Mankind Driving Global Methane Emissions

R B Jackson and M Saunois and A Martinez and J G Canadell and X Yu and M Li and B Poulter and P A Raymond and P Regnier and P Ciais and S J Davis and P K Patra, Human activities now fuel two-thirds of global methane emissions, Environmental Research Letters, September 2024, IOP Volume 19 , 10.1088/1748-9326/ad6463, https://dx.doi.org/10.1088/1748-9326/ad6463

A recent study (cited above) found that Mankind is responsible for two-thirds of global methane emissions. The research article cited above is from Rob Jackson and the Global Carbon Project. Rob Jackson is Stanford’s Michelle and Kevin Douglas Provostial Professor. Dr. Jackson and his lab examine the many ways people affect the Earth.  They're currently examining the effects of climate change and droughts on forest and grassland ecosystems. They are also working to measure and reduce greenhouse gas emissions through the Global Carbon Project (globalcarbonproject.org), which Dr. Jackson chairs. The Global Carbon Project also updates its Global Methane Budget (GMB) every few years. I have excerpted sections of the article.

Global average surface temperatures have reached another  all-time high 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 (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.

The amount of methane (CH4) in Earth’s atmosphere continues to rise. Concentrations of methane are now about 2.5 times as much as was in the atmosphere in the 1850s. Methane is the second most important anthropogenic greenhouse gas after carbon dioxide ( CO2). Despite an increasing policy focus on methane as a potent greenhouse gas, methane emissions continue to rise (as do carbon emissions). Global anthropogenic methane emissions are now 15%–20% higher than they were 2000–2002. Global average methane concentrations reached 1.9 parts per million (ppm) in January of 2024 (Lan et al 2024). Annual increases in methane are also accelerating for reasons that are not fully understood and debated. 

Some gases are more effective than others at making the planet warmer and "thickening the Earth's atmospheric blanket." For each greenhouse gas, a Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, typically a 100-year time horizon, relative to the emissions of 1 ton of carbon dioxide (CO2). Gases with a higher GWP absorb more energy, per ton emitted, than gases with a lower GWP, and thus contribute more to warming Earth. Thus, though methane lasts much less than 100 years in the atmosphere, it is described in terms of the 100 years by it’s Global Warming Potential.

Methane’s lifetime in the atmosphere is much shorter than carbon dioxide (CO2), CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 is 28 times greater than CO2 over a 100-year period. Over a 20-year period, it is 80 times more potent at warming than carbon dioxide. Carbon dioxide concentrations in the atmosphere are currently 490 ppm 250 times higher than methane, so even at the higher Global Warming Potential it is still smaller than the impact from CO2. Since the signing of the Paris Climate Accord, global greenhouse gas emissions have continued to rise. We are further from net zero emissions than we were in 2015.

from EPA

Methane comes from both natural and anthropogenic sources. Total global methane sources, both natural and anthropogenic, both rose. The largest natural sources are wetlands and freshwater lakes, rivers, and ponds where methane-emitting bacteria thrive. Human activities that release methane include biofuel and fossil fuel burning, agriculture, and waste (landfills).

Dr. Jackson and his team performed both a bottom-up estimate and a top-down estimate using monitoring equipment (both satellite and ground-based) to identify the total and sources of methane. The methods proposed slightly different numbers. The absolute concentration of methane in the atmosphere was determined by the top-down method.

Dr. Jackson et al states that “Recent analyses suggest that methane mitigation may be cheaper than CO2 mitigation for a comparable climate benefit. Better quantification and attribution of methane sources are needed to support such mitigation efforts locally, regionally, and globally.” The study found that direct anthropogenic methane emissions were responsible for 65% of all methane released each year. It is even higher if land use changes are considered.

Natural sources of methane are likely to increase with increasing temperatures. Methane removal techniques is still in its infancy. So, we are left with mitigation for now. According to the last Global Methane Budget: Wetlands contributed 30% of global methane emissions, with oil, gas, and coal activities accounting for 20%. Agriculture, including enteric fermentation (cow belching), manure management, and rice cultivation, made up 24% of emissions, and landfill gas contributed 11%. Sixty-four percent of methane emissions came from the tropical regions of South America, Asia, and Africa, with temperate regions accounting for 32% and the Arctic contributing 4%.

Methane emissions rose most sharply in Africa and the Middle East; China; and South Asia and Oceania. Each of these three regions increased emissions by an estimated 10 to 15 million tons per year during the study period. The United States followed behind, increasing methane emissions by 4.5 million tons, mostly due to more natural gas drilling, distribution and consumption. Europe was the only region where methane emissions decreased over the study period, attributed to reductions chemical manufacturing and growing food more efficiently with better management of manure and landfills.

According to Dr. Jackson and his colleagues, curbing methane emissions will require reducing fossil fuel use and controlling fugitive emissions such as leaks from pipelines and wells, as well as changes to the way we feed cattle, grow rice and eat. “We’ll need to eat less meat and reduce emissions associated with cattle and rice farming,” Dr. Jackson said, “and replace oil and natural gas in our cars and homes.”