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The Fundamental Science of Climate Change

For most of human history, changes in the Earth's climate resulted from natural causes that took place over hundreds of thousands of years. But today, human activities are beginning to affect our climate in serious and immediate ways by rapidly adding greenhouse gases to the atmosphere. These gases trap in Earth's heat that would otherwise escape to space, intensifying a natural phenomenon called the "greenhouse effect." The result is a long-term rise in the average temperature of the Earth-global warming.

The concentration of carbon dioxide (CO₂), the key greenhouse gas of concern, is at its highest level in more than 160,000 years and is still climbing. Atmospheric levels of other greenhouse gases are also climbing rapidly as a result of human activities. Compared to pre-industrial times, atmospheric concentrations of CO₂, methane (CH₄) and nitrous oxide (N₂O) are 30%, 145%, and 15% higher. Growing in importance are the hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF₆), all very potent greenhouse gases.

Over the last century the average surface temperature has increased by 1^oF; the ten warmest years on record have occurred since 1983, with seven of them since 1990. Evidence of global warming is further confirmed by melting glaciers, decreased snow cover in the northern hemisphere and even warming below ground.

Scientists think the accumulation of greenhouse gases in our atmosphere is at least partially responsible for this warming trend. But other factors such as solar variability and natural climatic variability make it difficult to attribute all or part of the warming to one exact cause. Over the next century, scientists project that the temperature will rise 2 to 6^oF as a result of rising concentrations of greenhouse gases. Scientists also state this rate of global warming would be unprecedented compared to the past 10,000 years. This threatens our health, agriculture, water resources, forests, wildlife and coastal areas.

Sources of Greenhouse Gas Emissions

Most of the energy in the U.S. is produced by the burning of fossil fuels (coal, oil, and natural gas). The carbon dioxide released from the burning of these fuels accounts for 85% of all greenhouse gas emissions in the U.S. as well as other major air pollutants.

Methane sources include landfills, coal mines, agriculture, and oil and natural gas production. Nitrous oxide is emitted from fertilizers and some industrial sources.

HFCs are primarily used as replacements for chlorofluorocarbons, the now banned ozone-depleting substances. PFCs and SF₆ are associated with aluminum smelting, semiconductor manufacturing, electric power transmission and distribution and magnesium casting.

Part of the Solution

Did you know that your home and office contribute to global warming? Energy used in our everyday activities turning on electrical appliances, driving cars, and heating and cooling our homes is responsible for air pollution that contributes to climate change. Technologies are available today that can cut this energy use significantly and, at the same time, improve our quality of life.

The EPA has launched a wide range of Programs to help businesses and individuals save energy, thereby reducing energy bills and protecting the climate.

U.S. Environmental Protection Agency

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