A carbon footprint is the amount of carbon dioxide (from burning fuels) that is produced from daily activities. It is like a footprint when you step on the ground, except that it is in the atmosphere and our footprints can travel to have effects very far from where they started. The carbon footprint is calculated based on all the activities in a time period, usually one year.
Carbon Offsets
One way people have been trying to reduce the effect of their carbon footprints is by setting off their carbon emissions away through projects that either create few emissions or help to reduce the existing emissions. There are a few types of offset projects: producing renewable energy, making energy use more efficient, destroying sources of pollutants and creating land areas with plants/trees that can absorb carbon in the atmosphere – like you can see in the calculator above!
Large companies often have to buy these offsets to make up for the pollution of their activities. Individuals also have many options of offsets to invest in that help to reduce the carbon they produced in their daily lives and travels. If the total of your activities do not add any extra CO2 into the atmosphere, you are carbon neutral.
Green House Gases (GHGs) and Carbon Dioxide Equivalents (CO2 eq).
Many things we do for industrial and manufacturing processes produce gases that lead the overall temperature of the earth to increase. These are called Green House Gases (GHGs), because they make the earth hotter, the way it feels inside a green house. Normally, these gases help to keep earth at a comfortable temperature. But in the past 100 years, industrial processes, like burning petroleum and cutting down forests, have put too many of these gases into the atmosphere. Each gas each affects the atmosphere and temperature a different amount. To make things simpler, in a carbon footprint, all gases are counted as if they were carbon, counting as much carbon as is equal to that gas.
Importance of Human-produced Greenhouse Gases.
Importance of Human-produced Greenhouse Gases. This diagram shows the relative importance of the major human-produced GHGs to current warming. CO2 is the most important followed in descending order by methane, CFCs, ozone and nitrous oxide.
Source: Koshland-Science-Museum.org

Main human activities that release GHGs (above) and the relative amounts of gases that are released from these activities (below).


Natural and human-caused sources of gases that warm the earth (above). Even though they are only a small part of the whole cycle, the human-caused GHGs have a big influence on the atmosphere.


National carbon dioxide (CO2) emissions per capita. (2005). (Source: UNEP/GRID-Arendal Maps and Graphics Library).
As you can see, the average North American generates about 20 tons of CO2-eq each year, while the rest of the world produces only about 4 tons of CO2-eq per year, on average.
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Things you can do to reduce your carbon footprint: and go more carbon neutral:
Source: DavidSuzuzi.org