'Global change' refers to large-scale change in the Earth's biological, geological, hydrological, and atmospheric systems, whether of natural or human origin. The Agricultural Research Service (ARS) conducts a strategic National Program entitled 'Global Change' because agriculture is vulnerable to environmental change and because agriculture can, in turn, affect some of the factors contributing to these changes. We need to address the likelihood and consequences of long-term environmental changes (e.g., Earth's atmospheric characteristics, energy balance) on agricultural and other terrestrial ecosystems. Concurrently, we must investigate the potential for agriculture to play a role in mitigating the factors affecting environmental change.

The Earth's atmosphere contains trace concentrations of several gases that absorb part of the radiation being reflected back to space, warming the 7-to-10 mile area above the Earth's surface called the troposphere. This 'greenhouse effect' is an important process that maintains temperatures near the Earth's surface within the range necessary for life, but there is concern that rising concentrations of these gases may be causing changes in climate, and therefore, among vegetation and ecosystems. Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased substantially since the beginning of the Industrial Revolution about 200 years ago, and are among the 'greenhouse gases.' Agriculture has played a role in these changes in atmospheric chemistry. Carbon dioxide was liberated by conversion of forest and grassland to agricultural use; soils of the Great Plains have lost up to 64% of their original organic carbon to the atmosphere as carbon dioxide. Agriculture also produces about 50% and 70% of human-induced emissions of methane and nitrous oxide, respectively. Some analyses indicate that the global mean surface temperature has already increased between 0.5 to 1.0 degree Fahrenheit since the late 19th century, due to the combined influence of all greenhouse gases from all sources, including agriculture. Based on continued increases in gas emissions, some analyses indicate a further rise in global mean temperatures of about 3.5 to 7 degrees Fahrenheit by the year 2100. Understanding agriculture's contributions to, and mitigation of, global change is the goal of this National Program.