Carbon is the chemical element on which all forms of life on Earth are based. Carbon dioxide is the colourless, odorless gas that is released by respiration of living things and decay of dead things.
Although we talk about CO2 in the atmosphere, we tend to talk about carbon in trees (roughly 25% of a tree's biomass is carbon). In greenhouse gas terms, one tonne of carbon has the same effect as 3.67 tonnes of CO2. Care should be taken in conversations about carbon footprints over whether one is talking about carbon or CO2.
When talking about greenhouse gas emissions, the convention is to use CO2, or more specifically CO2 equivalent (CO2e). This allows us to describe the warming potential of any greenhouse gas in terms of the equivalent atmospheric warming effect of CO2, effectively a common currency.
For example, one tonne of methane released into the atmosphere has the same impact on the climate as 23 tonnes of CO2, whereas nitrous oxide is 296 times more potent than CO2.
A real nasty, such as sulphur hexafluoride -- used in the manufacture of electrical systems -- has 22,200 times the global warming potential of carbon dioxide!
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