"The global environment is changing rapidly as a result of human activities. Over the last half-century, population growth and urbanization, economic growth, energy production, natural resource use, and other trends have accelerated at a rate unprecedented in human history, driving profound changes in ecosystems, oceans, ice, the composition of Earth's atmosphere, and other systems that influence human life. These global changes are causing climate change, ocean acidification, air and water pollution, species loss, and other impacts; and these changes pose both risks and opportunities that present complex challenges for communities, governments, and businesses across the Nation and the world. As the impacts of global change progress, demand for information on response measures is rising. Global-change science is needed to inform adaptation actions to cope with risks created by a changing climate, and to inform mitigation actions (e.g., greenhouse gas reduction measures) to decrease the risks associated with climate change, especially over the long-term. The global-change research enterprise faces the challenge of further advancing fundamental understanding of the causes and effects of change while providing information needed for response measures of many kinds and at different scales."
U.S. Global Change Research Program: http://www.globalchange.gov/