Editor's commentsThe report published by the National Research Council of USA in 2010 on "Verifying Greenhouse Gas Emissions" is reviewing the methods currently used to calculate Greenhouse Gas Emissions by countries. The report is very useful to help us understand the accuracy and limitation of each method.

Under the UNFCCC, countries are required to inventory the human activities that cause greenhouse gas emissions. Uncertainties in the self-reported national inventories depend on the data and methods used to create them, which depend on each country's institutional and technical capabilities. Uncertainties for the net CO2 emissions from agriculture, forestry, and other land uses and from all sectors can be less than 25% in some countries and greater than 100% in others.
The second method, called tracer-transport inversion, is based on atmospheric and/or oceanic measurements of the gases and mathematical models of air and water flow. The method estimates the net sum of anthropogenic and natural sources and sinks. Uncertainties are less than 10% for the net global CO2 flux to the atmosphere, but greater than 100% for anthropogenic CO2 fluxes at national scales.
The third method using information on land cover. It can be used to estimate emissions from both natural sources and land-use activities, such as agriculture and forestry. The information from satellite imagery is converted into estimates of emissions using biogeochemical models. Satellite imagery is particularly useful for constraining forestry activities and can be used to determine the area of deforestation and forest degradation. The total annual change in forest area has an uncertainty of 10 to 25% in northern forests and up to 100% in tropical forests. Uncertainties in emissions from deforestation, reforestation, and forest degradation are high ranging from 25 to 100% because of uncertainties in parameters used to translate deforested area into CO2 emissions.

Figure : The Global carbon cycle and changes (source : Le Que're', International Geosphere-Biosphere Programme/Global Carbon Project, 2009)

source : Verifying Greenhouse Gas Emissions- National Research Council