Public release of whole-atmosphere monthly mean carbon dioxide concentration
based on observations by Greenhouse gases Observing SATellite "IBUKI" (GOSAT)
November 16, 2015
Ministry of the Environment, Japan
National Institute for Environmental Studies
Japan Aerospace Exploration Agency

The project of the Greenhouse gases Observing SATellite "IBUKI" (GOSAT), the world’s firstsatellite designed specifically for monitoring greenhouse gases from space, is jointly promoted by theMinistry of the Environment, Japan, the National Institute for Environmental Studies, and Japan
Aerospace Exploration Agency. The satellite has been in operation since its launch on January 23,
2009.
The whole-atmosphere monthly mean concentration of carbon dioxide (CO2), calculated by using
GOSAT data that reflect CO2 levels in all layers of the atmosphere, was found to have reached 398.8
ppm in May 2015, while showing seasonal oscillation and yearly rise over the analyzed period. Itwas also confirmed that the trend line of the whole-atmosphere CO2 mean, derived by removing
averaged seasonal fluctuations from the monthly CO2 time series, had reached 398.2 ppm in July
2015. The trend line is expected to exceed 400 ppm within the year 2016, given that the rising trend
continues. The GOSAT observation elucidates for the first time that CO2 concentration averaged
over all layers of the atmosphere will soon reach the level of 400 ppm, and demonstrates theimportance of global greenhouse gas monitoring from space.

● About Greenhouse gases Observing SATellite “IBUKI”
The Greenhouse gases Observing SATellite "IBUKI" (GOSAT) is the world's first satellite designed
specifically for the monitoring of greenhouse gases from space. Its primary purpose is to measure theatmospheric concentration of carbon dioxide (CO2) and methane from space so as to improve theestimation of the surface fluxes of these two gases and, further, to contribute to refining the prediction offuture carbon cycle. The satellite has been in operation since its launch on January 23, 2009. The GOSAT
Project is jointly promoted by the Ministry of the Environment, Japan, the National Institute forEnvironmental Studies (NIES), and Japan Aerospace Exploration Agency (JAXA) (hereafter the threeparties).
● 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 havelong been reported by the World Meteorological Organization and several other meteorological agencies
1around the world. To further facilitate an understanding 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 tovary with altitude. Model predictions of whole-atmosphere CO2 mean 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 to rising 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 atmospheric column (this is referredto as column-averaged CO2 concentration).
● Whole-atmosphere monthly mean CO2 concentration as seen by GOSAT
The whole-atmosphere mean CO2 concentration was calculated based on GOSAT measurement.
Observational data collected by the satellite over a period exceeding six years, between May 2009 andJuly 2015, were used for this calculation. Over the analyzed period, the monthly mean CO2 concentration
continually rose, with seasonal fluctuations due to photosynthetic activity by plants that intensifies andsubsides over a single year in the Northern Hemisphere. The monthly mean reached 398.8 ppm in May
2015. The trend line of the global CO2 mean, obtained by subtracting averaged seasonal fluctuations fromthe monthly CO2 time series, reached 398.2 ppm in July 2015 1). It was also found that the trend line will
exceed 400 ppm within the year 2016, if the rising trend continues. It is expected that the monthly mean
concentration will reach 400 ppm earlier than the trend line does. We note here that areas that GOSAT
measurement can cover are limited to parts of the globe without cloud cover and where the local solar
altitude is above a specific threshold. Therefore, the global distribution of column-averaged CO2
concentration, needed for the calculation of the whole-atmosphere mean CO2 concentration, was estimatedfrom GOSAT data 2). Shown below are the time series of the monthly mean CO2 concentration and thetrend line calculated from the monthly time series 3). The values shown here are found to be smaller by 1-2
ppm than those based on CO2 measurements at the surface level 4).

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Whole-atmosphere mean CO2 concertation (ppm)Monthly mean CO2
CO2 trend

Note: The error bar on the red circle indicates uncertainty (one standard deviation) associated with thewhole-atmosphere monthly mean.

● Public release of GOSAT observation results
The three parties will publicly release the above-mentioned whole-atmosphere monthly mean CO2
concentration, estimated from GOSAT observations collected over clear-sky areas of the globe. The data
will be released on November 16, 2015 from the website of the NIES GOSAT Project. The released data
will be updated regularly over the remaining lifetime of the satellite. This public release is intended tohighlight the reality of rising CO2 levels and to contribute to efforts for reducing greenhouse gas
emissions.
The released data can be obtained from the webpage “Whole-atmosphere monthly mean CO2
concentration” (http://www.gosat.nies.go.jp/en/recent-global-co2.html) found on the NIES GOSAT
Project website.
The three parties will continue the public dissemination of new findings from GOSAT observation. Also,
the parties plan to continue the ongoing space-based greenhouse gas observation with the GOSAT
successor (GOSAT-2), which is planned to be launched in 2018. Results of the continued observation will
be utilized for the elaboration and refinement of global warming predictions.
3Notes:1)

Some of the GOSAT data used in this analysis, dated after February 2015, are still preliminary,pending final validation.

2)

See Appendix for more details on the estimation approach used.

3)

Result for January 2015 is missing due to lacking data for instrument adjustment

4)

US National Oceanic and Atmospheric Administration reported that global mean CO2 concentration
based

on

surfacelevelmeasurements

reached400

ppm

inMarch2015.

Source:http://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/11153/
Greenhouse-gas-benchmark-reached-.aspx[Contact Information]
About GOSAT data and analysis results:
NIES GOSAT Project Office
Phone: +81-29-850-2966
About GOSAT, onboard sensors, and observation status:
Masakatsu Nakajima
JAXA Space Technology Directorate I
GOSAT-2 Project Team
Phone: +81-50-3362-6130

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