What do ‘carbon neutral’ and ‘carbon footprint’ mean?

Many activities in people's daily lives lead to an increase in greenhouse gases in the atmosphere. Either directly, like flying, or indirectly, such as the energy it takes to produce products that we buy. Greater public consciousness about the problem has led to people making efforts to avoid or minimise the flow of these gases, such as carbon dioxide, methane and nitrous oxide, into the atmosphere.

A carbon 'footprint' is a way of describing what amount of greenhouse gases were added to the atmosphere as a result of some activity, as measured in the equivalent amount of carbon dioxide (CO2e). For example, the carbon footprint of someone who drives a petrol-fuelled car to work will be larger than for someone who uses a bus to travel the same distance, because the car driver is responsible for more CO2e emissions than the bus commuter.

A carbon neutral activity is one that has a carbon footprint of zero. Some activities which produce a lot of greenhouse gases are sometimes linked to others which reduce the levels of greenhouse gases in the atmosphere, such as switching land over to growing trees. This is known as carbon offsetting, and is one way activities or products can be presented as 'carbon neutral'.

In some cases, an activity's carbon footprint includes all of the emissions produced in its life cycle. This is known as Life Cycle Analysis. 

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Auckland motorway (Gavin Fisher)