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.

“Here is collapse identified in

the archaeological and historical records as essentially political breakdown and regional abandonment known from high resolution through archaeological and historcal records,” Weiss said in his lecture.

Joseph Manning, the William K. and Marilyn Milton Simp- son professor of classics and his- tory, focused on climate change as a result of volcanic eruptions. He spoke about the Nile River and the fall of both Egyptian and the Roman empires. Manning cross-referenced ancient accounts of plague and famine with scientific evidence, using these references as signs of volcanically induced climate change. He asserted that nature, along with political and social issues, caused the fall of these two empires.

To conclude the event, Mendel- sohn, a professor at both the School of Forestry and Environmental Studies and the School of Manage- ment, traced climate change from prehistoric times up to the pres- ent, explaining that climate varies both organically and inorganically. He cited evidence that the earth has

cooled organically over millions of years and that periods of cool tem- perature and warm temperature can cycle.

“Climate change is not new,” Mendelsohn said. “Maybe man- made climate change is new. But precipitation and temperature changes have been going on for a long time and will continue to go on.”

These organic cycles overlap with human history and can show researchers how humans have been able to adapt over the past thou- sands of years.

According to Mendelsohn, the issue is that, in recent centuries, temperatures have grown increas- ingly volatile as a result of increasing carbon dioxide levels since World War II. He explained that periods of increasing temperatures have forced people to immigrate to find food. He added that he worries increasing temperatures could have repercus- sions for future generations and lead to a “massive reallocation of people.”

Marian Chertow FES ’00, a pro- fessor at the School of Forestry & Environmental Studies, lauded the three professors for their integration of history and science.

“The opportunity to bring more objective science to the study of history can only be considered an opportunity to understand the complexities more,” Chertow said. “At the same time, you don’t want to go from saying the social causes weren’t the real causes to saying that the climate is the full cause either.”

Carbon dioxide levels have increased 35 percent from 1918– 2018; these levels had only increased 5 percent from 1850–1917, according to data collected by NASA.

Nick Tabio |