Greenhouse gases are molecules in Earth’s atmosphere that trap some of the heat radiating from the surface of our planet and prevent it from being radiated into space. These include carbon dioxide (CO2), water vapor, methane, nitrous oxide and a suite of halogen-bearing gases, like chlorofluorocarbons. Some are naturally-produced, but human activities since the Industrial Revolution have caused a steady increase in atmospheric concentrations of these long-lived greenhouse gases.

The Global Atmosphere Watch, or GAW, program conducts surface and airborne measurement and analysis to monitor long-lived greenhouse gas concentrations. In 2022, NOAA collected and analyzed air samples from sites in the international GAW network, including more than 50 cooperative sampling stations around the world. The data are compiled and reported each spring to the public.

NOAA focuses on the three primary long-term drivers of climate change: CO2, methane and nitrous oxide. These are the three greenhouse gases with the largest anthropogenic global warming potential, based on their capacity to warm the planet by reflecting and absorbing some of the solar radiation that reaches Earth.

The concentration of each greenhouse gas is measured in parts per million. The graph below shows the historical accumulation of these gases in the atmosphere since the beginning of the Industrial Revolution, and how they compare to pre-industrial values. The bars represent the annual average concentrations of each gas in ppm of air. Whiskers on each bar represent the possible error range of the measurement.