Understanding and predicting global climate change may be one of the most complex scientific challenges we face today. MIT’s School of Science launched the Lorenz Center, a new climate think tank devoted to fundamental inquiry, to foster creative approaches to learning how climate works. **Peter Molnar** describes when ice covered Canada for the first time, three million years ago during the first Ice Age in hundreds of millions of years. Concurrently, mountain lions crossed the Isthmus of Panamá from North America to South America, while Armadillos moved into North America, in the Great American Interchange. Many geologists imagine that the Isthmus of Panamá emerged three million years ago not only to provide a land bridge for the Interchange, but also to facilitate Ice Ages. During Ice Ages, however, Panamá cools and dries out. Could it have been global climate change instead, associated with an ice-covered Canada, that temporarily transformed Panamá’s uninviting jungles into a savanna highway conducive to overland travel? The annual Carlson Lecture features exciting new results in climate science each year to the general public; it is made possible by a generous gift from MIT alumnus John H. Carlson to the Lorenz Center at MIT.