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Environment: treading lightly on the Earth
Environment: treading lightly on the Earth

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1 What is the carbon footprint, and why is it important?

The carbon footprint is the annual amount of greenhouse gas emissions, mainly carbon dioxide, that result from the activities of an individual or a group of people, especially from their use of energy and transport and consumption of food, goods and services. It’s measured as the mass, in kilograms or tonnes per year, either of carbon dioxide (CO2) emissions alone, or of CO2 plus the mass of other greenhouse gas (GHG) emissions converted into their carbon dioxide equivalent (CO2e) global warming effect.

The carbon footprint can also be calculated for an event such as a music festival, or for making and distributing a product such as a car or computer.

The carbon footprint is an environmental indicator – a way of measuring impacts on the environment, in this case mainly climate change. This means that the carbon footprint doesn’t measure other impacts, except sometimes indirectly. For example, driving a petrol or diesel car, as well as emitting CO2, results in air pollution from nitrogen oxides (NOX), especially the irritant gas nitrogen dioxide (NO2) and other engine emissions; so the larger your carbon footprint from driving, the more air pollution you are creating.

There are many other environmental indicators that measure different impacts, including air and water pollution, loss of landscapes and biodiversity, and depletion of mineral and water resources. The UK Government, the European Union (EU) and the United Nations publish sets of ‘sustainable development indicators’ which – as well as measures such as economic growth, life expectancy and levels of inequality for different countries – include environmental indicators such as wildlife populations, pollution levels, recycling rates and annual GHG emissions. Another often used environmental indicator is the ecological footprint, which is based on the availability of land and sea to support a population (see Box 1).

Box 1 The ecological footprint

The ecological footprint (EF) is a measure of the environmental impact of a population (e.g. a household, city or nation) based on the area of land and sea theoretically required to indefinitely support its lifestyle at a given level of technology.

The ecological footprint measures the area of land and sea required to produce the population’s food and accommodate its roads, buildings, etc., as well as the forested area required to absorb the population’s CO2 emissions. So the EF measures the carbon footprint component of a population’s environmental impact using land and sea area. Sometimes 10% land area is added to the ecological footprint for biodiversity conservation. The EF is the indicator used to show that about three planet Earths would be needed if everyone in the world tried to live the current lifestyle of an average European in the long term, which is clearly unsustainable.