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Gwen Shlam

This question and answer is part of the Guardian's ultimate climate change FAQ

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"Carbon" is shorthand for greenhouse gas emissions, including CO2, methane, nitrous oxide and F-gases. These gases are released by many different types of activity ? not just the burning of fossil fuels, but also farming, deforestation and some industrial processes.

Global emissions can be allocated to human activities in various ways. One of the most granular analyses is this one from the World Resources Institute (WRI), which breaks down total global emissions from 2005 into the following headline sectors:

Energy
?�Electricity & heat (24.9%)
?�Industry (14.7%)
? Transportation (14.3%)
?�Other fuel combustion (8.6%)
?�Fugitive emissions (4%)
Agriculture (13.8%)
Land use change (12.2%)
Industrial processes (4.3%)
Waste (3.2%)

These sectors are then assigned to various end uses, giving the following results (nicely visualised here):

Road transport (10.5%)
Air transport (excluding additional warming impacts) (1.7% )
Other transport (2.5%)
Fuel and power for residential buildings (10.2%)
Fuel and power for commercial buildings (6.3%)
Unallocated fuel combustion (3.8%)
Iron and steel production (4%)
Aluminium and non-ferrous metals production (1.2%)
Machinery production (1%)
Pulp, paper and printing (1.1%)
Food and tobacco industries (1.0%)
Chemicals production (4.1%)
Cement production (5.0%)
Other industry (7.0%)
Transmission and distribution losses (2.2%)
Coal mining (1.3%)
Oil and gas production (6.4%)
Deforestation (11.3%)
Reforestation (-0.4%)
Harvest and land management (1.3%)
Agricultural energy use (1.4%)
Agricultural soils (5.2%)
Livestock and manure (5.4%)
Rice cultivation (1.5%)
Other cultivation (1.7%)
Landfill of waste (1.7%)
Wastewater and other waste (1.5%)

It should be stressed that there is a fair degree of uncertainty about the precise contribution of some activities, especially those which include biological processes such as land use change and agriculture. Indeed, the total contribution from deforestation is much lower in the data above than it was in the equivalent figures from 2000, due to a change in the underlying methodology ? as described in the WRI's accompanying paper (pdf).

The other point to note is that emissions levels are permanently changing. Total global emissions are significantly higher now than they were in 2005, and the ratios between sectors will also have changed. But global datasets take a long time to compile, hence there is usually a multi-year lag before reliable figures are published.

The numbers provided above are broadly consistent with the 2004 data published in the latest UN IPCC report.