[ScienceDaily, 2009: Volcanoes cause global warming]
Researchers here have discovered the pivotal role that volcanoes played in a deadly ice age 450 million years ago.[ScienceDaily, 2002: Volcanoes cause global cooling]
Perhaps ironically, these volcanoes first caused global warming -- by releasing massive amounts of carbon dioxide into the atmosphere.
When they stopped erupting, Earth's climate was thrown off balance, and the ice age began.
The changes wrought by Pinatubo's sulfuric acid cloud, which blocked a large percentage of sunlight from reaching the earth, initially included cooler summers and warmer winters, an overall net cooling at the earth's surface and altered winds and weather patterns, Robock said.