Geoengineering is no longer a useful term

The Labadie Power Plant is a 2,389.4-megawatt coal-fired power plant in Missouri. In 2023, it was the largest single point source of sulfur dioxide pollution in the U.S., emitting roughly 44,000 tons of SO₂. It likely remains one of, if not the largest, sources of sulfur dioxide pollution in the U.S. in 2026. Coal burning generally is a predominant source of sulfur dioxide pollution globally, particularly when plants haven't been retrofitted with sulfur scrubbing technology (the Labadie Power Plant hasn’t). Yet, despite the degree to which sulfur dioxide readily changes the Earth’s radiative forcing dynamics, no one is decrying the power plant’s continued operation (and lack of scrubbers) as a geoengineering experiment.

When nascent fields get mired in semantic controversies, it can be beneficial to set aside linguistic abstractions, opting instead for the time-honored tradition of getting precise about exactly what we’re talking about. With respect to the field of what I’ll refer to as “climate interventions”—i.e., direct interventions in climate systems to protect them against destabilization, shift climate system dynamics, and otherwise moderate climate change or its impacts to buy time for mitigation and removals—we should abandon the “geoengineering” term and agree on other terms and taxonomies. As interest and investment in interventions grow, geoengineering, as an umbrella term, is, most charitably, an imprecise and impractical catch-all for a diverse, varied set of potential intervention strategies. Less charitably, it lends itself to strawman arguments about “playing god” that artificially constrain reasonable efforts to advance the field.

Where “geoengineering” started and stands today

The prefix geo- is derived from the Greek word gē or gaia. In the context of the word “geoengineering,” we can understand it as meaning “earth.” One of the earlier, seminal uses of the term was in Cesare Marchetti’s 1977 paper, “On Geoengineering and the CO2 Problem,” published in the journal Climatic Change. Marchetti wrote (bold emphasis added):

What Marchetti describes at the end as an example of geoengineering is an early vision for ocean‑based carbon storage. Despite its role in originating the term, carbon removal and storage aren’t typically considered geoengineering today. So what is it?

Looking towards definitions from climate organizations and bodies with sway, we find geoengineering variously defined as:

• “...a broad set of methods and technologies that aim to deliberately alter the climate system in order to alleviate the impacts of climate change…” (the IPCC)

• “...a deliberate intervention in the planetary environment of a nature and scale intended to counteract anthropogenic climate change and its impacts.” (An expert group under the Convention on Biological Diversity, working with UNEP)

• “...the deliberate large‑scale manipulation of the planetary environment to counteract anthropogenic climate change.” (a now classic 2009 report from the Royal Society)

The throughlines here are found in emphasis on intent and deliberateness, as well as in at least two of the above and perhaps implicitly in all three, planetary-scale impacts. This agrees with Marchetti’s original definition, particularly his focus on “solutions to global problems…attempted from a global view.”

But there are many challenges with these conditions. Yes, umbrella terms are allowed to be coarse; after all, the point is that they are broad enough to “catch” a lot of subsidiary elements. But, even if geoengineering were used consistently (and, as we will soon see, it isn’t), surely defining it simply as deliberate interventions with the potential to deliver planetary-scale climate impacts is too broad. When used at that level of generality, deciding what counts as geoengineering versus what doesn’t becomes quite nebulous quite quickly, creating confusion and muddying important conversations that deserve specificity (as we will also show).

Perhaps the most discussed (and likely most fraught) intervention that the term geoengineering calls to mind is stratospheric aerosol injection (SAI). SAI proposes spraying aerosol-inducing chemicals into the upper atmosphere, where the aerosols would have a net cooling effect by reflecting solar radiation. A similar dynamic is at play in Earth’s climate today; the IPCC’s sixth assessment identified that sulfate pollution from power plants and cars, as well as several other sources, has produced a global cooling effect estimated somewhere between 0.2°C and 0.9°C to date (with 0.5°C as the anchoring midpoint, designated with “medium confidence”).¹

While there are meaningful differences between the two (sulfate pollution and SAI) in terms of where in the atmosphere they induce aerosols, cooling, and for how long—as a consequence of atmospheric elevation—that effect lasts, there is no doubt that adding additional aerosols to the atmosphere generally produces a global impact on Earth’s energy balance.

As such, SAI is certainly in scope across all prominent geoengineering definitions. But if we focus on things that can alter Earth’s energy balance, strategies like cloud seeding would not be geoengineering. Sure, it involves spraying things into the air. But it does not physically alter Earth’s energy balance: It deals in making rain. So perhaps it’s best understood as weather modification, not geoengineering. Yet, in present-day usage, cloud seeding is often proffered as a prime geoengineering example (and target).

In Tennessee, recently proposed legislation defines geoengineering as the “intentional injection, release, or dispersion, by any means, of chemicals, chemical compounds, substances, or apparatus into the atmosphere with the express purpose of affecting temperature, weather, or the intensity of the sunlight.” Here we still have the “intentional” element but have shifted from planetary scale to local, and away from radiative and energetic balances to also include weather alongside temperature. In stretching to include cloud seeding, this varies considerably from the other established definitions.

Moreover, the “spraying” and “into the atmosphere” conditions would also exclude many radiation management techniques and other proposed climate interventions also normally identified as geoengineering. Is deploying nanobubbles to enhance the reflectivity of the ocean’s surface to protect coral reefs geoengineering? Would glacial restabilization efforts, which similarly don’t deal in shifting Earth’s energy balance, at least not exclusively, count? I imagine groups like the IPCC might say so, but apparently Tennessee’s legislature wouldn’t. Granted, Tennessee is landlocked and glaciar-less, so perhaps the legislators are to be forgiven.

Elsewhere, in Missouri, HB 2656, the “Clean Skies Act,” prohibits any entity from engaging in “any form of geoengineering, weather modification, or cloud seeding.” Here, no definition of geoengineering or weather modification is really even offered, which begs the question of why those words were used at all. If the thrust of the legislation is focused on banning cloud seeding, why not just focus on that specifically? The answer probably lies in the pathos, not the logos.

We need not try to answer all these questions here; we have already illuminated sufficient tension in how the word geoengineering is applied (or weaponized). The overarching problems evident here are of inconsistent application, the degree to which stretch efforts are made to include the term “geoengineering” when it could simply be omitted in favor of specificity, and the extent to which its inclusion in certain settings conflicts with the general manner in which it is used in media, science, technological discussions, and other governance settings. We have different stakeholders discussing different things while referring to them using the same terms. Absent reconciliation, it seems like it would be better to drop references to geoengineering altogether.

The pernicious problem of scale

Even if we set aside the disagreements in application and return to definitions of geoengineering anchored in deliberateness and the possibility of inducing global impact on Earth’s energy balance, we continue to encounter problems. Homing in on the planetary-scale condition, the pernicious question of how to define scale comes to the fore. Many interventions that alter albedo dynamics or greenhouse gas flows technically impact Earth’s energy balance. This is where the term approaches a cliff of linguistic utility; if we fail to interrogate what’s in versus out for the scale condition, invariably, we’ll stumble into more conflicts in application.

Trying to decide where to set some nodal inflection point for where “planetary scale” begins and ends isn’t straightforward, however. Core definitions (IPCC, Royal Society, CBD, C2G, etc.) all emphasize “large‑scale” or “planetary‑scale” intervention but don’t specify a numeric cut‑off in area, fraction of radiative forcing, or share of global emissions affected.

To cut to a logical extreme, does planting a tree that otherwise would not have been, which will take up additional carbon dioxide and change the albedo of the land surface, count as geoengineering? Intuitively, it doesn’t “feel” like it should count. Clearly, some threshold of scope and scale matters. Some sort of de minimis argument. Should painting the roofs of buildings white count, insofar as it changes albedo, and could be applied at ever-increasing scales?

On this point, Wim Carton and Andreas Malm offer some useful ideas in their new book “The Long Heat: Climate Politics When It’s Too Late.” In defining geoengineering, one approach they apply focuses on defining it as based on the potential for an intervention to trigger cascading, negative, second-order impacts. They write:

Elsewhere in the book, to expand on this idea, they note:

Here and elsewhere, in enumerating and elaborating on these risks, Carton and Malm are really focused on large-scale SAI, deployed globally and continuously. So, while they offer concrete thoughts on a necessary threshold of scale and impact, this seems like another instance in which the use of the term “geoengineering” could be replaced by specifying the strategy or strategies, and at what scopes and scales of their deployment, produce the effects in question.

Further, another challenge arises in deciding whether carbon removal should be considered geoengineering. Applied at a large scale, by reducing atmospheric carbon dioxide concentrations, it could similarly produce the asymmetric outcomes across geographies that Carton and Malm worry about and use to define geoengineering. What’s interesting in this line of inquiry is that before material carbon removal industries took shape over the past decade and before international climate scientists concretized around the idea that significant carbon removal capacity is essential to preserve the viability of temperature targets like 1.5°C, it was often lumped into the geoengineering category. Now, mostly it isn’t.

Perhaps what the carbon removal example demonstrates is that, in practice, what’s considered geoengineering has more to do with how fringe or not a proposed solution or set thereof is. Perhaps the very acceptance of carbon removal into the climate mainstream is what ushered it out from under the geoengineering umbrella, rather than any shifts in technical or scientific definitions. Regardless, we have shown that geoengineering suffers not only from inconsistent application in general, but also from significant ambiguities regarding one of its two primary conditions, namely, where to set the defining boundaries of what “planetary impact” really is.

Addressing the second primary condition: intent

While we’re at it, we can also make progress undermining the other key condition of geoengineering, namely intent, as readily as we might seek to defend it. This returns us to the opening question of why no one lambasts the impact of coal power plants in geoengineering terms. Similar to scale, where does intentionality really begin and end? Perhaps I’ve already convinced you that geoengineering isn’t a particularly useful term for anything, given the pervasiveness of its inconsistent use and the questions surrounding scale. But if we were to continue using the term geoengineering in some capacity, as, perhaps, a category or categories of intentional interventions defined perhaps by what they are not (namely, mitigation or carbon removal), we would still need to create clear definitions for the intentionality component.

The word “engineering” does imply intentionality, as it originates from the Latin ingenium (meaning “cleverness”) and ingeniare (”to contrive, devise”). These are inherently active, purposeful, deliberate terms. On its surface, this seems to provide one helpful distinction. Without it, the geoengineering term would suffer from yet another problem, namely an inability to exclude the large-scale, ongoing drivers of climate change, such as greenhouse gas emissions, aerosol-inducing emissions (as discussed above), and large-scale land use change, which reshapes the topography of Earth directly while also producing emissions and albedo changes.

Absent the intentionality clause, legislation banning spraying chemicals in the air would suddenly ban internal combustion vehicles, power plants, and industrial facilities, to the unbridled joy of ardent climate activists. Were geoengineering not inherently defined as dealing with advertent endeavors, perhaps we’d make two buckets for it, one for “ameliorative” interventions to assuage climate change’s impacts and another for the ongoing, “aggravative” geoengineering that causes them in the first place. But then we’d be at risk of categorizing most all human endeavors as geoengineering, the way “Eukarya” is a classification for all animals.

I am somewhat sympathetic to the idea that fossil fuel burning isn’t “geoengineering,” given that the climate change it drives seems to be an inadvertent consequence of the advertent activity. But how inadvertent are the consequences really? The activity itself (burning fossil fuels) is extremely intentional, attracting trillions of dollars to advance it. And if an engineering activity is intentional, shouldn’t all its predominant impacts be considered to some degree in its linguistic and taxonomical classification? Stafford Beer, a famous leader in operations research from the United Kingdom, offered a famous heuristic, stating that “the purpose of a system is what it does.” Sure, one could say the primary purpose of burning fossil fuels isn’t geoengineering. But geoengineering is what the system of fossil fuel burning does. It’s one of the things it does best.

Similarly, one could further question how inadvertent the climate change driven by fossil fuel development is, especially when cast in relief against how well documented the scientific evidence linking greenhouse gasses to climate change has been for decades. Companies, countries, financiers, and policymakers have known that part of the engineering that goes into building offshore oil rigs, doing enhanced oil recovery, or then burning the oil also yields geoengineering. Yes, it’s the sale and demand for the oil that finances the development. But the negative externalities of its burning, insofar as they aren’t priced, do too by keeping financing costs lower. Does wilfully ignoring a consequence make it an inadvertent one? Can we say that power plant developers and operators release greenhouse gasses and other pollutants, like sulfur dioxide, that can alter Earth’s energy balance into the atmosphere unintentionally when they have other options (carbon capture and sequestration)? The intent may not be to alter Earth’s energy balance. But it’s part of the program.

New terms for new paradigms

Clearly, there are many problems with the term geoengineering, so many and of such semantic and ponderous philosophical qualities, that there’s little use trying to definitively solve them here. This creates a vacuum in need of filling, ideally with new terms to categorize specific groups of climate interventions. “Weather modification” feels appropriate for time-bound, more localized interventions, like cloud seeding. Solar radiation management, or radiation/albedo management more generally, feels appropriate for interventions such as stratospheric aerosol injection, marine cloud brightening, mixed cloud thinning, and others, though additional distinctions based on scope and scale, as well as likely other factors, will be warranted. Some interventions, like glacial restabilization efforts, may be difficult to group with others, though some could fit within larger groupings such as “catastrophic impact prevention” measures and approaches.

Finding the right words will take time, iteration, and, to an extent, may happen naturally, especially once we free ourselves from the hangover of geoengineering’s past usage and present inadequacies. Where there is need for a new umbrella term, perhaps “climate interventions” can suffice as a catch-all for things defined based on what they are not, namely, concerned with greenhouse gas emissions management, whether in reduction or removal, or efforts to adapt to climate change that don’t alter climate system dynamics or albedo (think seawalls and such). All these linguistic quandaries also pale in comparison to the scientific challenges, as well as the need to build social license for, fund research, and advance global governance frameworks for “interventions,” or whatever else we might call them, anyway.

Still, the overarching point remains: “geoengineering” is used inconsistently, broadly ineffective at creating cohesion, and artificially constraining, as it carries baggage and lends itself to fearmongering. The science required, governance challenges, and important moral hazard considerations inherent to the field of climate interventions require and deserve better.

1. Forester, P et. al., “Climate Change 2021: The Physical Science Basis.” Figure 7.7. IPCC Sixth Assessment Report, Intergovernmental Panel on Climate Change, 2021. doi:10.1017/9781009157896.009.