Green House Gas Emissions

Measurements from Antarctic ice cores show that before industrial emissions started, atmospheric CO₂ levels were about 280 parts per million by volume (ppmv), and it appears that concentrations stayed between 260 and 280 during the preceding ten thousand years.[29] One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide levels above 300 ppm during the period seven to ten thousand years ago[30], though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO₂ variability.[31][32] Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.

The seven sources of CO₂ from fossil fuel combustion are (with percentage contributions for 2000–2004)

1. Solid fuels (e.g. coal): 35%	2. Liquid fuels (e.g. gasoline): 36%
3. Gaseous fuels (e.g. natural gas): 20%	4. Flaring gas industrially and at wells: <1%
5. Cement production: 3%