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Last Updated: Sunday, 3 June 2007, 18:36 GMT 19:36 UK
Quick guide: Carbon footprints
Economic development in much of the world has entailed burning fossil fuels on an industrial scale.

This has produced more carbon dioxide (CO2) emissions, a key contributor towards climate change, and added to our carbon footprint.

What is CO2's role in climate change?

Quick guides are concise explanations of topics or issues in the news.

CO2, one of several greenhouse gases, is released into the atmosphere when fossil fuels - our main source of energy - are burned.

Fossil fuels are made of organic materials over millions of years, and include crude oil, coal and natural gas.

Mankind's use of these fuels has been blamed for the increased concentration of CO2 in the earth's atmosphere.

Scientific evidence suggests that unless we dramatically reduce our greenhouse gas emissions we could face irreversibly damaging climate change.

What does the term carbon footprint mean and can it be measured?

There is no one way to measure a carbon footprint.

But at its most comprehensive, a carbon footprint denotes the total amount of CO2 emitted throughout a process or in a product's lifetime - from sourcing raw materials, to production, delivery, consumption and disposal.

Industries such as car production have a carbon footprint, but so do many aspects of everyday life - such as watching TV.

Often only emissions from part of the supply-chain are accounted for.

For example, the carbon footprint of a T-shirt might be defined as emissions used for UK distribution.

But if the whole process - from growing cotton in India, to mass production in China and delivery to UK retailers - is included, the footprint rises significantly.

What are some of the ways to reduce our carbon footprint?

Carbon offsetting is one of the most commonly used ways to achieve this. Put simply, one party pays for someone else to reduce their emissions.

For each tonne of CO2 emitted, an equivalent tonne is theoretically removed elsewhere, for example by using energy efficient light bulbs.

What matters is the reduction, regardless of location.

Firms, government and consumers can all offset emissions. Offsetting flights has become popular among consumers, at relatively little cost.

What do the terms carbon neutral and zero carbon mean?

Increasingly firms are using the term "carbon neutral" to imply that the damage done by CO2 emissions has been entirely mitigated, by dint of some equivalent action.

"Zero-carbon" implies something that does not emit CO2.

The UK government has defined the zero-carbon house as a property with "zero net emissions of carbon dioxide from all energy use in the home".

But its definition does not include transport, materials or demolition costs.

Recently a UK village, Ashton Hayes, said it would aim to be the first carbon neutral village in England.

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How do we know which schemes genuinely reduce emissions long term?

We don't. In January 2007, the UK government announced plans to set standards for carbon offsetting, following a lack of transparency and inconsistent prices.

Verifying whether offsetting schemes work is another hurdle.

Planting trees was one of the earliest forms of offsetting, but has been criticised for its short term benefits. CO2 is released both when trees die and when they are planted.

As for corporate claims about products or services being carbon neutral, there is no consistency as to how they plan to achieve this.

Calculating the exact emissions for any single item - from its inception to finalisation - is nigh-impossible, let alone an equivalent.

BSI British Standards, Carbon Trust, and the UK government are working together to define a standard for measuring greenhouse gas emissions (including CO2) across a number of products and services.

Why all the attention on reducing CO2 emissions?

Carbon emissions
Industrialisation has involved burning fossil fuels

CO2 released over the past century has soared, increasing 10-fold between the years 1900 and 2000, and rising even more dramatically in the last 50 years.

The Intergovernmental Panel on Climate Change (IPCC) has forecast that if greenhouse gas emissions (including CO2) keep rising, temperatures could increase between 1.4C and 5.8C by 2100.

If the CO2 from burning fossil fuels is so environmentally damaging, why can't we switch our energy?

If only it were that simple.

No single energy source can meet our needs based on our current economic and social model using existing infrastructure, while also being low in carbon dioxide emissions.

Going carbon neutral is an appealing idea - but given the complexity of the problem, it is far easier said than done.

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