The underlying question of the Carbon-CAP project was to assess whether a consumption based carbon accounting and associated climate policy could have an added value to the existing production based approach as a means to reduce greenhouse gas emissions. A production based approach requires a geographically identified system. A consumption oriented approach requires something different: a functional, cradle-to-grave or “footprint” approach, usually including processes in different geographical areas.

So far, policy has mainly focused on production and nations, and therefore, has used a territorial approach. This is also apparent when looking at greenhouse gas emission databases: they are organised by country and by activity. A consumption based approach needs something different. A consumption based approach should have the following features:

• It is essential that the greenhouse gas emissions are first linked to sectors of production and then to consumption categories such as food, housing, transport, recreation and suchlike. Usually, as many supply chains are international, many national authorities are involved.
• The information base should allow for an analysis of consumption systems that cannot be confined to geographical boundaries.
• The relevant scale lies beyond nations and activities, ranging from the micro-level of consumers and products, via the national level where some policies are implemented, up to the global level where products are traded and the (climate change) impacts take place.
• The data quality should be sufficient as a base for policy, i.e. it should not put policy on the wrong foot and the margins of uncertainty should not be so large that results are meaningless. As consumption based accounting and modelling is relatively new, this is probably a major issue.
• Data for the past can also be used to assess hotspots and identify the most important consumption categories, setting priorities for policy.

On this basis, the project reviewed the following approaches and the results are presented in the table below.

The conclusion was that for assessing the past and the present, environmentally extended Input-Output (IO) analysis, possibly hybridized with Life Cycle Assessment, seems the best approach. This enables assessments at the micro- as well as the macro-level. Chains can be traced back to the point of extraction and hotspots can be identified. Burden shifting to other locations, and in theory also to other impact categories, can be detected. Other approaches miss essential elements.

The disadvantage of the approach is that significant work must be done on the integration of the process based life-cycle inventories with the macro IO tables. As such, only for product groups containing highly divergent products in terms of embodied carbon content is integration suitable