Human activities are now responsible for at least two-thirds of global methane emissions
Photo: Dan Meyers / Unsplash.Researchers from the Finnish Meteorological Institute and international research institutes found that methane (CH₄) emissions due to human activities account for at least two-thirds of Earth’s total methane emissions. These include direct anthropogenic sources from fossil fuel exploitation and use, agriculture, waste handling, biomass and biofuel burning, and indirect sources from rivers and reservoirs. Among those, emissions from agriculture and waste sector (e.g., ruminants, rice paddies, landfills) are the largest, accounting for approximately twice of those associated with fossil fuels.
They also found that global methane emissions from fossil fuels, agriculture and waste have continued to increase. Methane emissions from human activities are now 20 per cent or 61 million metric tons of CH₄ per year larger than two decades ago. Emissions from cows and other ruminants and from landfills and other waste both rose by approximately 15 million metric tons of CH₄ per year between 2000‒2002 and 2018‒2020, representing an increase of 14 per cent from agriculture and approximately 24 per cent from waste.
Fossil fuel emissions rose by an estimated 18 to 27 million metric tons of methane (18 per cent to 28 per cent), as estimated by different approaches.
"If this trend were to continue for the years after, this could jeopardize the success of the Global Methane Pledge, international commitment to reduce methane emissions 30 per cent by 2030", says Aki Tsuruta, Senior Research Scientist at Finnish Meteorological Institute.
Even wetland emissions have increased
Emissions from aquatic ecosystems, and in particular wetlands, are climate sensitive. Natural emissions of methane from aquatic ecosystems such as wetlands, lakes, ponds and rivers are estimated to be 248 million metric tons of methane per year for the 2010 decade. Wetland emissions have increased by 4 per cent between the 2000s and the 2010s, mainly from the tropics and the mid-latitude regions.
In wetlands, methane is generally produced more actively in warmer and wet conditions. Therefore, rising temperatures was the primary driver of the increase while precipitation and rising atmospheric Carbon dioxide concentrations played secondary roles. This climate feedback on natural emissions may require a stronger reduction in anthropogenic emissions to limit climate warming.
Due to increased anthropogenic methane emissions, the Earth's atmospheric methane concentration reached 1923 parts per billion (yearly average) in 2023. This is 2.6 times higher than its pre-industrial (1750) level. Methane accumulation in the atmosphere has accelerated in the past decade, with higher growth rates over the past three years (2020‒2022) than any previous observed year since 1986 when reliable measurements began.
"This rate of increase follows the IPCC’s most pessimistic illustrative future GHG trajectories, which lead to global mean temperatures above 3°C by the end of this century", says Aki Tsuruta.
Methane is more powerful greenhouse gas than carbon dioxide
Methane is the second most important anthropogenic greenhouse gas after carbon dioxide leading to human-induced global warming. Methane is a 28-times more powerful greenhouse gas than carbon dioxide over a time horizon of 100 years, but 80 times more powerful than carbon dioxide over a time horizon of 20 years. Since atmospheric lifetime of methane is about 10 years only, actions to reduce its emissions would have an effect in near future.
Researchers at Finnish Meteorological Institute (FMI) contributed to the study by providing valuable measurements of atmospheric methane and state-of-art methane emission estimates from a top-down model. FMI has been measuring atmospheric methane from surface stations such as at Pallas-Sammaltunturi, Muonio, since 2004, and providing data and models for validation of satellite data for high latitudes. FMI also provides global and national estimates of methane budgets using top-down models using surface measurements and satellite retrievals.
The Global Carbon Project is an international research project within the Future Earth research initiative on global sustainability and a research partner of the World Climate Research Programme. It aims to develop a complete picture of the global carbon cycle and budgets of carbon dioxide, methane, and nitrous oxide, including both its biophysical and human dimensions, together with the interactions and feedbacks between them. This Global Methane Budget 2024 is the fourth such budget and the third one as a living data collection in the journal Earth System Science Data.
More information:
Senior Researcsh Scientist Aki Tsuruta, Finnish Meteorological Institute, aki.tsuruta@fmi.fi
Principal Scientist Tuula Aalto, Finnish Meteorological Institute, tuula.aalto@fmi.fi
Saunois et al. (2024) Global Methane Budget 2000-2020. Earth System Science Data. https://doi.org/10.5194/essd-2024-115
Jackson et al. (2024) Human activities now fuel two-thirds of global methane emissions. Environmental Research Letters https://doi.org/10.1088/1748-9326/ad6463