Climate change represents one of the greatest forces reorganising biodiversity this century. This climate-induced biodiversity change has significant consequences for human well-being. The loss of species from ecosystems undermines ecosystem function, diminishing the life-supporting benefits people derive from nature; for example, where food production relies on a diversity of pollinator species. Even when species do not go extinct, their changing distributions due to climate change can have significant impacts on food security, income and health; for example, by shifting fishing grounds the expansion of the range of disease-transmitting mosquitoes.
In 2010 the Convention on Biological Diversity adopted decision X/33 stating that “no climate-related geo-engineering activities that may affect biodiversity take place, until there is an adequate scientific basis on which to justify such activities.” Since this decision, interest in potential climate engineering technologies as a way offset the worst impacts of global warming has grown. However, the consequences of climate engineering for biodiversity have continued to receive little research attention from ecologists.
Now, a team of ecologists and climate scientists (lead by the author) has published a study on the potential consequences for biodiversity from solar geoengineering—the injection of aerosols into the upper atmosphere to reflect sunlight back to space, cooling the Earth.
Aerosol injections are the most prominent solar geoengineering scheme, and a tempting one: at under $10 billion annually the estimated direct costs are low when compared to the trillions of dollars in climate damages they might help to offset. But what about the indirect costs of solar geoengineering?
A major finding of our research was that if solar geoengineering started and then decades later stopped suddenly (e.g., due to interstate conflict), there would be a great increase in the climate change threat to biodiversity. Compared to temperature increases without geoengineering, rapid climate warming from a sudden termination would require species to shift their distributions almost three times as fast to remain in their climate niches. That is a breakneck pace that would likely drive many species to extinction. We also found that a rapid start to solar geoengineering would cause El-Niño-like warming of the tropical Pacific Ocean, potentially causing drought and widespread forest fires in the Amazon and Southeast Asia.
Here, I highlight some further research and policy directions based on this work:
Our study does not show that all solar geoengineering schemes would be bad for biodiversity. The cooling from solar geoengineering could help some important but heat-threatened ecosystems such as coral reefs that provide livelihoods to millions of people. However, a key point is that solar geoengineering would expose biodiversity to risks that otherwise would not be present. We now know a sudden stop to solar geoengineering would be more dangerous for biodiversity globally than never doing solar geoengineering in the first place. The same could apply to a sudden start. The 1992 pledge in the Framework Convention on Climate Change is to “prevent dangerous anthropogenic interference with the climate system”. This pledge applies to greenhouse gas emissions. If the same applies to solar geoengineering, and if we cannot guarantee that there will never be rapid implementation or termination, should we ever even consider doing it? Aggressive reductions in greenhouse gas emissions are the most effective way to reduce the risks to biodiversity from climate change, as well as to human well-being that depends on biodiversity.
We used climate models to estimate how fast species would have to move to keep pace with climate change due to a sudden termination of solar geoengineering. The climate model uncertainty for this is relatively low, but it is important to separate the model uncertainty from the uncertainty of a sudden termination scenario. For example, there is disagreement on whether interstate conflict could cause geoengineering to fail, and whether unintended consequences such as extreme droughts could drive demand for a sudden termination, even if direct attribution of these events to geoengineering could not be demonstrated.
Scenarios provide plausible, albeit simplified, descriptions of how the future may develop, based on a coherent set of assumptions about key driving forces. Scenario planning is an important tool for identifying alternative futures and thinking through the consequences of decisions in the face of high uncertainty. Well-founded scenarios are powerful because they focus scientific research, and shape how people think about the future. The Geoengineering Model Intercomparison Project (GeoMIP) is engaged in scenario development for solar geoengineering. These scenarios have proven very useful for understanding climate responses to solar geoengineering. Ideally, future scenarios for solar geoengineering will also be constructed by a diverse group of people from both natural and social sciences, as well as policy makers, to enhance scenario credibility for policy making, and the understanding of key uncertainties within scenarios. These scenarios can then be fed into models to quantify potential outcomes of solar geoengineering for people and the environment.
Decisions on whether or not to deploy solar geoengineering must rely heavily on understanding the positive and negative impacts to social and ecological systems, as well as comparing these to climate change without geoengineering. Solar geoengineering is now at a critical point where assessment by the climate impacts research community is urgently required to advance any discussion of how solar geoengineering could contribute to reducing climate risks. There is a lot that can already be done in this regard. However, an updated and limited set of scenarios that are credible from both a science and a policy perspective, and yet diverse enough to capture key differences among potential deployment strategies will be essential for guiding these impact assessments.
Our study on the biodiversity consequences of a sudden start or stop to a global solar geoengineering deployment does not predict biodiversity responses to small-scale outdoor experiments. Such experiments should be judged on their scientific merit, as well as the broader governance and ethics concerns around solar geoengineering, which should include potential biodiversity responses when the intention is to inform solar geoengineering deployment at the global scale.
Christopher Trisos, PhD, is a Postdoctoral Fellow at the National Socio-Environmental Synthesis Center. His PhD research at the University of Oxford used ecology and evolutionary biology to test the importance of dispersal, interspecific competition and habitat for explaining biodiversity patterns in South American birds.