Greenhouse gases are substances in the atmosphere that trap heat near Earth’s surface and prevent it from radiating out into space. They are often called ‘climate change gases’, and they include carbon dioxide (CO2), methane, nitrous oxide, and a suite of halogen-bearing chemicals (like chlorine and fluorocarbons). The natural greenhouse effect allows some of the sun’s energy to warm Earth, but if these warming gases were absent then Earth would be significantly cooler than it is now. Human activities have largely contributed to the increase in greenhouse gas levels in our atmosphere.
These gases are long-lived, meaning they stay in the atmosphere for a significant time (decades to centuries) before breaking down via chemical reactions or cycling into the biosphere or ocean. Each one has a characteristic global warming potential relative to CO2—that is, it absorbs and radiates heat more effectively than does CO2. Their concentrations in our atmosphere are also affected by tectonic processes and by natural processes involving soil, wetland, and ocean sources and sinks of the gases.
The GAW program collects and analyzes atmospheric samples from a network of stations around the world to measure concentrations of the main long-lived greenhouse gases, including CO2, methane, and nitrous oxide. The results are published each spring. The data are compiled and distributed by the World Data Centre for Greenhouse Gases (WDCGG) and RAMCES, part of the Integrated Carbon Cycle System, at JMA. The Scientific Advisory Group for Greenhouse Gases advises on the programme development.