Geoengineering: Symmetric precaution (Science)

Edward A. Parson

As alarm about climate change and calls for action intensify, solar geoengineering (SG) is seeing increased attention and controversy. Views on whether it should or will ever be used diverge, but the evidentiary basis for these views is thin. On such a high-stakes, knowledge-limited issue, one might expect strong support for research, but even research has met opposition. Opponents’ objections are grounded in valid concerns but impossible to fully address, as they are framed in ways that make rejecting research an axiom, not a conclusion based on evidence.

Supporters of SG research argue that it can inform future decisions and prepare for likely future calls for deployment. A US National Academies of Sciences, Engineering, and Medicine (NASEM) report earlier this year lent thoughtful support to this view. Opponents raise well-known concerns about SG such as its imperfect climate correction, its time-scale mismatch with greenhouse gases (GHGs), and the potential to over-rely on it or use it recklessly or unjustly. They oppose research based on the same concerns, arguing that usage can never be acceptable so research is superfluous; or that sociopolitical lock-in will drive research toward deployment even if unwarranted. Both support and opposition are often implicit, embedded in debates over additional governance of SG research beyond peer review, program management, and regulatory compliance.

At present, potential SG methods and claimed benefits and harms are hypothetical, not demonstrated. The strongest objections to research invoke potential consequences that are indirect, mediated by imprudent or unjust policy decisions. Because the paths from research to these bad outcomes involve political behavior, claims that these “could” happen cannot be fully refuted. Understanding and limiting these risks require the same research and governance-building activities that opponents reject as causing the risks.

To reject an activity based on harms that might follow is to apply extreme precaution. This can be warranted when there is risk of serious, unmitigable harm and the alternative is known to be acceptable. That is not the case here. Rejecting SG research means taking the alternative trajectory of uncertain but potentially severe climate impacts, reduced by whatever emissions cuts, GHG removals, and adaptation are achieved. But these other responses needed to meet prudent climate targets carry their own risks: of falling short and suffering more severe climate change, and of collateral environmental and socioeconomic harms from deployment at the required transformative, even revolutionary, scale.

Suppressing research on SG might reduce risks from its future use, but this is not assured: Rather than preventing use in some future crisis, blocking research might make such use less informed, cruder, and more dangerous. Even if these risks are reduced, this would shift increased risks onto climate change and crash pursuit of other responses. Total climate-related risk may well increase—and be more unjustly distributed, because the largest benefits of SG appear likely to flow to the most vulnerable people and communities.

Yet the concerns that motivate opposition to research are compelling. SG use would be an unprecedented step, affecting climate response, international governance, sustainability, and global justice. Major concerns—about reckless or rivalrous use, or over-reliance weakening emissions cuts—are essential to address, even if they cannot be avoided with certainty. A few directions show promise for doing so. Research should be in public programs, in jurisdictions with cultures of public benefit and research accountability. The NASEM call for a US federal program is sound. Other national programs should be established. Research governance should be somewhat stronger than for less controversial research, including scale limits on field experiments and periodic program reassessments. Exploration of governance needs for larger-scale interventions should begin well before these are considered. Research and governance should seek broad international cooperation—promptly, but not as a precondition to national programs. Broad citizen consultations are needed on overall climate response and the role of SG. These should link to national research and governance programs but not have veto power over specific activities.

Precaution is appropriate, even necessary. But precaution cannot selectively target risks from one climate response while ignoring its linkages to other responses and risks. Suppressing SG research is likely to make the harms and injustices that opponents fear more likely, not less.

Volume 374 • Issue 6569 • 12 November 2021

Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Published online: 11 November 2021