Global warming is primarily a problem of too much carbon dioxide in the atmosphere. This carbon overload is caused mainly when we burn fossil fuels like coal, oil and gas or cut down and burn forests. There are many heat-trapping gases (from methane to water vapor), but carbon dioxide (CO2) puts us at the greatest risk of irreversible changes if it continues to accumulate unabated in the atmosphere.
CO2, more than any other climate driver, has contributed the most to climate change between 1750 and 2005. CO2 has the highest positive radiative forcing (RF) (see Figure) of all the human influenced climate drivers compared by the IPCC. Other gases have more potent heat-trapping ability molecule per molecule than CO2 (e.g. methane), but are simply far less abundant in the atmosphere and being added more slowly. Read more