The Earth has a natural greenhouse effect due to trace amounts of water vapour (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the atmosphere. These gases let the solar radiation reach the Earth’s surface, but they absorb infrared radiation emitted by the Earth and thereby lead to the heating of the surface of the planet. One needs to distinguish between the natural greenhouse effect and the enhanced greenhouse effect. The natural greenhouse effect is caused by the natural amounts of greenhouse gases, and is vital to life. In the absence of the natural greenhouse effect the surface of the Earth would be approximately 33 degrees Celsius cooler. The enhanced greenhouse effect refers to the additional radiative forcing resulting from increased concentrations of greenhouse gases induced by human activities. The main greenhouse gases whose concentrations are rising are carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and ozone in the lower atmosphere.
The Global Atmosephere Watch (GAW) observes, analyses and publishes greenhouse gas data collected by fifty countries around the globe from the High Arctic to the South Pole. The greenhouse gases monitored include:
- Carbon Dioxide (CO2) (incl. Δ14C, δ13C and δ18O in CO2, and O2/N2 Ratios)
- Methane (CH4)
- Nitrous Oxide (N2O)
- Halocarbons and SF6
- Molecular Hydrogen (H2)
The data are collected and distributed by the World Data Centre for Greenhouse Gases (WDCGG) at the Japan Meteorological Agency. The GAW Scientific Advisory Group for Greenhouse Gases (SAG-GHG) advises on the programme development. GAW issues the annual Greenhouse Gas Bulletin, which reports on the latest trends and atmospheric burdens of the most influential, long-lived greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as a summary of the contributions of the lesser gases.