On the y-axis it says ‘AGGI (climate warming influence of greenhouse gases, relative to 1990).’ AGGI stands for Annual Greenhouse Gas Index, and is a measure NOAA uses since 2004 to quantify the cumulative atmospheric effect of (elevated) emissions of the various kinds of greenhouse gases – or ‘CO2 equivalents.’

As the measure is relative to 1990, the base year for the Kyoto Protocol and the future new climate treaty under the UNFCCC it offers an easy to understand how GHG climatic forcing has developed.

NOAA says in 2010 the AGGI reached 1.29, which means the combined heating effect has increased by 29 percent in two decades time.

The graph shows how climate forcing grows almost linear with time. Also remarkable is the steadiness, as emissions of various greenhouse gases seem to even out each others plateaus and periods of acceleration.

About the most important gases NOAA concludes the following:

• CO2: “Carbon dioxide levels swing up and down in natural seasonal cycles, but human activities – primarily the burning of coal, oil, and gas for transportation and power – have driven a consistent upward trend in concentration.” [The world is now very close to passing a noteworthy threshold, as the atmospheric CO2 concentration will reach 400 ppm soon – rising from around 280 ppm at the start of the Industrial Revolution. The 2009 CO2 downturn, the 2010 CO2 record and for instance the 2002 coal renaissance are masked within the AGGI graph.]
• Methane: “Methane levels rose in 2010 for the fourth consecutive year after remaining nearly constant for the preceding 10 years, up to 1799 parts per billion. Methane measured 1794 ppb in 2009, and 1714 ppb in 1990.”
• Nitrous oxide: There is a continued steady increase of nitrous oxide (laughing gas) “emitted from natural sources and as a byproduct of agricultural fertilisation, livestock manure, sewage treatment and some industrial processes.”
• CFCs: “There has been a continued recent drop in two chlorofluorocarbons, CFC11 and CFC12: Levels of these two compounds – which are ozone-depleting chemicals in addition to greenhouse gases – have been dropping at about one percent per year since the late 1990s, because of an international agreement, the Montreal Protocol, to protect the ozone layer. [See further CFC climate mitigating potential.]

So, excluding natural climate feedbacks, does the above picture show all antropogenic climate forcing? No – there’s one thing missing: aerosols. Or actually two. The graph excludes climate-cooling sulfur – and climate warming soot, which adds 14.5 percent to the current GHG climate forcing. [When you mix the two kinds of air pollution up, as in the Asian brown cloud, a net aerosols-induced warming effect remains.]

© Rolf Schuttenhelm | www.bitsofscience.org