Greenhouse gases (GHGs) are chemicals that absorb and radiate energy, causing the atmosphere to warm. Small changes in atmospheric concentrations of these gases can have large impacts on Earth’s climate. Human activities are dramatically increasing the amount of greenhouse gases in the atmosphere, causing global warming.

Carbon dioxide (CO2) is the most important of the long-lived greenhouse gases, but there are many other pollutants contributing to the warming. Some, such as methane (CH4) and nitrous oxide (N2O) are produced both naturally and by humans, while others such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and perfluorocarbons (PFCs) are entirely manmade. Human activities increase the atmospheric levels of these gases by burning fossil fuels, clearing forests, and producing agricultural products.

Despite their comparatively low global warming potentials (GWP), the increase in the atmospheric concentrations of these gases is largely responsible for current levels of global warming. Together with water vapour, they make up the bulk of the total radiative forcing due to human activities.

Levels of these three most important human-caused greenhouse gases continued to climb in 2023, and they are now higher than the pre-industrial level. The rising levels of these gases are driving global temperature rises, which can have significant impacts on oceans, polar regions, and terrestrial ecosystems.

To measure the levels of these gases, NOAA scientists use satellite, airborne, and surface networks that collect data over a wide range of time and locations. In addition, these instruments need to be able to operate in challenging conditions such as cloudy skies. The US GHG Center brings together observations and models to provide a single source of trusted greenhouse gas information for U.S. government decision makers.