A new paper just published in the PNAS identifies different culprits.

Abstract

The growth rate of the atmospheric abundance of methane (CH₄) reached a record high of 15.4 ppb yr⁻¹ between 2020 and 2022, but the mechanisms driving the accelerated CH₄ growth have so far been unclear. In this work, we use measurements of the ¹³C:¹²C ratio of CH₄ (expressed as δ¹³C_CH4) from NOAA’s Global Greenhouse Gas Reference Network and a box model to investigate potential drivers for the rapid CH₄ growth. These measurements show that the record-high CH₄ growth in 2020–2022 was accompanied by a sharp decline in δ¹³C_CH4, indicating that the increase in CH₄ abundance was mainly driven by increased emissions from microbial sources such as wetlands, waste, and agriculture. We use our box model to reject increasing fossil fuel emissions or decreasing hydroxyl radical sink as the dominant driver for increasing global methane abundance.
https://www.pnas.org/doi/10.1073/pnas.2411212121

Methane (CH₄) is the second-most abundant anthropogenic greenhouse gas and has global warming potential (GWP) of 28 over 100 y (1); as a result, CH₄ has consequential near-term radiative effects and is a prominent target for mitigation (2). Following a short pause in growth from 1999 to 2006, both the abundance and growth rate of atmospheric methane have been increasing (3). During 2020–2022, the observed CH₄ growth rate reached a record high since NOAA measurements began in 1983, averaging 15.4 ± 0.6 ppb yr⁻¹ (4). Understanding the mechanisms driving this accelerated growth is essential for predicting its future climate impact and providing scientific support for climate mitigation strategies (2).

The carbon isotopic composition of atmospheric CH₄ (δ¹³C_CH4) is a powerful tool for tracking the sources and sinks of atmospheric CH₄. Different CH₄ sources have distinctive δ¹³C_CH4 values: Microbial CH₄ emissions (wetlands, livestock, landfills, etc.) have lower δ¹³C_CH4 values (global mean of –62‰) than pyrogenic (biomass and biofuel burning, global mean of –24‰) and fossil fuel CH₄ emissions (global mean of –45‰) (5). Various sinks of atmospheric CH₄ also have distinctive isotopic effects. Therefore, combined observations of atmospheric CH₄ mole fraction and δ¹³C_CH4 can provide unique constraints on the changes of global CH₄ sources and sinks during the post-2006 rapid CH₄ growth.

The National Oceanic and Atmospheric Administration’s Global Monitoring Laboratory (NOAA/GML) has been carefully monitoring the global CH₄ burden through the Global Greenhouse Gas Reference Network (GGGRN) for over four decades. The collaboration between NOAA/GML and the Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado Boulder has enabled δ¹³C_CH4 measurements from the GGGRN since 1998, currently measuring weekly or biweekly from 22 globally distributed background sites (6). The dataset has been widely used for studying the evolution of global CH₄ sources and sinks (7–9). Here, we report our most recent observations of atmospheric CH₄ mole fractions and δ¹³C_CH4 values through the end of 2022 and then use a box model to examine and quantify the contributions of potential drivers of the record-high CH₄ growth rate.

The rest of the paper can be found here.

This is unlikely to mollify climate zealots as agriculture is listed among the potential causes. With biological activity exploding across the world, due to CO2 fertilization, I personally wonder how much of this is increasing wetland productivity as well as flourishing soil microbes.

H/T Steve Milloy.