As we approach the end of the year 2022, we have seen a number of extreme weather events. Japan was hit by a cold wave last week and over the weekend, while in the United States, the Arctic blast reportedly covered large swaths of the country, and social disruption caused by the historic cold wave hit the Christmas vacation season. The Arctic Ocean is particularly affected by climate change and is known to have an impact on global extreme events. Efforts to reduce greenhouse gas emissions are strongly called for.

Methane is considered to be a very potent greenhouse gas. Atmospheric methane can come from natural sources such as wetlands or from anthropogenic activities such as agriculture, fossil fuel mining, landfills, waste, and fires. Once emitted into the atmosphere, methane remains for an average of nine years before decomposing and disappearing through reactions with OH radicals (hydroxyl radicals). Methane is equivalent to one-fifth of the greenhouse gases in the atmosphere due to anthropogenic activities, and the concentration of methane in the atmosphere today is nearly three times higher than it was before the Industrial Revolution.　

According to the Global Methane Assessment, released in May 2021, which was previously featured in Pick Up, data from the National Oceanic and Atmospheric Administration (NOAA) showed that while the COVID-19 pandemic slowed the economy in 2020 and did not result in a record year for carbon dioxide (CO2) emissions, methane in the atmosphere reached record levels.

The rate of increase in atmospheric methane concentrations in 2020 was nearly double the average annual rate of increase from 2007-19. Initially, scientists reportedly considered this a puzzling phenomenon in light of the economic stagnation during the COVID-19 pandemic. The paper published in Nature pointed to warm, wet weather in the Northern Hemisphere and, ironically, a slowdown in emissions of methane-decomposing atmospheric pollutants (OH) during the lockdown to contain the COVID-19 pandemic as the reasons for the rapid increase in atmospheric methane concentrations in 2020.

The Nature editorial noted that the complex mechanisms of sources, sinks, and feedbacks that determine global methane concentrations are difficult to predict and require data supported by a network of sensors and satellites that allow for further observations and sophisticated regional models.

As recently featured in Pick Up, this past November, the World Meteorological Organization announced that methane concentrations had renewed the largest increase in the rate of change from 2020 to 2021. While the cause is not yet clear, the agency mentioned the possibility of a climate change feedback in which warming causes methane emissions to increase due to faster decomposition of organic matter in the water in the absence of oxygen. Analysis of the factors explaining this phenomenon is also required.

According to the Intergovernmental Panel on Climate Change (IPCC) scenario analysis, global methane emissions must be reduced by 40-45% by 2030, along with reductions in other greenhouse gas emissions. On the other hand, methane, unlike carbon dioxide, which has been in the atmosphere for centuries, can rapidly reduce the rate of global warming in the short term because it breaks down easily and is mostly gone after a decade. The Global Methane Assessment report states that emissions of methane from human activities can be reduced by up to 45% over the next decade through existing technologies and measures, thereby limiting the global temperature increase to 1.5°C, in line with the Paris Agreement on climate change.

The sources of methane generation in the agricultural sector are livestock manure, fermentation in the digestive tract, and paddy rice cultivation, but there is a need to develop technologies to control methane generation while maintaining yields. JIRCAS, in collaboration with partners, is also conducting international joint research to develop methane generation suppression technology and evaluate sustainability and yield.

References
Nature 612, 413-414 (2022)　doi: https://doi.org/10.1038/d41586-022-04352-6
Peng, S., Lin, X., Thompson, R.L. et al. Wetland emission and atmospheric sink changes explain methane growth in 2020. Nature 612, 477–482 (2022). https://doi.org/10.1038/s41586-022-05447-w 

Contributor: IIYAMA Miyuki (Information Program)