Putting Greenhouse Gases In Your Face

DBCCA, the know-the-number host, discusses their expression of the relationship between ppm, CO2e, and metric tonnage: "Greenhouse gas concentrations are frequently expressed as an equivalent amount of Carbon Dioxide (CO2). This CO2-equivalent concentration in parts per million (ppm) can then be expressed in terms of metric ton of CO2, a standard of measurement, which as a stock of gases in the atmosphere is readily understood. According to the IPCC AR4 Synthesis Report, atmospheric CO2 concentrations were 379 ppm in 2005. The estimate of total CO2-eq concentration in 2005 for all long-lived GHGs is about 455ppm. On June 18th as the counter started, long-lived GHGs in the atmosphere were estimated to be 3.64 trillion metric tons, growing at 2 billion metric tons per month, or 467 ppm, of which CO2 was 385 ppm." http://www.dbcca.com/dbcca/EN/carbon-counter.jsp

Which isn't a ready translator, but a sort of an understanding.

A good carbon-equivalent number is a trick I can't perform, what with the various gases have different global warming potentials, different atmospheric lifetimes, and individually fluctuating concentrations. ORNL's Carbon Dioxide Information Analysis Center has a chart from December '08 (and may have newer data somewhere else that I didn't turn up) showing atmospheric concentrations of various greenhouse gases in ppm, ppb, and ppt - http://cdiac.ornl.gov/pns/current_ghg.html - CO2 (by itself, not as an equivalency expression) was at 383.9 at the time; 350.org reports it as 387 currently; as noted above, know-the-number has it at 385.