Methodology

Our Carbon Offset Methodology

At Offset Britain, transparency and scientific rigour underpin everything we do. This page outlines the methodology we use to calculate carbon emissions, source carbon credits, and ensure the integrity of every offset we sell.

Emission Calculation Standards

Our carbon calculators are built on internationally recognised emission factor databases and methodologies, including:

• UK Government GHG Conversion Factors - Published annually by the Department for Energy Security and Net Zero (DESNZ), these are the official UK emission factors for company reporting.
• IPCC Guidelines - The Intergovernmental Panel on Climate Change provides the global scientific framework for greenhouse gas accounting.
• GHG Protocol - The World Resources Institute and WBCSD’s Greenhouse Gas Protocol is the most widely used international accounting standard for greenhouse gas emissions.
• ICAO Carbon Emissions Calculator - For aviation emissions, we use methodology aligned with the International Civil Aviation Organization’s calculator, factoring in aircraft type, distance, cabin class, and radiative forcing.

How We Calculate Personal Carbon Footprints

Our personal carbon calculator considers the following emission categories:

• Home Energy - Electricity and gas consumption based on UK average tariffs and grid carbon intensity (currently approximately 0.207 kg CO₂e per kWh for electricity and 0.183 kg CO₂e per kWh for natural gas).
• Transport - Vehicle emissions by fuel type and mileage, public transport usage, and domestic/international flights.
• Diet & Lifestyle - Estimated emissions from food consumption patterns, ranging from approximately 1.5 tonnes CO₂e/year for a vegan diet to 3.3 tonnes CO₂e/year for a high-meat diet.
• Goods & Services - Consumption-based emissions from purchases, services, and general spending patterns.

Flight Emission Calculations

Our flight offset calculator uses a methodology consistent with ICAO and DEFRA standards. Key factors include:

• Great circle distance between airports plus a 9% uplift factor for non-direct routing
• Aircraft fuel burn rates by distance band (short-haul, medium-haul, long-haul)
• Cabin class multipliers (Economy: 1x, Premium Economy: 1.6x, Business: 2.9x, First: 4x) reflecting the additional space and weight per passenger
• A Radiative Forcing Index (RFI) multiplier of 1.9 to account for the additional climate warming effects of emissions at altitude, including contrails and NOx

Carbon Credit Sourcing

We source carbon credits exclusively from projects verified under the following standards:

• Gold Standard (GS) - Requires projects to demonstrate measurable sustainable development co-benefits alongside emission reductions.
• Verified Carbon Standard (VCS) by Verra - The world’s largest voluntary carbon credit programme, requiring third-party validation and verification.
• UN Clean Development Mechanism (CDM) - Emission reduction projects in developing countries verified under the Kyoto Protocol framework.

Additionality & Permanence

Every project we support must demonstrate additionality - meaning the emission reductions would not have occurred without the carbon finance provided by offset purchases. Projects must also address permanence, ensuring that carbon sequestration is maintained over the long term, with appropriate buffer pools and monitoring.

Retirement & Transparency

When you purchase an offset through Offset Britain, the corresponding carbon credits are permanently retired on the relevant registry (Gold Standard Registry, Verra Registry, or UNFCCC CDM Registry). This means the credits are removed from circulation and cannot be resold or double-counted. Each retirement is linked to a unique serial number that you can independently verify.

Annual Review

We update our emission factors annually in line with the latest UK Government conversion factors, typically published each June. Our calculators are reviewed and updated accordingly to ensure accuracy.