Interactions and Global Climate Change: Some Lessons from Earth History

Over the last 100 years of the industrial revolution, human civilization has been performing a remarkable experiment on Earth’s climate system. Because of a variety of activities related to population growth and economic development, most notably the burning of fossil fuels, humans have increased the concentration of carbon dioxide in the atmosphere by approximately 30%. Carbon dioxide is a greenhouse gas, absorbing long-wave radiation emitted from the planet surface and warming Earth’s surface temperature. There is now a consensus that Earth’s climate has been influenced discernibly by the increase in CO2 (e.g., Houghton et al., 1996), although considerable controversy exists over how much the climate will change over the next several centuries as atmospheric CO2 continues to rise. The realization that humans are changing Earth’s climate is profound, yet it is not the only way in which humans are changing the physical and biological environment. The arrival of humans to the Americas at the end of the last ice age, approximately 14,000 years ago, was accompanied by the extinction of most large mammals, includ-