Carbon Dioxide (CO2) is a natural atmospheric gas that contributes to the greenhouse effect. The proportion of CO2 in the atmosphere is known to vary, but recently the concentrations of carbon dioxide have risen rapidly. This is mostly attributed to anthropomorphic internal forcing, i.e. the effects of man-made pollution, although CO2 can come from a variety of natural sources too.
Since 1958 precise measurements of carbon dioxide levels have been taken at the Mauna Loa observatory on Hawaii. These measurements show an increase from 315 ppm by volume (parts per million) to about 380 ppm today, which is an increase of approximately 20 per cent in only 50 years.
Below is a pie chart detailing the sectors that contribute the most to anthropomorphic carbon dioxide emissions. CO2 makes up approximately 72% of the total greenhouse gases emitted, so it is important to understand where the emissions are coming from.
Source: Smithson et al, 2008, Fundamentals of the Physical Environment, Routledge.