Three main types of solar geoengineering that are now being studied.
Graphic: US National Academy of Science
It sounds like something out of a bad science fiction movie — artificially blocking sunlight to keep global warming from overheating the Earth. Nevertheless, a small cadre of researchers is studying the option — so that if humankind ever needs to use it, it will be an informed decision.
The latest report from the Intergovernmental Panel on Climate Change (IPCC), released in early August, made it clear that humankind needs to take immediate action to curb global warming. There’s hope that international climate talks in Glasgow this November may finally result in strong enough greenhouse gas emission limits to make a difference.
But just in case, an international group of researchers, including NTNU’s Helene Muri, has been studying a technology called solar geoengineering as an action of last resort.
Solar geoengineering is exactly what it sounds like, where various technologies are used to block sunlight and cool the Earth. Typically, three main approaches — none of which is currently technologically ready — are being studied for their ability to block sunlight and lower ground temperatures. (See box)
Muri, a senior researcher at the university’s Industrial Ecology Programme, has spent the last decade looking at how solar geoengineering might — or might not — work.
In June, she and her colleagues from the US, China and the UK published a paper in Nature Food that used computer models to assess solar geoengineering’s potential effects on agriculture in a high emission world. Their findings sparked international media coverage because they found that solar geoengineering in those scenarios could actually have a positive effect on crop growth from higher humidity.
Other studies that used simpler models found either a limited effect or losses for rainfed crops, since there could be less rainfall with the lower temperatures that come with solar geoengineering – depending on the way the technology is used to cool the Earth.
Now, as the world prepares to debate limits on CO2 emissions during November’s climate talks, it’s worth a look at the measures being examined by researchers like Muri — and an assessment of their possible risks and pitfalls.
Any discussion of solar geoengineering has to acknowledge that it’s far from a perfect fix, Muri says.
“Solar geoengineering, no matter how well we do it, will never perfectly offset the effects of climate change,” she said.
The problem is that solar geoengineering may cool the Earth, but doesn’t get rid of the excess carbon dioxide and other heat-trapping substances in the atmosphere. And carbon dioxide does more than simply warm the Earth.
There is no one silver bullet. It’s not the one solution that can fix everything.
It fertilizes plants — which could be a good thing — but because much of it gets dissolved in sea water, it makes the oceans more acidic.
“There will always be things that you cannot fix with solar geoengineering, specifically ocean acidification,” she said. “A more acidic ocean affects everything in the food chains in the ocean, including coral reef diebacks, which is terrible for the ecosystem as a whole. That becomes evident as soon as you really start looking at it. There is no one silver bullet. It’s not the one solution that can fix everything.”
Muri says that any discussion of geoengineering also assumes that CO2 emissions will be dealt with at the same time any solar geoengineering is deployed.
Alan Robock, a climate researcher at Rutgers University in the US who is leader of an international cooperative research project of called GeoMIP, of which Muri is a part, agreed.
“It’s not a solution to global warming at its best. If it were ever used as a band-aid — or a tourniquet — it doesn’t solve the root problem,” he said.
Many unknowns, but still need to know
Muri says there is still much that is unknown about solar geoengineering, in part because most climate change research is focused on issues other than geoengineering.
“Just to put the level of research into context, for the last 5 to 10 years, there have been about 100 to 130 papers published per year on solar geoengineering,” she said. “When it comes to climate change it’s more like 30,000 papers per year over that period. The important thing is that it is a vastly, hugely different amount. It’s just a minority of effort and funding going into researching solar geoengineering.”
Who sets the thermostat and how would you go about agreeing on something like that?
At the same time, she says, the US National Academies of Sciences, Engineering and Medicine published a comprehensive report on solar geoengineering that said the urgency of the risks posed by climate change meant that “the U.S. should pursue a research program for solar geoengineering — in coordination with other nations, subject to governance, and alongside a robust portfolio of climate mitigation and adaptation policies.” The report recommended US funding of about $100 million-$200 million over the first five years.
Muri says that climate researchers’ main focus needs to remain on climate change itself, because society needs to know what the effects will be, how to adapt, and how to mitigate these effects. Nevertheless, she says, researchers do need to study solar geoengineering to see if it could be helpful as a stopgap measure while the world transitions away from fossil fuels.
“The question is if it could contribute to reduce some level of harm from climate change for a certain period, whilst we are trying to sort out both emissions of CO2 and concentrations of CO2 within the climate system,” she said. “Nobody sees it as a one and only solution, but it’s not clear yet whether it could be helpful or not. At the moment, there are too many unknowns and uncertainties to really say whether it’s overall a good idea or a bad idea.”
His group at Rutgers University is “doing research to evaluate the risks of doing solar geoengineering versus the risks of not doing it. And that’s the information that governments will need in the future to decide whether or not to ever implement it,” he said. “I spend millions of dollars of taxpayer money to do my research. And if I find a danger to society, it’s my obligation to warn people about it.”
A cooler Earth but potentially changed monsoons
Robock’s group is looking at the benefits and risks of using stratospheric aerosols to cool the planet, which emulate a volcanic eruption.
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