Greenhouse gases are molecules that absorb infrared radiation (heat energy) and radiate it back to Earth, warming the atmosphere. Scientists agree that increasing concentrations of greenhouse gases in the atmosphere will lead to global warming, with harmful effects on human-built environments and natural systems. The relative impact of each type of greenhouse gas depends on its chemical nature, concentration in the atmosphere and ability to absorb and radiate infrared radiation. These factors determine a greenhouse gas’s “radiative forcing”—the effect it has on the amount of solar radiation impinging upon Earth.
The scientific community has identified carbon dioxide as the main contributor to warming, and it is also the most abundant greenhouse gas in the atmosphere. Other important gases are methane, nitrous oxide, hydrochlorofluorocarbons (HCFC), and perfluorocarbons and sulfur hexafluoride (PFCS).
Emissions of these gases are based on human activities that burn fossil fuels, produce agricultural products from land and sea, and operate machinery. Greenhouse gas emissions vary from year to year, partly because of the economic cycle and the price of fuel.
WMO maintains a global greenhouse gas monitoring network called the Greenhouse Gas Reference Network and a database of atmospheric concentrations of long-lived greenhouse gases, CarbonTracker. The network monitors the sources and sinks of carbon dioxide, methane, nitrous oxide and other anthropogenic greenhouse gases in the world’s air.
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