Scientists: Maybe If We Only Dim the Sun a Little It Won’t Backfire Horribly

By Brian Kahn on at

When it comes to geoengineering the planet to cool the climate, there’s rightfully a lot of hesitation. Blocking incoming sunlight might seem like a quick fix to rising temperatures, but doing so could quickly tie up humanity in a decades-long project with alarming side effects like shifting precipitation patterns and changes in hurricane season.

Which is what makes a new paper released today in Nature Climate Change so alluring. It shows that undertaking half measures to block the sun could end up providing the benefit of a cooler planet without many of the adverse impacts on other parts of the climate system. The results suggest there could be a role for geoengineering to play in saving us from a climate catastrophe, though it’s hardly the last word on what that role could be, or even if it’s worth the risk. And there are a few important caveats showing that there’s still a lot of research needed on the topic.

Most research on geoengineering has focused on how humans could offset all the global warming associated with greenhouse gas pollution. The new study takes a different path, though. Using high resolution climate models, researchers first doubled the concentration of carbon dioxide in the atmosphere. They then used the models to reduce incoming sunlight enough to offset half of the warming associate with the rise in carbon pollution. Basically it’s like two steps forward, one step back.

They then looked at geoengineering’s impact not just on temperature but precipitation, evaporation, and tropical cyclones. Precipitation and evaporation are crucial components of the hydrological cycle that humanity relies on for drinking water, agriculture, and more while cyclones can cause massive amounts of damage and suffering. Climate change is already causing more heavy downpours and could be playing a role in increasing hurricane intensity (and is likely to keep doing so in the future).

The new findings show, though, that using a geoengineering half measure could reduce temperature and moderate the adverse impacts on the hydrological cycle associated with both climate change and full-on geoengineering. According to the study, tropical cyclone intensity would be reduced as well.

“Surprisingly we find only a very small fraction of places see the effects of climate change exacerbated,” said Peter Irvine, a postdoctoral researcher who led the new study. “If you kept cooling, you’d keep getting benefits of temperature but diminishing returns on hydrological variables. Offsetting all warming, and you’re beginning to introduce problems that are new.”

Indeed, some previous research that maxes out geoengineering indicates that the hydrological cycles would slow down, causing drought in a number of locations around the world like the Sahel region of Africa. The uneven nature of these adverse impacts has led to calls for the global south to be more involved in any decision making around it. The new findings don’t necessarily change the need for inclusive governance, but they do show one way geoengineering could be a potential tool in the fight against climate change.

That said, the findings come with some caveats. For one, no single study is a cause for action, especially when it comes to something as dramatic as intentionally altering the climate. The methods used to analyse the efficacy of halving global warming also might not paint a full picture of the impacts.

“[T]he study would have been more policy-relevant if it concentrated on a realistic (transient) global warming scenario and represented solar geoengineering using stratospheric aerosols,” said Anthony Jones, an aerosols research who published a recent paper on geoengineering and hurricanes.

Jones said that rather than looking at an abrupt doubling of carbon dioxide, using a scenario where pollution changes over the course of a century would yield more decision-oriented results. Ditto for replicating a specific solar geoengineering technique like injecting aerosols into the atmosphere (which can cause the stratosphere to warm and have other unintended consequences) rather than just turning down the incoming sunlight. Nevertheless, he said the results “strengthen the notion that a moderate solar geoengineering application would be highly effective at ameliorating most regional climate changes caused by global warming.”

That doesn’t mean sun-dimming will be coming to a stratospheric location near you anytime soon. And it doesn’t offer a substitute for what really needs to be done to address climate change. Irvine was blunt in his assessment that it’s only one piece of the puzzle, and a speculative one at that.

“This can’t solve climate change,” Irvine said. “Nothing about this gets rid of the fact that to stop the climate from changing, you need to reduce emissions to zero.”

Featured image: Gavin White (Flickr)