Climate Engineering: Possible? Dangerous? Necessary?
Volcanoes have repeatedly cooled the Earth by injecting small particles into the stratosphere, where they deflect incoming solar radiation away from the Earth. Because solar radiation warms the Earth, decreasing planetary absorption of solar radiation cools the Earth. It has been shown, for example, that if the effective cooling from the 1991 Mt. Pinatubo eruption in Indonesia could be sustained, this would be more than enough to cool the Earth even with a simultaneous doubling of atmospheric CO2 content. This natural experiment has led to idealized model simulations of intentional planetary climate engineering. These studies indicate that reductions in sunlight will never exactly offset greenhouse gas warming, but a high-CO2 world with climate engineering is more similar to the pristine pre-industrial world than is a high-CO2 world without climate engineering. It appears that the cost of planetary climate engineering could be low, perhaps a few billions of dollars per year or less. These considerations raise a wide array of environmental, ethical, political, game-theoretic, and economic questions.