Society’s awareness of the effects of greenhouse gas (GHG) missions has increased markedly in recent decades due to the potential for significant negative global effects on the environment and on people.

Policy and fiscal drivers, as well as stakeholder pressure, encourage the assessment of GHG emissions and the implementation of strategies for their reduction. For example, in the waste sector, the Landfill Directive encourages the diversion of biodegradable municipal waste (BMW) from landfill to avoid GHG emissions. The 2007 review of the national waste strategy sets a reduction target for GHG emissions of 10M tonnes by 2020.

For developers and the regulatory authorities, techniques for calculating the quantity of GHG emissions are increasingly important in demonstrating the sustainability credentials of a project, with the potential to influence procurement decisions, project design and regulatory consents.

Carbon footprint assessment is a tool used to measure the level of GHG emissions generated during the life-cycle of a product or service. Units are usually expressed as grammes of carbon dioxide equivalents (CO2e) which accounts for the different global warming potential (GWP) of different GHG. Carbon assessments can include:

• lifecycle emissions inventory from a single facility or project or a strategic network
• optioneering – comparative assessments of different facilities or networks
• assessing the effect on emissions of alterations or upgrades to facilities and networks
• construction – options for the use of sustainable materials
• technologies/strategies – identifying opportunities to reduce GHG emissions, perhaps as input to a corporate social responsibility (CSR) strategy

The key aspect of carbon footprinting is the definition of robust emission factors and understanding the uncertainty associated with these. A crucial component of the footprinting exercise is to establish the project boundary: the identification of all the potential sources of GHG emissions associated with the project. This is important if the results are to be credible. We have found that the most robust studies are returned by involving project stakeholders at an early stage.

It’s also important that the footprinting methodology takes account of emissions that are avoided or offset by the production or recovery of useful products, so avoiding the need to consume resources that release GHG to atmosphere. Examples include methane emissions avoided by capturing landfill gas for power generation, and the use of recycled aggregate from on-site demolition materials, avoiding the emissions produced in quarrying, processing and transporting virgin materials.

At Mott MacDonald, our track record in carbon assessment means we have developed a keen understanding of the crucial issues involved, supported by the wide-ranging expertise available in house. For example, we are fully conversant with the regulatory background, the implications of distance and mode of transport, and the effects on emissions of waste composition.

Recent project examples have included an analysis of CO2e emissions for Crossrail, a major cross-London rail scheme, carbon footprinting of a proposed wind farm in Scotland, and a CO2 emissions inventory as part of the environmental impact assessment for the Bexhill-Hastings Link Road.