Earth's climate has fluctuated over the course of several billion years. During that span, species have arisen, gone extinct, and been supplanted by others. Humankind and our immediate ancestral species have survived the sometimes drastic fluctuations of the past several million years of our evolving climate quite handily. Although human beings and their ancestors have always changed the environment in which they have lived, human actions since the advent of the Industrial Revolution may be producing impacts that are not only local but also global in scope. Ever-growing fossil fuel use and other activities associated with industrialization have altered the concentrations of several atmospheric gases, including carbon dioxide. Theoretically, these alterations can cause alterations in the overall heat retention of Earth's atmosphere. Scientists around the world are engaged in studies to determine whether these changes in the atmosphere pose a risk of significant, negative environmental and...