How did volcanism trigger climate change before the eruptions started?

Enlarge / Loads of lava: Kasbohm with a few solidified lava flows of the Columbia River Basalts. (credit: Joshua Murray)

As our climate warms beyond its historical range, scientists increasingly need to study climates deeper in the planet’s past to get information about our future. One object of study is a warming event known as the Miocene Climate Optimum (MCO) from about 17 to 15 million years ago. It coincided with floods of basalt lava that covered a large area of the Northwestern US...