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This article is part of the Verdigris series of stories about understanding the environmental impact of print. The Verdigris project is supported by founder members Agfa Graphics, Canon Europe, Digital Dots, drupa, HP, Kodak, Ricoh and Unity Publishing, and associate members EFI, Pragati, and Xeikon.

It has taken a long time, but we are finally beginning to see progress in carbon footprint calculations. Two of the leading press manufacturers are now calculating their carbon footprints accurately and accountably. More importantly they appear to be doing so with some consistency. Heidelberg and HP Indigo each have invested substantial sums into this work, and are using their numbers as the basis for offsetting so that they can deliver carbon neutral presses to their customers.

This work is extremely complex and expensive to do. It requires specialist knowledge and experience with environmental science. Fortunately both Heidelberg and HP Indigo recognise this and are making the necessary human resource investments. For instance, all HP Indigo facilities and Heidelberg manufacturing plants are ISO 14001 accredited. In all industries the need for investment into environmental knowledge can only get more urgent.

But it is especially important in the printing industry where printing companies have been driving carbon footprints steadily lower for many years. Without certified numbers calculated in a consistent fashion for their capital equipment, printers cannot measure the carbon footprint of their businesses or the products they produce. Without consistency in methods and reference data sets, the industry's collective effort is handicapped.

One of the hardest parts of calculating the carbon footprint of print media is the availability and reliability of data. Heidelberg and HP Indigo have each approached the problem from their own perspectives, but have conducted their work following some common principles. Both, for instance, work as much as they can with primary data – data that can be directly collected at the source of the emissions. Both have sourced their secondary data from the EcoInvent database for emissions factors.

Both want to offset all of the carbon footprints of their presses, starting with each machine's Bill of Materials, that is, the raw materials required to build the press. They are both calculating emissions cradle-to-gate, which is supposed to take into account absolutely everything necessary to build a machine. This includes raw materials, freight of raw materials to the factory, sub assemblies, energy, media (paper, plastics and so on) waste generated during manufacture, consumables used in the manufacturing process, freight materials and final press assembly, right up to the point when the press is packed and ready for shipping.

Perhaps the most significant commonality in the approach of Heidelberg and HP Indigo is their use of EcoInvent, the world's leading database of generic Life Cycle Inventory (LCI) data. Now at version 2.2, the EcoInvent data is a list of over 4,000 LCI datasets covering a range of industries, but the bits of interest to the printing industry are energy supply, transport, chemicals, materials, packaging materials, ICT and electronics. The data has been compiled by world-renowned research organisations and consultants. The data belongs to the Swiss Centre for Life Cycle Inventories and is available in the curiously named EcoSpold format. Based on XML, it has become the most widely used and complete format for LCI data exchange.

Purchasing EcoInvent data costs €2,500 (£2,015) for the first year for a single user. The data is available either direct from EcoInvent or through resellers, such as Pré Consultants, the Belgian developers of SimaPro or GABI, a German developer. Both of these companies bundle the EcoInvent licence with their software, which is designed for modelling systems and products from a lifecycle perspective.

The EcoInvent data provides a common reference point for the Heidelberg and HP Indigo studies. This is important because it provides the printing industry as a whole with a common point of origin from which to build up data sets, so over time carbon footprinting studies should become more comparable.

It should be kept in mind, however, that comparison is not recommended by environmental standards boffins, because carbon footprinting is still so very nascent. Comparison is only possible with like-for-like carbon footprinting studies, and rarely are such studies identical in every respect. And differences in any carbon footprinting study mean that the studies should be evaluated independently, rather than in comparison. Carbon footprint values are complex and cannot be treated in the same way as dots per inch or metres per minute.