The perturbation to radiative climate forcing which has the largest magnitude and the least scientific uncertainty is the forcing related to changes in long-lived and well mixed greenhouse gases, in particular carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and the halocarbons (mainly CFCs).  All of these gases have been monitored around the world since the 1970’s mainly by NOAA’s Climate Monitoring and Diagnostics Laboratory (CMDL), in Boulder, Colorado, and its forerunner, the Geophysical Monitoring for Climatic Change (GMCC) program.  CMDL operates four fully instrumented baseline climate observatories at Pt. Barrow, Alaska; Mauna Loa, Hawaii; American Samoa; and South Pole Station, Antarctica, where the concentrations of the greenhouse gases are measured continuously as well as by air sampling.  In addition, air samples are collected through several global networks, including a cooperative program which provides samples from over 50 global sites.  All air samples are analyzed for gas concentrations and carbon and oxygen isotopic ratios in Boulder.  These data will be presented and analyzed in terms of their changes and the changes in radiative forcing during the 25-year period encompassing 1979 through 2003.  The most notable change in the past several years is an increase in the fraction of the radiative forcing related to carbon dioxide from about 59% to 62%.  This is mainly due to the fact that the radiative forcing by CFCs and CH₄ have declined or grown only slowly in recent years.  The interannual changes in global radiative forcing, especially due to carbon dioxide, are substantial but are generally veiled in the much larger total radiative forcing.  In order to emphasize these interannual changes, which are related to important source/sink processes, we introduce the Annual Greenhouse Gas Index (AGGI), which is the annual change in total radiative forcing (milliwatts per square meter) due to changes in all the major greenhouse gases.  Possible causes of these variations are discussed.