The Azimuth Project
Carbon footprint (Rev #7, changes)

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Definition and calculation

There are several definitions of carbon footprint, some of which disagree slightly.

According to the European Commission:

Carbon footprint is the overall amount of carbon dioxide (CO2) and other greenhouse gas emissions (e.g. methane, laughing gas, etc.) associated with a product. A carbon footprint is a life cycle assessment with the analysis limited to emissions that have an effect on climate change.

The international standards ISO 14040-14044 can be used to calculate a carbon footprint.

According to the UK Carbon Trust

A ‘carbon footprint’ measures the total greenhouse gas emissions caused directly and indirectly by a person, organisation, event or product.

The footprint considers all six of the Kyoto Protocol greenhouse gases: Carbon dioxide (CO 2CO_2), Methane (CH 4CH_4), Nitrous oxide (N2O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs) and Sulphur hexafluoride (SF 6SF_6).

A carbon footprint is measured in tonnes of carbon dioxide equivalent (tCO 2et CO_2e). The carbon dioxide equivalent (CO 2eCO_2e) allows the different greenhouse gases to be compared on a like-for-like basis relative to one unit of CO 2CO_2. CO 2eCO_2e is calculated by multiplying the emissions of each of the six greenhouse gases by its 100 year global warming potential.

A carbon footprint should not be confused with an ecological footprint. Note: the term “carbon footprint” is widely used as shorthand for the amount of anthropogenic greenhouse gas emissions; however, in the ecological footprint methodology, it rather translates the amount of anthropogenic carbon dioxide into the amount of productive land and sea area required to sequester carbon dioxide emissions.

Carbon emission per unit energy

We need information on the CO2 emission per joule of energy for many forms of energy.

For example, A Path To Sustainable Energy lists 70g/kWh for nuclear power, which seems high. As explained on our page about that paper, 4g/kWh comes from Jacobson’s estimate of what a small nuclear war would create! But the first 66g/kWh comes from a paper by Sovacool.

On the Azimuth Forum, David Pollard writes:

To be fair to Sovacool, his paper does provide some explanation as to why the estimates on which the 66 g/kWh headline figure is based vary between 2.82-22 and 10-200. The main differences are in ‘frontend’ costs: mining, milling, conversion, enrichment, fuel fabrication, and transportation which range from 0.58 to 118. Construction costs differ between reactor types and assumed lifetimes, ranging from 0.27 to 35. Overall the estimates of total emission go from 2 to 200.

The name Roberto Dones seems to be associated with careful assessment. Here’s one of his papers for the European Commission which will take a while to digest: Externalities of Energy containing detail of various different environmental costs for energy, heating and cars.

Research from the Paul Scherrer Institute, Life Cycle Assessment looks useful.

This also includes a Critical note on the estimation by Storm van Leeuwen J.W. and Smith P. … which explains why some of the estimates of CO2 lifecycle emissions attributed to nuclear energy may be anomalously high.

We need to track down some of this information and present it here!

Carbon footprint of coal plants

In the 5th wedge of their Stabilization wedges paper, Pacala and Socolow suppose that in 2054 we have coal power plants working at 90% of capacity with an efficiency of 50%. They say that 700 gigawatts worth of coal plants like this emit 1 gigaton of carbon per year.

Carbon footprint of transportation

For US data see:

This says US transportation produced 27% of all US greenhouse gases in 2003, and 1.87 gigatons of CO2 equivalent. This was up from 1.51 gigatons in 1990, an increase of 24 percent. Greenhouse gases from all other sectors increased by a total of 9.5 percent over the same timeframe.

Carbon footprint of livestock

The greenhouse gas emissions produced by raising livestock greatly exceed their carbon footprint due to CO2 emissions, because cattle burp out a lot of methane, and there are also large N2O emissions. See:

Some figures from this report:

  • Fossil fuel in manufacturing fertilizer may emit 41 megatonnes of CO2 per year. (This figure was computed by totalling figures estimated for 11 large countries.)

  • On-farm fossil fuel use may emit 90 megatonnes of CO2 per year.

  • Livestock-related land use changes may emit 2.4 gigatonnes of CO2 per year.

  • Livestock-related releases from cultivated soils may total 28 megatonnes of CO2 per year.

  • Releases from livestock-induced desertification of pastures may total 100 megatonnes of CO2 per year.

  • Respiration by livestock is not a net source of CO2.

  • Methane released from enteric fermentation may total 86 megatonnes per year.

  • Methane released from animal manure may total 18 megatonnes per year.

  • CO2 emissions from livestock processing may total several 10s of megatonnes per year.

  • CO2 emissions from transport of livestock products may total several 0.8 megatonnes per year.

  • Total CO2 emissions from livestock activities are roughly 2.7 gigatonnes per year, or 0.16 gigatonnes per year not counting land use or change in land use.

  • Total CH4 emissions from livestock activities are 2.2 gigatonnes CO2 equivalent per year.

  • Total N2O emissions from livestock activities are also 2.2 gigatonnes CO2 equivalent per year.

  • The grand total of greenhouse gas emissions from livestock activities are roughly 7.1 gigatonnes CO2 equivalent per year, or 4.6 not counting land use or change in land use.

category: carbon