Geoengineering could reverse climate change but might have dire effects if abruptly stopped: study

23 January 2018 | Mitigation

One of the leading potential strategies for dealing with climate change — spraying gases into the sky to reflect sunlight back into space, known as geoengineering — comes with major risks for the Earth’s biodiversity should it ever be abruptly shut down, according to a new scientific paper.

The problem is basically that it is so effective, it can cause surface temperatures to drop dramatically and quickly, like global warming in reverse, with dire effects on plants and animals.

The idea is to use a custom designed fleet of high-altitude jets to spray sulphur dioxide into the stratosphere, higher than most clouds, and essentially mimic the meteorological effects of major volcanic eruptions, which have historically been followed by periods of global cooling.

“We know from pas volcanic eruptions — the last big one was Mount Pinatubo in 1991 — that it will create a cloud of sulphuric acid droplets in the stratosphere, where there’s no rain to wash it out. It will last for a couple of years and it will reflect sunlight,” said Alan Robock, a meteorologist and distinguished professor of climate science at Rutgers University.

After that eruption, for example, Canada was about 3 degrees Celsius colder than normal in the summer, and ice stayed in Hudson Bay an extra month or so, leading to a banner year for polar bear cub births.

“We know that this can cause climate change, so the idea is to emulate that,” Robock said.

There are many potential problems, however, and Robock’s new paper with colleagues in Nature Ecology & Evolution is part of a broader effort to scientifically quantify the risks and benefits of geoengineering — large scale projects designed to halt, slow or reverse climate change. So far, the risks to biodiversity, for example, have been “almost completely unexplored,” the paper claims.

By modelling the effects on biodiversity of a major project to spray sulphur dioxide for 50 years, then stop abruptly, the researchers highlight one of the most dangerous problems of all — the fickle will of geopolitical leaders.

One basic mechanical problem in the spraying scheme is that aerosols eventually fall down, but that can be solved by continually replenishing them. Another is that spraying sulphur dioxide also produces acid rain and acid snow, but the amount in this latest scenario of 5 million tonnes a year is only 5 per cent of what humans are already putting into the lower atmosphere by burning coal and oil.

“Locally it can be quite polluting but globally it’s not that much,” Robock said.

There is also a question about what will happen on the level of particles. If you spray particles of sulphur dioxide into a cloud, they might clump into other existing particles, making them heavy, so they fall to earth faster, and be less effective at scattering sunlight.

ut the real problem is with political leaders. The paper speculates that a geoengineering scheme could fall apart for any number of reasons, from drought to war.

“Interstate conflict could cause geoengineering to fail, and unintended negative consequences or regionally severe climate events such as extreme droughts could force rapid termination, even if direct attribution of these events to geoengineering could not be demonstrated,” the paper reads.

In that case, a controlled experiment on the Earth’s climate could be shut down overnight. A gradual build up would be stopped abruptly. The effect would be an increase in what are known as climate velocities, or the speeds at which an animal or plant would have to migrate in order to stay in their climatic comfort zone.

Some animals can simply walk, fly or swim as their climate changes, to keep the same average temperature by moving up in either altitude or latitude. Others cannot. Some of the ecosystems likely to pay the highest price, according to the paper, are tundra, boreal forests and temperate grasslands.

Many tropical species also have very narrow ranges of acceptable temperatures. “Extreme climate velocities from geoengineering termination thus represent a potentially acute threat to species survival in the most biodiverse regions on Earth,” the paper reads.

There is often a concern among advocates of climate change mitigation that the more successful the strategy, the more comfortable people get in the expectation that science will find a way out of the problem, Robock said in an interview.

But that is flipped when people hear serious discussion of spraying sulphuric acid into the air, which sounds dramatically intense.

“It often works in reverse,” Robock said. “People become more concerned about doing something about global warming when they find out that people are considering doing this.”



Source: National Post