What Are Emission Conversion Factors? 

Emission conversion factors, also known as “emission factors”, are numerical values used to convert quantities of one unit into another. In the context of carbon emissions, these factors translate various activities, such as energy consumption or transportation, into an equivalent amount of carbon dioxide (CO₂) emissions.  

Let’s say you want to calculate the emissions associated with a 200 km train journey. Conveniently for us, the Department for Environment, Food & Rural Affairs (DEFRA) has an emission factor for an average National Rail journey of 0.03546 kgCO₂e per passenger km. So we can simply multiply the two and work out that the footprint of your journey was 7.092 kgCO₂e. 

This allows organisations and individuals to estimate the environmental impact of their actions in a standardised and comparable way. 

What Are They Used For?

Emission conversion factors are essential for measuring and reporting greenhouse gas (GHG) emissions. They are used in carbon accounting, helping organisations understand their carbon footprint and enabling them to set and achieve reduction targets.

For example, an emission factor for electricity might reflect the average carbon intensity of the UK's energy grid, while a factor for a specific vehicle type would account for its fuel efficiency and emissions per mile. These factors are crucial for understanding the relative impact of different actions and for making informed decisions about reducing emissions.

How Are They Calculated?

Emission conversion factors are typically calculated by governmental or environmental bodies using comprehensive data on energy consumption, vehicle efficiency, waste processing, and other relevant metrics. In the UK, DEFRA provides annual updates to these factors based on the latest research and data. The calculations involve assessing the carbon content of fuels, the efficiency of energy use, and the emissions associated with different activities.

DEFRA Emission Conversion Factors

DEFRA has been publishing emission conversion factors for UK activities annually since 2002. These factors allow organisations and individuals to calculate greenhouse GHG from a range of activities including:

• Energy Consumption
• Water Consumption
• Recycling and Disposal
• Freight and Shipping
• Travel and Commuting

Several factors can influence annual changes to these conversion factors, including changes in technology, energy mix, vehicle efficiency, and updates in methodological approaches.

The 2024 update to the UK emissions data has highlighted some significant changes in various scopes and categories. Let's explore some of the most noteworthy shifts.

Top Changes in UK Emissions

Scope 2 - Battery Electric Cars: Emissions for battery electric cars have decreased by 13.56%, driven by the penetration of newer, more efficient electric vehicles into the fleet. This reflects the ongoing transition towards cleaner transportation options and the improvements in battery technology and vehicle design.

Scope 3, Travel & Commuting - Average Local Bus: Emissions for an average local bus journey have increased by 6.18%, largely due to a recovery in bus travel following the COVID-19 pandemic. As public transportation usage rebounds, so too do the associated emissions, highlighting the complex relationship between societal behaviours and carbon footprints.

Scope 3, Transport & Distribution - Average Size Laden HGV: Emissions in this category have seen a slight increase of 0.11%. This is attributed to newer heavy goods vehicles (HGVs) being more energy-intensive per kilometer or mile, as indicated by the Vehicle Certification Agency's (VCA) performance database.

Top Changes Due to Methodology Updates

Scope 3 - Waste - Disposal of Metals, Electricals, and Plastics: Emissions have decreased dramatically by 69.88%, due to the correction of a previous error in methodology. This significant adjustment underscores the importance of accurate data and methodologies in emissions reporting.

Scope 3, Transport & Distribution - Average Size Vans (both petrol and diesel): Emissions for these vehicles have increased by 9.75% and 8.19%, respectively. This rise is due to the inclusion of additional cold start excess, a factor that was previously overlooked, but now provides a more accurate reflection of emissions in real-world conditions.

Scope 1 & 2 - Plug-In Hybrid Cars: Changes to the methodology now more accurately reflect the percentage of journeys that use electric power versus fuel. This has resulted in a significant increase in Scope 1 emissions by 42.07% and a decrease in Scope 2 emissions by 46.82%. This change highlights the complexities of hybrid vehicle emissions and the importance of accurate modelling in understanding their environmental impact.

Other Key Areas to Flag

One notable area that hasn't seen a reduction is electricity emissions. Despite advancements in renewable energy, the emission factor for electricity has remained unchanged since last year. This could indicate a plateau in the decarbonisation of the energy grid or a lag in the adoption of cleaner energy sources. It raises important questions about the pace of energy transition, and the challenges in further reducing emissions in this critical sector.

Conclusion

Understanding and utilising emission conversion factors is essential for accurate carbon accounting and effective emissions management. However, we understand that doing these calculations for an entire business with constantly changing emission factors is a massive challenge, so if you’d like some support, check out our Calculate page or BOOK A CALL with us to learn more.

Get Our Free Comparison Guide!

Olivia has put together an in depth DEFRA Emission Conversion Factors Comparison Guide that clearly details the key update to the UK Government Greenhouse Gas Conversion Factors, as published by DEFRA in July 2024.

CLICK HERE to download our guide and get a side-by-side comparison of 2023 vs 2024 UK emissions, including explanations for changes and what this could mean for the UK's path to Net-Zero by 2050.

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