Precaution and Solar Radiation Management
Lauren Hartzell, 9/20/2010
For The Ethics of Geoengineering Workshop:
Investigating the Moral Challenges of Solar Radiation Management
At the University of Montana, October 18-20, 2010
I. Introduction
For all the attention it has garnered, there remains much confusion surrounding the precautionary principle. This principle captures the intuition that it is better to be safe than sorry and/or that we sometimes ought to act in advance of scientific certainty. The precautionary principle may at first glance seem to either support solar radiation management (SRM) as a precautionary measure against climate change or reject such a measure as being too risky. This paper will explore the relationship between precaution and SRM by asking: Does precaution justify research into SRM techniques? Under what circumstances would precaution require us (or allow us) to implement geoengineering ‘solutions’ to the climate crisis? Does the precautionary principle help us differentiate solar management approaches in terms of the risks associated with their implementation?
Answering these questions is complicated by the fact that one of the most significant problems the precautionary principle faces is that there is no consensus as to how it should be formulated or interpreted. At first glance the precautionary principle may seem obvious or intuitive but closer examination reveals confusion over this alleged principle’s nature and content. I therefore (elsewhere) defend the Precautionary Principle that addresses threats of catastrophe (hereafter the Catastrophic Precautionary Principle or CPP), which requires appropriate precautionary measures against catastrophic threats of harm to humans. (Hartzell
2009) I further distinguish Precautionary Principles from the Precautionary Decision-Making
Framework (hereafter PDMF). I argue we need a PDMF that can help us discern what CPP – or any Precautionary Principle – requires of us. (A precise formulation of CPP and an outline of what PDMF requires can be found in the following section.)
In this paper I will explore what CPP and PDMF imply about the status of SRM, differentiating between techniques when relevant. Given that elsewhere I have established CPP requires us to take precautionary measures against climate change, I will assess under what

Precaution and SRM 2 conditions SRM techniques may constitute appropriate precautionary measures. I will suggest that any geoengineering techniques that pose threats of catastrophe violate CPP, making them inappropriate as precautionary measures against climate change. Understanding the risks of various SRM techniques (via research) may therefore be critical to determining the viability of such techniques as precautionary measures against climate catastrophes. CPP does not, however, support the argument that we should ‘Arm the Future’ 1 with SRM just in case we should someday reach a point where risking catastrophe is our only option.
II. CPP and PDMF
In other work I argue that neither the content nor nature of the precautionary principle has been clearly or consistently identified or applied in either the philosophical literature or in environmental policy. (Hartzell 2009) I argue that rather than thinking of the precautionary principle as a loose family of principles that share a common structure (a view implied by the work of Manson 2002, Gardiner 2006, Tickner 2003, Hickey and Walker 1995, and Sandin 2007 among others) or as a decision-making procedure (a view implied by the work of Goklany 2001 and Resnik 2003 among others), we should recognize that ‘better safe than sorry’ cannot universally justify precautionary action – a conclusion that Sunstein (2005) has emphasized as reason to reject this principle outright. Nonetheless, there are some cases in which we ought to take precautionary measures; in such cases a Precautionary Principle of limited scope must be identified, defended and consistently applied.
This means that rather than asking of a particular situation, “what does the precautionary principle say in this case?”, we should ask, “is there a Precautionary Principle that applies in this case, and if so what does it require?” This understanding of Precautionary Principles clarifies that ‘the’ precautionary principle cannot be used to justify any and all precautionary action (see also Sandin 2007). This is because if a Precautionary Principle is to have any real normative force it must pick out a unique prima facie moral obligation. All things being equal, in some (but certainly not all) cases we ought to take a better safe than sorry approach and act in advance of scientific certainty. There is thus a family of Precautionary Principles, but each Precautionary
Principle is an independent moral principle that must be independently identified and justified.
1 See Gardiner 2010 for a discussion of ‘Arm the Future’ arguments for sulphate injection, which may apply to SRM techniques more broadly.

Precaution and SRM 3
This interpretation returns meaning and normative force to precaution in the limited cases in which precaution is morally called for.
In particular, I defend the CPP, which says all things being equal we ought to take appropriate precautionary measures against threats of catastrophe (with some caveats – see below). As others have pointed out, understanding complex and often uncertain threats of harm calls for a new paradigm of decision making, but this process must be kept distinct from any particular principles because it is about how to realize certain moral obligations rather than a part of these obligations. The challenges of decision making under conditions of uncertainty necessitate a PDMF in order to understand what CPP requires of us. I define CPP and PDMF as follows:
Catastrophic Precautionary Principle (CPP)
Appropriate precautionary measures should be taken against threats of catastrophe.
Where:
• Threats of catastrophe are those in which many millions of people could suffer severely harmful outcomes (defined as severely detrimental to human health, livelihood or existence).
• Appropriate precautionary measures must not create further threats of catastrophe and must aim to prevent the potential catastrophe in question.
• Imminent threats of catastrophe require immediate precautionary action.
• Threats of catastrophe that involve an imminent threshold or point-of-noreturn for effective precautionary action (beyond which precautionary measures are limited or unavailable) also require immediate precautionary action aimed at preventing this threshold from being crossed.
• Non-imminent threats of catastrophe might warrant further study before further precautionary measures are implemented, provided a delay in taking precautionary measures will not prevent such measures from effectively preventing the catastrophic outcome in question.
• All that is needed is a good reason to think an outcome could be catastrophic for precautionary measures to be required (i.e. there is a low standard of evidence).
• The likelihood (or probability) of a catastrophically harmful outcome may affect what precautionary measures are taken, but not that precautionary should be taken. That is, a low probability outcome/event might warrant more minimal precautionary measures (e.g. monitoring) than a similar high probability outcome/event (which might require aggressive mitigation measures).
• What precautionary measures should be taken and by whom should be determined on a case-by-case basis by appeal to the Precautionary
Decision-Making Framework.

Precaution and SRM 4
The Precautionary Decision-Making Framework (PDMF) – Overview
Aims:
1.
To determine whether the Catastrophic Precautionary Principle generates an obligation to act.
2.
To determine an appropriate course of precautionary action for addressing a threat of harm that has been deemed to require precautionary measures.
Key Considerations for Achieving these Aims:
•
Multiple sources of information: draw on all available sources of information.
• Uncertainty: identify and assess uncertainties in knowledge.
•
Catastrophe: determine whether there is good reason to think the threat of harm meets CPP’s criteria (i.e. is a threat of catastrophe).
• Causation and potential outcomes: identify what is causing and/or contributing to the threat of harm and what the potentially harmful outcomes are.
• Likelihood: assess the likelihood of potential harmful outcomes under different scenarios.
•
Available precautionary measures: identify all available courses of precautionary action and assess the extent to which these measures could eliminate or reduce the threat.
•
Thresholds: assess whether there are any points beyond which available precautionary actions are limited.
• Appropriate precautionary measures: determine which of the available precautionary measures are appropriate to address the threat of harm so as to eliminate (if possible) or mitigate the threat.
• Responsibility: identify specific actors who should be held responsible for taking and paying for the prescribed precautionary measures.
•
Other normative considerations: identify whether there are any other relevant normative considerations that should be taken into account when implementing the proposed plan of precautionary action; modify the proposed plan as necessary.
I believe defending CPP is quite straightforward (though I cannot fully elaborate on this here). If we owe our future selves or future people anything, it seems plausible that, all things being equal, we have an obligation to take precautionary measures against foreseeable catastrophes. It is the severity of such potential catastrophes that morally obliges such measures and underlies CPP. While we cannot take precautionary measures against every possible threat of harm, there is something to this intuition. We at least ought to take precautionary measures against the very worst kind of outcomes, namely those that would be catastrophic. Further, the fact that we are sometimes uncertain about the likelihood or nature of possible catastrophes does not seem to undermine the intuition that we ought to do something to prevent them.

Precaution and SRM 5
I intentionally leave out of the formulation of CPP a precise specification of what constitute precautionary measures, which I believe must be sorted out on a case-by-case basis.
The nature of a threat, how much we know about it and how likely or imminent it appears to be will determine what kind of precautionary measures are appropriate to take. Sometimes a harmful outcome that is merely possible will at first warrant only minimal research into the nature and likelihood of the threat so as to better understand what precautionary measures are available and which of these might eliminate the threat of catastrophe; at other times a wellunderstood threat of harm might warrant immediate and aggressive precautionary measures. The main question for this paper is then what CPP (via PDMF) says about SRM as a potential precautionary measure against the threats of catastrophe posed by climate change.
III. CPP and SRM
Scientific evidence suggests climate change poses threats of catastrophe, which increase as global average temperature rises.
2 CPP therefore requires precautionary measures be taken against these potentially catastrophic climate impacts. The two primary kinds of precautionary measures that can be taken against climate change are mitigation measures and adaptation measures, where the former aim to minimize the extent of climate change (i.e. how much global average temperatures increase) and the latter aim to minimize the harmfulness of climatic changes that do (or may) occur. SRM may be understood as falling into a special category of mitigation; it is a form of geoengineering whose aim is to reflect solar radiation thereby reducing the amount of solar energy in the atmosphere. Whereas standard mitigation efforts aim to reduce the amount of greenhouse gases in the atmosphere by reducing emissions, SRM techniques aim to mitigate climate change without requiring such a reduction in emissions by artificially offsetting the affects of greenhouse gases in the atmosphere. Terrestrial forms of SRM include land use changes (e.g. increasing reflective vegetation), increasing the number of white roofs and surfaces, and desert reflectors. More technologically involved forms of SRM include stratospheric sulfate injections, cloud brightening via tropospheric cloud seeding, and space-
2 I will not argue this point here, but rather take this as given. Elsewhere (Hartzell 2009) I argue that four of the five IPCC “reasons for concern” correspond to threats of catastrophe, per the definition in CPP. (IPCC 2007)

Precaution and SRM 6 based reflective surfaces.
3 The relevant question is whether any of these or other SRM strategies will ever be an appropriate precautionary measure to take against climate change.
Given that one of the requirements of CPP is that precautionary measures themselves not violate CPP by creating new threats of catastrophes, any SRM measures that does so cannot be considered as an appropriate precautionary measure against climate change.
4 The relevant worry about all SRM techniques is that they involve manipulating global systems in a way that could have unknown and/or unintended, potentially catastrophic side effects. Cloud brightening or tropospheric cloud seeding, for example, is meant to increase cloud cover, but this could in turn affect local environments or ecosystems in unexpected ways. Land use management, on the other hand, could have unanticipated affects for local plant and animals. In order to violate CPP, side effects would have to severely threaten many millions of people, and given the complexities and scale of the systems involved it at least seems plausible that SRM techniques could be catastrophically harmful.
Put one way this means that SRM may become an option so long as whatever measures are taken do not present any new threats of catastrophe. On the other hand the burden of proof of safety is set extremely high by CPP because it implies that a precautionary measure cannot introduce a new threat of catastrophe, however remote or unlikely that threat is. CPP, remember, states that all that is needed is a good reason to think an outcome could be catastrophic for precautionary measures to be required and that likelihood not be taken into account (at least not at the stage of determining whether a threat should be deemed catastrophic). This implies that precautionary measures must meet these standards and cannot introduce even remote or unlikely threats of catastrophe, if they are to fully satisfy CPP.
5 Painting a few roofs white will not be catastrophic, but before a massive roof painting campaign is initiated the bar will be set very high for proving that the solar radiation reflected by white roofs will not catastrophically alter the climatic (or other) system.
CPP implicitly implies that the burden of the proof of safety of SRM techniques will rest with those who want to implement them. It does so because it is formulated to primarily address
3 See Parkinson 2010, Goodell 2010, and Kintisch 2010 for overviews of the origins and state of knowledge of available geoengineering ideas.
4 See section IV for a potential exception to this requirement.
5 The question of whether precautionary measures may introduce threats of catastrophe as measures of last resort is taken up in section IV.

Precaution and SRM 7 existing threats of catastrophe, thereby applying to any further precautionary actions taken in response to an existing threat.
6 CPP, however, does not directly imply who ought to be implementing precautionary measures against climate change in the first place. PDMF may provide guidance on this issue to the extent that appropriate decision makers are attempting to fulfill CPP (e.g. that those causally responsible for creating a threat should implement precautionary measures), but who should be responsible for identifying the threats of catastrophe posed by climate change and act appropriately in the first place is beyond the scope of both CPP and PDMF. Worries about parties unilaterally implementing SRM technologies cannot be addressed by CPP (and rightly so since CPP addresses a limited moral obligation and PDMF is meant as a guide to implementing CPP and no more).
Given that there are currently precautionary measures that could be taken to avert, or at least greatly reduce, the risk of catastrophic climate change and that CPP places such a high burden of proof on the safety of precautionary measures, it seems the precautionary route would be to aggressively mitigate climate change while preparing to implement adaptation measures aimed at preventing climate impacts from becoming catastrophic. Only if these less risky precautionary measures fail will CPP potentially recommend SRM. A lingering question, though, is whether CPP recommends researching SRM techniques now so that should other precautionary measures fail we better understand whether any of these techniques are viable options. The PDMF does guide decision makers to consider all available precautionary measures, which may sometimes include encouraging research into unproven or untested measures such as
SRM. And as the possibility of successfully mitigating climate change fades, SRM techniques arguably start to come to the forefront as available precautionary measures. So it seems precaution does warrant research into SRM measures as options become limited, so long as such research aims at determining whether such measures satisfy CPP (i.e. do not pose further threats of catastrophe).
Without delving too deeply into scientific details, given that it seems technologically involved SRM techniques are more likely to raise new catastrophic risks than terrestrial ones, the
6 Some proponents of ‘the’ precautionary principle have argued that it shifts the burden of proof of safety to whoever wants to implement a new technology. I will not engage with this debate here. SRM technologies would not be implemented except as a precautionary measure against climate change, therefore making mute the question of whether such technologies should be implemented for independent reasons.

Precaution and SRM 8 latter at first glance appear more likely to comply with CPP. We cannot know the risks involved for any of these technologies, however, if we do not research these options thoroughly. As soon as it is shown that a SRM technique would create new threats of catastrophe, such a technique no longer can be considered an available precautionary measure against climate change, if we are to follow CPP, unless such risks can be virtually eliminated. If we are to follow CPP and take the precautionary course of action, after all, we should act in accordance with precaution and not take new risks with our planet that could threaten us and future generations in new ways.
IV. If Catastrophe is Our Only Option
Before concluding I want to briefly consider a lingering question: What if a climate catastrophe is imminently upon us and our only hope of averting it is to inject sulfates into the stratosphere, to brighten clouds in the troposphere, to launch space-based reflective surfaces, or implement some other SRM technique even though we believe these technologies pose additional threats of catastrophes? What if we fail to avert catastrophe using appropriate means and are only option is to radically geoengineering our planet, reducing the threat of one catastrophe in lieu of a different threat? My first response to these questions is that we better hope that such a day never arrives. But should we arrive at a point where a potentially risky SRM technique is our only option for averting a climate catastrophe, it seems CPP will then suggest we ought to begin by reducing imminent threats of catastrophe first, especially when we have a high degree of certainty about the imminent threat in question. If a climate catastrophe is upon us, only then will precaution dictate taking risky precautionary measures such as SRM techniques that invite new (albeit lesser) threats of catastrophe.
The question is: Should this change how we think about researching SRM techniques?
Should we ‘Arm the Future’, as Gardiner (2010) would say, with a better understanding of SRM techniques? It seems the answers to both of these questions is ‘no’. CPP does not argue for
‘Arming the Future’ by researching SRM techniques now, at least not if these invite new catastrophic risks. After all, what CPP requires of us is to take precautionary measures to avoid being in such a position in the first place. And, in my informed opinion, we could avert or at least dramatically reduce the threats of catastrophe posed by climate change through standard mitigation efforts and by preparing to implement adaptation measures in areas most at risk of being catastrophically impacted. CPP does not call for preparing for the worst or ‘arming the

Precaution and SRM 9 future’ when we can avoid being in such a situation in the first place. Thus precaution, at least as is dictated by CPP, does not at this point justify researching SRM techniques once these are shown to pose their own threats of catastrophe.
V. Conclusion
‘The’ precautionary principle is meaningless when it is used to justify all and any kinds of precautionary measures. The Catastrophic Precautionary Principle, however, identifies a particular prima facie moral obligation and not only justifies but requires precautionary measures against threats of catastrophe such as those posed by climate change. CPP does not, however, require that the most extreme precautionary measure be taken in all cases. It logically requires that precautionary measures not themselves violate CPP and that they be appropriate given the nature of the threat. SRM will only become a viable precautionary measure against climate change if specific methods are shown not to create new threats of catastrophe. If they do they may someday become our option of last resort, but precaution (as captured by CPP) does not justify researching technologies we know may invite new threats of catastrophe. What CPP does justify is taking action now to prevent future catastrophes. If painting roofs white or installing reflectors in the dessert can safely help us accomplish this goal, these measures should be considered as viable options. The burden lies with those who want to implement such measure to demonstrate their safety.

Precaution and SRM 10
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