Spraying aerosols into the atmosphere to mimic the cooling effect of a major volcanic eruption might work to limit global warming, and has received more attention from scholars and policymakers in recent years as an “emergency brake” option. But if this solar geoengineering technique were turned off, temperatures would suddenly spike faster than many species could handle, according to new research, dooming much of life on earth.
How could proponents of such a disastrous plan have not considered this possibility? It turns out that they have.
Ecologists wanted to model the effects on biodiversity if such an emergency brake of solar radiation management (SRM) were suddenly released. They imagined a scenario where from 2020 onward, airplanes would be dispatched annually to spray 5 million tonnes of sulphur dioxide into the stratosphere, resulting in a lowering of average global temperature by a quarter of a degree. Then suddenly in 2070, the SRM abruptly halts.
In their model, as a result of the SRM termination, temperatures climbed by almost three quarters of a degree over the course of just a decade. The researchers, whose work appeared in Nature Ecology and Evolution this week, concluded that in order to keep pace with this temperature change rate, terrestrial species would have to shift their range by 10 kilometres a year, some four times faster than they are having to migrate to keep up with the temperature changes we are already seeing. Marine species would need to migrate six times faster under this scenario of “climate velocity,” the term they use to describe the speed and direction that species need to move to track changes in climate.
Climate velocities would be highest in tundra, boreal forests, temperate grasslands and the tropics. The authors fear that extreme climate velocities caused by abruptly ending geoengineering may pose an acute threat to species survival in the most biodiverse regions on Earth.
But according to scholars who have been working on the topic of geoengineering governance, the risk of a sudden halt to SRM, or “termination shock,” has been known for about a decade. Edward Parson, UCLA environmental legal scholar and expert on geoengineering governance, said this recent paper is a good example of how awful such an event would be. “No one needed this paper to know that a 2C global heating in 10 years is bad for biodiversity,” he told the Climate Examiner. “Suddenly turning it off and on would be an obviously bad way to use geoengineering.”
A central concern has long been ensuring SRM is used in a way that avoids risks such as termination shock, he said. There is considerable uncertainty about how geopolitically likely the risk is that SRM would be used in this way. Some scholars have argued that a slow phase-out would be more likely and correctible in real time. For example, SRM could be gradually wound down without any temperature rises at all if the termination were coupled with the large-scale use of CO2 removal techniques such as direct air capture.
Energy economist Mark Jaccard helped design BC’s carbon tax, and he still supports it. But he questions just how politically viable a stringent tax—at the level needed to meet climate targets—can really be. So he also continues to explore how other policies that the public find more acceptable could work.