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Peter Hale Molnar, professor of geological sciences at the University of Colorado at Boulder and a fellow at the Cooperative Institute for Research in Environmental Sciences in Boulder, Colo., presents the 2014 John Carlson Lecture at 7 p.m. on Thursday, Oct. 16 at the New England Aquarium.
The title of his talk is: “Big Cats, Panamá, and Armadillos: A Story of Climate and Life."
Three million years ago, ice covered what is now Canada for the first time in the first “ice age” in hundreds of millions of years. In that ice age, the sheet of ice covering North America reached as far south as modern-day Missouri. Approximately 100 subsequent ice ages have occurred since that time, with the retreat from the last one occurring between 20,000 and 10,000 years ago.
Concurrently, ancestors to mountain lions crossed the Isthmus of Panamá, from North America to South America, to wreak havoc among animal life there, while giant armadillo-like animals moved in the opposite direction into North America. Mountain lions and armadillos are but two among many species that made such journeys, in what biologists call the “Great American Interchange.”
Many geologists who study past climates — paleoclimatologists — imagine that the Isthmus of Panamá emerged 3 million years ago, not only to provide a land bridge for the interchange of animals, but also to isolate the Atlantic and Pacific Oceans, and, as a consequence, to alter ocean circulation. That circulation today includes features like the Gulf Stream, an ocean current that transports warm water from the eastern coast of the U.S. to western Europe. These paleoclimatologists infer that the marked change in ocean circulation created conditions that allowed ice sheets to grow on the North American continent and to give us recurring ice ages.
Suppose, however, that you were a mountain lion, or an armadillo; would anything draw you into the swamps and jungles of hot, humid Panamá? Would you not prefer to remain in your semi-arid savanna than deal with snakes and crocodiles?
During ice ages, Panamá cools a bit and dries out, making it like the more arid climates where mountain lions, armadillo, and their brethren flourish. So, alternatively, could global climate change associated with that first big glacial period have temporarily transformed Panamá’s mosquito-infested, uninviting jungles into a savanna highway conducive to overland travel? In terms of cause-and-effect, rather than the Great American Interchange signaling a change in the configuration of land and sea whose resulting ocean circulation facilitated the first ice age, could the interchange, instead, be a consequence of the global climate changes due to that first glacial period, whose cause would lie elsewhere, independent of the emergence of the Isthmus of Panamá?
In his talk, Molnar will grapple with this and related questions as he explores different theories about our planet’s climate history spanning human and geological time scales.
The John Carlson Lecture communicates exciting new results in climate science to the general public. Free of charge and open to the general public, the lecture is made possible by a generous gift from John H. Carlson '83 to the Lorenz Center in the MIT Department of Earth, Atmospheric and Planetary Sciences.