Although most climate scientists have their eye on the human causes of increased atmospheric carbon dioxide (CO2) levels, a team of researchers from the University of Texas are exploring a different side of climate change: volcanoes. In a new study, they explore how ancient volcanic activity might have influenced historical climate shifts.

The team examined plate-tectonic movement of continents that might underlie the climate shift from hot to cold that Earth experienced over the course of its million-year history. In particular, the researchers made sure to focus on the long-terms shifts in Earth's baseline climate instead of short-term or man-made changes.

The results reveal that over the past 720 million years, periods of time when volcanoes were more active along continental arcs correlate with warmer conditions. Conversely, less active continental arc volcanoes are associated with colder conditions.

When volcanoes along continental arcs are active, the oceanic plate descends under the continental plate, stimulating the mixing of magma with carbon from Earth's crust, leading to the release of CO2 into the atmosphere during the eruption.

"Continental arc systems are plumbed through the Earth's crust and they tend to interact with carbon reservoir rock preserved beneath the surface," said Ryan McKenzie of Yale University and lead researcher of the study.

Although scientists known that atmospheric CO2 influences Earth's climate, the new study might be the answer to the question of what caused the fluctuations in CO2 that are observed in the Earth's geologic record.

The team used 200 published studies in combination with their own fieldwork to reconstruct the history of volcanoes located on continental margins over the past 720 million years.

"We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years," said Brian Horton, professor at the University of Texas' Jackson School of Geosciences and co-author of the study. "The distinguishing part of our study is that we looked at a very long geologic record - 720 million years - through multiple greenhouse-icehouse events."

The data shows connections between cooler icehouse periods with less continental volcanic activity and between warmer greenhouse periods and increased continental volcanic activity.

The findings were published in the April 22 issue of the journal Science.