(for Part One)
Engineering the Planet (PDF)
by David W. Keith
Forthcoming in “Climate Change Science and Policy” Steven Schneider and Mike Mastrandrea editors, to be published by Island Press.
If we decreased the amount of sunlight absorbed by the earth we might engineer a cooling effect sufficient to counterbalance the warming caused by CO2.
It might be possible to shield some sunlight by adding aerosols to the atmosphere, where they would scatter sunlight back into space and might also increase the lifetime and reflectivity of clouds (the average planetary reflectivity is called “albedo,” so such methods are often called albedo modification).
Alternatively, it might be possible to engineer giant shields in space to scatter sunlight away from the planet.
These are the oldest and best known geoengineering proposals so I will discuss them in some detail.
The cost of injecting aerosols into the stratosphere was analyzed by the US National Academy of Sciences in 1992, they examined several delivery methods including high-altitude aircraft and naval guns, and found that annual costs of over $100 billion would be sufficient to produce a 1% reduction in effective insolation (average solar radiation) reaching the lower atmosphere.
While this cost may sound high, it is roughly a factor of ten lower than the cost to achieve an equivalent reduction in climate change through reductions in CO2 emissions.
Moreover, later analysis has shown that it is technically possible to design aerosols that are far more effective per unit mass at scattering light which could reduce costs by a factor of 10 to 1000 (Teller et al. 1997).
Like many other tools for geoengineering, the use of aerosols imitates natural phenomena. Aerosols injected into the stratosphere by large volcanoes can cause global cooling.
The eruption of Mount Tambora in present day Indonesia, for example, was thought to have produced the “year without a summer” in 1816.
Likewise, the 1991 eruption of Mount Pinatubo in the Philippines caused a readily detectible change in global temperatures.
In the 1970s, when Budyko proposed injecting sulfate aerosols into the stratosphere, he called the process “artificial volcanoes” (Budyko 1982).
In addition to imitating natural processes, proposals for geoengineering the planet often employ methods that mimic or amplify existing human impacts.
Combustion of fossil fuels, particularly coal, already creates great quantities of aerosols.
Human activities have substantially increased the global aerosol burden, altered the lifetime and reflectivity of clouds, and so changed the amount of sunlight absorbed by the planet.
Indeed, the cooling effect due to aerosols generated by industrial pollution currently offsets part of the warming caused by CO2.
Geoengineering might therefore be seen as adding one pollutant—aerosols—to counteract the effect of another—CO2.
Like any technology, geoengineering will entail risks and side-effects.
If reflective aerosols are injected into the stratosphere, for example, they will generate impacts such as ozone loss that may sensibly be called pollution.
But, geoengineering is not in and of itself pollution. Intent matters.
The political implications of geoengineering, the institutional coordination required to implement it, and the moral implications of so doing all differ radically from the generation of aerosol pollution as a byproduct of fuel combustion.
Geoengineering may be ill-advised, the activity of geoengineering may generate pollution as a side-effect, but it is not simply a continuation of our long history of polluting the planet.
Deliberate planetary engineering would be a new chapter in humanity’s relationship with the earth.