By Dr Rebecca Fisher and Dr James France, Department of Earth Sciences, Royal Holloway University of London
Relevant United Nations’ SDG goals:
It’s now a year since over 100 countries signed the Global Methane Pledge at COP26, aiming to cut global emissions of methane by 30% by 2030.
Methane is an important greenhouse gas, responsible for at least a quarter of the 1.1°C temperature increase seen since industrialisation. It has a fairly short atmospheric lifetime of about a decade, which means that reducing emissions now should lead to a reduction in atmospheric methane concentrations over the next 10 years.
The Greenhouse Gas Research Group in the Centre of Climate, Oceans and Atmosphere at Royal Holloway measures methane and its isotopic composition (δ13C and δ2H) both in situ and in flasks collected at sites around the world. The isotopic composition acts as a fingerprint for sources, telling us which source sector emissions are changing. For example biogenic sources (e.g. wetland, agriculture and waste) are depleted in 13C and 2H, whereas thermogenic (fossil fuel) and pyrogenic (combustion) sources are more enriched in 13C and 2H. Over the last 15 years we have measured rising methane concentrations, and a decline in δ13C which suggests that the contribution from biogenic sources of methane has increased. The WMO Greenhouse Gas Bulletin shows that globally in 2021 there was the highest increase in methane concentrations since regular measurements started 40 years ago. Global atmospheric methane concentrations are now over 1900 ppb, more than two and a half times pre-industrial values and the atmospheric measurements show an increase in growth, rather than the decline we need. It is likely that much of the recent increase in biogenic methane is a result of a climate feedback effect from wetlands, where warming leads to higher methane emissions, and then more warming.
Whilst measuring methane emission changes on a global or even national scale can be achieved through the various regional monitoring networks – measuring how much reduction is taking place at a city level or single industrial facility is very challenging. Efforts are underway to try to bridge this gap by developing tools and best practice to demonstrate to companies and governments that accurate measurement and reporting of emissions is possible, and that it is an important requirement so that progress in methane emissions reduction can be physically measured – rather than assumed through spreadsheet based calculations and assumptions.
Royal Holloway’s Greenhouse Gas Group operate a mobile laboratory, MIGGAS (Mobile Integrated Greenhouse Gas Assessment System), allowing us to locate and identify opportunities for methane emission reduction efforts such as fugitive emissions from gas distribution, biogas, agricultural waste management and landfill. Many of these fugitive emissions, particularly from the gas distribution sector) can be economical to fix.
Politicians signing a pledge is one thing, translating that to a real measurable decrease in emissions is a major challenge. Atmospheric measurements of methane concentrations and isotopic composition will be able to tell whether an emissions decrease really occurs and in which sectors. Activities such as the United Nations Environment Programme International Methane Emissions Observatory will assist in providing some clarity by integrating company reporting, scientific studies, government reports, and satellite data into a coherent and policy-relevant global public dataset.
The measurements of atmospheric methane concentrations we make over the coming decades will be extremely interesting. Will we globally be able to cut emissions enough to see a significant change in atmospheric concentrations? Will we see a drop in concentrations from the deep cuts in anthropogenic emissions pledged? Or will we continue to see a worrying increase in methane due to increased emissions from warmer, wetter wetlands or hydrate or permafrost degradation?
Royal Holloway’s MIGGAS – Mobile Integrated Greenhouse Gas Analysis System (NERC capital equipment)
Global average atmospheric CH4 and δ13C(CH4) measured by the global WMO GAW network, smoothed (red lines) and deseasonalized (blue lines) - Source WMO Greenhouse Gas Bulletin, 2022, https://library.wmo.int/doc_num.php?explnum_id=11352