In modern times, volcanic activity adds just a fraction of the CO2 to the atmosphere that human activity contributes. However, massive eruptions such as the Yellowstone Caldera’s last super-eruption 640,000 years ago caused widespread climate change around the Earth because it sent enough ash into the stratosphere to partially block the sun from warming the Earth for years. The blast is thought to have been so violent that it blew some material completely out of Earth orbit and into open space.
Given the Yelowstone supervolcano’s timetable, with eruptions 2.1 million years ago, 1.3 million and 640,000 years ago—we could be due for a repeat at any time.