Climate challengesBlocking the Sun to Control Global Warming

By Nancy Bazilchuk

Published 22 September 2021

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.

Band-aid or Tourniquet?
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.

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.