Geoengineering Revisited

Late last month the National Academy of Sciences released a report recommending that the U.S. initiate a $200 million research program to understand the potential for and potential consequences of geoengineering to mitigate the effects of global climate change.

The observation that particles—ice crystals, sulfate aerosols and volcanic ash—injected into the stratosphere will cool the Earth has stimulated interest among those who wish to engineer Earth’s climate, rather than simply suffer the consequences of global warming.  They recommend that we take an active role in stabilizing Earth’s climate in the face of inexorable rising concentrations of greenhouse gases in the atmosphere from fossil fuel combustion.

We know little about how geoengineering might be achieved and what its effects might be—both purposeful and inadvertent. Some research investigations would be welcome to clear away our ignorance.  As a scientist I am always curious about how our planet functions, and supportive of new research programs that deepen insight.

Geoengineering the Earth’s climate garners support among those who have abandoned all hope that we will ever cut our emissions of “greenhouse” gases from fossil fuel combustion. A small fleet of rockets could deliver sulfate and other particles to the stratosphere, where they would reflect incoming solar radiation for a few years, before themselves falling back to Earth’s surface under gravity.

Some investigators suggest that sulfate aerosols might stimulate the depletion of the stratospheric ozone layer, just now beginning to heal following the abandonment of chlorofluorocarbons (CFCs) in refrigerants.  As an alternative, others suggest that we could focus on aerosols made from common rock minerals, such as calcium carbonate, that might be injected into the stratosphere. These would be less likely to deplete ozone.

All attempts to seed aerosols into the stratosphere are fraught with the difficulty of maintaining the particles aloft and in the right amount to balance greenhouse warming of the planet.  The mean residence time of stratospheric air is about 2.6 years.  When a large volcano erupts, its effects on climate diminish rapidly. We can expect the same for sulfate and mineral particles carried to the stratosphere in rockets.  Once started, we’d have to keep transporting new particles into the stratosphere if we hope to avoid an abrupt return to global warming.

Scientific investigation is always advised, but experience suggests some caution in the application of geoengineering of our planet.  Apparently, others are worried too: witness the recent cancellation of a geoengineering trial by public outcry in Sweden.

My long experience with environmental matters finds a poor track record among large-scale attempts to manipulate nature on our behalf—in this case to prolong the use of fossil fuels.  We know the basis of the ongoing climate change, and we can anticipate and estimate its cost and consequences.  We do not need to add another layer of human perturbation to the Earth to prolong the use of fossil fuels.

E.B. White may have said it best, “I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit nature and more time tasting her sweetness and respecting her seniority.”  (from Coon Tree,  June 14, 1956).




Zarnetske, P.L. J. Gurevitch, J. Franklin and 11 others. 2021.  Potential ecological impacts of climate intervention by reflecting sunlight to cool Earth.  Proceedings of the National Academy of Sciences 118: doi: 10.1073/pnas/1921854118

4 thoughts on “Geoengineering Revisited

  1. Thanks for this summary, Bill, but I respectfully disagree with your suggestion that geoengineering is on the table as a means to “prolong the use of fossil fuels.” To be sure, there is the risk of moral hazard that geoengineering could mislead political leaders into thinking the technology affords fossil fuels a new life line. But serious proponents of geoengineering reject that idea. They instead argue that we have likely missed the 1.5 C target due to GHG pollution that has already been admitted, and that we now need to reconsider options that had been rejected in the past as too risky. The argument is that we cannot possibly keep warming under the 2 C threshold outlined in the Paris Agreement without (1) rapid decarbonization across all sectors (electrify everything from transportation to manufacturing while transitioning to a zero-carbon electricity grid), (2) aggressive deployment of negative emissions technologies (afforestation, reforestation, and direct air capture), and (3) some amount of geoengineering in the short term to allow (1) and (2) to ramp up. I’m not necessarily on board with geoengineering, but I do think it needs to be part of the discussion.

    1. You have greater faith in the behavior of politicians than I seem to be able to muster in recent years.

  2. Colleagues at U Illinois and I, a few years back, modeled the effects of a small reduction in incident irradiation via geoengineering on global NPP. We hypothesized that reduced light would decrease global photosynthesis but have no effect on soil respiration, decreasing both NPP and net ecosystem production. Didn’t work out that way, instead global ET was spatially redistributed. I’d hate to do this experiment for real!

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