A review of how global warming is measured

In June 2018 a research paper by Dr Myles R Allen et al was published in The Climate and Atmospheric Journal proposing an alternative measure to the accepted CO₂ equivalent which Allen calls Global Warming Potential* (GWP*)¹. Allen’s findings indicate that the widely accepted and recognised global warming potential (GWP¹⁰⁰) measure misrepresents short lived climate pollutants such as methane from ruminants and should not be used in the measurement of short lived gas emissions.

In October 2020 the BMPA published the first of many articles flagging Allen’s work and the need for the introduction of a more appropriate and relevant way of measuring ruminant greenhouse gas emissions. Also in 2020 the Centre for Innovation Excellence in Livestock (CIEL) published their Net Zero Carbon & UK Livestock report, which first mentioned that alternative metrics like GWP* can enhance our understanding on how each greenhouse gas affects climate change differently.

In 2021 GWP* was featured in the Intergovernmental Panel on Climate Change (IPCC) special report on ‘Global Warming of 1.5 °C’ and was assessed as part of its 6^th assessment report. Within the 6^th assessment technical summary the IPPC stated² in relation to GWP*

“Ultimately, it is a matter for policymakers to decide which emissions metric is most applicable to their needs. This Report [IPCC] does not recommend the use of any specific emissions metric, as the most appropriate metric depends on the policy goal and context”

In November 2022 the NFU in collaboration with CIEL held a workshop on GWP measurement to highlight the differences between GWP¹⁰⁰ and GWP*. Following presentations from Dr Allen and Prof Gideon Henderson, DEFRA’s chief scientific adviser, there was a facilitated session to highlight some of the most popular themes under a variety of headings covering policy, communication and current knowledge gaps. These included a clear strategic direction with government support to encourage carbon audits and good data collection, standardisation of GHG audits and clear and simple messaging to consumers.

In March 2023 the Department for Energy Security and Net Zero published The Carbon Budget Delivery Plan³. Within the text under the heading of unquantified proposals and policies there is an action to:

 “Assess the role and efficacy of introducing agriculture specific emissions targets, such as targets split between individual greenhouse gases to drive decarbonisation across the agriculture and land use sectors”

It goes on to state that:

“Emissions targets, or targets split between individual greenhouse gases, could help us reduce emissions in the agricultural sector. This is an early-stage proposal and next steps have not yet been determined. The potential emissions reductions are contingent on further research”.

In May 2023 the NFU released an update on their position regarding Methane calculations⁴ stating that GWP* provides a more accurate representation of the current contribution of UK ruminant agriculture to climate change and are asking for:

• Dual accounting with reporting on emissions from agriculture using GWP¹⁰⁰ and GWP*.

• Incorporating GWP* into on-farm GHG calculation tools.
• Consistent messaging to consumers on the temperature impacts from methane.
• Finding a suitable way for the carbon footprint of a food product to be measured.
• The use of GWP¹⁰⁰ and GWP* to measure reductions in methane as a result of selective breeding and improved genetics.
• A joined up approach to GHGs across government departments when looking at air quality.

In addition the NFU are looking for capital investment from government to encourage consistent GHG audits, innovation focused on utilizing methane for energy production and incentives for methane reduction.

It is encouraging to see the NFU taking a lead on GWP* and BMPA supports this bold initiative and will continue to push for the adoption of GWP*. We hope other meat industry associations and levy bodies follow the NFU’s lead and that both GWP¹⁰⁰ and GWP* are used concurrently to accurately report on short lived gas emissions.

¹ A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation | npj Climate and Atmospheric Science (nature.com)

²Technical Summary (ipcc.ch)

³Carbon Budget Delivery Plan (publishing.service.gov.uk)

⁴NFU updates position on GWP* metric – NFUonline

About Lucas Daglish

Lucas is Sustainability Manager at the British Meat Processors Association (BMPA). He has worked in a variety of operational and senior food procurement roles in the hospitality sector. Since 2006 he has been focused on red meat procurement, animal welfare policy implementation and livestock sustainability in his previous roles as Senior Category Buyer and then Group Food and Beverage Policy Manager at Whitbread PLC.