The footprint data on electricity generated by nuclear power. Before 2008, nuclear power was treated as equivalent, per kilowatt, to the world average footprint of fossil-fuel derived electricity. As of the 2008 edition, this footprint component is no longer included in national calculations and is calculated separately. This does not mean that the use of nuclear energy is free of risk or demands on the environment, only that these risks and demands are not easily expressed in terms of biocapacity.