Annual increase in whole-atmosphere mean methane concentration for 2021 marks the largest since 2011

The National Institute for Environmental Studies (NIES) has promoted the Greenhouse gases Observing SATellite Series (GOSAT Series), a Japanese satellite project for greenhouse gas observation from space, jointly with the Ministry of the Environment of Japan (MOE) and the Japan Aerospace Exploration Agency (JAXA). The first satellite of the series, Greenhouse gases Observing SATellite “IBUKI” (GOSAT), has been observing column-averaged concentrations of the two major greenhouse gases, carbon dioxide and methane for more than 12 years since its launch. The second satellite, GOSAT-2 (IBUKI-2) was launched in 2018 and started observing carbon monoxide in addition to carbon dioxide and methane. Furthermore, the third satellite, Global Observing SATellite for Greenhouse gases and Water cycle (GOSAT-GW) is under development for the launch in 2023.

GOSAT and GOSAT-2 data are publicly available from the following sites.
　GOSAT Data Archive Service (GDAS):
　　https://data2.gosat.nies.go.jp/index_en.html
　GOSAT-2 Product Archive:
　　https://prdct.gosat-2.nies.go.jp/index.html.en

Some meteorological agencies in the world including the World Meteorological Organization (WMO) have released global mean surface concentrations calculated from data observed at ground surface stations managed by each agency. In general, greenhouse gas concentrations, including methane, vary with altitude, so the data from ground surface stations alone cannot represent the average concentration of the Earth’s atmosphere. In contrast, GOSAT can measure the total amount of greenhouse gases in the atmosphere, from the ground surface to the top of the atmosphere, not only the surface concentrations. The future greenhouse gas concentrations referred in the Sixth Assessment Report (Working Group 1) published by the Intergovernmental Panel on Climate Change (IPCC) in August 2021, are the average concentrations in the atmosphere; therefore, calculating mean greenhouse gas concentrations throughout the globe is important in estimating the risks from global warming posed by future greenhouse gas increase, and it is vital to have an average picture of the “whole-atmosphere” including upper atmosphere. In addition, the Global Methane Pledge for reducing global methane emission was launched at the 26^th session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 26) held in November 2021, drawing renewed attention to the importance of monitoring methane concentration and controlling the emission.

In these circumstances, the National Institute for Environment Studies (NIES) has been calculating “whole-atmosphere mean concentration”, which is equivalent to the average concentration in the entire Earth’s atmosphere, and releasing the monthly preliminary values and the past data along with the calculation methods starting from November 2015 for carbon dioxide and June 2017 for methane, from the following sites.
CO₂: https://www.gosat.nies.go.jp/en/recent-global-co2.html
CH₄: https://www.gosat.nies.go.jp/en/recent-global-ch4.html

Figure 1 shows the whole-atmosphere mean methane concentrations (monthly values, in black) and the annual means (in red) for the period from April 2009 to December 2021. Since 2009, the whole-atmosphere mean methane concentration has increased gradually showing seasonal fluctuations with minimum values in May to July and maximum values in October to January every year. From a more detailed analysis, an upward trend can be seen in the pace of concentration increase from around 2020.

Table 1 shows the annual mean and increase of whole-atmosphere (monthly) mean methane concentrations based on GOSAT observations. The average annual increase from 2011 to 2020 was 8 ppb, while the increase in 2021 was 17 ppb, double the previous 10 years.

The recent increase in methane concentration has been confirmed by observations other than GOSAT. To elucidate the causes of the increase, many studies which focus on methane emissions from biological and fossil fuel sources and on variations in the amount of atmospheric methane removal due to chemical reactions are actively underway around the world. Although it will take some time to clarify the causes, they may become significant problems in predicting future methane concentrations and confirming the implementation status of emission reduction measures by each country under the Paris Agreement.

Analysis by the National Oceanic and Atmospheric Administration reveals that the surface concentration of methane surged from 2019 to 2020*. Accordingly, the results of this study by GOSAT indicate that the increase in methane concentration occurred not only in the surface but also in the whole-atmosphere.

This prompt release of the global annual increase in 2021 is the result of taking advantage of the preliminary report of global observations by GOSAT.
*https://research.noaa.gov/article/ArtMID/587/ArticleID/2742/Despite-pandemic-shutdowns-carbon-dioxide-and-methane-surged-in-2020

It is currently not clear whether the increase in methane concentration observed in 2021 will continue after 2022, and whether the rate of increase will accelerate in the future. Consequently, continuous observations of global methane concentrations are necessary.

NIES has been calculating the whole-atmosphere concentrations of carbon dioxide and methane based on GOSAT data and also preparing for the release of the whole-atmosphere concentrations based on GOSAT-2 data. In the future, we plan to provide the whole-atmosphere concentrations for over 20 years from 2009 by using the data of GOSAT-GW to be launched in FY2023.

We hope that the whole-atmosphere concentrations of greenhouse gases based on “GOSAT Series” data will contribute to monitor progress on greenhouse gas emission reduction in each country under the Paris Agreement.

The calculation of whole-atmosphere mean concentrations of carbon dioxide and methane based on GOSAT data is financially supported by the management expenses grants for NIES and a contract with MOE, "FY2021 Consignment Study Regarding Generation of Greenhouse gases Observing SATellite (GOSAT) Series Higher Level Products and Their Applications".

[Title]
Whole-atmosphere monthly mean CH4 concentration based on GOSAT observations－Recent data－
[Author]
GOSAT Project, Satellite Observation Center
National Institute for Environmental Studies
[URL]
https://www.gosat.nies.go.jp/en/recent-global-ch4.html

[Contact for this research]
Tsuneo Matsunaga, Director
Satellite Observation Center
Earth System Division
National Institute for Environmental Studies

[Contact for this press release]
Public Relations Office, Planning Division
National Institute for Environmental Studies
E-mail: kouhou0 (please append ‘@nies.go.jp’ to complete the e-mail address)
Phone: +81-29-850-2308

○Methane in the atmosphere
Methane is the second most important greenhouse gas contributor to global warming after carbon dioxide and, according to the IPCC’s Fifth Assessment Report, has 28 times greater global warming potential than carbon dioxide. Methane is emitted from natural sources such as wetlands and termites, and a variety of anthropogenic sources including rice agriculture, livestock (ruminants such as cattle and sheep), landfills, and fossil fuel mining and burning. On the other hand, methane is removed by reacting with hydroxyl radicals in the atmosphere.

Although the surface concentrations of methane had been stable in the range of 700–750 ppb until the 18th century, they have increased substantially due to human activities and exceeded 1,800 ppb in recent years.

○Global Methane Pledge
An initiative jointly led by the United States and the European Union to reduce global methane emissions by at least 30% from 2020 levels by 2030. Over 100 countries and regions including Japan have signed the Pledge.

○Related press releases
1) June 2, 2017
Public release of whole-atmosphere mean methane concentration based on observations by Greenhouse gases Observing SATellite "IBUKI" (GOSAT)
https://www.nies.go.jp/whatsnew/20170602/20170602.html(in Japanese)
2) October 27, 2016
Whole-atmosphere monthly mean CO2 concentration detrended with average seasonal variation tops 400 ppm!
- Preliminary GOSAT monitoring results -
https://www.gosat.nies.go.jp/en/news/20161027pressrelease.html
3) May 20, 2016
Whole-atmospheric monthly CO2 concentration tops 400 ppm
- Preliminary GOSAT monitoring results –
https://www.nies.go.jp/whatsnew/20160520/20160520-e.html
4) November 16, 2015
Public release of whole-atmosphere monthly mean carbon dioxide concentration based on observations by Greenhouse gases Observing SATellite "IBUKI" (GOSAT)
https://www.nies.go.jp/whatsnew/20151116/20151116-e.html