The Ethical Dimensions of Geoengineering: Solar Radiation Management through Sulphate Particle Injection (Working Paper)

Tuana (2013) – Ethics of Geoengineering – Click for Download


 The slow progress on an adequate policy solution in light of growing scientific understanding of the impacts of a warming world, limited success on efforts to mitigate the causes of anthropogenic climate change, and awareness of the high costs and the limits to adaptation have led some scientists and some policy-makers to consider geoengineering as a potentially viable option to avoid “threshold responses” and dangerous climate change.[1] Some approaches to climate engineering, indeed, even proposals to field test climate engineering technologies such as ocean iron fertilization or increasing the reflectivity of the atmosphere to reduce the amount of sunlight that is absorbed, raise serious and complex ethical issues. Given this, proposals to deploy geoengineering technologies, or even to field test some of them, must be accompanied by serious consideration of the ethical dimensions of geoengineering.[2]  However, adequate ethical analyses must be grounded in and arise from a robust understanding of the relevant scientific accounts of such technologies and their potential impacts, and an appreciation of any correlated uncertainties.  Indeed, ethical analysis may require and point to needed scientific research in cases where there are coupled ethical-epistemic issues, that is, where ethical judgments require additional knowledge.  Hence, the science and ethics of geoengineering are intertwined.

 A full review would have to address the ethical issues specific to each type of technology and approaches to implementation. In this paper, I will use concepts and dimensions of ‘justice’ as a lens through which to filter ethical questions, as well as focus on a particular geoengineering technique: solar radiation management through sulphate particle injection (SPI). I base this choice on current assessments that i) the technology needed to deploy this approach might potentially be scaled up over a relatively short period of time (± a decade) given that we may be able to model it on existing technologies, ii) many believe it has the best potential of all geoengineering approaches for cooling the planet rapidly and inexpensively; iii) given i) and ii), it is being given serious consideration by a significant number of scientists and policy-makers; iv) SPI, unlike most geoengineering approaches that focus on absorbing carbon from the atmosphere (carbon dioxide management technologies), has the potential to rapidly create a novel atmospheric state, with significant regional or global climatic effects, but one of which we have limited knowledge;[3] and v) it would, on its own, not mitigate the  high concentrations of greenhouse gases.  For these reasons, SPI is arguably the approach most likely to be considered for deployment and partial deployment for testing, but is also the geoengineering approach most fraught with ethical issues.

 The domain of ethical and coupled ethical-epistemic issues regarding SPI is very large.  Indeed an entire entry could be written on each one of its many aspects.  My aim in this essay will be rather to map a research agenda by working to identify some of the many issues in need of additional analysis regarding the ethical issues surrounding SPI.  While I do not claim that the list is exhaustive, its length and complexity signal the importance of work on such topics prior to any decision as to whether to deploy SPI, as well as decisions about field testing.

Projected SPI Impacts on Temperature, Precipitation, and Society

 Understanding the relevance of dimensions of justice requires an appreciation of the complexity of the impacts of SPI, and thus must be informed by an appreciation of our current scientific accounts and, in turn, work to identify value decisions embedded in the scientific analyses.  Furthermore, ethical analysis must also be informed by an adequate analysis of the uncertainties in the science, and, ideally, partner with science to identify uncertainties due to missing domains of information that are required for adequate ethical analyses, as well as clarify which domains are due to deep uncertainties that are impossible to resolve through research.  To frame the justice dimensions of SPI, this section provides an admittedly brief overview of some aspects of our current scientific understanding that are relevant to justice dimensions of SPI, while acknowledging that these details have been covered in greater strength elsewhere.

 Modeling studies suggest that SPI, over the course of an 80-year simulation, would likely stabilize average global-mean surface air temperatures at levels approximately plus or minus half a degree from the temperature at which the SPI activities were initiated[4], but nonetheless may result in regional temperature disparities in that the poles may be relatively warmer and tropics cooler.[5] Moreover, if SPI is not matched with serious mitigation efforts over time, the temperature differences between regions are likely to increase such that within six to seven decades “there is often no scenario that can place a region back within one standard deviation of both its baseline temperature and precipitation”.[6] In other words, different regions will likely experience different ‘climates’ the longer the forcings continue, and the forcing scenario needed to return one region to the designated baseline (e.g., a late twentieth-century climate) will be significantly different than that required for another region the longer SPI continues.

 Most current models also indicate likely negative impacts of SPI on the hydrological cycle: a global reduction in precipitation with more acute changes regionally, likely leading to an intensification of both droughts and floods greater than would result from the effects of elevated CO2 alone.[7]  But the changes in precipitation will not be consistent across regions, and some regions will experience greater deviations than others in amount and seasonality of precipitation than others dependent on the intensity and duration of the SPI.[8]   Given the likelihood of distinct regional differences in the response to different levels of SPI, the decision as to the choice of the optimal target for SPI (temperature or precipitation) is often regionally dependent.

 Furthermore, precipitation changes due to SPI would likely have disproportionately negative impacts on those regions already experiencing high levels of poverty that have historically not significantly contributed to climate change.  Based on natural experiments such as the Mount Pinatubo eruption and information from computer simulations, SPI is likely to decrease average annual precipitation in Africa, South America, and southeastern Asia.[9] Such changes in regional precipitation could compromise basic rights of individuals in these regions by resulting in food and water insecurity.[10]

 Regional differences in precipitation impacts, however, are not the only component of ethical issues raised by SPI targets.  Irvine et al (2012) found there to be strong tensions between SPI targets that would aim to reduce the rate of temperature change vs. the rate of sea-level rise. They demonstrate that addressing sea-level rise would require significantly greater forcing than would be required to stop surface warming.  The greater forcings required for targeting sea-level rise, however, carry a significantly higher risk of abrupt or disruptive cooling.[11]

 The temperature and precipitation impacts of SPI will not only impact human well-being, but will also affect ecosystem and species well-being.[12] Furthermore, since CO2 levels will likely continue to increase during SPI, ocean acidification will continue to be a serious problem.[13]   Ozone depletion may be another side-effect of SPI[14] which would increase the risk of human health impacts  as well as the well-being of various species and ecosystems.

The Question of Justice and Differential Impacts  

 There are at least five dimensions of justice relevant to SPI, including distributive justice, intergenerational justice, corrective justice, ecological justice, and procedural justice.  While it is valuable to understand and examine each of these justice vectors, they almost always intersect in the case of SPI, greatly complicating the ethical analysis.  In this section, I will discuss each aspect of justice relevant to SPI separately in order to clarify the types of issues relevant to each domain, following each description with a number of coupled ethical-scientific research questions in order to clarify the nature and range of coupled ethical-scientific issues that must be addressed to determine whether or not SPI could be considered as an ethically responsible choice.  It is my intent to clarify the salience and complexity of issues of justice that are relevant to SPI, catalyze appreciation of the complexity of the intertwined ethical-scientific issues, and urge that this work be incorporated into the SPI research agenda. In addition, it is imperative that we recognize that these dimensions of justice often intersect and, indeed, at times conflict.

Distributive justice involves the principle that harms and benefits of an action should be fairly or equitably distributed.  Strict egalitarian theorists argue, for example, that distributive justice requires that harms and benefits be shared equally.  Rawlsian inspired difference theorists allow that differential impacts are justified on the condition that the least well off are better off than they were previously.[15]  In the case of SPI, the appropriate measure would be spatial- namely, do all regions of the Earth equitably benefit and are any of the resulting harms fairly distributed?

Research Questions:

  1. Are the temperature and/or precipitation disparities caused to some regions by SPI outweighed by the benefits to other regions?  What levels of confidence of impacts would be required to make this judgment?
    1. What would be a morally salient difference between regions that might justify a positive response?  For example: density of population; uniqueness of species; vulnerability of region to temperature and precipitation change.
    2. How should existing climate conditions be considered when assessing the impacts of SPI-induced changes in climate? For example, should a dry region getting drier be treated in the same way as wet region getting drier?  Can we actually disaggregate the SPI impacts from other impacts on such conditions (e.g. land use changes, etc.)?
    3. If temperature and precipitation impacts resulting from SPI cannot or should not simply be aggregated, what is the best way to quantify them?  For example:
      1. In weighing impacts, what is the ethically responsible way to compare positive/negative impacts from temperature changes with those of precipitation?
      2. How are regional variations regarding the risks of higher temperatures vs. modified precipitation to be weighted?
      3. Are there certain harms from SPI that could not be justified regardless of the benefits to others?  For example:
        1. Compromising basic human rights, such as food, shelter, and health, of populations in some regions?
        2. Loss of a culturally significant way of life?
        3. Loss of citizenship (climate refugees) or in extreme cases an entire country’s sovereignty (an entire country becoming uninhabitable due to extreme weather conditions such as flooding) ?
        4. What levels of confidence in the probability of such impacts would be required to decide against using SPI?
        5. Given that temperature and precipitation differences between regions are very likely to increase the longer SPI is continued, is there a time limit to SPI after which continued SPI would no longer be ethically justifiable?
        6. Is the deployment of SPI to avoid “threshold” responses more just than the deployment of SPI to prevent global mean temperatures from rising above a certain degree?  And if so, why?
        7. Are there situations in which we would have a moral responsibility to use SPI rather than allow humans, other species, and ecosystems to suffer the harms of unremediated climate change?  What would constitute the conditions that would make SPI a moral imperative?  Are we able to measure such “thresholds”?  What level of confidence in SPI’s effectiveness regarding such a target should be required?
        8. How do we weigh social benefits against risks to individuals?  What measurements are actually possible and at what levels of confidence?

Intergenerational justice takes into consideration the impacts of SPI on future generations.  Many see this version of justice as similar to that of distributive justice, but adding a temporal measure by comparing harms and benefits to current populations to those of future generations.  However, even when attention is given to the impacts of a geoengineering approach to anthropogenic global warming upon future generations, an adequate ethical analysis must combine attention to impacts on future generations with attention to the spatial dimension of the impacts, as would an account of distributive justice, in those instances when future impacts might disproportionately benefit or harm different regions.

Research Questions:

  1. How would the harms to future generations of long-term SPI deployment compare to other scenarios (such as business as usual, mitigation efforts without SPI, etc.)? Are we able to effectively model such scenarios?  In such models, what is included as a benefit and what is included as a harm?  Under what scenarios do the comparative benefit/harm ethically justify SPI deployment?
  2. Are there SPI scenarios (intensity/duration) that are ethically untenable regardless of the benefit to current generations because they would put future generations at ethically unacceptable levels of risk?  What level of confidence would be required to make this judgment?

Corrective justice diverges from the egalitarian approach of typical accounts of distributive justice, by arguing against an “aggregate” measure of benefits and harms and embracing a desert-based measure, which holds that harms and benefits ought to be shared among persons according to the degree persons deserve those harms and benefits. Through this lens, whether or not the impacts of an action are just requires that we consider the extent to which individuals or groups are morally deserving of those impacts.  In the case of anthropocentric global warming, desert-based accounts of justice are often based on responsibilities for emissions.  A key element is historical contributions to climate change that are disproportionately due to the activities of a group of industrialized nations which benefited from the industrialization and land use changes that led to high emission levels, but at the cost of the well-being of other countries.  Indeed this form of corrective justice is recognized in the framework of the UNFCCC’s “polluter pays” principle.

However, historical responsibility is not the only relevant measure.  The inequities in emissions, and thus their inequitable contributions to the problem of anthropogenic climate change, continue to be an issue.  For example, based on information from 2008, the United States emitted approximately four times the amount of CO2 as India and more than ninety times the emission of CO2 of Bangladesh.[16] [17]  If responsibility is correlated with population, however, issues of desert get more complicated.  For example, while China’s total CO2 emissions where approximately 20% higher than those of the US in 2008, average individual emissions in China are significantly lower than individual emissions in the US, where on average, each US citizen emits almost three times more CO2 in comparison to individuals in China.  But average emissions also ignores that individual emission levels are linked to economic class standing, with the poor even in the highest emitting countries often having low emissions and the wealthy in the lowest emitting countries often live life-styles that result in GHG emissions similar to wealthy individuals in high emitting countries.[18] Corrective justice can also be de-coupled from responsibility for the causes of greenhouse gas emissions, and focus, as does prioritarianism, on the position that justice requires that benefits to the worst off should be given more weight than benefits to the better off.[19]

And finally, just as intergenerational justice requires attention to the spatial distribution of harms and benefits at different times in the future (i.e., which regions at a particular time are likely to benefit or be harmed by the action), corrective justice must also embrace a temporal dimension, considering not only desert and culpability in the present case, but also projecting into the future to adequately apply such an account of justice.

Research Questions:

  1. In choosing targets for SPI (temperature/sea level rise, etc.) should the decision be based on the greatest overall positive impacts or should those regions most negatively impacted by climate change be those regions that benefit most from SPI? Can we actually target in ways that would allow us to meet what is determined to be just targets? And how should historical and/or contemporary responsibility for greenhouse gas emissions be factored into the decision concerning which targets are the most just?
  2. Should a “polluter pays” principle be applied to any responsibility for compensation for harms of SPI so that those most responsible for anthropocentric climate change become the most responsible? And if so which of the following measures are ethically relevant?  Should these measures include discounting?
    1. Historical responsibility for greenhouse gas emissions
    2. Per capita emissions
    3. A country’s total emissions
    4. Temperature and/or precipitation changes will impact regions differently dependent on the general resilience/vulnerability of that region.  How should the political-economic situation of a region be factored into the analysis of the impacts of SPI?  Would such targets be technically feasible?
      1. Does justice require that benefits to poorer regions of SPI deployment provide these regions with greater benefits and fewer harms?
      2. Should those countries historically responsible for any political-economic vulnerabilities of a region be responsible for compensating vulnerable regions negatively impacted by SPI?
      3. Are those regions that benefit most from SPI then responsible for compensating those regions which benefit less or which are negatively impacted?  And if so, how should historical and/or contemporary responsibility for greenhouse gas emissions be factored into the decision about compensation?
      4. Should current generations compensate future generations for the impacts of SPI?
      5. What are ethically acceptable forms of compensation?  For example, if a nation loses sovereignty because its land has been made inhabitable for SPI, does compensatory justice require providing its people with comparable land where they can claim sovereignty?
      6. Should regions likely to be harmed be provided financial support for adaptation prior to or during SPI deployment?  And who is responsible for providing that support? For example:
        1. Historical responsibility for greenhouse gas emissions
        2. Benefits from SPI

Ecological justice is a non-anthropocentric dimension of justice, which includes consideration of the impacts on nonhuman life and on ecosystem sustainability.  Here, the emphasis of ethical analysis is the harms and benefits of SPI upon animals, plants, and ecosystems in general.  As with the impacts of geoengineering on humans, the effects on other life forms and on ecosystems are dependent on the intensity and the length of SPI.  And as with humans, animals, plants, and ecosystems in some regions will likely benefit, while others will likely be harmed.  For example, geoengineering would not address the problem of ocean acidification.  We know that high levels of CO2 alter ocean chemistry and can negatively affect the shell formation ability of marine calcifying organisms such as corals, with subsequent impacts on the ecosystem level.[20]    SPI will have the effect of lowering ultraviolet radiation levels, which might enhance plant health, but as this effect is likely intertwined with other changes, both to precipitation and to seasonal climate, the benefit might not be to the plants currently growing in a particular region, but rather to new species that may or may not be beneficial to ecosystem health.

Research Questions:

  1. How do we weigh the moral standing of nonhuman species and/or ecosystems in comparison to that of humans in order to determine how to balance ethical responsibilities to current and future human populations with ethical responsibilities to current and future species and to ecosystems from SPI impacts?
  2. Are there certain harms to species or ecosystems from SPI that could not be justified regardless of the benefits to humans?  What levels of confidence would be required to make this judgment?

Procedural justice focuses once again on the human domain, but in this case on how to ensure that decision procedures are ethical.  Following Rawls, many have argued that in order to be procedurally just, all those affected by the decision must have the ability to contribute to the decision process or have their interests represented.[21]  Others argue that procedural justice also requires that the rationales for the policy decisions be transparent and public, the decision process be based on relevant ethical principles, and the process allow for a mechanism for appeal and regulation to ensure fairness.[22] In the instance of SPI, procedural justice issues are relevant in a number of domains, including who makes the decision about whether to test or implement SPI, when to stop testing or deploying SPI, as well as what should be the target of SPI.

Research Questions:

  1. Since SPI will very likely affect all nations, must any just decision process for implementation be an international process?
    1. Is there an existing body like the United Nations that would be appropriate for this process?  Does it provide sufficient representation of all those likely to be impacted?
    2. Is the nation-state the ethically relevant representative group for making a just decision about SPI?  If not, what would be?
    3. How widespread must agreement be on SPI deployment for it to satisfy the demands of procedural justice?
    4. What principles and procedures are best suited for making an ethical decision about SPI targets?
    5. If there are individuals, groups, or nations who do not consent to SPI deployment, are they thereby more deserving of compensation for resulting harms?
    6. Is there ever a condition in which it would be ethically acceptable for one group (e.g., a nation) or a small federation to make the decision to geoengineer without consultation with other groups/nations?

The applicability of the various dimensions of justice in the case of SPI arises from the well-recognized fact that SPI deployment will likely have serious side-effects. “A world cooled by managing sunlight will not be the same as one cooled by lowering emissions”.[23]  But it is also linked to the fact that the speed and intensity of SPI deployment options correlate both to different climate “remediation” impacts as well as to different distributions of harms and benefits.[24]

The Question of Intentionality 

One of the reasons SPI is seen as raising serious ethical issues is the issue of intentionality.  As noted by many ethicists writing on climate change, climate change is often not viewed as an ethical issue because it does not embody the characteristics of a paradigm moral problem. According to Jamieson “…a paradigm moral problem is one in which an individual acting intentionally harms another individual; both the individuals and the harm are identifiable; and the individuals and the harm are closely related in time and space”.[25]  While Jamieson argues persuasively that climate change nonetheless raises ethical issues, the link between moral responsibility and harm for SPI is arguably clearer and stronger due to the fact that those acting will be acting with knowledge that their actions have a high probability of violating the basic rights of people in some regions and could potentially be damaging to the rights of future generations as well as to nonhumans.

Jamieson refers to various types of geoengineering, particularly large-scale projects like SPI, as “intentional climate change.”  While we now know that many human activities from agricultural practices to energy choices are impacting the climate, the fact is that SPI has as its primary intention to modify the climate, and would be done knowing that there are various risks and highly probable harms, as noted above. Jamison argues that this places large-scale geoengineering projects like SPI in a different ethical domain in that the decision to modify the climate would be the intent of the actions, and thus the consequences of the action to deploy, including the unintended harms, would have a stronger ethical tie to the action.

Research Questions:

  1. Is intentionally creating novel climates for the purposes of alleviating at least some of the harms of anthropocentric climate change ethically more problematic than business as usual greenhouse gas emissions now that we know that these emissions contribute to anthropocentric climate change?
  2. SPI will only, at best, lessen some of the negative impacts of anthropocentric climate change and not the causes, thereby allowing greenhouse gases to continue to accumulate. Under what conditions, if any, is it ethically permissible to deploy SPI alone, that is, without mitigation efforts?
  3. Does the fact that SPI intentionally creates novel and unpredictable climates entail that the individuals or groups who elect deployment are ethically responsible for any resulting harms?
  4. If the intentionality of SPI entails greater ethical responsibility for resulting harms, does this result in a greater responsibility for those who agree to deployment to compensate those who are harmed?

The Question of Risk and Uncertainty

Intentionality often raises what has been called the “principle of double effect.”  According to this principle, an action is ethically acceptable even if those acting cause or allow something bad as long as a) no evil is intended as an ends or a means; and b) the potential harm is not out of proportion with the anticipated good.  However, the relationship between intention (to slow down the aggregate warming) and consequences (the harms and benefits of SPI) is made significantly more complex due to the fact that there are uncertainties linked to the probabilities of various impacts of SPI. Sidgwick, for example, influentially argues that “it is best to include under the term ‘intention’ all the consequences of an act that are foreseen as certain or probable; since it will be admitted that we cannot evade responsibility for any foreseen consequence of our acts by plea that we felt no desire for them”.[26]

To include all the consequences of SPI deployment “that are foreseen as certain or probable” puts us in the domains of risk management and decision-making under uncertainty.  At least some of the uncertainties relevant to SPI can be mitigated through additional scientific research.  However, the question of testing itself raises a series of complex ethical questions.  I will reserve a discussion of these concerns for the next section, and focus here on some of the ethical dimensions of decision making and risk management under conditions of uncertainty.

Various principles have been advocated by those working on the ethical dimensions of risk management.[27] One is the principle of justification, which requires that for any action that entails the risk of harm, the benefits should outweigh the harm.  While necessary, theorists argue that additional principles are required for an action to be ethically justifiable.  One is the principle of optimization which implies that the likelihood of harm, the number of people exposed, and the magnitude of the harms “should all be kept as low as reasonably achievable, taking into account economic and societal factors—meaning that the level of safety should be the best under the prevailing circumstances maximizing the margin of benefit over harm”.[28] A third principle is that of individual protection, namely that the risk incurred by any individual should be restricted.  This principle is designed to go beyond calculations of aggregate harms and focus attention on the magnitude of harms to individuals, in order to determine if there are limits that must be imposed on risk to individuals, for example, risk to satisfaction of basic needs.

Each of these principles requires transparency regarding the relevant value judgments that would be involved in its application.  For example, the principle of justification would require weighting harms and benefits, which will likely be significantly different in kind.  It will also have to take into consideration the various ethical dimensions noted above of differences in harms/benefits to various regions and between current and future generations.  While perhaps providing guidelines for ethical decision-making, principles such as these still leave unsettled large domains of ethical analysis.

In addition to value judgments such as these that are involved in decisions concerning acceptable levels of risk, what to count as a harm and to whom/what, or how to weight different types of harms and/or benefits, the question of uncertainty raises additional ethical concerns.  Various types of uncertainties are relevant to SPI.  There is significant epistemic uncertainty in that we currently have incomplete knowledge about the impacts of SPI.  Research on the impacts of SPI has been to date limited, and much of the research that has been done has been on natural experiments or modeling.  To gain additional knowledge would likely require additional research, including at least partial deployment for testing, that itself raises coupled epistemic-ethical concerns as well be discussed below.  Epistemic uncertainties can be reduced with sufficient time and resources, but ethical issues are relevant to how long we can wait to resolve such uncertainties before deciding whether or not to act.  There is also ontological uncertainty, or what some have called deep uncertainty, in that aspects of the interactions between SPI and the natural systems are complex and nonlinear and thus unpredictable. These are uncertainties that are inherent in the complexity and coupled nature of the problem, and will not be mitigated with additional research.[29] And third, SPI involves ethical uncertainty, in that there are different values and principles concerning how to weigh the harms/benefits of SPI, different judgments about the seriousness of those harms/benefits, different interpretations of who and what is to be included in the domain of moral standing (e.g. are nonhuman species and ecosystems to be included), and uncertainty about what future generations would view as the most salient ethical values or principles.[30]

The ethical dimensions of decision-making under conditions of uncertainty is a new domain of ethical analysis[31], but one essential to SPI.  Robust Decision Making[32] and Dynamic Adaptive Policy Pathways[33] are two relatively recent approaches to decision-making under conditions of uncertainty, including ontological uncertainty.  In both instances, the authors of these approaches appreciate the need to have ethical analyses closely intertwined in the analyses.  While these approaches are not specific to SPI, they offer strategies for identifying ethically responsible ways to make decisions under conditions of uncertainty, including all three of the domains of uncertainty noted above.  While uncertainty clearly makes responsible decision-making more difficult, it is a condition underlying many of our most trenchant global issues and thus work to identify ethically responsible decision-making approaches.

Research Questions:

  1. To what extent must we reduce epistemological uncertainty in order to make an ethically responsible decision about SPI deployment?
  2. Does ontological uncertainty about SPI deployment entail following a precautionary principle and not deploying at all or unless the potential harm of not doing so would clearly outweigh the uncertainty of doing so?
  3. What are the best ways to manage ethical uncertainty about SPI?

The Question of Testing

As noted above, there is significant epistemic uncertainty surrounding SPI deployment, which some believe can and should be lessened through scientific testing.  Indeed, it has been argued that there is an urgent need for research into geoengineering options such as SPI and that this research should go beyond modeling or the analysis of natural events, such as volcanic eruptions, and include field studies (Keith et al., 2010).  This type of testing is believed by some to be a necessary and ethically responsible step prior to partial and/or full-deployment of SPI for geoengineering and is seen as providing the basis for evaluating SPI technologies, testing the response of the system, and exploring possible unintended consequences.  However, this position assumes that testing can occur that is a) significantly different than deployment and b) can lessen the epistemic uncertainties concerning SPI impacts.

Tuana et al. argue that testing in the defined above may not be possible for a variety of reasons.[34]  First, there are major uncertainties in climate models such as “vertical mixing in the ocean[35], evolution of polar ice (including ice sheets and glaciers)[36], radiative feedbacks in the atmosphere[37], and clouds and precipitation” which would be highly sensitive to SPI deployment.  Second, nonlinear feedbacks in the climate system can result in bifurcations of the system leading to abrupt shifts or transitions between states, such as the shutdown of the ocean’s merdional overturning circulation, resulting in markedly different climate conditions.    This is relevant to the question of testing as posed in that there may be a significant difference between small forcings of the kind that would be deployed for testing and the forcing levels and time trajectories needed for intentional climate modification.  As forcing increases, the climate system could reach a threshold where it transitions to unstable conditions.  In such a case, the SPI is happening in a significantly different climate state than that in which it was tested.  Third, the system may exhibit hysteresis, or strong memory, in which reducing the forcing after the testing may not return the system to the original climate.  Fourth, there will likely be delayed system responses to forcing.  We know that different time scales govern ocean and atmosphere circulations, such that oceanic responses to SPI forcings may not manifest for years to decades longer than atmospheric responses.  Because of this, impacts from SPI deployments for the purpose of testing may not be fully realized by the climate system until long after stopping the testing.  Given the above noted variables, the type of learning projected from small-scale deployment for testing may not be possible.  Given that these experiments can have negative impacts, both the ethical and the scientific justification for conducting such experiments is at issue.

Given these concerns there are a variety of ethical concerns regarding field-testing of SPI.  Here I will identify some of the ethical issues directly related to field-testing per se, but it is important to underscore that many of the ethical issues noted about regarding issues of distributive justice, intergenerational justice, compensatory justice, ecological justice, and procedural justice apply to field-testing as well given the “side-effects.”  Note that these are examples of coupled scientific-ethical issues.

Research Questions:

  1. What can be inferred from the limited scale experiments about the potential of a full-scale experiment, and what cannot?
    1. Is it possible to estimate the large-scale system response from a small-scale field test?
    2. Will this knowledge be adequate for making an ethically responsible decision?  Will this knowledge be sufficient to warrant the risks of field-testing?
    3. What “side-effects” will result from field-testing and can they be predicted?
    4. What scientific and ethical knowledge is required to responsibly decide whether to start SPI field-testing?
      1. What is the basis for deciding on acceptable risk levels for field-testing?
      2. What measures of impacts would be used to determine that the costs of field-testing are higher than the benefits of field-testing and should be halted?
      3. What level of learning would justify risks of side-effects?
      4. What is the boundary between field-testing and deployment?

Political Risks of SPI Research and Testing

Another cluster of ethical issues concerns the psychological or political impact of SPI research or field-testing.  Some researchers have raised the concern that geoengineering research might pose a moral hazard by causing people to be less concerned than they otherwise would be with respect to the risks posed by climate change.[38]  Some have begun to question whether or to what extent SPI research would impede research into other responses to climate change or reduce the political will to mitigate greenhouse gas emissions.[39]  There are also concerns that conducting SPI research would lead to unregulated, unilateral, or self-interested uses.[40]  Others have argued, to the contrary, that a credible threat of unilateral SPI might strengthen global mitigation efforts to avoid potential costly side effects of SPI.[41]

Conclusion: The Centrality of Ethics for SPI

Given the potentially harmful impacts of SPI there is widespread agreement that SPI deployment raises important ethical issues.[42] The 2009 Royal Society Report, to give just one example, affirmed that “it is clear that ethical considerations are central to decision-making in this field”[43] and concluded that “the acceptability of geoengineering will be determined as much by social, legal and political factors, as by scientific and technical factors”.[44]  However, in closing, it is important to stress that the ethical analyses of SPI are not simply an addition to the scientific analysis, to be put into play once the scientific research is complete.  Ethically significant decisions are often embedded in the scientific analysis itself, as well as in how scientific models represent impacts and vulnerabilities.

Ethical analysis is dependent upon and must be intertwined with robust and sound scientific knowledge and effective and ethically responsible decision-making tools.  As we have seen from the above discussion, since SPI testing and deployment would involve nontrivial risks of harm across many dimensions such as time, space, species, and socioeconomic status[45], an epistemically and  ethically sound characterization of the underlying probabilities and risks requires a well-integrated analysis spanning fields such as Earth sciences, statistics, and economics.[46]  Hence, many of the ethical issues identified in this essay require additional and targeted coupled scientific-ethical research to ensure that we are developing epistemically responsible knowledge about geoengineering and comparing it to mitigation options.

One example of such an effort is the NSF funded research network for Sustainable Climate Risk Management (SCRiM).[47]  The aim of this research network is to study what are sustainable, scientifically sound, technologically feasible, economically efficient, and ethically defensible climate risk management strategies.  One research domain of this group is “How do uncertain climate threshold responses affect the trade-offs between mitigation, carbon sequestration, and geoengineering?”  One of the particular concerns of this network is to develop better integrated assessment models (IAMs) that better represent i) different time scales (from 50 years to centuries to millennia), ii) differences in regional impacts, and iii) potential low-probability/high impact events.  Since these events are, thus far, quite poorly represented in the current generation of Earth system models[48], integrated collaboration between climate scientists, economists, and ethicists is essential to begin to address decision-relevant research questions that will allow us to respond to the types of complicated ethical questions identified in this essay.  SCRiM thus provides a model for ethically responsible research on SPI that embeds an analysis of ethical issues into the development of the scientific research itself.  Only in this way are we able to determine what types of knowledge we need to make ethically responsible decisions about SPI in the natural and social sciences.

Hence, while acknowledging the importance of the Royal Society’s recognition that ethical issues are central to decision-making, what is in fact required goes beyond ethical analyses of the science of geoengineering.  It is essential that the ethical analysis be coupled with scientific analysis by including ethicists within scientific research teams in order to infuse ethical analyses into the science of geoengineering.  This will, of course, require scientists and funding agencies alike recognize the importance of such work and provide ample resources for coupled ethical-scientific analyses within SPI research.  SCRiM is one example of such a practice, but the importance of this knowledge entails that far more work like this is required.  I close then with the admonition that this important field of study be strengthened prior to and included in considerations of the feasibility of SPI deployment as well as pre-deployment for testing.

Acknowledgements: This research was conducted with the support of National Science Foundation Grant Number 1135327 and richly informed by collaborations with Klaus Keller, Ryan L. Sriver, Peter J. Irvine, Jacob Haqq-Misra, Toby Svoboda, and Roman Olson.  I would also like to gratefully acknowledge the reviewers whose insightful comments helped improve this article.


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[1] Crutzen 2006; Fox and Chapman 2011; Hansen et al., 2006; Lenton et al., 2008; Wigley 2006

[2] Preston 2012; Scott 2012

[3] Morrow et al. 2009, 2

[4] Ricke et al. 2010

[5] Brovkin et al. 2009; Govindasamy et al. 2003; Lunt et al. 2008

[6] Ricke et al. 2010, 538

[7] Bala et al. 2008; Irvine et al. 2010; Lunt et al. 2008; Robock et al. 2009

[8] Irvine et al. 2010; Ricke et al. 2010

[9] Matthews and Caldeira 2007

[10] Brewer 2007; Robock et al. 2008

[11] Irvine et al. 2012

[12] Naik et al. 2003

[13] Doney et al. 2009; Fabry et al. 2008; Hoegh-Guldberg et al. 2007; Raven et al. 2005

[14] Rasch et al. 2008; Tilmes et al. 2008; Moan et al. 2008

[15] Rawls 1971

[16] The US emitted 5461014 thousand metric tons of CO2 in 2008.  Bangladesh emitted 46527 thousand metric tons.

[17] UN 2008

[18] Harris 2010

[19] Parfit 2007

[20] Doney et al. 2009;  Hoegh-Guldberg et al. 2007

[21] Rawls 1999; Grasso 2007; Müller 1999

[22] Daniels and Sabin 1997

[23] Keith et al. 2010

[24] Irvine et al. 2012

[25] Jamieson 2007, 1

[26] Sidgwick 1907, 202

[27] Wikman-Svahn 2012

[28] González 2011, 2

[29] For greater detail on the nature of epistemological and ontological uncertainty, see Walker et al. 2003.

[30] My taxonomy is somewhat similar to that of Tannert et al. 2007, however, my interpretation of ethical uncertainty diverges significantly from their account of subjective uncertainty, which includes what they call moral uncertainty, but define differently than what I mean by ethical uncertainty.

[31] Tannert et al. 2007; Caplan 1986

[32] Hall et al 2012; Bryant and Lempert 2010; Groves and Lempert 2007; Lempert and Collins 2007

[33] Haasnoot et al. 2013.

[34] Tuana et al. 2012

[35] Goes et al. 2011; Wunsch and Ferrari 2004

[36] Meehl et al. 2007

[37] Bony and Dufresne 2005

[38] See essays in Preston (ed.) 2012

[39] Bunzl, 2009

[40] Victor 2008

[41] Millard-Ball 2012

[42] Crutzen 2006; Keith 2000, 277-278; Kiehl 2006; MacCracken 2006; Morgan and Ricke 2010; Robock 2008; Shepherd 2009, Tuana et al. 2012

[43] Shepherd et al 2009, 39

[44] Shepherd et al 2009, 50

[45] Crutzen 2006; Goes et al. 2011; Svoboda et al. 2011

[46] Goes et al 2011

[47] Refer to the SCRiM website at

[48] Meehl et al 2007; Keller et al 2008; Urban and Keller 2009

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