It is time to rebalance the risk equation

The fear of unintended consequences is frequently used to argue against conservation interventions that range from climate engineering, to genetic editing of imperiled species, to actions as seemingly mundane as using seeds from non-local sources in restoration projects. There is no denying that unintended consequences are real and worthy of concern. Indeed, environmental textbooks are filled with descriptions of past interventions gone awry (such as the introduction of cane toads to Australia for biocontrol, the impacts of long-term wildfire suppression, or the use of DDT to control insect pests). However, there are also numerous counterexamples of interventions turning out as planned (for instance, barging salmon smolts around Snake River dams and human-assisted hybridization rescuing the depleted gene pool of Florida panthers). For actions under consideration, the question is how to weigh the possible unintended consequences versus the highly likely intended benefits. A June 2020 workshop (https://reviv​erest​ore.org/inten​ded-conse​quences), organized by Revive & Restore, assembled an international group of conservationists (including wildlife biologists, restoration scientists, geneticists, ethicists, and social scientists) to re-examine the precautionary principle and its associated focus on unintended and unanticipated consequences. Two observations make apparent the need for this reassessment. First, accelerating anthropogenic climate change and the expanding human footprint create ever-greater urgency for actions that could avert disasters or prevent human-driven extinctions. With most rivers dammed, a nitrogen cycle dominated by human alterations, and such severe global warming that within 50 years as many as one in three humans could be forced to migrate in search of a habitable environment (https://nyti.ms/2E5a0Wi), conservationists do not have the luxury of “doing nothing” out of fear of unintended consequences. Caution is prudent, but paralysis is unconscionable. Second, the science of risk assessment has advanced so that, although it is impossible to eliminate uncertainty, the likelihood of horrific ecological surprises is much less now than in previous decades. Ecologists today better understand ecosystems and indirect effects than they did in the 1960s and 1970s when several well-intended, but ill-fated, introductions were conducted (eg introducing the American red squirrel to Newfoundland to augment the diet of pine martens; introducing the seed weevil Rhinocyllus conicus to control exotic thistles in North America). Lessons learned with each intervention reduce the chance for future errors. Not only is risk assessment improving, but some of the tools for intervention are becoming refined. For example, the genomic and phenotypic changes that result from gene editing are much more precise than those wrought by more widely accepted techniques like hybridization and mutagenesis. Obviously, the answer is not to blithely ignore unintended consequences and adopt an “anything goes” attitude. However, it is time to recalibrate our traditional cautionary approach to environmental decision making with fine-tuning in four dimensions. First, the intended consequences of proposed interventions must carry more weight in analyses. Consider the public debate over transgenic Bt crops. The intended benefit of reducing the application of broadly toxic insecticides has largely been overshadowed by fears of environmental harms, for which there is no convincing evidence. Second, scientists should avoid being overly influenced by examples of disaster from generations ago and give more credit to recently accumulated empirical evidence. From reintroductions to genetic rescues, the vast majority of contemporary environmental interventions have produced their intended positive outcomes, yet a few historical cases of problematic outcomes continue to dominate public perception. Moreover, all actions, including inaction, entail the potential for unintended consequences. For instance, growing evidence shows that protected area creation – an intervention largely embraced by conservationists – typically displaces, rather than curtails, environmental harms and can prove counterproductive if local communities are alienated. Third, risk assessment relies on tools ranging from controlled experiments and practical experience to models and simulations. All of these tools help characterize risk, but empirical data should be far more reassuring than theoretical, but untested, models. Thirty years of globally widespread Bt crops with no ill-effects ought to inspire confidence, whereas speculative interventions such as solar geoengineering warrant greater precaution. Lastly, and most importantly, scientists need to recognize that the worst unintended consequences may not be environmental or ecological, but rather social. A carbon tax might be a great way to reduce greenhouse-gas emissions and a protected area may secure a remnant population of a declining species, but such actions disproportionately impose costs on marginalized human communities. A wider variety of voices must be invited to weigh in on what intended outcomes are desired, and how best to achieve them. While risk reduction efforts now better recognize and minimize unintended environmental harms, much work remains to address unintended social and cultural consequences. MICHELLE MARVIER Santa Clara University, Santa Clara, CA PETER KAREIVA Aquarium of the Pacific, Long Beach, CA

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