If we abruptly started or stopped engineering the climate, reptiles and mammals moving at 1.7 km/year on average will have to move faster than 10 km/year to remain in their preferred climatic zones.
Foreseeing that emission cuts alone are unlikely to combat global warming, controversial geoengineering interventions are receiving attention from policy makers and scientists alike. One such technology, inspired by volcanoes, entails spewing sulphate aerosols into the upper atmosphere to deflect sunlight and artificially cool the planet.
A recent study, however, shows that rapid application, followed by abrupt termination of this temporary tech-fix can in fact accelerate climate change. The increase in temperature from the abrupt termination is so quick that most species, terrestrial or marine, may not be able to keep up with it and eventually perish.
Treading into uncharted territory, Christopher Trisos, a postdoctoral fellow at the National Socio-Environmental Synthesis Centre, Maryland, and colleagues were keen to explore the lesser-known, indirect consequences of solar geoengineering. In particular, they wanted to predict the fate of biodiversity if five billion kilograms of sulphur dioxide were to be injected into the atmosphere, every year, 2020 onwards, and suddenly stopped in 2070, say, due to political challenges.
“We chose to study this scenario because rapid implementation and termination may have the most significant impacts on biodiversity,” said Trisos.
The study uses climate simulations to calculate the speed at which temperatures will change across Earth’s surface between 2020 and 2090 and thus the speed and direction in which animals will have to move to track these changes. By matching these with the actual speeds animals are capable of moving at, the team could estimate extinction risks.
As expected, the climate would begin to cool once geoengineering commences. This initial cooling phase, would provide relief, particularly for species that were unable to keep up with past warming. Also, mobile taxa – such as birds and fish, which may have moved in response to elevated temperatures in the past – will possibly turn back.
But during this period, human activities still continue to emit greenhouse gases, although these are managed with ongoing mitigation measures. So from around 2030, the climate begins to warm again and the annual five billion kilograms of aerosol injection is not enough. “It only partially offsets the warming,” explained Trisos. Animals now have to move as far and fast as they would otherwise have had to in a scenario without any geoengineering.
What if this outcome discourages governments and they lose the will to invest in further climate engineering? As it turns out, a decision to suddenly terminate the mission would make things terribly worse. “This would lead to a rapid increase in temperature, two to four times more rapid than climate change without geoengineering. This increase would be dangerous for biodiversity and ecosystems,” Trisos cautioned.
Tropical biodiversity hotspots, particularly the Amazonian forests and tropical oceans, are forecast to take the heat (quite literally). Reptiles, mammals, fish and birds that have been moving at 1.7 km/year on average will now have to move faster than 10 km/year to remain in their preferred climatic zones. This raises serious concerns, especially for less-mobile animals like amphibians and corals.
Not just species but entire ecosystems could collapse by suddenly hitting the stop button on geoengineering. For example, temperate grassland and savannahs, which are maintained by specific combinations of temperature and rainfall, may experience increasing rates of temperatures, but an opposing trend in rainfall, after 2070. The situation would not be very different to a rubber band stretched in two different directions. It eventually snaps.
Peter Irvine, an expert assessing broader impacts of solar geoengineering at Harvard University, Cambridge, told The Wire, “These findings only apply to an extreme, rapid onset and rapid termination case. This presents a missed opportunity to understand biodiversity impacts of a more policy-relevant scenario. For example, if solar geoengineering were ramped up slowly to half the rate of warming over the coming decades, then it seems likely it would reduce many climate risks.” Then: “Solar geoengineering deployment can be ended without the impacts of a termination shock if it is gradually ramped down over decades.”
In any case, the potential costs and benefits associated with deploying solar geoengineering in one form or another still need investigation. In the meantime, two aspects are certain: under no scenario could climate engineering serve as a substitute to reduced greenhouse gas emissions, and it would be irresponsible to implement such technologies without more nuanced research.
“Future research should focus on identifying scenarios which would best reduce the risks of climate change,” Irvine added.
The study was published in the journal of Nature Ecology and Evolution on January 22, 2018.
Priyanka Runwal is an ecologist and researcher affiliated with the National Centre for Biological Sciences, Bengaluru. She is interested in savanna and grassland ecosystems.