CO₂, Natural & Anthropogenic

As any basic chemistry book will tell you, CO₂ is an odourless, colourless gas.  The compound itself consists of a carbon atom and two oxygen atoms, but I’m not here to give you a chemistry lesson and I am quietly confident that this is incredibly familiar information.  But where does the CO₂ in the atmosphere come from?  Sources of atmospheric carbon dioxide can be categorised as either natural or anthropogenic.  Even a basic illustration of the carbon cycle can highlight this nicely.



http://www.wpclipart.com/space/solar_system/Earth/ecology/carbon_cycle_NOAA.jpg.html

As you can see there are a number of sources of atmospheric CO₂ including plant and animal respiration, organic decomposition , volcanic outgassing/eruption as well as anthropogenic sources, namely via combustion of fossil fuels.



http://www.ipcc.ch/activities/activities.shtml 

According to the most recent report from the Intergovernmental Panel on Climate Change (IPCC), The Fifth Assessment Report (AR5), which was released between September 2013 and November 2014 (http://www.ipcc.ch/activities/activities.shtml).  2011 saw CO₂ levels reach 390.5ppm which represents a 40% increase from the levels of 1750, which the IPCC AR5 reports to of been 278ppm.

Just as a point of interest, the AR5 also states that during the same time interval there were also increases in Methane (CH₄) and Nitrous oxide (N₂O) levels.  The report also states that levels of all three (CO₂, CH₄ and N₂O) exceeded any levels measured for the past 800,000 years (http://www.ipcc.ch/report/ar5/wg1/  [Chapter 6, page 467]). 

Furthermore, the AR5 states that ice cores show that atmospheric CO₂ levels for the last 7000 years preceding 1750 saw slow increases from 260ppm to 280ppm.  But CO₂ levels have also seen fluctuations from 180ppm during glacial periods over the past 800,000 years up to 300ppm during interglacial periods (http://www.ipcc.ch/report/ar5/wg1/  [Chapter 6, page 468]).