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Why new proposals to restrict geoengineering are misguided

We need more research, including outdoor experiments, to make better-informed decisions about such climate interventions.

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The public debate over whether we should consider intentionally altering the climate system is heating up, as the dangers of climate instability rise and more groups look to study technologies that could cool the planet.

Such interventions, commonly known as solar geoengineering, may include releasing sulfur dioxide in the stratosphere to cast away more sunlight, or spraying salt particles along coastlines to create denser, more reflective marine clouds.  


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The growing interest in studying the potential of these tools, particularly through small-scale outdoor experiments, has triggered corresponding calls to shut down the research field, or at least to restrict it more tightly. But such rules would halt or hinder scientific exploration of technologies that could save lives and ease suffering as global warming accelerates—and they might also be far harder to define and implement than their proponents appreciate.

Earlier this month, Tennessee’s governor signed into law a bill banning the “intentional injection, release, or dispersion” of chemicals into the atmosphere for the “express purpose of affecting temperature, weather, or the intensity of the sunlight.” The legislation seems to have been primarily motivated by debunked conspiracy theories about chemtrails. 

Meanwhile, at the March meeting of the United Nations Environmental Agency, a bloc of African nations called for a resolution that would establish a moratorium, if not a ban, on all geoengineering activities, including outdoor tests. Mexican officials have also proposed restrictions on experiments within their boundaries.

To be clear, I’m not a disinterested observer but a climate researcher focused on solar geoengineering and coordinating international modeling studies on the issue. As I stated in a letter I coauthored last year, I believe that it’s important to conduct more research on these technologies because it might significantly reduce certain climatic risks. 

This doesn’t mean I support unilateral efforts today, or forging ahead in this space without broader societal engagement and consent. But some of these proposed restrictions on solar geoengineering leave vague what would constitute an acceptable, “small” test as opposed to an unacceptable “intervention.” Such vagueness is problematic, and its potential consequences would have far more reach than the well-intentioned proponents of regulation might wish for.

Consider the “intentional” standard of the Tennessee bill. While it is true that the intentionality of any such effort matters, defining it is tough. If knowing that an activity will affect the atmosphere is enough for it to be considered geoengineering, even driving a car—since you know its emissions warm up the climate—could fall under the banner. Or, to pick an example operating on a much larger scale, a utility might run afoul of the bill, since operating a power plant produces both carbon dioxide that warms up the planet and sulfur dioxide pollution that can exert a cooling effect.

Indeed, a single coal-fired plant can pump out more than 40,000 tons of the latter gas a year, dwarfing the few kilograms proposed for some stratospheric experiments. That includes the Harvard project recently scrapped in light of concerns from environmental and Indigenous groups. 

Of course, one might say that in all those other cases, the climate-altering impact of emissions is only a side effect of another activity (going somewhere, producing energy, having fun). But then, outdoor tests of solar geoengineering can be framed as efforts to gain further knowledge for societal or scientific benefit. More stringent regulations suggest that, of all intentional activities, it is those focused on knowledge-seeking that need to be subjected to the highest scrutiny—while joyrides, international flights, or bitcoin mining are all fine.

There could be similar challenges even with more modest proposals to require greater transparency around geoengineering research. In a submission to federal officials in March, a group of scholars suggested, among other sensible updates, that any group proposing to conduct outdoor research on weather modification anywhere in the world should have to notify the National Oceanic and Atmospheric Administration in advance.

But creating a standard that would require notifications from anyone, anywhere who “foreseeably or intentionally seeks to cause effects within the United States” could be taken to mean that nations can’t modify any kind of emissions (or convert forests to farmland) before consulting with other countries. For instance, in 2020, the International Maritime Organization introduced rules that cut sulfate emissions from the shipping sector by more than 80%, all at once. The benefits for air quality and human health are pretty clear, but research also suggested that the change would unmask additional global warming, because such pollution can reflect away sunlight either directly or by producing clouds. Would this qualify?

It is worth noting that both those clamoring for more regulations and those bristling to just go out and “do something” claim to have, as their guiding principle, a genuine concern for the climate and human welfare. But again, this does not necessarily justify a “Ban first—ask questions later” approach,  just as it doesn’t justify “Do something first—ask permission later.” 

Those demanding bans are right in saying that there are risks in geoengineering. Those include potential side effects in certain parts of the world—possibilities that need to be better studied—as well as vexing questions about how the technology could be fairly and responsibly governed in a fractured world that’s full of competing interests.

The more recent entrance of venture-backed companies into the field, selling dubious cooling credits or playing up their “proprietary particles,” certainly isn’t helping its reputation with a public that’s rightly wary of how profit motives could influence the use of technologies with the power to alter the entire planet’s climate. Nor is the risk that rogue actors will take it upon themselves to carry out these sorts of interventions. 

But burdensome regulation isn’t guaranteed to deter bad actors. If anything, they’ll just go work in the shadows. It is, however, a surefire way to discourage responsible researchers from engaging in the field. 

All those concerned about “meddling with the climate” should be in favor of open, public, science-informed strategies to talk more, not less, about geoengineering, and to foster transparent research across disciplines. And yes, this will include not just “harmless” modeling studies but also outdoor tests to understand the feasibility of such approaches and narrow down uncertainties. There’s really no way around that. 

In environmental sciences, tests involving dispersing substances are already performed for many other reasons, as long as they’re deemed safe by some reasonable standard. Similar experiments aimed at better understanding solar geoengineering should not be treated differently just because some people (but certainly not all of them) object on moral or environmental grounds. In fact, we should forcefully defend such experiments both because freedom of research is a worthy principle and because more information leads to better decision-making.

At the same time, scientists can’t ignore all the concerns and fears of the general public. We need to build more trust around solar geoengineering research and confidence in researchers. And we must encourage people to consider the issue from multiple perspectives and in relation to the rising risks of climate change.

This can be done, in part, through thoughtful scientific oversight efforts that aim to steer research toward beneficial outcomes by fostering transparency, international collaborations, and public engagement without imposing excessive burdens and blanket prohibitions.

Yes, this issue is complicated. Solar geoengineering may present risks and unknowns, and it raises profound, sometimes uncomfortable questions about humanity’s role in nature. 

But we also know for sure that we are the cause of climate change—and that it is exacerbating the dangers of heat waves, wildfires, flooding, famines, and storms that will inflict human suffering on staggering scales. If there are possible interventions that could limit that death and destruction, we have an obligation to evaluate them carefully, and to weigh any trade-offs with open and informed minds. 

Daniele Visioni is a climate scientist and assistant professor at Cornell University.

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