The Costs of Solar Geoengineering

Scientists at Harvard University are gearing up to begin an outdoor field experiment of solar engineering. They aim to test stratospheric aerosol injection, a technique that blocks out some of the sun’s incoming radiation by inserting reflective particles into the earth’s stratosphere. Although their tests could potentially help us better understand stratospheric aerosol injection, their framing of solar geoengineering masks its true costs, while simultaneously overstating the barriers to reducing greenhouse gas emissions.

The team’s promotional video for its research opens with the line: “A new tool to address climate change.” Professor Daniel Schrag then tells us that moving away from fossil fuels will take “at the least, many, many decades, and probably much more than a century.” It will be expensive, he says, costing trillions of dollars for the United States alone. Schrag has “a feeling” that we may not be able to switch our energy system over in time to address the worst impacts of climate change.

On the other hand, David Keith tells us that geoengineering could be very inexpensive. According to him, it would cost just $10 billion, or one ten-thousandth of global GDP, whereas its benefits could be more than 1 percent of global GDP—a return one thousand times greater than its cost. While Keith warns that solar geoengineering does not spare us the need to reduce emissions, other team members do not seem so convinced.

Fellow Harvard teammate Richard Zeckhauser tells us that “solar geoengineering is the most promising technology we have today.” It is so promising that Zeckhauser says he would be fine if we redirected some of our efforts from greenhouse gas emission reduction to geoengineering, a statement that borders on encouraging moral hazard – a worry that pursuing geoengineering research will discourage emissions reductions efforts.

The group’s characterization of the potential need for­ and benefits of geoengineering may be an effective way to get funding for its research. However, it projects a rather overconfident, one-sided, and problematic view of solar geoengineering.

An Unproven and Potentially Expensive Tool

For years, solar geoengineering proponents like Keith have characterized geoengineering as cheap relative to the supposedly expensive project of reducing emissions. However, like many deals too good to be true, it is cheap only if we take a limited view of the costs at hand.

While solar geoengineering can help to offset some of the effects of increased global temperatures, it does not address many of the grave and substantial harms of fossil fuels, such as air and water pollution, ocean acidification, increased energy costs, water usage, the violation of indigenous and community rights, political instability, violence, and more.

For instance, estimates show that switching to clean energy would save millions of lives, and generate enough benefits from reduced air pollution alone to more than offset the costs of the clean energy. Additionally, a clean energy transition could result in around $70 trillion in avoided fuel costs alone. Thus, a reliance on solar engineering could be deeply expensive, particularly if it leads to continued reliance on fossil fuels.

Keith’s estimate of the cost of solar geoengineering also misleadingly refers only to the costs of spraying aerosols into the atmosphere. To borrow an analogy from Stephen Gardiner, that is equivalent to saying that surgery only costs as much as a scalpel. There’s much more to planetary “surgery” than just spraying aerosols.

For instance, if we are to eventually stop solar geoengineering rather than continue it for thousands of years, we will presumably have to get rid of the emissions that solar engineering was deployed to offset. That means we will have to use negative emissions technologies to pull emissions out of the air. The more we emit now, the more we would have to pull out of the air later, and the more expensive and risky a geoengineering program will be.

Worryingly, as John Shepherd highlights, negative emissions technologies are potentially very expensive and resource intensive, with recent estimates suggesting that if we significantly overshoot our emissions targets, negative emissions technologies could cost as much as $500 trillion. They are also highly speculative, as it is unclear that we have the technical capacity to do them at the scales required. As such, Henry Shue has called our reliance on negative emissions technologies an unjustified form of wishful “climate dreaming.”

Negative emissions technologies are not the only uncertain element. While experiments like that of the Harvard group might help in narrowing some uncertainties, research I co-authored shows it may not be possible to acquire important knowledge about potential regional impacts of solar geoengineering, at least not on time scales relevant for a realistic deployment scenario aimed at stabilizing or slowing the impacts of climate change.

The “Most Promising” Technology?

Contrary to Schrag’s “feeling” that the fossil fuel transition will be expensive and take “at least many, many decades,” an affordable clean energy revolution is arguably already within reach. Researchers from NOAA and University of Colorado have demonstrated that “a transition to a reliable, low-carbon, electrical generation and transmission system can be accomplished with commercially available technology and within fifteen years.”

Less ambitiously, numerous studies show that we can move to a predominately renewable energy future by mid-century. For instance, the Solutions Project, led by Stanford's Mark Jacobsen, has developed economically prosperous pathways to 100 percent clean energy by 2050 for the United States and 139 countries around the world. Recognizing this potential, forty-seven of the world's least developed countries have committed to reach 100 percent clean energy between 2030 and 2050, providing the rest of the world little excuse not to act.

Solar, wind, electric vehicles, and battery storage have reached critical economic tipping points. With the right policy support, these advances can allow us to rapidly and economically reduce greenhouse gas emissions. Yet the team from Harvard is telling us that action on climate change is costly and slow, and that our “most promising technology” is not clean energy, but an uncertain, risky, and potentially very expensive solar geoengineering strategy.

While Harvard’s research program could help us to better understand solar geoengineering, they should be careful not to oversell their program at the cost of broader climate action, particularly as there are a range of ethical and governance questions they have not adequately addressed. Likewise, we should be careful not to think their program provides an excuse to avoid rapidly reducing our dependence on fossil fuels and carbon emissions. With the window to avert some of the worst impacts of climate change rapidly closing, the stakes could not be higher.