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Although there are many other "greenhouse" gases, carbon dioxide (CO2), generated by natural processes and by the burning of wood, coal, oil, gasoline, and natural gas, is currently believed to be the most important contributor to global warming because of its long atmospheric lifetime and ability to trap heat. CO2 concentration in the atmosphere has increased by 25% over the past two centuries. Part of this increase is a by-product of energy consumption and deforestation to meet human needs.

However, global warming has occurred in pre-industrial eras. The potential for future global warming, and the relative contributions of natural processes and human influences are still poorly known. A better scientific understanding of these changes and an improved predictive capability are important elements of the U.S. Global Change Research Program.

Why is Reliable Global Change Prediction Important?

The effects of natural variability and human activity in the global system can have profound economic, environmental, social, and national security implications. For example, the single 1982-1983 "El Niño" event caused billions of dollars in economic losses worldwide, and this natural fluctuation in the climate system is know to be a recurring event of varying magnitude and periodicity.

Potential changes accompanying a global warming trend might have even greater impact on regional temperature regimes and precipitation patterns. These could result in changes in agriculture policies, modes of energy production and usage, utilization and protection of natural resources, and coastal-zone management. Reliable estimates of the magnitude and rate of these changes would be needed at many decision levels within society: individuals (e.g., farmers), industry (e.g., energy producers), and government (e.g., regulators).