While the concept of ‘joint implementation’ of greenhouse gas (GHG) emission reduction projects (also called "carbon offset projects") was launched at the United Nations Conference on Environment and Development (UNCED, “the Earth Summit”), the early carbon offset projects of the 1990s suffered from a lack of specialised services to support them. One service of particular importance is that of independent verification of carbon offsets, as offsets are dependent on proving a shift of behaviour in relation to a baseline (this shift is referred as "additionality", in the sector).