Many people these days talk about their ambitions to buy carbon offsets to make their business a bit greener. But at least in the voluntary market it is quite nebulous how they made the first step of this process: the calculation of their CO2-emissions.
Many of them simply take the energy-bill from the last year and multiply the kilowatt hours with some emission factors they found in the internet. Of course this sarcastic approach is not on the agenda of every company. Most of them really try to find some guidelines or even standards to carry out their emission calculations properly.
One approach could be the GHG Protocol (http://www.ghgprotocol.org/) which provides descriptive reporting methods and contains also motivational reasons for GHG reporting. Another similar document is the standard ISO 14064 et seqq. which only real difference is the treatment of indirect emissions. Last December ISO, WRI and WBCSD announced a cooperation on the accounting and verification of GHG.
The European Commission (EPLCA) has also recognized the demand for carbon footprint information. A leaflet was issued in late 2007 which clearly indicates that “a carbon footprint is a life cycle assessment with the analysis limited to emissions that have an effect on climate change”. (http://lca.jrc.ec.europa.eu/) According to this the carbon footprint is a sub-set of the data covered by the Life Cycle Assessmet (LCA) with the standardized methods from ISO 14040 et seqq. .
All documents adress the important methodological questions such as completeness, accuracy, system boundaries and the robustness of the indicators. One of the most important questions is, if the individual calculation reflects all life-cycle impacts of services or goods used. If not the findings could be misconceived.