From Christopher Preston

Geoengineering and Environmental Ethics

(helpful summary of technologies envisioned)

Geoengineering has been coarsely but helpfully defined by Canadian researcher David Keith as “the intentional, large scale manipulation of the environment.” Footnote Keith adds that current discussion of geoengineering is almost exclusively targeted towards the question of what can be done to steer the planet away from the most harmful effects of climate change. Footnote The two categories of geoengineering currently attracting the most attention are carbon dioxide removal (CDR) and solar radiation management (SRM). Footnote While there is disagreement about what legitimately counts as geoengineering, Keith’s rather broad definition is helpful for getting a sense of the projects being considered under these two main categories.

            Small scale removal of carbon dioxide from the atmosphere has been taking place at the hands of humans for centuries. The planting of a tree in my back yard could be construed as a personal effort at carbon dioxide removal, though the amount of carbon removed and the time frame during which it would be sequestered are both too small to have any effect on global climate. On the other hand, a global project to plant 5-10 billion acres of trees may make enough of a difference to earth’s carbon budget to qualify for the label. Footnote Scale counts for something with CDR technologies. Other CDR schemes involve deploying hundreds of thousands of CO2 scrubbing machines (sometimes called “artificial trees”), adding iron to thousands of square miles of nutrient rich (but iron deficient) regions of the world’s oceans to create vast phytoplankton blooms, enhancing the natural weathering process of rocks, increasing the alkalinity of the oceans, and producing billions of tons of biochar for sequestering carbon in agricultural soils. Each of these technologies can be scaled to cause a significant reduction in atmospheric carbon. Footnote When pursued expressly for this purpose, each of these schemes becomes an example of climate engineering. At a large enough scale, they meet Stephen Schneider’s technical definition of geoengineering as the “manipulation[s] of stocks and flows of components of the Earth’s biogeochemical processes to alter the radiative balance of the atmosphere.” Footnote

Carbon dioxide removal technologies have a number of considerations in their favor and a number against. On the down side, they are likely to be relatively slow acting. Not only would it take time to bring carbon levels down to pre-industrial levels by removing carbon incrementally from the atmosphere but there is also a built-in inertia to global temperature change due to the huge mass of the oceans and the relatively high specific heat of water. Even as the carbon gets removed, global temperatures are unlikely to fall fast. Another disadvantage of CDR is that some of the carbon removal schemes (e.g. CO2 scrubbing with artificial trees and enhanced weathering of rocks) are relatively high cost.

            On the other hand, CDR has the benefit of directly treating the cause of the climate change problem. They physically remove carbon from the atmosphere. Most CDR schemes also have the advantage of being able to start small. This would allow those managing the geoengineering project to monitor and evaluate their effects as the scale is ramped up. An additional advantage of CDR schemes is that most of them (with the exception of ocean fertilization) could likely proceed without new international regulations or agreements. The distinction between carbon capture at, say, a coal fired power plant (traditional pollution control) and carbon scrubbing in the adjacent two states (geoengineering with CDR) is not conceptually clear. If carbon dioxide is regulated as a pollutant, then CO2 removal can be viewed as simply a type of pollution control. Footnote Perhaps for this reason, CDR techniques are often viewed as the less controversial of the two types of geoengineering scheme.

            It would be a mistake, however, to suggest that CDR is entirely controversy-free. Challenges concerning how to sequester the captured carbon in the long-term and worries about the ecological effects of ocean fertilization and enhanced weatherization of rocks mean that CDR schemes still generate significant concerns. It was worries about these side-effects that caused two recent ocean fertilization projects to be abandoned on environmental grounds, in one case, even after the ships for deploying the iron had left port. Footnote


Proposals to deal with the problem of global warming through the management of solar radiation tend to be even more controversial than strategies that actively remove carbon dioxide. SRM technologies seek to reflect back some of the solar energy reaching Earth’s surface and/or the atmosphere. As with CDR, it is possible to imagine small scale versions of some SRM technologies. For example, I could paint the roof of my house or the driveway of my home white to increase the amount of solar energy reflected back into the atmosphere rather than absorbed by my property. Some of this reflected solar energy would end up back in space. In so doing, I would make my house cooler and, if all my neighbors did the same, we could do something to counter the urban heat island effect in our neighborhood. On the scale of a few roofs, this is not going to qualify as geoengineering. Scaled up to hundreds of millions of roofs, it might. Footnote

Another SRM technique that works on similar principles is to brighten existing ocean clouds to prevent solar energy from being absorbed into the ocean. Footnote Marine clouds can be brightened by increasing the number of the condensation nuclei around which moisture forms. This can be achieved by spraying a fine mist of sea water into the natural convective currents above the ocean and letting the mist rise into existing clouds. To be have a real influence on earth’s solar budget, cloud brightening advocates say it would require a concerted effort on the ocean commons on the scale of about 1500 spray producing vessels operating continuously. Footnote Cloud brightening has the advantage, say its supporters, that the cooling effects would cease within a day or two of the spray nozzles being turned off.

            Two more SRM schemes to reflect sunlight, the injection of stratospheric aerosols and the deployment of space-based mirrors, generate considerably more controversy. With both of these schemes, a reflective agent is place high in (or above) the stratosphere to act as a barrier to incoming short-wave radiation. In the case of stratospheric aerosols, this agent is most likely to be sulphate particles formed as a consequence of the intentional delivery of sulphide gases to the upper atmosphere. Once the particles had formed, it is projected that global cooling could occur very rapidly due to the amount of solar energy that would immediately be prevented from penetrating the atmosphere. Footnote

            Though most geoengineering schemes have not, for obvious reasons, been tested on a global scale, advocates of the deployment of stratospheric aerosols claim that this experiment has already been run. When Mount Pinatubo erupted in 1991, it sent 20 million tons of sulphur dioxide into the atmosphere in addition to many additional tons of pyroclastic debris. The dust and the sulphur dioxide (which soon formed sulphuric acid droplets) caused a stratospheric haze which effectively shielded a portion of the sun’s rays for two years. Temperatures in the northern hemisphere fell by 0.5-0.6 degrees Celsius almost immediately. Footnote Earlier eruptions such as El Chicon (1982), Krakatau (1883), and Tambora (1815) showed similar, if less finely documented, effects. Of all the SRM strategies being discussed, stratospheric aerosols are considered by some to be capable of creating the fastest and most reliable drops in temperature. Footnote

Using SRM as a strategy to combat global warming has a number of factors in its favor as well as a number against it. In the case of stratospheric aerosols, the technology could be deployed relatively cheaply and its effects would be felt relatively quickly. On the negative side, shielding the sun does nothing to reduce concentrations of atmospheric carbon leading to the likelihood of very rapid warming if aerosol deployment was suddenly stopped (known as the “termination problem”). The maintenance of high levels of carbon would also ensure continued ocean acidification with serious effects on the ability of marine life to form shells and corals. To add to the problems, stratospheric sulphur aerosols also appear to facilitate ozone depletion – as witnessed after the Pinatubo eruption – and they have a relatively unpredictable effect on precipitation patterns. A major political disadvantage presented by the fact that they take place on the global commons is that maritime cloud brightening, stratospheric aerosols, and space mirrors would all require the creation of new international mechanisms to ensure that the process could be managed legally and in an open and transparent way. Footnote

            It is widely acknowledged that all of the schemes described above would require careful ethical analysis before implementation. This analysis would have to include consideration of the likelihood of side-effects, the distribution of costs and benefits, the efficacy of the technology in reducing temperatures, balancing of risk and uncertainty, and planning for governability. As already indicated, these concerns (and others like them) are clearly the most pressing ethical concerns that geoengineering faces. Numerous additional, and perhaps surprising, considerations are also relevant. For example, stratospheric aerosols would likely reduce the effectiveness of photovoltaic panels. They would also create a whitening of the sky. The deployment of reflective mirrors in space would introduce an additional form of space junk. Hundreds of thousands of artificial trees would create an aesthetic nightmare. Each of these concerns, as well as numerous legal and political ones, would need serious consideration as part of the complex decision-making process about whether (and how) to proceed with geoengineering. But none of these are concerns that on their own reach to the foundations of environmental ethics. To do this, one needs to consider what is sometimes viewed as the most startling “philosophical” consequence of climate engineering, the implications of living on a managed earth.