Passage VII

Volcanoes put sulfur into the troposphere and the stratosphere, where the sulfur reacts to form sulfate aerosols (liquid droplets suspended in air). For locations at 50°N latitude, aerosols present at altitudes below 11 km scatter incoming solar energy, resulting in cooler air, while aerosols present at higher altitudes absorb incoming solar energy, warming the air.

Figure 1 shows the air temperature deviation at the surface of, and at 2 different altitudes above, a particular volcano (located at 50°N latitude), before and after it erupted. Figure 2 shows the maximum surface air temperature deviation associated with the specific mass of sulfate aerosols formed in the stratosphere after each of 8 volcanoes erupted.

Figure 1 adapted from Haraldur Sigurdsson, "Evidence of Voicanic Loading of the Atmosphere and Climate Response." ©1990 by Elsevier Science Publishers.

Figure 2 adapted from Michael Rampino, "Supereruptions as a Threat to Civilizations on Earth-like Planets." ©2002 by Elsevier Science (USA).