Scientific advice on Solar Radiation Modification: An interview with Naki Nakićenović and Benjamin Sovacool#
Naki Nakićenović MAE and Benjamin Sovacool MAE reflect on the recent work on SRM by the Scientific Advice Mechanism and their role within it.
Professor Benjamin Sovacool and Professor Naki Nakićenović
In December 2024, the Scientific Advice Mechanism published a Scientific Opinion on Solar Radiation Modification
(SRM), informed by an Evidence Review Report produced by SAPEA. The evidence review was coordinated by Academia Europaea Cardiff Knowledge Hub, with AE acting as the Lead Academy.
Professor Naki Nakićenović MAE was co-lead in the Group of Chief Scientific Advisors that delivered the Scientific Opinion. He is Deputy-Chair of the Group, as well as Emeritus Research Scholar at the International Institute for Applied Systems Analysis
(IIASA). Professor Nakićenović was elected as member of the Economics, Business and Management Sciences section in 2021.
Professor Benjamin K. Sovacool MAE co-chaired the SAPEA Working Group responsible for the Evidence Review Report. Professor Sovacool specialises in energy policy, climate change mitigation, and energy justice. He serves as the Director of the Boston University Institute for Global Sustainability
and also holds posts at Sussex University (UK) and Aarhus University (Denmark). Professor Benjamin K. Sovacool was elected as member of the Economics, Business and Management Sciences section in 2020.
Read the interview#
Professor Nakićenović, what was your interest in co-leading the work on the Scientific Opinion for the Group of Chief Scientific Advisors?
“I was happy to take on the co-lead for the Group of Chief Scientific Advisors, together with Eric Lambin. It’s a topic that goes back 50 years. The first paper was in 1975 by a Russian climatologist, Mikhail Budyko, with a very simple model to forecast exactly what would happen if greenhouse gas emissions did not decline.
When we started this work, we were not yet over 1.5 degrees Celsius. As of last year we are, and so probably on average this decade is going to be very hot. I think this is one of the reasons to look at all of the options available; SRM is one of those options. However, SRM poses a much higher risk than climate change mitigation.
That was my main motivation to work on this Scientific Opinion. We are on a very slippery slope of ever-increasing temperature and negative impacts of climate change. I had a strong feeling that Europe should be in the lead in becoming the first climate-neutral continent. I realise that based on the scientific evidence there are many risks associated with SRM. There might possibly be an opportunity in the long run, as the science and methods of deployment progress, but it should certainly not detract from mitigation and adaptation.”
Professor Sovacool, why did you decide to take up the role of Co-Chair of the SAPEA Working Group on SRM?
“I first learned about these options about 20 years ago. We explored them in a 2011 book, looking at global energy security and climate change. Our thinking then was that we had three main types of approach. These were mitigation, climate adaptation and geoengineering options, which included carbon dioxide removal (CDR) and solar radiation management (SRM). Even back in 2009 when we were writing the book, there was a proposed moratorium at the UN. We became aware of the potential of these options, especially low-cost and low-risk ones like albedo management, all the way to options like ocean fertilisation, aerosol injection and sunshades. I’ve been following them with great interest as a social scientist.
It wasn’t until we won a large ERC synergy grant called GENIE (GeoEngineering and Negative Emissions pathways in Europe) that we could explore further. I was PI of GENIE, and we’ve been doing work with wonderful colleagues at IIASA.
The current work for the Scientific Advice Mechanism was an opportunity I couldn’t resist, because it was a real chance to contribute to what I knew would be a major influential report on a controversial topic, that needed representation from the social sciences.”
(GeoEngineering and Negative Emissions pathways in Europe) that we could explore further. I was PI of GENIE, and we’ve been doing work with wonderful colleagues at IIASA.
The current work for the Scientific Advice Mechanism was an opportunity I couldn’t resist, because it was a real chance to contribute to what I knew would be a major influential report on a controversial topic, that needed representation from the social sciences.”
Benjamin, your foreword in the Evidence Review Report states that this is a highly controversial topic. Could you tell us something about this? How did an interdisciplinary Working Group manage to navigate its way through the process of reviewing the evidence?
“‘Controversial’ and ‘contested’ are two words that accurately describe it. It’s a multi-faceted controversy that you can address at technical, economic, political, social and ethical levels. Technically, there are still huge debates over what type of deployment we might undertake, for example, stratospheric aerosol injection (SAI), mirrors, reflectors or sunshades at high altitude. The engineering community hasn’t yet come to a consensus over how we do it. At such an early stage of technology development, we can’t agree.
Then, there is no single way to go about it politically. For example, who would deploy and who is liable for managing risks? How is it governed economically? Is it cost-effective, and what would the impact be on our approach to mitigation? Ethically, we need to think about termination shock and moral hazard, particularly in the context of indigenous groups. Who decides on these issues? We need to think about the conditions under which decisions are made.
In one of our GENIE papers cited in the recent report, we map a whole ecology of public participation that shows that the public is fragmented on what it wants. Some people don’t care at all and want no engagement, others want strict regulation and governance, and those in the middle want referendums, focus groups and citizens’ assemblies. The public is even contested regarding their own role, and how they envision it going forward.
The beauty of the recent report is that it captures all those nuances and contestations in the literature, because we present both sides. We give symmetry to both the technical and non-technical, and to the risks and the benefits. That’s what makes the report unique and independent.”
Then, there is no single way to go about it politically. For example, who would deploy and who is liable for managing risks? How is it governed economically? Is it cost-effective, and what would the impact be on our approach to mitigation? Ethically, we need to think about termination shock and moral hazard, particularly in the context of indigenous groups. Who decides on these issues? We need to think about the conditions under which decisions are made.
In one of our GENIE papers
cited in the recent report, we map a whole ecology of public participation that shows that the public is fragmented on what it wants. Some people don’t care at all and want no engagement, others want strict regulation and governance, and those in the middle want referendums, focus groups and citizens’ assemblies. The public is even contested regarding their own role, and how they envision it going forward.
The beauty of the recent report is that it captures all those nuances and contestations in the literature, because we present both sides. We give symmetry to both the technical and non-technical, and to the risks and the benefits. That’s what makes the report unique and independent.”
Naki, did the nature of this topic influence the way the Group approached its task of producing a Scientific Opinion?
“I would say in principle no, because our process is always the same, regardless of the topic. I think all the Advisors thought it was a good idea and an important topic. I was very happy to see that SAPEA organised a great team to work on it. I did expect the topic to be very controversial. Indeed, I expected it to be even more controversial than it turned out, since the scientific uncertainty is huge. The problem of climate change is itself very difficult, and is typical of a ‘wicked’ problem.
We also knew that there was going to be a report by the European Group on Ethics, which is independent from the Advisors. It was important to us that the Evidence Review Report looked into the ethical and societal issues. All in all, this Scientific Opinion had many unique facets.”
We also knew that there was going to be a report by the European Group on Ethics
, which is independent from the Advisors. It was important to us that the Evidence Review Report looked into the ethical and societal issues. All in all, this Scientific Opinion had many unique facets.”
Benjamin, what were the most important points that came out of the evidence review, from your perspective?
“We ended up with three core social science chapters. Each of them is very novel and reflects the evidence.
The first is about actors, stakeholders and social acceptance. Chad Baum captured every single study looking at social acceptance of SRM going back 30 years, as well as a content analysis of the seven or eight themes in all that literature. There is also an assessment of actor networks, and a summary of all the expert participation surveys going back 30 years. This is the first time that this evidence has been compiled neutrally and objectively.
The second looked at ethics and risks. These include geopolitics and security, economic and institutional risks, and all the ethical risks in terms of not just justice, but also responsibility, indigenous groups and future generations.
The third was policy, governance and legal issues. I have not seen such a comprehensive treatment of the legal issues, from the UN Law of the Sea, to the London Convention, to the precautionary principle.
The report is a synthesis of evidence that no one else has yet done. The fact that half of the report focuses on these social science issues is probably the single biggest strength. Apart from it also being very recent and up to date, it gives you where the evidence was as of 2024.”
The first is about actors, stakeholders and social acceptance. Chad Baum captured every single study looking at social acceptance of SRM going back 30 years, as well as a content analysis of the seven or eight themes in all that literature. There is also an assessment of actor networks, and a summary of all the expert participation surveys going back 30 years. This is the first time that this evidence has been compiled neutrally and objectively.
The second looked at ethics and risks. These include geopolitics and security, economic and institutional risks, and all the ethical risks in terms of not just justice, but also responsibility, indigenous groups and future generations.
The third was policy, governance and legal issues. I have not seen such a comprehensive treatment of the legal issues, from the UN Law of the Sea, to the London Convention, to the precautionary principle.
The report is a synthesis of evidence that no one else has yet done. The fact that half of the report focuses on these social science issues is probably the single biggest strength. Apart from it also being very recent and up to date, it gives you where the evidence was as of 2024.”
Naki, what were the key recommendations of the Group of Chief Scientific Advisors?
“Picking up on what Benjamin said, we have an entire section in the Scientific Opinion dedicated to policies. It’s important to consider not just the European Union, but also global policies as the context for making our recommendations. Our recommendations are based on the evidence, and I’d also like to mention that a comprehensive literature review conducted by SAPEA was extremely helpful in shaping our work. This forms the background to our approach.
As important as it was that the Evidence Review report was comprehensive, equally important was that our recommendations are succinct, so that decision-makers might read them. Against that backdrop, we agreed on five principal recommendations.
Our number one and most fundamental and general recommendation is that mitigation- the reduction of emissions and adaptation to climate change- is a must and needs to be the highest priority. We know it can be done if sufficient investments and sufficient consumer behaviour goes in that direction.
Our second recommendation is that the European Union should propose a moratorium on SRM deployment as a measure for combating climate change- at least for 5 or 10 years. As one of a number of sub-recommendations, we highlight that deep uncertainties about SRM deployment need to be considered, and that it might be inconsistent with the precautionary principle that is so important in the European Union.
There is a recommendation also to negotiate a global governance system that Europe should take a lead on for the research and deployment of SRM. It needs to be anchored in international organisations and governmental bodies like the UN. The position of Europe in those negotiations should be for the non-deployment of SRM in the foreseeable future, until we have more information and more certainty.
The fourth recommendation is about SRM research. It should be conducted with rigour, responsibility and in accordance with the European principles of ethical research. We already have those- they’re applied to essentially all European research projects that are funded under the Horizon programme, ERC grants etc. One must declare any conflict of interest and ethical issues of concern.
The fifth recommendation is to reassess the scientific evidence every 5 or 10 years, because it’s likely to evolve very quickly. The evidence review mentions citizens’ assemblies, and my personal experience with citizens’ assemblies is very positive. Equally important is that the scientific community needs to be supported on climate research and on SRM research. There should also be funding for the European scientific community to participate in international intergovernmental assessments. A sub-recommendation was to develop techniques and experimental platforms for the detection and attribution of deployment of SRM anywhere in the world. Particular emphasis needs to be on rogue deployment, however one defines that.”
As important as it was that the Evidence Review report was comprehensive, equally important was that our recommendations are succinct, so that decision-makers might read them. Against that backdrop, we agreed on five principal recommendations.
Our number one and most fundamental and general recommendation is that mitigation- the reduction of emissions and adaptation to climate change- is a must and needs to be the highest priority. We know it can be done if sufficient investments and sufficient consumer behaviour goes in that direction.
Our second recommendation is that the European Union should propose a moratorium on SRM deployment as a measure for combating climate change- at least for 5 or 10 years. As one of a number of sub-recommendations, we highlight that deep uncertainties about SRM deployment need to be considered, and that it might be inconsistent with the precautionary principle that is so important in the European Union.
There is a recommendation also to negotiate a global governance system that Europe should take a lead on for the research and deployment of SRM. It needs to be anchored in international organisations and governmental bodies like the UN. The position of Europe in those negotiations should be for the non-deployment of SRM in the foreseeable future, until we have more information and more certainty.
The fourth recommendation is about SRM research. It should be conducted with rigour, responsibility and in accordance with the European principles of ethical research. We already have those- they’re applied to essentially all European research projects that are funded under the Horizon programme, ERC grants etc. One must declare any conflict of interest and ethical issues of concern.
The fifth recommendation is to reassess the scientific evidence every 5 or 10 years, because it’s likely to evolve very quickly. The evidence review mentions citizens’ assemblies, and my personal experience with citizens’ assemblies is very positive. Equally important is that the scientific community needs to be supported on climate research and on SRM research. There should also be funding for the European scientific community to participate in international intergovernmental assessments. A sub-recommendation was to develop techniques and experimental platforms for the detection and attribution of deployment of SRM anywhere in the world. Particular emphasis needs to be on rogue deployment, however one defines that.”
Naki and Benjamin, any reflections on the path SRM could take from here, both in Europe and worldwide?
(Naki) “We are not where we should be. We have exceeded the lower Paris Agreement target, and we are going to exceed 2 degrees as well. In this kind of reality, SRM may play a more prominent role, but one of the risks is that it’s deployed before we know whether we actually should deploy it or not. You can try to assess the risks through modelling and analysis, and analogues. But we don’t really know the risks until we have clarity in the laboratory, and the first attempted experiments would need to be controlled very carefully. We have to be extra-cautious on the way forward. At the same time if we continue in this direction and we cause a tipping in the Earth systems- not just climate, but in ecosystems as well – that could increase pressure ever more towards SRM.
On the other hand, we know mitigation and adaptation would bring many co-benefits for everybody. Our general recommendation is that this should be the way forward. If SRM works, we’ll be lucky to have another option- but we need to rely on the things that we know will definitely work.”
On the other hand, we know mitigation and adaptation would bring many co-benefits for everybody. Our general recommendation is that this should be the way forward. If SRM works, we’ll be lucky to have another option- but we need to rely on the things that we know will definitely work.”
(Benjamin) “There’s so much uncertainty that I think anyone would be foolish to try to guess on levels of deployment. Our expert elicitation studies showed that. Even then, it could be 2055 onwards for any largescale deployment.
GENIE has run large-scale surveys. We found although the Mexican government is moving to a ban, the Mexican publics were the most supportive of SRM technology. In our global survey of 22 countries, including 11 in the Global North and 11 in the Global South, we found that Global South countries strongly prefer deployment and research, and also less restrictive governance compared to the Global North. Indigenous groups preferred it more than non-indigenous groups, and when we started to get into some of the reasons why, we could see that exposure to climate hazards was a strong predictor of whether they support or oppose.
I suspect if you look at SRM options, albedo management, white roofs and white roads, will be deployed – they already are in Sierra Leone, for example. It’s low-tech, low risk- a win-win approach. Other methods being deployed include marine cloud brightening, cloud thinning, fogging, and shading, which are already being deployed in the Great Barrier Reef. Fogging and shading is just mist and seawater, so relatively low-risk and low-intervention, with immediate benefits to lower temperature stress.
The key question is over aerosol injection and sunshades. I think the public is still largely against it, or at least the active public. I can’t see SAI being deployed, at least in the next 5 years. As part of our research, we asked people to imagine a global geoengineering future by 2030. We had 299 distinct futures, amazingly- but 5 of those recurred. There were two SRM futures, both negative. I think it’s interesting that the public, when they think about a future of sunshades and SAI, think of dystopian futures that have far more risks than benefits.”
GENIE has run large-scale surveys. We found although the Mexican government is moving to a ban, the Mexican publics were the most supportive of SRM technology. In our global survey of 22 countries, including 11 in the Global North and 11 in the Global South, we found that Global South countries strongly prefer deployment and research, and also less restrictive governance compared to the Global North. Indigenous groups preferred it more than non-indigenous groups, and when we started to get into some of the reasons why, we could see that exposure to climate hazards was a strong predictor of whether they support or oppose.
I suspect if you look at SRM options, albedo management, white roofs and white roads, will be deployed – they already are in Sierra Leone, for example. It’s low-tech, low risk- a win-win approach. Other methods being deployed include marine cloud brightening, cloud thinning, fogging, and shading, which are already being deployed in the Great Barrier Reef. Fogging and shading is just mist and seawater, so relatively low-risk and low-intervention, with immediate benefits to lower temperature stress.
The key question is over aerosol injection and sunshades. I think the public is still largely against it, or at least the active public. I can’t see SAI being deployed, at least in the next 5 years. As part of our research, we asked people to imagine a global geoengineering future by 2030. We had 299 distinct futures, amazingly- but 5 of those recurred. There were two SRM futures, both negative. I think it’s interesting that the public, when they think about a future of sunshades and SAI, think of dystopian futures that have far more risks than benefits.”
Watch the SRM webinar series#
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<iframe width="640" height="360" src="https://www.youtube.com/embed/XlKaKTgo9H8" title="SAM webinar - Solar Radiation Modification: What’s at stake for society?" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
The interview was posted on the 25th February 2025 and conducted by the Academia Europaea Cardiff Knowledge Hub.
For further information please contact AECardiffHub@cardiff.ac.uk.
.For further information please contact AECardiffHub@cardiff.ac.uk
.
