Whole-atmosphere monthly mean CO2 concentration detrended
with average seasonal variation tops 400 ppm!
- Preliminary GOSAT monitoring results -The Ministry of the Environment, Japan (MOEJ), National Institute forEnvironmental Studies (NIES), and Japan Aerospace Exploration Agency (JAXA)
have been monitoring carbon dioxide (CO2) and methane (CH4) by theGreenhouse gases Observing SATellite "IBUKI" (GOSAT). A recent analysis ofGOSAT observational data up to May 2016 shows that the whole-atmospheremonthly mean CO2 concentration detrended with average seasonal variation(CO2 trend) exceeded 400 ppm in February 2016 for the first time since
GOSAT was launched in 2009. Further, whole-atmosphere monthly meanCO2, which first exceeded 400 ppm in December 2015, reached a recordhigh of 402.3 ppm in May 2016.
This result will be reported at a side event of the 22nd Conference of the Parties(COP 22) to the United Nations Framework Convention on Climate Change(UNFCCC) scheduled to take place in Marrakech, Morocco, from November 7-18,
2016.
The whole-atmosphere monthly mean CO2 concentrations based on GOSAT
observation will continue to be reported periodically.

－1－● Whole-atmosphere monthly mean CO2 concentrations as seen byGOSAT
The three parties – The Ministry of the Environment, Japan (MOEJ), National Institutefor Environmental Studies (NIES), and Japan Aerospace Exploration Agency (JAXA) have published the whole-atmosphere monthly mean CO2 concentrations (observations
made vertically through the whole atmosphere up to the altitude of about 70 km) and themean global CO2 trend (average seasonal variation removed), which were estimatedfrom GOSAT observational data from May 2009 to May 2016, on the website: NIESGOSAT Project, "Whole-atmosphere monthly mean CO2 concentrations – Recent data–"1.
“CO2 trend” is derived by removing average seasonal variation from the observed
monthly CO2 concentration, which value is similar to the annual average concentration
for the period of six months before and after the observation. The atmospheric CO2
concentration shows seasonal and inter-annual variations and estimating “CO2 trend” iscrucial to monitor long-term global atmospheric changes.
As announced in the press release on May 20, 2016, the whole-atmosphere monthly
mean CO2 concentration first exceeded 400 ppm in December 2015 with a record of400.2 ppm. The recent analysis of GOSAT data up to May 2016 shows that CO2 trend
exceeded 400 ppm in February 2016 (400.2 ppm) (Figure 1). This is the first time to be
confirmed that the whole-atmosphere CO2 trend exceeded 400 ppm based on GOSAT
data. The CO2 trend has been increasing continuously since the GOSAT launch in 2009.
The monthly mean concentration also reached the highest record of 402.3 ppm in May
2016.
From May 2010 to April 2016, the average increase of CO2 in one-year (annualincrease)2 was about 2.2 ppm/year; however, from summer 2015 to April 2016, itexceeded 2.5 ppm/year. The similar trend has already been reported based on theground-based observation by Japanese research institutions including the Japan
Metrological Agency (JMA) and National Institute for Environmental Studies (NIES). In
addition to these reports, GOSAT observation provides evidence that this is not aphenomenon appeared only near the ground surface or specific regions, but appearedon a global scale.

12

http://www.gosat.nies.go.jp/en/recent-global-co2.html
The difference of CO2 trend compared to the same period of the previous year－2－

(JMA ground based observational data)
http://ds.data.jma.go.jp/ghg/kanshi/ghgp/co2_e.html(NIES monitoring station on Hateruma island (Okinawa, Japan))
http://db.cger.nies.go.jp/portal/ggtus/hateruma?lang=eng(NIES monitoring station at Cape Ochi-ishi (Hokkaido, Japan))
http://db.cger.nies.go.jp/portal/ggtus/ochiishi
These results are based on a preliminary analysis of the systematic bias of GOSAT.
For more information about the analysis method and explanation, please see thewebsite below:"Whole-atmosphere monthly mean CO2 concentration"(http://www.gosat.nies.go.jp/en/recent-global-co2.html). An explanatory document(PDF) is available on the website.

• Global CO2 concentration above 400 ppm and its meaning
CO2 concentration, which was around 280 ppm before the Industrial Revolution, hasbeen increasing continuously and the present rate of increase is about 2 ppm per year.
According to the Fifth Assessment Report (AR5) of the Intergovernmental Panel on
Climate Change (IPCC), with scenarios limiting global greenhouse gas concentration to450 ppm CO2 equivalent or below by 2100, it is likely to keep global mean temperature
increase (compared to pre-industrial levels) less than 2.0 °C until the end of 21stcentury.

• Future course of action
The three parties will continue the public dissemination of new findings from GOSAT
observations. Also, the parties plan to continue the ongoing space-based greenhousegas observation with the GOSAT successor, GOSAT-2, which is planned to belaunched in the Japanese fiscal year 2017. The results of the continued satellite
observation will be utilized for the elaboration and refinement of global warming
predictions.
This result will be reported at a side event of the 22nd Conference of the Parties(COP 22) to the United Nations Framework Convention on Climate Change (UNFCCC)
scheduled to take place in Marrakech, Morocco, from November 7-18, 2016.

－3－Figure 1. Whole-atmosphere CO2 concentrations derived from GOSAT data:
Monthly mean (●) and trend (・).

[Acknowledgement]
For the analysis of GOSAT observational data, two weather analysis datasets wereused: GPV (Grid Point Value) data provided by the Japan Meteorological Agency andJCDAS data generated in the JRA-25 long-term reanalysis project by the Japan
Meteorological Agency and the Central Research Institute of Electric Power Industry.
[Contact Information]
Tsuneo Matsunaga
GOSAT Project, Satellite Observation Center,
National Institute for Environmental Studies
Phone: +81-29-850-2035; +81-850-2838－4－

[References]• About the Greenhouse Gases Observing SATellite “IBUKI” (GOSAT)The Greenhouse gases Observing SATellite "IBUKI", developed jointly by theMinistry of the Environment, Japan (MOEJ), the National Institute for EnvironmentalStudies (NIES), and the Japan Aerospace Exploration Agency (JAXA) is the world's firstsatellite designed specifically to monitor greenhouse gases from space. The satellite
has continued to fulfill its main mission in monitoring atmospheric carbon dioxide (CO2)and methane concentrations from space to improve the accuracy of sink/source
estimates, and achieve its target to contribute to precision refinement for the ongoing
elucidation of carbon cycles, since its launch on January 23, 2009.
• Characteristics and significance of greenhouse gas observation by GOSAT
CO2 changes at surface-level monitoring sites and the global CO2 mean based on
those observations have long been reported by the World Meteorological Organizationand several other meteorological agencies around the world. To further facilitate anunderstanding of overall trends for CO2 in the atmosphere, knowledge of“whole-atmosphere” CO2 mean is necessary, and for this, more CO2 information in thevertical direction is needed. In fact, from past measurements taken by aircraft, CO2
levels are known to vary with altitude. Model predictions of whole-atmosphere CO2mean have appeared in the fifth assessment report by the Intergovernmental Panel on
Climate Change, as they are important for predicting the risk of global warming due torising greenhouse gas levels. This is where CO2 observation by GOSAT comes in useful,as the satellite measurement encompasses levels from the surface to the top of theatmosphere and provides CO2 concentration averaged over an entire atmosphericcolumn (this is referred to as column-averaged CO2 concentration).
• The method to remove seasonal variations from whole-atmosphere monthly
mean CO2This time, trigonometric functions are used to fit whole-atmosphere monthly mean
CO2 to define average temporal variations in 6 and 12 months. By subtracting suchtemporal variations, seasonal variations are removed from the monthly mean CO2. In
the calculation of CO2 trend, subtle variations observed in shorter periods are also
removed.

－5－Thursday, October 27, 2016
Director

Akio Takemoto (ext. 6730)

Director

Tsuneo Matsunaga

Fellow

Tatsuya Yokota

Kazuo Isono (ext. 6733)

Researcher

Hibiki M. Noda

Satoshi Chijimatsu (ext. 6733)

Senior Researcher

Isamu Morino and Yukio Yoshida

Shinji Urita (ext. 7718)

Satellite Observation Center

Deputy Director

Research and Information Office,+81-29-850-2035

Policy and Coordination Division,Global Environment Bureau,

HeadToshinobu Machida

Ministry of the Environment, Japan

Office for Atmospheric and Oceanic Monitoring

Phone: +81-3-3581-3351

Center for Global Environmental Research
National Institute for Environmental Studies (NIES)－6－