Carbon footprints: National emissions
There are several different methods of determining the national emissions of different countries, including the total amount emitted by a nation, the ‘per capita’ amount emitted for each of its citizens, and the cumulative amount the nation has emitted over the entire historical period. Each approach gives different insights. However, calculating the comparative carbon footprints of different countries isn’t straightforward, and different methods can give conflicting results.
There are a number of ways in which greenhouse gas emissions from a country can be calculated. Perhaps the most straightforward of these is calculating the current total emissions from each country. In 2006, according to this method, China emitted the largest quantity of greenhouse gases: 6206 megatonnes (Mt) of carbon dioxide equivalent. The second largest emitter was the USA (5770 Mt), and the UK came in ninth with emissions of 545.4 Mt. While this method can be a useful way of seeing the total emissions for each country, it doesn’t take into account levels of population or whether these emissions are related to products or goods being consumed by other countries.
One method of calculating a country’s greenhouse gas emissions is by considering the ‘per capita’ emissions for each citizen. This is done by taking the total amount of greenhouse gases produced by a country in a year and dividing it by the country’s population. This effectively expresses the average citizen’s personal carbon footprint. In 2006 the country ranked highest on per capita emissions was Qatar at 46 tonnes of carbon dioxide equivalent per capita. According to this method, the US has higher emissions than China, with US per capita emissions standing at 19.3 tonnes of carbon dioxide equivalent per capita to China’s 4.7 tonnes. This means that the average US citizen is responsible for the same amount of emissions as 4–6 Chinese citizens.
Because carbon dioxide accumulates in the atmosphere – remaining for over 100 years on average – emissions from decades past can continue to have an impact on the climate. One method of calculating a country’s emissions aims to take this into account by including the cumulative historical emissions of each country. This involves adding up all the carbon dioxide emitted since 1850. According to this method, the US has the highest total emissions, having put over 333,000 megatonnes (Mt) of carbon dioxide equivalent into the atmosphere since 1850. The cumulative emissions of the European Union are in second place with 305,000 Mt since 1850. China is third with 99,000 Mt. The UK on its own comes sixth in the world with 68,000 Mt.
In 2008 the UK’s greenhouse gas emissions were calculated to be 627.6 megatonnes of carbon dioxide equivalent. Examining the sources of these emissions shows that 35% originated from energy production, with the vast majority of this coming from coal- and gas-fired power generation. A further 21% of the UK’s emissions came from transport, mostly from passenger cars. Business and industry accounted for 15% of UK emissions in 2008 and 13% came from activities in residential buildings, primarily the use of natural gas for heating. Agriculture contributed 7% to national emissions, with a quarter of this amount resulting from methane emissions produced by cattle. Of the remainder, most came from waste (3%) and industrial processes (2%).