Another Big Issue: Reduction of Methane Updated in July 2020

Since President Trump decided to pull United States out of the Paris Agreement, moves to counter global warming have stalled. United States is the world’s second largest emitter of greenhouse gases. The Paris Agreement* of December 2015 created greenhouse gas reduction targets for each country and obligated countries to take domestic measures to achieve those goals. Japan for instance, is to aim for “a 26% reduction in emissions on 2013 levels by 2030,” while China is to “cut emissions per unit of GDP by 60-65% of 2005 levels by 2030.” Each country is setting its own reduction target and is working towards it.

*The Paris Agreement, a multilateral agreement on climate change mitigation was adopted by the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21-UNFCCC), held in Paris in December 2015. The Agreement went into force in November 2016. It defines global warming countermeasures after 2020.

<Methane Emissions Distribution Map for East Asia>

Research results that may contribute greatly to such efforts were published on 17 June by the National Institute for Environmental Studies (NIES) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The research team has examined how much methane is released into the atmosphere in East Asia per each source of emission and prepared a distribution map that allows you to see the amount of emissions at a glance. Methane is considered to be a greenhouse gas with the second largest impact on global warming next to CO₂, but actual efforts to reduce output are not as advanced as CO₂ countermeasures. One reason could be that sources and actual locations of methane emissions were not clear enough compared to carbon dioxide.

In nature, wetlands are the largest source of methane emissions. Microorganisms which obtain energy from organic matters can easily thrive in an environment without much oxygen. As a result, microorganisms emit large amounts of methane in wetlands. Methane emission can also occur in areas where termites grow. Microorganisms that live inside termites’ intestines break down plant fibers and produce methane. Furthermore, wildfire smokes from incomplete combustion of trees can also release methane. Methane found in forests, grasslands and deserts on the other hand, can be absorbed due to the mechanism of methane-oxidizing bacteria found inside the soil.

Methane in the atmosphere would be decomposed by photochemical reaction in 12 years or so. Through analysis of old atmospheric components trapped within the Antarctic ice sheet and direct atmospheric observation data, we know that methane concentration in the atmosphere was regular until the late 18th century industrial revolution. The released amount was well-balanced with the decomposition process in the atmosphere and those absorbed in the soil by methane-oxidizing bacteria. Like CO₂ however, methane concentration in the atmosphere continued to rise after the industrial revolution due to man-made factors like mining and consumption of fossil fuels.

This time, NIES and JAMSTEC calculated the amount of emission for each source using emission models and statistical data. From analysis of the Antarctic ice sheet, direct observation of the atmosphere, and recent satellite observations, we can see changes in the amount of methane found in the atmosphere. Such top-down studies however, could not determine where and how much methane is being released or absorbed. Through a bottom-up approach, the NIES-JAMSTEC team succeeded in compiling a map which shows the distribution of emitted methane and the actual amount.

<Nearly 90% of Methane Come from Man-made Source>

From the balance between methane emission and absorption in the East Asian region, the team found that the absorbed amount by methane-oxidizing bacteria in the soil is merely 3.4% compared to the total released amount. After all, it has become clear that an average of 67.31 million tons of methane is being released out to the atmosphere from East Asia on an annual basis throughout 2000-2012. This corresponds to about 13% of the global atmospheric methane levels known from top-down studies. When amounts of methane in the soil absorbed by bacteria were subtracted from naturally-emitted methane caused by wetlands, termites, wildfires and so on, the final emission figure was 11.2%. The rest of the output resulted from man-made causes.

The largest sources of man-caused emissions were related to fossil fuel mining, like leaks from gas fields and pipelines. This amounts to an annual average of 17.33 million tons which accounts for 25.7% of all emissions. The second largest source was paddy fields and agriculture amounting to 15.84 million tons (23.5% of total emissions). Paddy fields are in fact man-made wetlands─a major methane source. Next come waste and landfill which emit 10.77 million tons (16.0%), livestock which emit 10.34 million tons (15.4%), wetlands which emit 9.43 million tons (14.0%), and finally industry, transport and urban activities which give out 5.5 million tons (8.1%).

By country and region, China is by far the largest emitter with 61.7 million tons. This accounts for 91.7% of the whole East Asia region. Countries and regions following China are Japan (1.19 million tons), South Korea (1.45 million tons), North Korea (970,000 tons), Mongolia (750,000 tons), Taiwan (370,000 tons) and Hong Kong (150,000 tons).

<Methane’s Greenhouse Gas Effect 28 Times More than CO₂>

The amount of methane is not really that much in the atmosphere. Its amount is less than 1/200 (or 0.005) compared to CO₂. However, its greenhouse gas effect is 84 times more over a period of 20 years and 28 times more over 100 years, compared to the same amount of carbon dioxide. Similarly, the rise of methane in the atmosphere after the industrial revolution is 2.4 times greater than the rise of carbon dioxide (approx. 1.4 times). These are the reason why methane is considered to be the second most impactful cause of global warming next to CO₂.

While efforts to reduce CO₂ emissions are underway through renewable energy, electric vehicles, and experiments to capture carbon and store CO₂ underground, attempts to reduce methane emissions have been delayed. The results of this study are also useful to understand how far each country has achieved their greenhouse gas reduction goals, the NIES study says. This study may accelerate positive efforts to reduce methane emissions in many countries around the world. (T.K)

Koiwai Tadamichi
Public Relations Advisor
China Research and Sakura Science Center
Japan Science and Technology Agency