Thompson has spent his career trekking to the far corners of the world to find remote ice fields and then bring back cores drilled from their centers. Within those cores are the records of ancient climate from across the globe.

From the mountains of data drawn by analyzing countless ice cores, and a meticulous review of sometimes obscure historic records, Thompson and his research team at Ohio State University are convinced that the global climate has changed dramatically.  But more importantly, they believe it has happened at least once before, and the results were nearly catastrophic to emerging cultures at the time. He outlined his interpretations and fears today at the annual meeting of the American Geophysical Union in San Francisco.

The impact of a climate change of that magnitude on a modern world would be tremendous, he said. Seventy percent of the population lives in the world’s tropics and major climate changes would directly impact most of them.

“The climate system is remarkably sensitive to natural variability,” he said. “It’s likely that it is equally sensitive to effects brought on by human activity, changes like increased greenhouse gases, altered land-use policies and fossil-fuel dependence.

“Any prudent person would agree that we don’t yet understand the complexities with the climate system and, since we don’t, we should be extremely cautious in how much we `tweak’ the system,” he said.

“The evidence is clear that a major climate change is underway.”

Text for this article comes from a OSU press release.