Geoengineering. Gernot Wagner

Modern life is replete with such technofixes. It’s often a fine balance between decrying something as a technofix that simply serves to cement the status quo and celebrating an invention as a clear step forward. It is this constant back-and-forth, this constant internal debate, which characterizes many a geoengineering conversation. There is simply no easy answer, no clear line. Even the very idea of working on the topic comes with a number of judgment calls.

      A long history of healthy skepticism

      All of us having worked on solar geoengineering have stories on how we got to work on the topic. Most came to it hesitantly – some after a lifetime of work on cutting CO₂ emissions.

      Geochemist Wally Broecker left an indelible imprint on the climate science community. In 1975, he introduced the term “global warming” into the literature, after the phenomenon had previously been known by the slightly cumbersome moniker “inadvertent climate modification.”¹ In a video message, recorded from his hospital bed, for a 2018 “Planetary Management Symposium” at Arizona State University, Broecker said: “If we are going to prevent the planet from warming up another couple of degrees, we’re going to have to go to geoengineering.” Broecker did not arrive at this conclusion lightly, in what would turn out to be his final address to his scientific colleagues before his passing.

Broecker was, in fact, highly skeptical of solar geoengineering as a possible climate intervention. I remember him having a number of probing questions, when, in 2013, David Keith came to give a talk on the importance of solar geoengineering research at a climate policy seminar at Columbia University’s Faculty House. Broecker’s main worry, like that of most others, was that mere talk of geoengineering – especially, once again, the “solar” variety – might detract from the need to cut CO₂ in the first place, a concept often called “moral hazard.”

      It was precisely this worry that had led to a long-standing, self-imposed, unspoken near-moratorium on solar geoengineering research within the scientific community. Broecker had been a key member of the high-powered group that authored a section on CO₂ as part of a 1965 report by President Lyndon B. Johnson’s Science Advisory Committee on “Restoring the Quality of Our Environment.”² The report did not mention cutting CO₂ emissions as a possible option for addressing climate change. Doing so apparently seemed inconceivable at the time. Instead, it mentioned one possible method of addressing the problem: brightening ocean surfaces in an attempt to reflect more sunlight back into space and cool the planet.

      In hindsight, this singular focus on solar geoengineering in the 1965 report was a clear mistake, and one the scientific community has overcorrected for over the course of the coming decades. In 1974, Russian scientist Mikhail Budyko first proposed what has since become the most prominent solar geoengineering method: stratospheric aerosols – introducing tiny reflective particles into the upper atmosphere.³ Budyko’s proposal was translated into English in 1977. It was briefly known as “Budyko’s blanket,” but mentions of it in the scientific literature and especially public climate discourse soon disappeared.

A 1992 National Academies report picks up on the possibility,⁴ but it was not until the 2000s that the technology reemerged in broader scientific and climate conversations. After hearing vague mentions of solar geoengineering in the early 2000s, followed by quick dismissals, I first encountered solar geoengineering in earnest shortly after the late Nobel laureate Paul Crutzen wrote his now famous essay presenting stratospheric sulfur injections as a possible way “to resolve a policy dilemma.”⁵

      The dilemma: Air pollution in the form of sulfur dioxide (SO₂) kills millions each year; it also helps cool the planet. For example, Europe having begun to clean up its air pollution in the 1980s was clearly beneficial. Medieval cathedrals were no longer melting under acid rain. Forests – and people – are healthier. However, the Arctic is now around 0.5°C warmer as a direct result of decreased SO₂ emissions.⁶ These are clear tradeoffs.

      Crutzen, in his essay, presented this moral quandary. His essay was published jointly with one written by the late Ralph Cicerone, himself a famed atmospheric scientist and then the President of the U.S. National Academies of Sciences, who wrote in support of Crutzen’s controversial essay and of further research.⁷ While Crutzen and Cicerone’s essays did much to lift the self-imposed research moratorium, skepticism throughout the research and policy communities has remained to this day. I would hasten to add that much of that skepticism is, in fact, still healthy. Solar geoengineering is not a topic one should “embrace,” in any sense of the term. That goes for policymakers as much as for researchers “merely” trying to answer lingering scientific questions. To this day, much of the skepticism, in turn, can be explained by “moral hazard” worries, a topic we will discuss in depth in Chapter 7.

      Narrowing down “geoengineering”

A quick definitional detour is in order here, as “geoengineering” means different things to different people. In fact, the term is so vague and all-encompassing as to have lost much meaning, despite still being in frequent use. The term “geoengineering” itself is largely an artefact and a result of the term’s frequent use in popular discourse. Experts are typically more precise, and for good reason.

      Except for the book’s cover – mea culpa! – I do not use the term “geoengineering” in this book without further explanation, apart from in direct quotations. I instead use either “solar geoengineering” or “carbon removal.” The two are sometimes subsumed under the broad heading of “geoengineering,” but the two are, in fact, very different. Neither, in turn, is the only term used for either category of interventions.

      Solar geoengineering is sometimes also called “solar radiation management” (SRM), “solar radiation modification” (conveniently, also abbreviated as SRM), or traditionally also “albedo modification.” It is a largescale, deliberate intervention to cool the planet by sending a small fraction of sunlight back into space, or by increasing the amount of solar radiation that escapes back into space. The plethora of terms here already indicates the problem. While those working on the topic would immediately recognize the abbreviation “SRM,” and I have used it myself in peer-reviewed papers and op-eds alike, I will eschew its use here in favor of “solar geoengineering.” The reason for this nomenclature is simple: the “solar” modifies the all-too-popular broader term. That doesn’t make “SRM” any less accurate. It’s just another term for the same idea.

Here it’s also useful to dissect the definition a bit further. One operative term is “largescale.” Wearing white in the summer does not count, nor does painting roofs or streets white in an attempt to cool cities – though they are all good illustrations of the broader point. Black absorbs heat, white reflects it.⁸ Even all of us in any one hemisphere wearing black winter coats or white summer shirts at once, however, does not alter the global climate. Aerosols in the stratosphere do. “Budyko’s blanket” – stratospheric aerosols – thus, is the most commonly discussed method, though by far not the only one. (See Part I for more in-depth discussions of different solar geoengineering methods.) More precisely then, I will often refer to stratospheric aerosols as the specific solar geoengineering method.

      Sometimes I will also explicitly discuss another set of technologies that are often subsumed under the broader “geoengineering” heading but that are entirely different: a set of techniques typically called carbon removal, carbon dioxide removal (CDR), carbon geoengineering, or direct air capture. All of these technologies remove CO₂ from the atmosphere directly. Their big advantage: they address the root cause of climate change – excess atmospheric CO₂. Solar geoengineering does not. That makes carbon removal an important part of the world’s collective climate response, especially given where things stand today. Carbon removal also comes with its own set of important caveats. Many are entirely different from concerns about solar geoengineering. The one area where they do clearly overlap is vis-à-vis moral hazard considerations, their interaction with efforts to cut CO₂