Global average surface temperatures shattered all-time records in 2023 at 1.45 ± 0.12 °C above pre-industrial levels (WMO 2024). Worsened by climate change-induced drought, Canadian wildfires burned 18.5 million hectares, nearly three-times more land area than in any previous year on record (NRC 2023). Parts of the Amazon River reached their lowest levels in 120 years of data-keeping and, in places, recorded surface water temperatures near 40 °C (Rodrigues 2023). The world has reached the threshold of a 1.5 °C increase in global average surface temperature and is only beginning to experience the full consequences.
Methane (CH4) is the second most important anthropogenic greenhouse gas after carbon dioxide. It contributed 0.5 °C of warming in the 2010s relative to the late 1800s—two-thirds as much warming as CO2 (IPCC 2021). It is also far more potent than CO2 ton for ton, with a global warming potential (GWP) >80 and 30 times more than CO2 for the first twenty years and century after release, respectively (Forster et al 2021).
Methane is rising faster in relative terms than any major greenhouse gas and is now 2.6-fold higher than in pre-industrial times. Global average methane concentrations reached 1931 parts per billion (ppb) in January of 2024 (Lan et al 2024). Annual increases in methane are also accelerating for reasons that are debated. Global methane concentrations rose by 15, 18, 13, and 10 ppb each year from 2020 through 2023, respectively, the second, first, fourth, and fourteenth largest increases since the U.S. National Oceanic and Atmospheric Administration (NOAA) methane time series began in 1983 (Lan et al 2024).
The Global Carbon Project updates its Global Methane Budget (GMB) every few years (Saunois et al 2016, 2020, 2024). The GMB integrates results of: (1) bottom-up (BU) estimates based on process-based models for estimating wetland surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations, and (2) top-down (TD) CH4 emission estimates based on atmospheric observations and an inverse-modeling framework. Here, we summarize new estimates of the GMB based on the new GMB (Saunois et al 2024). We estimate CH4 sources and sinks for the periods 2000–2002 and 2018–2020, as well as for the most-recent year (2020), the last year that full global TD and BU methane datasets are available. We compare 3 year-average estimates to smooth the inter-annual variability signals from climatic variability such as the El Niño-Southern Oscillation (ENSO) that influence natural emissions from wetlands and other ecosystems, as well as from the chemical sink.
We provide insights on data for methane sources and sinks globally and for the geographical regions and economic sectors whose emissions have changed the most since 2000. We also provide additional data on changes in recent years using satellite-based inversions using the TROPOspheric Monitoring Instrument (TROPOMI) (e.g. Yu et al 2023).