© WWF / Henry Harrison

Turning down Earth’s thermostat with solar geoengineering

29 April 2019

This article originally appeared in The Circle: What happens after 1.5°C?. The Circle shares perspectives from across the Arctic, and the views expressed here are not necessarily those of WWF. See all Circle issues here.

As our planet warms, scientists are searching for ways to cool it. One experimental idea is to interfere with how sunlight reaches the Earth. FRANK KEUTSCH, a professor of chemistry and chemical biology at Harvard University, spoke to The Circle about a project he’s working on to investigate the risks of doing so. The Stratospheric Controlled Perturbation Experiment—or SCoPEx—is trying to determine some of the risks and efficacy of introducing sunlight-reflecting particles, such as sulfuric acid or calcium carbonate, into the Earth’s stratosphere to alter the climate.

What exactly is geoengineering?

The geoengineering we talk about in the context of climate change falls into two very different categories: carbon geoengineering and solar geoengineering. The difference between the two is the promise they hold. Carbon geoengineering addresses the cause of climate change. It is when you take carbon out of the atmosphere and store it underground or try to convert it into something else we can use. But it’s expensive, complicated and slow.

Solar engineering is cheap and fast, but it doesn’t do anything to address the causes of climate change. As opposed to reducing greenhouse gas emissions, the idea is to change the energy balance by reflecting sunlight back into space. We know that this will cool down the planet because there will be less energy coming in.

In fact, natural experiments have been conducted for us in the form of large volcanic eruptions that have resulted in a noticeable cooling of the troposphere. So we know this works— and it makes sense that if you have less sunlight, the surface will be cooler. We also know that there are a number of side effects from doing this.

What are the risks of reflecting the sun away from the Earth and back into the atmosphere?

The question we are trying to answer with respect to solar geoengineering is actually not “Can it cool down the planet?” but rather “What would the impacts be on climate and the Earth system overall?” For example, could it destroy the ozone layer or change the temperature of the stratosphere?

I like to compare solar engineering to opioids. When we take painkillers, they hardly ever address the problem. They address the symptoms by reducing the pain. One of the big dangers of solar geoengineering is that if we don’t notice the pain, we may continue the behaviours we shouldn’t be doing. We won’t get a warning signal telling us there’s something wrong.

A danger with using solar geoengineering is that the symptoms—the pain from climate change—will be less. As a result, there are people who will say, “Let’s address the cause later because it’s hard and it’s expensive and we don’t quite know how to do it now.” This is the moral dilemma that people have with solar geoengineering, and I think it is a very valid argument. In addition, if we put a foreign object or substance into a system, there will be side effects. The idea that there could be a form of solar geoengineering that has no side effects is, I think, entirely utopian.

So, what is the goal of your research?

I’m interested in knowing and quantifying different types of risks associated with solar geoengineering. We do not know the risks well enough. I believe if we don’t know the risks, then it’s very hard to talk about what solar geoengineering can mean as a tool in the climate change toolbox.

If we know there are risks involved, why consider solar geoengineering at it all?

The idea of putting millions of tons of sulfuric acid into the stratosphere would probably strike many people as crazy or scary. But if you look at the reality of climate change, I think the direction we’re headed in right now is also really scary. If you asked me, “Frank, can you tell me what exactly is going to happen when you do this?” I would tell you we may never have those answers. There will always be uncertainties. Yet at the same time, I think we already know that with climate change, there is a huge danger.

So we need to do something—and the reason to do research now is to get ahead of the game. We need to pursue a better understanding of the risks of solar geoengineering because we don’t want to find ourselves in a situation later where the climate impacts become so large that they create an overpowering pressure for some form of action—and then stratospheric solar geoengineering is pursued without enough knowledge of its risks and efficacy.

Frank Keutsch is a professor of chemistry and chemical biology at Harvard University.
For more information about the ScoPEx project, see the Keutsch Research Group’s site.