Climate change is often consid- ered a uniquely modern issue. But according to Yale professors Harvey Weiss, Joseph Manning and Robert Mendelsohn GRD ’78, humans have dealt with climate change since the dawn of civilization.

On Wednesday afternoon, the trio discussed the connections between history, climate change and human civilization at Kroon Hall. The talk was an abridged version of a presentation the three originally gave in October 2017, titled “Col- lapse! What Collapse?” and revived in response to high demand.

Each professor integrated history and scientific data to understand climate change. Two of the speakers used scientific evidence to explain the collapses of historical empires previously thought to have resulted from political or social collapse.

“It is not just political framework that explains everything,” Manning said. “No, there is a hell of a lot more going on.”

Structured as three 15-minute lectures, the event kicked o with Weiss, a professor of Near Eastern archaeology and Forestry and Envi- ronmental Studies.

He first explained the use of paleoclimate proxies, which are physical metrics of measuring historical climate change. Proxies fall into the categories of marine, lake, glacial, tree ring and speleothems. Weiss further elaborated on speleothems, describing them as the “most famous.” They are found from cave drippings and stalagmite formations, and have provided stable isotope values for both precipitation and temperature over hundreds of thousands of years. Using this information, scientists can track climate change over long periods of time. Weiss concentrated on climate change in South America. In particular, he noted the Mayan civilization’s response to megadroughts, or droughts that last longer than 10 years and prompt steep declines in precipitation. Such conditions plagued the Mayans around the start of the 11th century. Using data from speleothems and other proxies, Weiss claimed that a mega- drought was one of the underlying conditions for fall of the Mayan civilization, as the megadrought led to much lower food levels, as well as migration away from densely populated areas.