Carbon Emission

Caption Ford Factory at Sunset Image ID: JS005355 Photographer: Joseph Sohm Date Photographed: ca. 1992 Image or Work Type: Color photography Location Information: Cleveland, Ohio, USA Credit Line: CORBIS/Joseph Sohm; ChromoSohm Inc. The Cleveland Ford Factory is silhouletted against the sky at sunset. Ohio. Corbis UK Ltd. Photograph: Joseph Sohm/Corbis

What are carbon emissions?

Carbon emissions usually refer to the man-made production of a series of gases that accumulate in the atmosphere and help to warm it. Strictly speaking, not all of these so-called greenhouse gases contain carbon so some – including New York Times journalist Andrew Revkin – have labelled the phrase misleading. Some use the phrase as shorthand for emissions of carbon dioxide, which is the most important greenhouse gas produced. Often the emissions of other greenhouse gases are measured by converting them to the equivalent quantity of carbon dioxide needed to produce a similar warming effect – denoted as CO2[eq].

Why do they matter?

They trap heat sent from the Earth's surface in a physical trick discovered by Svante Arrhenius in 1896 known as the greenhouse effect. Sunlight, either direct from the sun or reflected back from shiny parts of the Earth, can pass straight through. But sunlight absorbed by the Earth and then re-emitted as thermal energy – such as from a tarmac road on a sunny day – is absorbed. As carbon emissions build up in the atmosphere, so the amount of heat they trap and send back to the surface increases. This steadily increases the temperature of the Earth's surface and drives global warming.

Where do they come from?

Mostly from energy use: fossil fuels such as oil, gas and coal have driven the world's economies since the industrial revolution and have released carbon emissions in the process. Almost all aspects of our lifestyles rely on access to cheap energy – from transport to central heating, which, in turn, rely on fossil fuels. Energy-intensive industries such as steel and cement have particularly high carbon emissions. Besides energy use, activities such as agriculture produce greenhouse gas emissions, either directly through changes in land-use or indirectly from fertilisers.

How much is produced?

About 26 billion tons of carbon dioxide every year, and rising. World emissions have increased sharply since 2000 mainly driven by the coal-driven economic boom in China. Carbon emissions are closely tied to GDP, so as the economy grows, so do emissions. The 2008/9 recession may reduce emissions slightly, but is not expected to have a significant impact in the long term.

Can they be reduced?

Only by the world using less energy, or making the switch to renewable energy such as wind power, which does not produce carbon pollution. Both are proving hard. Demand for energy is expected to soar over the next few decades and efforts to develop and introduce renewable alternatives are patchy at best. Another possible solution is to trap emissions underground, but the technology required is unproven on a large scale.

What about the Kyoto Protocol?

The 1997 Kyoto agreement is the world's only attempt to regulate carbon emissions. It set targets for rich countries, who collectively were supposed to reduce emissions by about 5%. While some countries such as Britain are likely to meet their 2012 target, many are way over budget. The US famously refused to participate in Kyoto, which significantly weakened its impact. The first phase of Kyoto expires in 2012, and the world is still trying to agree a successor.

What about carbon trading?

Carbon trading allows companies and rich countries to claim reductions in their emissions by paying others to make the required cuts. Supporters say it helps find the cheapest, quickest way to reduce overall pollution, but carbon trading has been criticised as flawed and open to abuse. The environmentalist James Lovelock has referred to the European Carbon Trading Scheme as a "scam".

Is there a limit to how much we should produce?

Scientists say the world can only burn a total of about a trillion tonness of carbon if we want to limit global warming to a 2C rise above pre-industrial levels. About half of this has already been used, and at current rates, we will burn the remaining half a trillion tonnes inside 40 years.

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