Should we reflect sunlight to cool the planet?

Start In 1991, Mount Pinatubo in the Philippines erupted becoming the second largest volcanic eruption of the 20th century and into the stratosphere dispersing a layer of aerosol particles around the whole world. Those particles formed a sort of solar umbrella that reflected sunlight away from the earth caused global temperatures to drop by about half a degree celsius for almost two years. It's not the first massive volcanic eruption to cool global temperatures.

El Chichón volcano lowered temperatures by a similar amount in 1982 as did other major eruptions over the past century. Today, scientists have been exploring whether we could replicate this phenomenon to fight global warming. Using a technology called solar geoengineering. Supporters say it's a tool we need to seriously explore as climate change worsens. Understanding more about these things that could potentially reduce suffering. That's worth a lot. But critics believe the technology's risks outweigh its rewards and shouldn't be a response to fighting global warming. Sometimes more technology is not always better. There are some things that have been invented that a lot of people would wish had never been invented. So which one is it? To understand the benefits and risks of solar geoengineering, I spoke to several scientists, lawyers, indigenous leaders with strong opinions on both sides. With stakes as high as the survival of the human race on earth, should we be exploring solar geoengineering? There's one thing scientists all agree on: Solar geoengineering could cool down the planet. Reflecting sunlight away from the earth stops heat from getting trapped in our atmosphere. We could do that by injecting aerosols into the stratosphere like volcanoes can do. That's the most commonly researched approach. Some scientists are also looking into brightening marine clouds so they're better at reflecting the sun. And other potential methods include reflective shields in outer space. These initiatives are still in different stages of the research phase but in order for us to deploy these technologies and get large scale cooling effects, we'd need to interfere with our complex climate on a massive scale. One of the main reasons some scientists support solar geoengineering is that we're currently on a pretty dire path. Our emissions, mainly carbon dioxide, keep rising.

There's really no question we must cut emissions in the long run. But even if you cut emissions to zero tomorrow, that does not eliminate climate risk. It just means you stop the climate risk getting worse because the climate risk comes from accumulated emissions. That's University of Chicago professor David Keith.

He explained to me that unless we think beyond emission reduction the climate change impacts we're already experiencing will continue to worsen.

A recent study showed that extreme weather accounted for nearly 10% of all global deaths and shows an increase in heat related ones. To mitigate those effects supporters argue that we need to explore climate processes use computer modeling, and develop technology to figure out if and maybe how this technology could safely be deployed globally along with other solutions. The thing is, messing with our global climate is very complicated. The whole climate system is wired together. People could technologically speaking, create major, unpredictable changes in the way the climate system responds.

Oxford Professor Raymond Pierre Humbert is referencing one of the big concerns about solar geoengineering. Adding new elements into our atmosphere or stratosphere will change precipitation patterns across the world... potentially worsening the extreme weather we're already experiencing due to climate change. Nearly everyone agrees on these risks. And you can't actually answer the most significant questions about the climate system response. Short of a full scale deployment. A full scale deployment would require unprecedented global cooperation not just in terms of scale, but in terms of time. But the carbon dioxide we have emitted since the industrial revolution and we emit today will continue to have a warming effect on climate for thousands of years from now even if we stop emitting. But in contrast, the solar geoengineering techniques proposed have a very short lifetime in the atmosphere.

To create a continued cooling effect we would need to deploy them constantly for centuries. That means that you're committed to having institutions and treaties that can be adhered to for thousands of years. And that's a really unprecedented sort of burden to put on future humanity. If there an international disagreement war, depression, or something that forces a sudden termination of solar geoengineering... then the world gets hit with this rapid warming.

That rapid warming is called termination shock. And the risk of it happening is one of the big reasons critics think solar geoengineering is ungovernable and unsustainable. And so far, we have a pretty poor record of figuring out how to move things forward. In 2021, Sweden rejected a pioneering project to test solar geoengineering technology. Environmental and indigenous groups issued a letter highlighting “the potential for creating drastically uneven, unpredictable changes on climate weather and biodiversity" and “geopolitical tensions it might awaken”. It would cause great changes to our environment and to our ecosystem and those precious ecosystems that we are advocating so hard for. To protect and safeguard and secure and strengthen. Opposition like this is one reason that most solar geoengineering research is taking place in labs with models and simulations. Turning the debate about solar geoengineering into one about how far we should take the research.

In January of 2022, 400 scientists issued a letter calling for a non-use agreement on solar geoengineering. It included five core commitments, among them no outdoor experiments, no public funding and no support from international institutions. Professor Pierre Humbert was one of the scientists who signed it. He explained that the signatories are okay with low risk research. So research that's on fundamental climate processes that doesn't develop the technology that leads to deployment that can provide useful information. Computer simulations and modeling are midway through the spectrum. Critics of solar geoengineering worry that the more modeling we do the closer we'll get to full scale deployment. But they acknowledge that some simulations are useful and a key part of overall science we can't eliminate. We are pretty clear on the idea that research that was essentially technology development that would lead to deployment was something that the signatories are opposed to.

Lili Fuhr, who works at the Center for Intenational Environmental Law told me something similar. Soon as we let the genie out of the bottle, and if we not only just theoretically research but completely develop a certain technology it will most certainly get used. We've seen that with other technologies as well. About a year later, in February of 2023, 110 scientists, including Keith, issued a letter in support of more research into solar geoengineering. They want a robust, international scientific assessment that includes experiments that could potentially advanced technology but stated that “while we fully support the research this does not mean we support the use of solar geoengineering tech.” We can't bind the hands of the future and force them never to use these technologies. So if we make a collective decision now not to do serious research that doesn't prevent people employing this technology in the future. It just means they will deploy them with less knowledge.

I asked Sarah Doherty, who studies maring cloud brightening at the University of Washington about research like this. Doing the research right now really is important, and it's important to making equitable decisions down the road. Because the cat's out of the bag. People know these options exist. Some people think we should be going out and doing them right now. So that tells you how likely it is people 20 years from now are going to be saying, “Let's go do this.” A big concern both sides agree on is the negative impact solar geoengineering could have on decarbonization efforts and that the tech might act as an excuse for oil and gas companies to keep selling fossil fuels.

To unleash the technology of solar geoengineering on the world at a time when we've just barely started to get people interested in doing the hard work of decarbonization, that will just inevitably increase the pressure to just take business as usual. I absolutely agree that a risk around these technologies is that they will be exploited by people who want to preserve emissions. But agreeing on the issue doesn't mean agreeing on the path forward. That is a political concern. In my view, it is not an ethical basis for restricting research on technologies that are potentially risk reducing. So far, Mexico is the only country that's banned solar geoengineering experiments. While the US is currently developing a solar geoengineering research plan.

World organizations focused on climate are now starting to make assessments and recommendations. I can't tell you which one is exactly right. What I can tell you is that each and every single person I spoke to on either side of the issue cares deeply about our future on this planet. And maybe that tension between them is actually a good thing because while it doesn't make our path forward clear, it can make us more thoughtful and rigourous about how to solve this giant mess we are currently in.