Science Snippets: Negative Consequences of Geoengineering

Draft script:

I have written and spoken frequently about geoengineering. The idea that humans can control incoming solar radiation to cool Earth emerged shortly after it became clear that human actions have overheated the planet. This idea is consistent with the usual attitude that humans are capable of anything we desire. Human supremacy over every non-human species and all planetary phenomena is consistent with the notion that we are supreme beings in a limitless world.

A CBC article published on 8 August 2018 is headlined Blocking sunlight to cool Earth may not save crops from climate change. My first thought upon reading this headline: duh! The subtitle is consistent with my thought: “Solar geoengineering may reduce heat stress, but less sunlight also takes its toll.”

The lede, along with another sentence to complete the initial paragraph, promises support for my perspective: “Over the past month, stories of record-breaking heat, forest fires and floods have dominated the headlines. Climatologists say this is the new normal, a result of the continuing rise of Earth’s temperature.”

The next two paragraphs offer the same inane solution as the headline: “Aside from reducing CO2 emissions, scientists have proposed geoengineering, the deliberate manipulation of the environment through technology, as a way to combat global warming.

One particular method is called solar radiation management, where various technologies are used to increase Earth’s albedo, or reflectivity. The more solar radiation goes back out into space, the cooler Earth gets. It’s basically what the Arctic does for the planet: the loss of bright white sea ice and snow that would typically reflect sunlight contributes to the rise in global temperatures.”

The next short paragraph introduces a peer-reviewed paper in the renowned peer-reviewed journal, Nature: But in a paper published in the journal Nature Wednesday, scientists say that one form of solar radiation management — called stratospheric veils or stratospheric aerosol injection — might not be the answer to global warming they’ve been looking for.”

The article in CBC continues with a description of the proposed idea: “When a volcano erupts, it spews sulphur dioxide high into the atmosphere. The gas stays trapped in the stratosphere and causes more solar radiation to be reflected back into space, cooling the planet. That’s how the idea of stratospheric aerosol injection was born.”

The following two paragraphs explain the problem with this approach: “The prevailing theory among scientists is that adding sulphur dioxide to the atmosphere would improve crop yields by reducing heat stress on plants as it reflected the sun’s rays.

Instead, researchers found that, while the reduction in heat stress was an added bonus as a result of the cooling, less sunlight resulted in lower crop yields.”

Beneath a subsection titled “Looking to the past,” we find the source of the geoengineering idea: “The research team looked at the aftermath of two major volcanic eruptions — Mexico’s El Chichon in 1982 and Mount Pinatubo in the Philippines in 1991 — that pumped considerable amounts of sulphur dioxide into the atmosphere, 7 and 20 megatons of it, respectively.

The Mount Pinatubo event was the largest eruption in the 20th century and cooled Earth by 0.72 C in 1991. The cooling effect lasted roughly three years.

The scientists found that, following the Mount Pinatubo eruption, global yields for crops such as rice, soy or wheat — which photosynthesize more efficiently in sunny and hot climates — dropped 4.8 per cent. For crops that do better in cool, wet climates, such as maize, yields dropped more significantly at 9.3 per cent.”

The first author of the peer-reviewed paper is then quoted in the CBC article: “We found that, as intended, the cooling that the technology provides, makes crops grow better. At the same time, however, we found the shading … acts to reduce crop yields. It reduced crop yields to such an extent that it washed out all the benefits that cooling provided.”

I now turn to the Abstract of the peer-reviewed, open-access paper in Nature. It cites additional peer-reviewed evidence: “Solar radiation management is increasingly considered to be an option for managing global temperatures, yet the economic effects of ameliorating climatic changes by scattering sunlight back to space remain largely unknown. Although solar radiation management may increase crop yields by reducing heat stress, the effects of concomitant changes in available sunlight have never been empirically estimated. Here we use the volcanic eruptions that inspired modern solar radiation management proposals as natural experiments to provide the first estimates, to our knowledge, of how the stratospheric sulfate aerosols created by the eruptions of El Chichón and Mount Pinatubo altered the quantity and quality of global sunlight, and how these changes in sunlight affected global crop yields. We find that the sunlight-mediated effect of stratospheric sulfate aerosols on yields is negative for C4 (maize) and C3 (soy, rice and wheat) crops. Applying our yield model to a solar radiation management scenario based on stratospheric sulfate aerosols, we find that projected mid-twenty-first century damages to scattering sunlight caused by solar radiation management are roughly equal in magnitude to benefits from cooling. This suggests that solar radiation management—if deployed using stratospheric sulfate aerosols similar to those emitted by the volcanic eruptions it seeks to mimic—would, on net, attenuate little of the global agricultural damage from climate change. Our approach could be extended to study the effects of solar radiation management on other global systems, such as human health or ecosystem function.”

The second author of the peer-reviewed paper, a Professor of Public Policy at the University of California-Berkeley, provides the bottom line with a quote in the article at CBC: “We know that chemotherapy … helps aid individuals with cancer, but it also has very dramatic side effects. So there are some cases in which those risks are judged to be worth the consequences in order to avoid potential larger harms from some initial condition.”

Aye, there’s the rub. Who makes the decision, on behalf of all life on Earth, to implement geoengineering. It’s one thing to leave decisions about personal health in the hands of medical doctors and patients. It’s quite another for the few to make critical decisions about applying geoengineering that impact the many.