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they would form microscopic particles to block sunlight. The
idea is based on a natural phenomenon. Every few decades a
volcano erupts so violently that it sends several millions of
tons of sulfur–in the form of sulfur dioxide–more than 10
kilometers into the upper reaches of the atmosphere, a region
called the stratosphere. The resulting sulfate particles spread
out quickly and stay suspended for years. They reflect and
diffuse sunlight, creating a haze that whitens blue skies and
causes dramatic sunsets. By decreasing the amount of sunlight
that reaches the surface, the haze also lowers its temperature.
This is what happened after the 1991 eruption of Mount Pinatubo
in the Philippines, which released about 15 million tons of
sulfur dioxide into the stratosphere. Over