Geoengineering: a bad idea whose time may come
Yesterday, at the annual meeting of the American Geophysical Union (AGU), climate change scientists discussed the risks and benefits of deliberately altering Earth's climate through "geoengineering". One measure of the concern scientists have about Earth's climate could be gauged by the standing-room only crowd of 200 that packed the presentation room. The eleven speakers at the session laid out some radical and dangerous ideas for deliberately altering Earth's climate. They uniformly cautioned that the uncertainties and dangers of implementing any of these schemes was high, but that geoengineering may be necessary if efforts to control greenhouse gases fail and the climate begins to undergo rapid and destructive changes.
David Keith presented the results of a week-long workshop held earlier this year that brought together ten of the world's experts on geoengineering. He emphasized that even if we stopped emitting CO2 today, the possibility of dangerous climate change capable of causing a "climate emergency" may still be higher than 1%, thanks to the tremendous inertia of the heat stored in the oceans. Of course, we're not going to stop emitting CO2 today. Dealing with a future climate emergency is technically feasible, if we inject large quantities of sulfur into the tropical stratosphere via aircraft, artillery, or tethered balloons with hoses. Sulfur injection into the stratosphere is considered to be the leading candidate for geoengineering, since nature has done this many times via volcanic eruptions, and we have some idea of what to expect. As I reported in a blog post earlier this year, the idea is being championed by Nobel prize-winning atmospheric chemist Paul Crutzen.
One problem with injecting sulfur into the stratosphere is that it tends to settle back to the surface in about ten months. A. V. Eliseev explained that in order to keep global temperatures under control in a world with ever-increasing CO2 emissions, we would have to inject an ever increasing amount of sulfur into the atmosphere. His computer model results showed that if a funding lapse occurred in, say, the year 2075, the atmosphere would rapidly warm by 5-9°F (3-5°C) over most of North America, Europe, and Asia, within a decade of cessation of the geoengineering efforts. The resulting shock to ecosystems would be extremely dangerous to civilization.
Richard Turco of UCLA estimated that injecting enough sulfur in the stratosphere to properly geoengineer the climate would require 3000 aircraft sorties per day, and cost $50-$100 billion per year. Model results he presented showed a large amount of uncertainty as to what might happen, and he cautioned that there was "no guarantee of success, and failure would be catastrophic".
A. Robrock of Rutgers disagreed with Dr. Turco, and estimated that the cost of injecting the required amount of sulfur into the stratosphere would by less that $5 billion per year, provided the U.S. military would let scientists use 167 of the existing fleet of 522 F15C Eagle jets to do the job. After all, he reasoned, why wouldn't the military want to use their aircraft to confront our enemy (global warming?) High-altitude fighter jets would be required to do the job, since ordinary jetliners cannot fly high enough to penetrate into the stratosphere. He cautioned that such a fleet of aircraft would have to fly three missions per day, and their exhaust gases would probably cause significant destruction of Earth's protective ozone layer. Furthermore, modeling studies show that we don't know what size particles to make, where to put the sulfur, and what uneven effects the efforts might have on Earth's climate. He concluded, "there are many reasons not to do geoengineering".
A more ecological approach to geoengineering was presented by Phil Rasch of Pacific Northwest National Laboratory, and by Jim Haywood of Britain's Met Office Hadley Center. They proposed building a fleet of wind-powered ships known as Fletter vessels (Figure 1) that would spray large amounts of sea salt into the air in regions where there are existing stratocumulus clouds. The sea salt would act as nuclei around which moisture could condense, making the clouds more reflective. A fleet of approximately 66 of these vessels would be required to seed the clouds over 30% of the globe, to balance a doubling of atmospheric carbon dioxide. However, they cautioned that while this solution would be relatively cheap, the technology to implement this scheme would be difficult. Furthermore, studies performed with climate models showed that the resulting climate shift would not be uniform, and many areas would experience drought. In particular, Dr. Haywood showed the possibility of severe drought in the Amazon rain forest and in the Southwest U.S.
Figure 1. A conceptual picture of Flettner spray vessel with Thom fences. These wind-driven vessels have vertical spinning cylinders that use the Magnus effect to produce forces perpendicular to the wind direction. Anton Flettner built a ship using this technology that crossed the Atlantic in 1926. The proposed geoengineering Flettner vessels would sail over ocean regions covered with stratocumulus clouds and make the existing clouds whiter by spraying small salt particles into the air. Image is copyright J. MacNeill 2006. For more information on these vessels, see Salter at al., 2008, "Sea-going hardware for the cloud albedo method of reversing global warming", Philosophical Transactions of The Royal Society A, 366, Number 1882, pp3989-4006, 13 November 2008.
Katharine Ricke of Carnagie Mellon University cautioned that the foreign policy community has virtually no awareness of geoengineering issues, and would be totally unprepared for the possibility of some country deciding to unilaterally attempt a geoengineering program on their own. She suggested that an effort needs to be made to promote international agreements on geoengineering, perhaps including binding treaties.