The paper in Nature Ecology & Evolution is here: http://go.nature.com/2DsfWUa
What if fleets of airplanes were flying up into the stratosphere every day spraying sulfur to create an artificial sulfuric acid cloud to reflect sunlight to cool Earth and counteract global warming, and then they had to stop? Imagine a severe drought in China or flooding in Bangladesh, and they said, “You [expletive deleted] geoengineers are causing this and you have to stop now,” even if they could not attribute those climate extremes to the aerosol cloud. Or what if a global financial crisis or war or pandemic eliminated the budgets for geoengineering? Or hackers or terrorists destroyed the equipment? Stopping cold turkey would not be wise, but it is not hard to imagine scenarios where it could happen.
Previous climate model simulations, as part of the Geoengineering Model Intercomparison Project (GeoMIP), have examined these very scenarios and found that the result is rapid global warming, at as much as 10 times the rate that would have occurred, and strong changes in precipitation patterns and other climate elements. At an American Association for the Advancement of Science meeting two years ago, I was on a panel presenting the new U.S. National Academy of Sciences report on climate intervention, which, among other suggestions, recommended no implementation of stratospheric aerosols now because of the possible negative impacts, including this termination shock. After the session, an ecologist, Jessica Gurevitch from Stony Brook University, introduced herself and asked about the ecological impacts of such rapid climate change, and I answered that this was indeed a concern, but nobody had studied it yet. Jessica and I then assembled a team of ecologists and geoengineering climate modelers to tackle the problem, and our new paper (Trisos et al., 2018) is the result.
We took advantage of GeoMIP G4 climate model simulations that had already been conducted, in which an RCP4.5 warming scenario is addressed by stratospheric injections of 5 Tg SO2 per year (equivalent to one 1991 Mt. Pinatubo eruption every four years) for 50 years, and then immediately stopped. Using climate velocities, the rate that animals would have to move to keep their climate constant, we compared the resulting temperature and precipitation velocities at implementation and termination of the sulfur injections to the rates that would have happened with global warming without climate intervention, and to those that different animals could normally move. We particularly paid attention to biodiversity hotspots on both land and in the ocean.
We found that not only would climate velocities outpace the average dispersal speed of 93% of mammal species at geoengineering termination, the temperature and precipitation velocities on land move in different directions in many places, fracturing ecosystems in biodiversity-rich tropical oceans and in the Amazon. Extinction would be threatened, particularly for corals, mangroves, amphibians and land mammals. One surprising side effect of rapidly starting geoengineering would be an El Niño warming of the sea surface in the tropical Pacific Ocean, which would cause a devastating drought in the Amazon.
The 1992 pledge in the Framework Convention on Climate Change to prevent “dangerous anthropogenic interference” with the climate system surely must also apply to stratospheric geoengineering, and if we cannot guarantee that there will never be rapid implementation or termination, should we ever even consider doing it?