1. Introduction

Solar geoengineering is a set of proposed emerging technologies that seek to cool the Earth either by reflecting sunlight away from the Earth or by allowing more heat to leave the Earth’s atmosphere. These proposed technologies range from low tech approaches like painting rooftops white, to space age solutions like installing giant mirrors in outer space. Given this diversity, there is great variation in the potential risks and benefits by technology type. We focus here on a particular proposed solar geoengineering technology known as stratospheric aerosol injection (SAI). Although some of the ethical issues discussed in this essay extend beyond SAI to other solar geoengineering technologies. If ever developed and deployed, SAI would inject reflective particles into the stratosphere to reflect sunlight away from the Earth. It is often described as inspired by large-scale volcanic eruptions, such as Mt. Pinatubo in 1991, after which temporary global cooling has been empirically observed [1].

SAI is controversial for a host of reasons. Some see it as a temporary measure to buy time and avoid some of the worst climate impacts while we continue ramping up emission reductions and enhancing adaptation capacity [2]. Others see it as a distraction, pulling time, money, and political will away from mitigation and adaptation. Although this ‘mitigation deterrence’ hypothesis has likely been the most prolific argument against SAI [3] there are many more reasons for concern [4]. These include concerns about technological lock-in (i.e., the idea that once we start using this technology it will be difficult if not impossible to stop using it) (McKinnon 2018), and termination shock (i.e.,what might happen if we suddenly had to stop using SAI for any reason), among other concerns [5,6].

Importantly, these concerns have catalyzed debates about justice. Some argue that in the shadow of decades of failed global climate diplomacy, SAI could be used to avert the worst impacts for the world’s most vulnerable populations [7]. Others argue it is impossible to govern SAI in a just and inclusive way [8,9]. Still others point out that the debate itself is unjust because justice claims have largely been leveraged by those in the global north on behalf of those in the global south, terming this practice ‘performatively colonial’ [10]. These competing perspectives around justice are also visible in the myriad governance proposals around SAI. Whereas justice is featured prominently in some [11,12], others are more reluctant to invoke justice at the level of principles [13–15]

Although there is a rich tapestry of informal governance structures, formal public governance has been challenging to establish [16]. Yet, formal public governance is needed more than ever with public and private actors aggressively moving into this largely unregulated space. The United Kingdom’s Advanced Research and Innovation Agency (ARIA) doled out more than $74million in 2025 for research on SAI and related technologies, including for what might be the world's first outdoor experiments. Stardust Solutions, a private firm headquartered in Tel Aviv and registered in Delaware, has raised at least $75million in venture-based capital with a view towards securing government contracts to deploy SAI, including from the U.S. Trump administration [17].

These developments suggest that SAI may be approaching an inflection point. It’s backed by more money than ever before, and it’s entering a largely unregulated space. The recommendations outlined in existing research governance reports [18,19] have been largely ignored by the private sector and justice does not appear to be part of the discussion. It is therefore more important now than ever to map the myriad justice issues surrounding SAI with a view to making clear for decision-makers what the issues are and how we can address them as SAI inches ever closer to the center of the political stage.

In what follows, we outline the discussions around three core narratives at the intersection of SAI and justice: intergenerational ethics; participatory justice; and recognitional/reparational justice. Rather than essentializing a justice claim based on pre-determined political agendas, we embrace the complexity of justice claims in this space, also as reflected in governance proposals as noted above. Our goal here is to illuminate the terrain so readers can see the multiple ethical challenges that must be navigated if SAI efforts are to make any plausible claim to avoiding severe injustices. We take no stand here on whether SAI efforts are - or could be - capable of meeting these challenges.

Our discussions have a procedural focus. In political philosophy, procedural justice is often understood as inhering in features of processes that are designed to deliver just outcomes. For example, if you want to achieve a fair distribution of cake as an outcome, then the person cutting the cake should be the last one to choose a slice. John Rawls’ famous ‘original position’ thought experiment for choosing principles of justice instantiates procedural justice in this sense [20]. Rawls invites us to imagine what principles of justice we would agree to if we were (inter alia) placed behind a ‘veil of ignorance’ denying us knowledge of our personal characteristics and circumstances such as our religious beliefs, race, gender, level of intelligence, class etc. Whatever principles would be chosen by people engaged in this imaginary process are just principles. The procedure guarantees that the principles of justice chosen will be fair and impartial: just procedures deliver just outcomes.

In evaluating and mapping the justice claims surrounding SAI, we adopt a catholic lens. We think that justice claims can legitimately focus on questions of participation, recognition and distribution, and adopt state-centric solutions (e.g., governance through existing institutions) [21]. But we also commit to questions of race, gender, colonization and capitalism as central to thinking about justice. This delivers calls for much deeper structural changes being necessary to remedy injustice (e.g., dismantling capitalism) [21–23]. Justice claims can be made using various concepts and critiques that deliver more, or less, revolutionary proposals for institutional change. We do not see frames along this spectrum as necessarily mutually exclusive or in competition. Indeed, we think that at least some important justice-based arguments from different places on this spectrum can point in the same direction: when all roads lead to Rome in this way we have powerful reasons for concern. For example, we can understand justice-based arguments for Global South leadership as related to, justice-as-recognition; that is, a justice-based requirement to accord respect to all people who could be affected by SAI. But we can also see these arguments in terms of empowering victims of colonialism in the face of SAI development that could further entrench historical injustices, which could be part of a much larger justice-oriented project of redistributing power from the Global North to the Global South.

All this said, it can also be the case that all roads do not lead to Rome; that is, that justice claims made in one domain can be in tension with those in other domains. For example, if intergenerational justice requires committing resources to building up SAI governance institutions to protect the far future, what does this mean for similar efforts to deliver on participatory and recognitional justice for presently living people? Is there a clash of justice claims here, or is it simply that case that justice requires we deliver on both intergenerational and intragenerational demands? We cannot settle such big questions here - we note them as an additional layer of complexity to be addressed as the implications of these justice claims are worked out.

2. Participatory justice

Participatory justice demands that impacted individuals and communities have the right to participate in decisions that impact them and are a pre-condition for social justice (Skinner-Thompson 2022, Schlosberg 2004). Importantly, participatory justice requires meaningful opportunities for engagement, where impacted parties have both access and capacity to offer input, and where undue burdens are not placed on marginalized communities [24]. As defined by the landmark First National People of Color Leadership Summit in 1991, environmental justice “demands the right to participate as equal partners at every level of decision-making, including needs assessment, planning, implementation, enforcement and evaluation” [25]. Although the directive is clear, the operationalization of participatory justice in the context of SAI in practice has been fraught. There has been much debate about who has the right to participate (scope), in what types of decisions (scale), and which constraints limit the depth of participation that is currently possible (depth). In this section we unpack some of the major areas of contestation along each of these three dimensions and illuminate the nuance and complication around the justice claims in this area.

Scope has been a central debate in the field. The distribution of risk for any SAI deployment would be global. Yet, existing forums that host global dialogue have been reluctant to take on the issue, making global engagement extremely difficult. Members of the United Nations Environmental Assembly (UNEA), for example, have twice now been unable to agree on even modest resolutions calling for definition of terms and assessment of existing science and governance [26–28]. Despite many calls for their engagement, the United Nations Framework Convention on Climate Change (UNFCCC) has also not substantively engaged the topic [29]. The difficulty of international engagement is compounded by a call from proponents of the non-use agreement who have asked countries to “object to future institutionalization of planetary solar geoengineering as a policy option in relevant international institutions, including in assessments by the Intergovernmental Panel on Climate Change” [8]. This call has contributed to stymieing the political will for international institutions, who have deep experience with hosting international engagement forums, such as UNEP, from taking on this work. Indeed, some countries are already beginning to voice support for a non-use agreement [30]. Whereas non-use proponents likely see this as justice ‘win,’ we are not so sure. We agree that there are deep justice concerns with SAI. However, we question whether an effort largely led by academics in the global north (~13 of 16 co-authors are based in the US, Europe, or Australia) calling for a removal of participatory mechanisms via international institutions for the rest of the world is rather an erosion of participatory justice? (We note that our disagreement with the procedural claims in the non-use agreement as related to international institutions does not necessarily mean we disagree with all elements of the proposal. For example, we agree with the authors that patents around solar geoengineering technologies is a dangerous proposition, and should be controlled through governance.)

An equally important debate around scope relates to the participation in the context of small scale proposed research, such as outdoor experiments. If an experiment takes place in a locality and is not projected to have any environmental impact, who must be notified and/or invited to participate in discussions around the experiment to meet the demands of participatory justice? Is it the local community only? Given the potential global reach if SAI is ever scaled up for deployment, is it rather the international community? Is it anyone at all if the experiment has no measurable environmental impacts? The recently cancelled small scale outdoor SAI experiment out of Harvard University, known as SCoPEX (Stratospheric Controlled Outdoor Perturbation Experiment) set up an advisory committee to help it sort out this, among other, governance issues. While the committee agreed that local communities have a right to participate and made extensive suggestions for how this should be done, the committee did not reach agreement on if and under what conditions any global publics have the right to engage around this proposed small scale outdoor experiment [31]. This debate has been reflected in other deliberative advisory bodies as well, such as the United Nations Environment Programme’s (UNEP) committee that wrote the One Atmosphere report on solar geoengineering [32].

The question of scale has been equally contested. Central to that debate is the question about if small scale research with no projected environmental impact requires public engagement or if engagement should be limited to deployment proposals. Again SCoPEx provides a useful lens through which to see the contested nature of these justice claims. In 2021, the advisory committee was divided about whether an engineering test flight in Sweden could proceed without public engagement. Ultimately, the majority of the committee decided it could, following a safety review [31]. This triggered massive resistance from the local indigenous community, the Saami, who in cooperation with several large international NGOs, was able to convince the committee to recommend against the experiment moving forward, and the experiment in Sweden was subsequently cancelled. This case highlights the importance of thinking about justice concerns beyond just the near term and the local. Rather, scientists and those that advise them on questions of participatory justice must also consider the global, long term, and even intergenerational impacts of this work.

A third dimension along which justice is contested in this space is related to the depth of the engagement. By depth, we focus here on the barriers that inhibit deep global engagement from happening. These barriers are often discussed in the literature as limits on scientific and governance capacity. On the former, despite high levels of climate vulnerability in the Global South, more than 90% of all academic papers on the topic across disciplines have been produced by scholars from North America and Europe [33]. This limits the ability of governments in the Global South to effectively participate in any ongoing political discussions about SAI. It has also historically limited the amount of scientific data available about potential geoengineering impacts (or benefits) in the Global South. This is a problem for participatory justice because it systematically excludes those who are most impacted by climate change and potentially by SAI from shaping the knowledge that can ultimately guide decision-making on this topic, whether that be to move it forward or ban it altogether. Some important strides have been made by UK-based NGO, The Degrees Initiative, which funds scholars in the Global South to conduct scientific research, including social sciences, on SAI. Since 2018, The Degrees Initiative has awarded more than $3M in grants to 193 scholars across 23 developing countries, which has resulted in 62 research articles to date [34].

Newer to discussions about capacity needs in the Global South are conversations about governance capacity. Underscoring calls from African scholars for more engagement in SAI science and governance [35,36], Dove et al (2024) argue that capacity building for science alone is insufficient to enable robust governance leadership. Following Dove and Talati (2023) they define governance by capacity building as: “A process through which individuals and/or organizations mobilize and sustain knowledge, skills, tools, and practices that enable them to engage in the development and implementation of local, national, and international forms of governance of research and deployment of emerging climate intervention technologies (2).” Importantly, they argue that such efforts should build on existing strengths and be ‘owned’ by Global South participants to ensure durable capacity over time. Talati’s NGO, The Alliance for Just Deliberation on Solar Geoengineering (DSG) has begun to take strides at catalyzing this work. DSG hosts capacity building workshops around the world with various types of interested parties, including NGOs and policy makers. They aim to increase awareness and foster dialogue between actors in the Global South with a view towards building capacity for governance engagement.

The capacity building work done by organizations like The Degrees Initiative and DSG, both based in the Global North, have also been a site of competing justice claims. The Degrees Initiative, for example, was recently accused of pushing a neo-colonial agenda and of “turning Africa into a laboratory” by the Hands Off Mother Earth (HOME) Alliance (2025). In response, a group of 30 African researchers who together form the Africa Climate Intervention Research hub, wrote a letter defending Degrees, and advocating for the importance of African scientists doing their own research, and for “equity through participation, not exclusion” [37]. This push and pull over claims to justice illuminates just how complex this terrain remains. What constitutes justice is contested and unclear.

3. Recognitional justice

Recognitional justice has also emerged as a critical dimension of SAI discourse. Recognitional justice demands acknowledgment, respect, and equal consideration of the identities, experiences, values, and knowledge systems of those affected by climate policies and environmental decision making [38,39]. It does not simply ask who participates, but whose ways of knowing are regarded as legitimate, whose concerns are considered credible, and whose visions of a desirable future for SAI shape governance. In the context of SAI, recognitional justice has become particularly important because the technology raises questions that cannot be answered through atmospheric science alone, but also require engagement with ethical, political, cultural, and historical understandings of climate risk and responsibility. Yet what recognitional justice requires in practice is sometimes contested.

One area of concern is about what forms of knowledge should inform SAI governance. Much of the existing research on SAI has been produced through Earth system modelling, atmospheric science, economics, and engineering, disciplines that are mainly concentrated within institutions in North America and Europe [40,41]. From one perspective, this concentration simply reflects where scientific expertise and research infrastructure currently exist. Proponents argue that robust physical science must necessarily provide the foundation upon which governance decisions are built, while acknowledging that broader societal engagement should accompany scientific progress. On this view, privileging scientific evidence is not a form of injustice but rather a prerequisite for responsible governance of a technology with potentially global climatic consequences.

Others, however, argue that this framing itself constitutes injustice because it privileges particular epistemologies while marginalizing others. Critics contend that the dominance of technocratic approaches systematically sidelines indigenous knowledge, local ecological knowledge, lived experience, and alternative understandings of human relationships with climate and nature [9,42]. As a result, questions considered central by many communities including cultural values, historical responsibility, spiritual relationships with the environment, and colonial legacies often remain peripheral. From this perspective, recognitional justice requires not merely expanding participation but fundamentally broadening what counts as legitimate knowledge in evaluating SAI and in governance discussions [43,44].

A second area of contest concerns whose vulnerabilities should shape research and governance priorities. SAI is a global technology yet climate risks are neither evenly distributed nor experienced in uniform ways [45,46]. Modelling studies suggest that SAI may alter regional precipitation patterns, monsoon systems, drought frequency, and agricultural productivity in ways that could disproportionately affect many regions of Africa, Asia, and Latin America [46–51]. This raises difficult questions about whose vulnerabilities should receive priority in both research and governance.

Here again competing justice claims emerge. There is an argument that because SAI seeks to reduce global climate damages overall, governance should focus primarily on aggregate welfare and climatic outcomes. Another argues that such an approach obscures historically produced inequalities and fails to recognize the differentiated vulnerabilities of communities already bearing disproportionate burdens from climate change. From this perspective, recognitional justice requires that research and governance agendas begin from the experiences and priorities of those most vulnerable to both climate change and potential SAI impacts, rather than treating these concerns as secondary considerations. This further relates to the concerns on leadership and authority in SAI governance as much of the scientific research, funding, governance scholarship, and institutional agenda-setting surrounding SAI remains concentrated within organisations based in Europe and North America (Parson 2021; McLaren and Corry 2021). This concentration has generated increasing concern that the framing of SAI research regarding acceptable risks, desirable climate futures, and appropriate governance arrangements are biased with Global North priorities.

At the same time, disagreement exists over how this imbalance should be addressed. Some scholars (Dove et al. 2026; Dove et al. 2024; Rahman et al. 2018) advocate expanding participation within existing international scientific and governance institutions through increased representation, funding, and capacity building for researchers and policymakers from the Global South as seen in organisations such as the Degrees Initiative and DSG increasing research and governance capacity across developing countries through grants, workshops, and regional dialogues to seek greater representation within existing systems. Critics question whether capacity-building initiatives led and funded primarily from the Global North does not risk reproducing existing asymmetries of power, framing, and agenda-setting [52]. Others also argue that inclusion alone is insufficient because existing institutional structures continue to privilege Northern assumptions and methodologies. Instead, they call for governance approaches in which Global South actors exercise genuine leadership over research agendas, governance priorities, and ethical frameworks calling for transforming who possesses authority to define the questions, methods, and purposes of SAI governance [36,53]. As with participatory justice, competing actors therefore invoke recognitional justice to support different governance pathways.

Finally, recognitional justice also extends beyond whose knowledge is recognized today to whose values shape the futures that SAI research implicitly seeks to create. According to Preston and Carr (2019), evaluating the justice of climate engineering requires greater attention to relationships, vulnerability, care, narrative, context, and power dimensions that conventional risk assessment frequently overlooks. Recognitional justice therefore requires making these underlying value commitments explicit and opening them to broader inclusive scrutiny. Decisions about acceptable climatic conditions, tolerable environmental risks, and desirable trajectories of technological intervention necessarily embed normative assumptions about human well-being and humanity's relationship with the natural world. Yet these assumptions often remain implicit within scientific assessments and governance proposals.

Taken together, these debates demonstrate that recognitional justice in the SAI context cannot be reduced to greater representation alone. Rather, it raises fundamental questions about epistemic authority, political power, and the legitimacy of different ways of understanding climate risks and futures. Whether recognitional justice is best achieved through expanding participation within existing institutions, transforming governance leadership, pluralizing accepted forms of knowledge, or some combination of these approaches remains unresolved. Like participatory justice, recognitional justice in the SAI debate is therefore best understood not as a settled ethical principle but as an active site of contestation over whose knowledge, values, and visions of climate futures should guide decisions with potentially planetary consequences.

4. Intergenerational justice & ethics

In order for SAI to fulfil its promise of ‘buying time’ for raising mitigation ambition, any deployment would have to be on a time scale of centuries [54]. This makes a commitment to intergenerational justice fundamental to the ethical acceptability of SAI research or deployment. We need to know that SAI efforts in the present take seriously what we owe to future people who may have to live with the consequences of these efforts. But what, exactly, this commitment means for SAI is contested.

For some, this means accelerating responsible research towards a safe deployable technology that can deliver SAI to future people who might need it in the face of an even worse climate crisis. That is, given a future nightmare scenario of climate catastrophe, SAI is the ‘lesser evil’. On this view, we we have a duty to ‘arm’ future people with SAI technology which means progressing research and development now.. This view is contested however. Some argue that ‘advance planning for a nightmare scenario is itself morally inappropriate when that nightmare is to be brought on by one’s own moral failure’ [55]. If climate catastrophe for future people will happen as a result of our failures to mitigate, is planning for this failure by progressing SAI R&D itself morally questionable?

A different way to interpret the demands of intergenerational justice in the SAI space is that the dangers of a future deployment are too great, and therefore we ought not to advance this technology at all. On this view, the risks to future people of an ungoverned (perhaps, ungovernable) SAI deployment include termination shock, the amplification of existing unjust global inequalities of power and advantage, and the weaponisation of the technology.

As with recognition and participatory justice, these concerns are not clear cut. Rather, there are many positions on what it means to commit to intergenerational justice with respect to SAI - in particular, with respect to research. Here, the terrain is less well mapped, yet urgent given that research is accelerating. In particular, the short time scales used in much SAI research raise concerns about intergenerational justice.

For example, an ethical commitment to take seriously the rights and interests of people in the – potentially far – future would mean making serious efforts to understand how what we are doing now could impact future people [56–58]. Yet, SAI research does not appear to include such efforts. Instead, geoengineering efforts might appear largely to serve only the interests of the contemporary generation [59]. There are at least three sets of examples of SAI research practice and assumptions that should raise alarm bells about this practice

First, SAI model runs typically use short time-horizons. Some models and scenarios use timeframes of the next 10–50 years when investigating the impacts of SAI [60–62], whereas others extend the horizon only to 70–100 years [63–65]. While there are a few useful exceptions [66,67], the overall trend leaves us largely blind to how future generations might be impacted by SAI. Second, most SAI models envision a ‘fast start’ in only 10–25 years [68–70]. This focus on the immediate future can preclude thinking about what people who need to start a deployment in, say, 100 years might need to know. Third, the questions of how to maintain SAI into the future, and ultimately how to exit any deployment, has a low priority in research. As late as 2022 the MacMartin group reported that “only one [paper] simulates a deliberate gradual phaseout to a warmer world” [71]. This creates a situation where most models effectively assume that SAI will be ongoing, continuing indefinitely into the future. While a few more papers have appeared since then [54,64], questions of maintenance and exit remain relatively neglected.These 2024 studies might lay a critical foundation for better integration of intergenerational justice considerations into future decision making around SAI.

A second set of worries about the alignment of SAI with intergenerational justice is more general, and is barely mapped at all. The core of these worries is that SAI could create a ‘new normal’ for future people living in a geoengineered world. That is, a SAI deployment could transform the natural world, rather than return it to an earlier climatic state. What would this do to nature? We do not know: at present, barely any SAI research addresses this question [72–74]. This in itself should cause grave concern: ethically acceptable geoengineering should take into account the interests of nonhuman nature [75–77]. With a focus on intergenerational justice, however, a particular question arises in the context of what we are learning from conservation biology about ‘shifting baseline syndrome’ [78]. Shifting baseline syndrome is the phenomenon whereby the baselines people use to make judgements about the quality of their environments reflect their own lived experiences rather than the realities of environmental decline (or improvement) over time. When this happens, people fail to notice environmental losses. A core driver of shifting baselines is the ‘extinction of experience’: the well documented progressive loss of direct human-nature interactions [79–82]. There is mounting evidence from conservation biology that shifting environmental baselines are common, operating in many types of environments, cross-cultural, and that these baselines can shift fast - sometimes over the course of just one generation [82–94]. Shifting environmental baselines can affect people’s motivations to improve their degraded environmental conditions [94]. Not surprisingly, if you fail to realise how much has been lost since your grandparents’ time, you are not well positioned to take action.

There are unmapped ethical questions about what shifting baselines and the extinction of experience mean for intergenerational justice more broadly in our times of environmental crisis. In particular, there are urgent questions about ‘intergenerational environmental blinding’ [59]. What questions are raised for ethically acceptable SAI in particular? Taking seriously the interests of future people means being committed to enabling future people to safely exit any SAI deployment [95]. A future geoengineered world could be one in which nature is ravaged yet the people of this world fail to notice. The environmental baselines of future people in a solar geoengineered world could shift to reflect their new circumstances, depriving them of knowledge and motivation that are likely to be crucial to winding down a deployment. Bearing in mind the potential multi-century scale of any deployment, the ‘environmental forgetting’ of future people could be significant, and potentially incapacitating. Discussions around the intergenerational justice dimensions of SAI have not engaged at all with the ethical questions this raises.

5. Conclusion

In exploring three core justice narratives in the context of SAI - intergenerational ethics; participatory justice; and recognitional justice -we have demonstrated that the justice terrain surrounding these technologies is complicated, at times contested, and not fully mapped. Rather than clear implications, each dimension reveals competing interpretations of what justice requires and how it should be operationalized. This reflects recent empirical studies that show divergences in the ways people across the globe perceive of and engage with SAI [96,97]. Given the increasingly rapid pace of funding allocation and technological development, including in the private sector, all of which continue to outpace the development of formal international governance arrangements, governance that centers justice is needed immediately. Rather than debating the justice implications of inherently unknowable outcomes of a technology that does not yet exist in the world, debates and research surrounding SAI governance should be focused on securing justice of the procedures and practices used in this space. The immediate challenge is to ensure that the processes through which decisions about SAI research and governance are made are themselves as just, transparent, reflexive, and inclusive as possible. This requires sustained attention to who participates in decision making, whose knowledge and values are recognized as legitimate, and how the interests of future generations are considered alongside those of present-day societies. Although some of this work is already being done by both NGOs (e.g., The Degrees Initiative and the Alliance for Just Deliberation on Solar Geoengineering), and scholars [35,36,98] far more work is needed on this issue if we are to minimize the injustices of SAI emerging within the current vacuum of public governance. Just processes and practices for technological innovation and governance could enhance our capacity to co-create a world where any decisions on SAI, whether to ban it or move it forward, are based on thoughtful, ethical, and participatory decision-making that speaks to the interests of all people- present and future- potentially affected by SAI.

Acknowledgments

McKinnon notes that her contributions to this paper draw on joint research with Stephen M. Gardiner, University of Washington and University of St. Andrews. Jinnah and Adade Williams are grateful to the Degrees Sociopolitical Fund for catalyzing this collaboration.