at the regional scales. The possibility that SRM may be able to reduce climate damage and alleviate climate change impacts has led to advocacy for research to establish whether SRM deployment could be a viable option in addition to mitigation and adaptation. 

Two framings of SRM deployment are envisioned: rapid (i.e. full deployment within a few years) and phased (i.e. full deployment ramped in over several decades or longer).If atmospheric CO2 concentrations continue to increase, and an SRM deployment was used to offset warming, the uncertainties and associated risk could scale with the amount and duration of SRM deployment. Impacts not compensated by SRM could be exacerbated, and the chance of a devastating impact on ecosystems of a sudden and sustained cessation of a large SRM deployment (the ‘termination shock’) would be increased. An SRM deployment does not eliminate the need to decarbonize the energy system or address other GHG emissions. 

The combined uncertainties of SRM – including technological maturity, physical understanding, potential impacts, governance, legality, ethics and potential impacts on sustainable development – could render SRM economically, socially or institutionally undesirable. As SRM does not reduce GHG emissions, and it does not address the causes of anthropogenic climate change, other environmental harms from increased concentrations of CO2 and other GHGs will continue. 

These risks increase with the amount of SRM, so there is strong agreement in recent literature that SRM deployment would therefore be at best a temporary measure that could operate in parallel with mitigation measures designed to achieve sustained net zero or net negative CO2 emissions globally. 

Hence, SRM should not be viewed as the main policy response to climate change.While this document encompasses several SRM approaches (Annex 1), focus is on stratospheric aerosol injection (SAI; Figures 1 and 3) because it has been the most studied and there is the largest amount of evidence relating to its potential feasibility and effectiveness. Observations of global cooling after major volcanic eruptions provide strong evidence that a deliberate injection of large amounts of reflective particles into the stratosphere would cool the Earth rapidly (Figure 4). 

However, the extent to which SRM can reduce climate change hazards and alleviate ecological damage and human suffering has not been robustly established. SRM deployment may also increase climate change damage or introduce a range of new risks to people and ecosystems, including risks to human health and global biodiversity. These benefits and risks may not be known fully without an actual SRM deployment. There is now only a limited set of scientific assessments of the impacts of potential SRM deployments on human and natural systems.

Many of the risks and concerns are associated with:

• the response of Earth’s climate and environmental systems (e.g. air and water quality); 

• how these uncertain changes will impact human health and natural ecosystems; 

• whether decisions would be made in an inclusive, equitable and transparent manner; 

• whether SRM discussions might shift financial, political and intellectual resources from mitigation and adaptation efforts (the ‘moral hazard’ problem); 

• how SRM deployment could lead to societal risks, including international conflicts; and

• how SRM could raise ethical, moral, legal and justice questions. 

There are important distinctions between indoor SRM research investigations, small-scale outdoor SRM experiments and potential large-scale operational SRM deployments. Indoor SRM research investigations have involved theoretical analysis, social science research, computer simulations using climate and Earth System models and laboratory experimentation. 

Small-scale outdoor experimentation might emit limited quantities of material over a limited time to examine critical and poorly understood SRM-related processes in the real atmosphere with negligible climatic impact. Operational SRM deployments would likely be of planetary scale and need to last for decades or more to be effective. It should, therefore, be possible to define a level beyond which an SRM experiment would no longer be small-scale.

Some scientists recommend that small-scale outdoor SRM experiments be a component of ongoing SRM research. 

Specific reasons offered for conducting such small-scale outdoor experiments include:

• Evaluating the potential for developing a SRM system;

• Identifying adverse consequences of SRM;

• Developing a comprehensive scientific foundation to inform policy decisions;

• Informing decisions on how to respond to possible deployment by ‘rogue’ parties.

An important question is how to balance general principles of freedom of scientific inquiry with the need to manage risks related to scientific and technical experimentation, especially in environments such as the stratosphere, where little exists in the way of regulatory or governance structures.

The principal reason offered not to conduct small-scale outdoor SRM experiments is that these experiments could make an operational SRM deployment more likely, and the decision to conduct experiments or deployments would be made in a process that is neither inclusive nor representative of the interest of all stakeholders (everyone on Earth). 

There is also concern about possible adverse direct environmental consequences of experimental activities. Further, because research capacity resides primarily in developed countries, asymmetries in SRM expertise and technological capacity could have adverse effects on the power relationship between nations. 

These concerns could be addressed with appropriate governance mechanisms.It is conceivable that an operational SRM system could be deployed and be successful at reducing some physical metrics of climate change, thus reducing climate change impacts. However, the possibility of an inequitable distribution of reduced or increased risks across regions and of the power to control such a system will exacerbate or create inequities, leading to decreases in certain societal aspects of human welfare.

In anticipating any decision regarding SRM deployment, proper consideration of the interdependence of the climate system, ecosystems and human society, and the competing interests among nations, will involve resolving thorny issues. Therefore, there is a need for equitable, transparent and inclusive discussions about the science of SRM and related governance issues.

 The expert panel’s reflections on actions for consideration:

• A globally inclusive, transparent and equitable scientific assessment process for SRM be established. The aim of the assessment would be to establish the natural and social science basis of SRM to guide research and serve as a foundation for governance and decision making. An assessment process would help to review evolving SRM literature and identify key scenarios, environmental and social consequences, uncertainties and knowledge gaps.

• Exploration of the prospects and possibilities for a multilateral SRM governance framework to evaluate and address concerns on both SRM research and potential operational deployment. Governance could be helpful to guide decisions surrounding acceptability of various possible SRM research activities and potential deployment. Governance of SRM indoor research, small-scale outdoor experiments and large-scale operational deployment should be differentiated.

• Creation of a broader framework for the governance of the stratosphere, which would address the changes from SAI activities. Other activities such as rocket launches may also be considered, as few regulatory or governance structures currently exist for the stratosphere. 

• Promote inclusivity in the evolution of SRM governance and research. This process needs to be adequately resourced to enable equitable participation and contribution in discussions on a broad range of issues with all stakeholders, especially those from developing countries, who are currently much less engaged in SRM discussion and research. The UN is well positioned to promote a globally inclusive conversation on SRM.

Source: UNEP