Carbon Dioxide
 Carbon dioxide is probably the most important of the greenhouse gases as it accounts for the largest proportion of the 'trace gases' and is currently responsible for 60% of the 'enhanced greenhouse effect'. It is thought that it's been in the atmosphere for over 4 billion of the Earth's 4.6 billion year geological history and in much larger proportions (up to 80%) than today.
Most of the carbon dioxide was removed from the atmosphere as early organisms
evolved photosynthesis. This locked away carbon dioxide as carbonate minerals,
oil shale and coal, and petroleum in the Earth's crust when the organisms
died. This left 0.03% in the atmosphere today.
 Atmospheric
carbon dioxide comes from a number of natural sources, mainly the decay
of plants, volcanic eruptions and as a waste product of animal respiration.
It is removed from the atmosphere by photosynthesis in plants and by
dissolving in water, especially on the surface of oceans. Carbon dioxide stays in the atmosphere for approximately 100 years.
The amount of carbon dioxide taken out of the atmosphere by plants is almost perfectly balanced with the amount put back into the atmosphere by respiration and decay. Small changes as a result of human activities can have a large impact on this delicate balance.
 Burning
fossil fuels releases the carbon dioxide stored millions of years ago.
We use fossil fuels to run vehicles (petrol, diesel and kerosene), heat
homes, businesses and power factories. Deforestation releases the carbon
stored in trees and also results in less carbon dioxide being removed
from the atmosphere.
The concentration of carbon dioxide in the atmosphere has increased more in the northern hemisphere where more fossil fuel burning occurs. Since the Industrial Revolution the concentration globally has increased by about 40%.
Greenhouse gases:
Methane
Nitrous oxide
Ozone
Water vapour
Halocarbons
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