When a major volcano erupts, it can inject sulfurous gases into the upper atmosphere—the stratosphere—about 5 miles above the Earth’s surface. These gases form tiny particles, known as aerosols, that reflect sunlight. For the couple of years that they spend in the stratosphere, before they mix down and are deposited on Earth’s surface, these sulfate aerosols cool our planet.
We saw this cooling for a couple of years after the 1991 eruption of Mt. Pinatubo in the Philippines, And after the massive eruption of Tambora in Indonesia in 1815, the summer in New England was so cold it snowed in June.
The cooling effect of stratospheric aerosols is so effective that several scientists have suggested that we launch rockets to deliver sulfur to the stratosphere as a way to combat global warming. The science behind the idea seems solid.
Should we be worried about massive human manipulation of our planet’s atmosphere?
Several unknowns suggest caution: What happens if the cooling is not distributed uniformly around the Earth? Will the eventual deposition of sulfate aerosols from the stratosphere exacerbate acid rain? Will sulfate aerosols disrupt the ozone layer in the stratosphere, where it protects all life from the harmful effects of the Sun’s ultraviolet radiation?
In medicine, it is always better to tackle the cause of a disease, rather than combat its effects. For our planet’s health, we could get serious about cutting fossil fuel emissions of carbon dioxide to the atmosphere. If geo-engineering is the therapeutic treatment, a kind of planetary chemotherapy, we need to be sure that it doesn’t lead to further suffering.
Photo, taken on November 20, 2010, courtesy of Albert Law via Flickr.