What are greenhouse gases and how do they affect the climate?
The greenhouse gases the United States emitted in 2007 included:1 • Carbon dioxide (82.6%) • Methane (9.6%) • Nitrous oxide (5.3%) • Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (collectively 2.4%) Additionally there are gases that have a positive warming influence but that are not counted in greenhouse gas inventories: • Water vapor is the most abundant greenhouse gas, but our influence on water vapor’s concentration in the atmosphere is thought by scientists to be negligible. • Ozone is also technically a greenhouse gas as it has a positive effect on temperature. However, at higher levels in the atmosphere (stratosphere), where it occurs naturally, it is needed to block harmful UV light. At lower levels of the atmosphere (troposphere) it is harmful to human health and is a pollutant regulated independently of its warming effects. These gases are transparent to incoming solar (short-wave) radiation but block infrared (long-wave) radiation from leaving Ea
The major greenhouse gases the United States emitted as a result of human activity in 2008 (and their share of total emissions) were:1 • Carbon dioxide (82.8%) • Methane (10.5%) • Nitrous oxide (4.3%) • Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (collectively 2.5%) There are other greenhouse gases that are not counted in U.S. or international greenhouse gas inventories: • Water vapor is the most abundant greenhouse gas, but most scientists believe that water vapor produced directly by human activity contributes very little to the amount of water vapor in the atmosphere, and therefore EIA does not estimate emissions of water vapor. Recent research by NASA suggests a stronger impact from the indirect human effects on water vapor concentrations. • Ozone is technically a greenhouse gas because it has an effect on global temperature. However, at higher elevations in the atmosphere (stratosphere), where it occurs naturally, it is needed to block harmful UV li
