Yes, We Should Try to Control the Weather

The Case for Geoengineering to Limit Natural Climate Variability, Not Climate Change

By Ted Nordhaus

Last month, the city council in Alameda, California voted to cancel a geoengineering experiment underway at a converted naval station that the city owns. The purpose of the experiment was to see if making clouds more reflective might be an effective way to keep a handle on global warming, at least until the world gets its act together to deeply cut emissions. 

As the council debated the issue, supporters and opponents weighed in from around the world, raising dueling catastrophic concerns about the effort. Supporters argued that the climate is at imminent risk of spinning out of control. Geoengineering might be necessary to buy more time to cut emissions. 

Opponents argued that the earth system is far too complex to understand and modify in this way. We can’t predict what will happen and the cure could be far worse than the disease, this latter point being a particular concern because if we start geoengineering and then suddenly stop, warming comes roaring back—a phenomenon known as “termination shock.” Geoengineering, many opponents also argue, creates moral hazard. If we know we can simply pump sulfur dioxide or similar into the atmosphere, we might not get serious about cutting emissions, which is the only solution over the long term.

Interestingly, most of the protagonists on both sides of the debate share the same view of climate risk, agreeing that the warming of the planet constitutes an existential threat to human societies. Both proponents and opponents of solar geoengineering largely accept the idea that the Holocene was a uniquely stable and “natural” climatological epoch that humans have disrupted, rather than one that humans created. And both actually ground their arguments in precautionary terms, with proponents arguing for geoengineering as a “break in case of emergency” technology that we might need if things get really bad, and opponents viewing it as just another form of dangerous human interference with the climate system that, one way or another, is likely to end badly. 

But what if climate change, as I have suggested elsewhere, is really just a garden variety environmental issue, a problem that has very significant negative consequences for non-human life but that human societies are amply capable of managing reasonably well? Is there a case for geoengineering if climate change doesn’t represent an existential threat to human societies? I believe there is. Indeed I’ll go further and suggest that if human societies ever actually undertake geoengineering, it is far more likely that we will do so in order to create a more stable climate by reducing natural climate variability than as a last ditch effort to avoid a climate crisis or emergency. 

What Do We Mean By Stable Climate?

The need for a stable climate is a well established trope in the climate discourse. The Holocene climate was, we are told, stable, allowing human civilization to flourish. The Anthropocene is not, and threatens human societies with dangerous warming. 

Like “stable climate,” the term “dangerous warming” is used constantly but is ill defined. Both terms are consistently used in ways that imply that they reference a clear, empirically derived definition. But both really refer to a precautionary ethic, not a scientifically precise definition of what constitutes a stable climate or how or when a warmer climate becomes dangerous. 

The notion that the Holocene was uniquely stable is only in reference to the prior glacial period, which lasted for virtually the entire existence of the human species. The Holocene was warmer and more stable than the prior period, during which much of the terrestrial surface of the Northern Hemisphere was covered by ice. But there is no evidence that the Holocene climate was more stable than prior interglacial periods. Nor that it lasted longer. 

Indeed, geologists often refer to the Holocene not as distinct but rather as just the most recent interglacial period of the prior epoch, the Pleistocene. What changed the climate was not the cycling of the Earth system between glacial and interglacial periods, which has proceeded fairly regularly over the last 2 million years of the Pleistocene epoch. It was us. 

During this most recent interglacial period, humans invented agriculture, which allowed for significantly larger human populations. We cleared large areas of forest to make way for agriculture, very gradually increasing carbon dioxide levels in the atmosphere. This likely prevented the Little Ice Age from becoming the next glacial period, extending the interglacial period long enough for humans to discover and exploit fossil fuels, which vastly increased the amount of carbon dioxide in the atmosphere and assured that this current interglacial period will last for thousands more years. 

In this regard, the Anthropocene, notwithstanding various stratigraphic debates about its starting point, does not represent the break from the Holocene that many suggest. The Holocene is better characterized as the early Anthropocene, a period that is distinct from the prior interglacial periods of the Pleistocene because humans had begun remaking terrestrial environments at large scale and increasing greenhouse gas concentrations in the atmosphere. 

But whether one considers the Holocene the last interglacial period of the Pleistocene or the early Anthropocene, it was neither more stable nor longer lived than prior interglacial periods during the Pleistocene. When people warn that temperatures today are warmer than at any point in the last 2 million years, what they are saying is simply that the climate is now warmer than it was during the brief interglacial periods of the Pleistocene, an epoch dominated by ice ages. 

Nor is there good reason to think that those brief Holocene conditions constituted an optimal “goldilocks” climate for human well-being. The climatic conditions that coincided with small nomadic bands of humans developing agriculture 10,000 years ago were not unique to the Earth or even the Pleistocene. They were just unique to Homo Sapiens, which had evolved from earlier hominid species as the last extended glacial period was beginning. 

Holocene conditions that coincided with the rise of agriculture and complex human civilizations, in turn, tell us next to nothing about the range of conditions in which a technologically advanced, globally interconnected world of 8 billion people might thrive. Indeed, whether the planet entered a new geological epoch called the Anthropocene in the last 400 years or the last 10,000 years, evidence in either case would suggest that a warming climate, one that was warmer, virtually from the onset, than any climate previously experienced by anatomically modern humans, has been one in which human societies have thrived.  

So What Makes The Climate Dangerous?

In the climate discourse, the halcyon stable climate of the Holocene is pitted against the specter of dangerous warming underway today. Dangerous warming does not refer to any well established threshold beyond which specific dangerous things happen. Rather, the stable Holocene/dangerous warming construct is really tautological. The warming climate is deemed dangerous, definitionally, because it is warmer than the Holocene. 

But there is no particular evidence that today’s climate, at an average global temperature of 59.3 degrees Fahrenheit, is less stable or more dangerous than it was in the 1950’s, with an average temperature of 57.5, or the 1900’s, with an average temperature of 56.9. It’s just warmer, which means that low temperatures won’t be as cold and high temperatures will be hotter. The same will be true of cold snaps, heat waves, and some peaks and valleys in the hydrological cycle (extreme rainfall and drought), which are reasonably closely connected to warmer temperatures because a warmer atmosphere can hold more water vapor. And again, by most metrics that we might use to look at the impact that that warmer climate has had on human societies, such as normalized economic damages or loss of life, it would appear to be less dangerous, not more so. 

The thing that actually causes climatic havoc for human societies is not the abstraction that is global average temperature, a synthetic statistical average of all the varied temperatures that people experience across an enormous temperature gradient in all sorts of different places. Rather, it is outlier or anomalous climate events. 

Human living arrangements in places that are very hot and dry all the time are well adapted to those conditions. The same is true of places that are very cold and wet. Consider that the majority of deaths associated with heat waves occur in places that aren’t that hot and the majority of deaths associated with cold snaps occur in places that aren’t that cold. It is the lack of adaptation to anomalous extreme events, not the relative extremity of the event, that is dangerous.

So the degree to which a climate is “stable” and associated with conditions that are better for human societies than the alternative depends on that climate having fewer anomalous or extreme events that the places experiencing them are not well adapted to. The reason that a strong hurricane or a very extreme heat wave is dangerous is because it is not a regular occurance. An extreme heatwave in Pittsburgh, for example, is just garden variety summer weather in Phoenix. But let a blizzard or an ice storm or a week of sub-zero temperatures settle over Phoenix, and one can reliably anticipate carnage.

Anomalous and extreme phenomena occur all the time and are unpredictable because the climate is, and always has been, highly unstable and variable. The natural variance in climate extremes, both between various geographies and topographies and across them, is far greater than anything that climate change currently or in the future can produce. 

This is why I am skeptical that we will ever seriously undertake geoengineering under the sorts of “break in case of emergency” scenarios in which it is almost always imagined by both proponents and opponents. Even two degrees of further warming over the course of the next century will result in trends in most extreme phenomena that will be hard to observe at any given location because the signal from warming is small relative to the noise of natural variability. 

For this reason, human settlements that have already adapted to far greater climatic variance globally over the course of decades and centuries seem to me likely to adapt quite effectively to the changes that anthropogenic warming is likely to produce over the course of the next century or two, especially given continuing technological advances and economic development, and even more so because mainstream projections of emissions and warming over the course of this century now project three degrees or less of total warming above pre-industrial levels. 

There is clearly a lot of opportunity to make a lot more progress in cutting and ultimately eliminating fossil fuels and the greenhouse gas emissions that come with them, which will be important for protecting biodiversity, reducing conventional air pollutants, and generally assuring that future generations will have a more moderate climate. But once you understand the limited influence that anthropogenic warming actually has on the magnitude of most climatic extremes, the dominant role that natural variability plays in producing those extremes, and the substantial and well-demonstrated adaptive capacities that human societies already have, it becomes clear that humans are capable of adapting to quite a lot of warming. 

Yet the fact that we are increasingly well adapted to an unstable and dangerous climate doesn’t mean we should accept that. Why settle for an unstable and dangerous climate when we could have a more stable and less dangerous one?

Natural Climate Variability Is Dangerous and Costly

Against the constant claims that extreme climate phenomena, and the impacts that result from them are driven by climate change, the sum total of the human and economic costs associated with extreme weather and other climatic events is overwhelmingly dominated by natural climate variability, not climate change. In 2023, global economic costs due to extreme weather exceeded $250 billion. Those costs have risen substantially in recent decades, almost entirely due to the overall growth of the global economy and continuing urbanization. Larger and wealthier global populations increasingly live in cities that are located in coastal areas and floodplains and are more exposed to many climate hazards. 

Most of that natural variability is difficult to predict, much less influence, and results from random variation in the movement of energy between the oceans and the atmosphere and across the surface of the planet. But one phenomenon that is somewhat easier to predict is the El Nino Southern Oscillation (ENSO), which influences weather patterns globally. The ENSO cycle is associated with droughts in the Amazon basin and Indonesia, rainfall in California and across the western United States, Atlantic hurricane frequency and intensity, and much else. 

It is now well established that strong El Nino conditions, the warm phase of the ENSO cycle, bring substantial costs to the global economy. One recent study concluded that ENSO variability had cost the global economy an average of .06% of GDP annually between 1960 and 2019, and a total of $13.5 trillion over that period. Over half of that was accounted for by three extreme El Nino cycles, 1982/83, 1997/98, and 2015/16. There is also good evidence that strong La Nina conditions can also produce a significant spike in climate related economic costs as well. 

Precise economic estimates of this sort, particularly when they estimate economic impacts years after the actual climatic events in question occurred, shouldn’t be taken too seriously. But it is clear that natural ENSO variability leads to significant loss of lives and economic damages. And ENSO variability, it turns out, is something we might have the ability to mitigate. 

Taking the Edge Off El Nino

Solar geoengineering has been discussed almost exclusively as a method to slow or reverse climate change. But it isn’t a permanent solution. Virtually all geoengineering interventions involve short-lived interventions that wear off relatively quickly if they are not sustained. Sulfur particles injected into the stratosphere only stay there for about a year and would need to be continuously injected in order to limit warming. Marine cloud brightening, the subject of the canceled experiment in Alameda, only lasts for a few weeks or months. 

As a climate solution, geoengineering is a stop gap measure to reduce warming until greenhouse gas emissions can be cut to zero, or even removed from the atmosphere. But because even very aggressive scenarios to achieve net zero emissions globally will take decades, that means that geoengineering measures, whether via the injection of aerosols into the stratosphere or marine cloud brightening, must be sustained for decades or potentially much longer. One recent study found that under the vast majority of IPCC mitigation scenarios, geoengineering would need to be sustained for at least a century. 

The problem with this is that if we begin geoengineering and then stop, the avoided warming will come right back. Except instead of coming back gradually, it will come back immediately. A decade or two or three of warming would materialize in a matter of years, a phenomenon called termination shock. And termination shock is exactly the sort of climate phenomenon that we know human societies are least resilient to, a step-change, as opposed to a gradual change or intensification of climatic phenomena that occur more regularly or predictably.

In the context of a cyclical phenomena like ENSO, however, rather than a secular trend like anthropogenic warming, termination shock becomes a feature, not a bug. Solar geoengineering to moderate or cancel out a developing El Nino phase would only need to last a few months, perhaps a year. As the cycle shifted back toward La Nina, termination of geoengineering would result in a short-lived forcing that would in turn moderate the La Nina phase of the cycle. Furthermore, if we decided to suddenly end this type of geoengineering, the system should simply equilibrate back to where it was, not snap into a new state. 

There are good reasons to not want to eliminate ENSO entirely. All sorts of ecosystem functions across the planet have evolved with the fluctuating temperature and hydrologic cycles that ENSO brings. But given how much of the social cost of ENSO is associated with strong El Nino events, moderating strong events could bring very significant social benefits without much downside for humans or the natural world. 

The most likely way to do that would be through marine cloud brightening, not stratospheric aerosol injection. One forthcoming study concludes that marine cloud brightening could have been effectively used to entirely mitigate the 1997/98 and 2015/16 El Nino events, restoring the southern ocean to an ENSO neutral state. But geoengineering at a scale capable of achieving a neutral state would not be necessary. Simply reducing the intensity of strong El Nino and La Nina events would likely be sufficient to mitigate most of the social costs that result from ENSO phenomena. Remember that over half the costs associated with ENSO over the last 60 years are associated with just three extreme El Nino events.

The idea of moderating ENSO is, of course, at best a thought experiment. We really have no idea whether we could effectively moderate ENSO through marine cloud brightening in the South Pacific, nor what it would cost to do so at a scale that would much effect strong ENSO events. But the same is no less true of various notions that we might use solar geoengineering to head off a climate emergency. 

Against Precautionary Hubris

Much of the case for mitigating climate change and against solar geoengineering is precautionary. The climate system is too complex to fully understand, much less manage, and faith that we might either adapt to or geoengineer our way around a warming climate is hubris. Both climate change and geoengineering represent vast and uncontrollable experiments. 

But the precautionary principle itself is also built upon a kind of hubris. The idea, after all, is that we should only act within a complex system like the global climate after we fully understand the consequences of our actions. This presumes that we are capable of doing so. Precautionary hubris, in other words, presumes that we can study and understand a complex system from some remove, without acting within it. This is not just a recipe for never acting. It also presumes a god’s eye view of systems that we exist within. 

But there is no laboratory Earth where we can test various actions without any possible consequence. Climate models are, at best, a map, not the territory. In the world in which we actually live, we can only understand the unique, complex systems that we inhabit by acting within them. We take actions and see what happens. If they produce outcomes that we want, we do more of it. If they don’t, hopefully, we stop. As we scale those actions up, the outcomes change. Sometimes things that seem to work at very small scales don’t work at larger scales. Sometimes they produce undesirable and unanticipated outcomes as they scale. 

Over the last decade or so, for instance, we’ve engaged in an unintentional form of termination shock, cleaning up many sources of sulfur air pollution associated with industry and transportation. The resulting reduction in sulfur aerosol emissions appears to have accelerated warming. That doesn’t mean we shouldn’t try to clean up sulfur pollution. Life is complicated. There are always tradeoffs. But it is also the case that we don’t actually know that much about things like this until we do something in the world and see what happens. 

This, writ large, is how we have made a planet that is far more habitable for its human inhabitants than the one we started with—through trial and error and experimentation. It is how we invented tools, agriculture, and most other technology. And it is basically the opposite of how we mostly think and talk about solar geoengineering, as a deus ex machina resolution to the passion play that is the climate issue, an entirely theoretical solution to an existential crisis that is also entirely theoretical. 

By contrast, stripped of its role as a set piece in various ideological battles within the climate discourse, we might come to see some solar radiation management efforts like cloud brightening more like cloud seeding or tree planting, as a way to moderate some of the extreme natural variance in the climate system that we live in today—as something to do, or at least try, to see if it might produce some real world benefits in the here and now. 

Will it work? Who knows. But without the risk of termination shock resulting in a rapid rebound in the global temperature, the consequences of doing so become a lot less significant. And at the very least, we’ll probably learn a lot of useful stuff about the climate system that we really can’t learn through ever more elaborate exercises in climate modeling.