There are two established methods for calculating carbon footprints.
The hybrid model uses the best of both, and a bit like a hybrid car has a much better performance.
This required a massive upfront investment in understanding the inputs and outputs for the entire economy. However having carried out this initial work then the carbon footprint for any process can be quickly established as soon at the items involved have been classified.
There is usually a boundary problem of trying to work out what is in the carbon footprint and what is not. Unfortunately this ability to define the boundary makes process based carbon footprints difficult to compare, and two identical products will have different carbon footprints depending on how the boundary is defined.
Having determined the boundary then the next challenge is finding all the inputs and outputs for the product. This is done on a one off basis for each product, and the effort can be surprisingly large.
The next stage is to find out the impact of all the inputs and outputs in the process. This means going downstream and repeating the process for each of the inputs untill all the significant inputs have been measured.
PAS 2050 is a process based model of carbon footprinting and the draft for a new ISO standard. The carbon trust and leading retailers such as Tesco have been trying to get their suppliers to calculate carbon footprints using PAS 2050, because of the lack of downstream footprint data carbon footprints calculated in this manner have normally cost 100's of thousands of pounds and this has brought the initiative to a standstill.
In the meantime the NHS has calculated its entire carbon footprint using input output models. The 2004 results were published in 2008 to give an idea of the scale of the task. This work has been combined with @UK PLC work on using artificial intelligence to understand raw product data. @UK PLC have now analysed over £ 100 billion of spend, and 3.6 million commonly purchased products.
Putting the two parts together means that @UK PLC now have the carbon footprints to over 3.6 million products.
This now makes carbon foot printing more accurate and affordable, and @UK PLC now have over 3.6 million level 0 carbon footprints.