Measuring global warming impact: carbon footprint

Measuring global warming impact: carbon footprint

How can I calculate my footprint?

A carbon footprint is the measure of the total set of greenhouse gas (GHG) emissions caused directly and indirectly by an individual, organisation, event or product; measured as ‘CO2 equivalent’
(UK Carbon Trust, 2008)

Typically a carbon footprint is calculated to manage the footprint and reduce emissions over time and to report the footprint accurately.

From an engineering standpoint a carbon footprint is calculated to:

  • Compare the footprint of different project options
  • Help drive down the carbon emissions of the chosen option
  • Encourage engineers to propose innovative solutions that mitigate the carbon footprint
  • Assess, benchmark and report carbon emissions of existing and future assets/infrastructure, to assist in project and investment decision making

Basis of calculating the carbon footprint

GHG quantity
is the quantity of GHG emissions. This can be expressed in Kg or m3. Emissions factor is the amount of GHGs emitted, expressed as carbon dioxide equivalent (CO2e) and relative to a unit of activity e.g. kgCO2e/kg. For countries signed up to the United Nations Framework Convention on Climate Change (UNFCCC), national sets of emission factors probably exist. However, for UNFCCC countries where a national set of emission factors does not exist, a specific set of emission factors developed by the Intergovernmental Panel on Climate Change (IPCC) can be used. If not, then the GHG Protocol includes emission factors recognised in all countries worldwide.
CO2e is the unit for comparing the radiative forcing of a GHG to carbon dioxide.

Use whole life carbon and whole life carbon costing

  • For any declared carbon footprint it is essential to know and understand the boundaries that have been assumed, to tell you what has been included and what has been left out. In the UK an industry standard, developed by BSI in 2008, is “PAS 2050:2008 - Specification for the assessment of the life cycle greenhouse gas emissions of goods and services”

  • The methodology used in carbon footprinting is drawn from life cycle analysis (LCA) which defines the boundaries for carbon accounting. LCA measures the environmental impacts of a product or process from 'cradle to grave' - i.e. from the beginning of producing the raw materials through manufacturing and processing to product use and waste

  • Once boundaries are defined the Whole Life Carbon (WLC) can be calculated

  • The WLC is a function of the ‘embodied carbon’ from initial construction and periodic asset maintenance, annual operational carbon and the asset design life

To balance the relative merits of alternative project solutions, the WLC can be converted to the whole life carbon cost (WLCC) by determining the net present value of carbon emissions using the shadow price of carbon (SPC). The SPC captures the damage costs of climate change caused by each additional tonne of GHG emitted.


Further reading

Carbon accounting in the UK Water Industry Guidelines for dealing with Embodied carbon and whole life carbon: UKWIR Report No. 08/CL/01/6
The Greenhouse Gas Protocol Initiative
Intergovernmental Panel on Climate Change, IPCC (2007) Climate Change 2007: Mitigation of Climate Change
IPCC Guidelines for National Greenhouse Gas InventoriesPAS 2050:2008 - Specification for the assessment of the life cycle greenhouse gas emissions of goods and services