(note: this is part 2 in our series from Paul Crutzen's Paper on geo-engineering, published in the Journal of Climate Change in 2006. PDF from Heartland.org, excerpt from pg. 2)
ALBEDO ENHANCEMENT BY STRATOSPHERIC SULFUR INJECTIONS: A CONTRIBUTION TO RESOLVE A POLICY DILEMMA?
An Editorial Essay by Paul J. Crutzen
Max-Planck-Institute for Chemistry
By far the preferred way to resolve the policy makers’ dilemma is to lower the emissions of the greenhouse gases. However, so far, attempts in that direction have been grossly unsuccessful.
While stabilization of CO2 would require a 60–80% reduction in current anthropogenic CO2 emissions, worldwide they actually increased by 2% from 2001 to 2002, a trend, which probably will not change at least for the remaining 6-year term of the Kyoto protocol, further increasing the required emission restrictions.
Therefore, although by far not the best solution, the usefulness of artificially enhancing earth’s albedo and thereby cooling climate by adding sunlight reflecting aerosol in the stratosphere might again be explored and debated as a way to defuse the Catch-22 situation just presented and additionally counteract the climate forcing of growing CO2 emissions.
This can be achieved by burning S2 or H2S (hydrogen sulfide), carried into the stratosphere on balloons and by artillery guns to produce SO2 (sulfur dioxide).
To enhance the residence time of the material in the stratosphere and minimize the required mass, the reactants might be released, distributed over time, near the tropical upward branch of the stratospheric circulation system.
In the stratosphere, chemical and micro-physical processes convert SO2 into sub-micrometer sulfate particles.
This has been observed in volcanic eruptions e.g., Mount Pinatubo in June, 1991, which injected some 10 Tg S, initially as SO2, into the tropical stratosphere.
In this case enhanced reflection of solar radiation to space by the particles cooled the earth’s surface on average by 0.5 ◦C in the year following the eruption.
Although climate cooling by sulfate aerosols also occurs in the troposphere, the great advantage of placing reflective particles in the stratosphere is their long residence time of about 1–2 years, compared to a week in the troposphere.
Thus, much less sulfur, only a few percent, would be required in the stratosphere to achieve similar cooling as the tropospheric sulfate aerosol. This would make it possible to reduce air pollution near the ground, improve ecological conditions and reduce the concomitant climate warming.
The main issue with the albedo modification method is whether it is environmentally safe, without significant side effects.