Geoengineering could hold back climate warming - but what if the dam bursts?

Solar geoengineering, if it works, could offset climate warming by reflecting sunlight back into space. But if we stopped doing it suddenly, the delayed warming would all happen at once.
Stratospheric clouds over Sweden. Artificial stratospheric clouds created by solar geoengineering would reflect some sunlight back into space, cooling the planet (Reuters)

Climate change is an undeniable fact and if we continue on the same emission-addicted trajectory, we will face a climate crisis sooner rather than later. Scientists are thinking about everything they can do to mitigate or offset climate change now and help us survive a warmer world. One suggested proposal is solar geoengineering.  

Geoengineering would involve creating clouds over 15 kilometres above Earth in the stratosphere to reflect the rays of the sun. A typical scenario would require airplanes to spray sulphur dioxide gas into the atmosphere where it will react with water to create sulphuric acid clouds that will reflect some sunlight back into space. The inspiration for the idea came from volcanic eruptions that release gases into the atmosphere and create semi-permanent clouds can last one or two years. These volcanic clouds have been observed to cause temporary climate cooling.  

The mount Pinatubo eruption in 1991 temporarily cooled the global climate by about 0.6 degrees C.

Geoengineering isn't without risks

The problem with geoengineering is that there are many ways it could go wrong. Dr. Alan Robock is a distinguished professor in the department of environmental sciences at Rutgers University and has thought a lot about what could possibly go awry if geoengineering becomes a reality. Geoengineering would mean rapid climactic shifts that will affect different areas of the world differently.

And some areas may suffer. Models suggest, for example, that the Amazon rainforest would experience less precipitation. There will be increased droughts in other parts of the world even though the global temperature will cool. We also need to worry about the fact that oceans will continue to acidify even after we've blotted out the sun.  And then there's the matter of the hazing of our blue skies.  

But as Robock's new paper in Nature Ecology & Evolution outlines, a major risk associated with solar geoengineering is what might happen if we stop. Any rapid stop to the program could be catastrophic to the world's ecosystems. A well-planned geoengineering program would be intended to last years — with a gradual tapering matched to other mitigation strategies. But it's easy to imagine a scenario in which a solar geoengineering program was halted suddenly. They suggest that a geopolitical dispute or fracturing of international cooperation might interrupt the project. Similarly terrorism or computer hacking could disrupt it. 

Robock outlines one such scenario. "You could imagine a drought in China, or a flood in Bangladesh and they say 'You geoengineers. You are causing this. You better stop.' And you say, 'You can't prove that, because there are always droughts and floods.' And they say, 'Well, we don't care, our citizens are demanding it and if you don't stop we'll shoot your planes down.''"

The effects on the ecosystems of the world

If any active geoengineering program were stopped quickly, it would be catastrophic for the animals that we share our planet with. With climate change models, Robock and his team simulated the effects of a rapid halt to any implemented geoengineering program and the results were troubling. If a program was stopped even after just a few years of intentional cooling, we would expect to see a 10-fold more rapid warming trend than even currently seen on Earth. Ecosystems would seriously suffer as the rate of change exceeded their ability to adapt.

Says Robock, "We calculated how fast a species would have to move to maintain the same temperature. At the same time, precipitation is changing and we calculated how fast it would have to move to maintain the same precipitation. And with this sudden termination, in many places in the world, they would have to go in different directions to maintain temperature or precipitation and ecosystems would become fragmented. That's a concern."

Robock's team calculated the 'climate velocities' or the speed at which animals would have to move to adapt to this changing world and the study estimated that 93 per cent of all the animals on the planet would not be able to move fast enough to survive.

So should we even study geoengineering?

According to Robock, research into geoengineering is crucial because it has the potential to give us a stop-gap measure to reduce carbon dioxide in the atmosphere. "The main benefit [of geoengineering] is, if you could do it, then it would reduce global warming and all the negative impacts of global warming. And that benefit — less sea level rise, fewer strong storms and fewer droughts and everything else. And so we are trying to quantify what the benefits are and the risks are so, at some time in the future policy makers can make informed decisions."

Robock makes it clear that this is not a cure for climate change. Depositing sulphuric acid in the stratosphere is not a viable long-term solution to preventing further changes to our climate. The real solution is controlling the drivers of climate change — greenhouse gases. But failing that, he says research and development into geoengineering and a full understanding of the possible risks is essential in case we have to resort to extreme measures in the future.