Joint Submission to the first Global Stocktake:The decadal global atmospheric greenhouse gas concentration trends
observed by Japan’s Greenhouse gases Observing SATellite(GOSAT)The Japan Aerospace Exploration Agency (JAXA) and the Institute for the Global Environmental
Strategies (IGES) are pleased to submit an input to the Global Stocktake of the Paris Agreement inresponse to the mandate of Decision 19/CMA.1, paragraph 19, 36 and 37. This submission provides
our input for mitigation guiding question 3 1:

Summary・ A decadal global JAXA/GOSAT GHG product shows continued increases in global CO2 and CH4,
which increased by 29 ppm and 97 ppb from June 2009 to June 2021, respectively. The productalso presents the seasonal cycles of concentrations that are primarily attributable to natural GHG
removals and the resulting carbon budget.
・ The Greenhouse gas Observing SATellite (GOSAT) 2 is the world’s first GHG-dedicated spacebased observatory launched in 2009 by Japan. GOSAT simultaneously monitors global changes
in CO2 and CH4 atmospheric concentrations.
・ GOSAT observations have collected CO2 and CH4 data over areas where ground-basedobservations are unavailable or sparse. GOSAT can monitor CO2 and CH4 at 100 times thenumber of locations than ground-based observation, filling in the observational gaps andcollecting data on areas where climate mitigation impacts are expected, such as megacities.
・ The JAXA/GOSAT GHG product is publicly available to assess CO2 and CH4 concentration
changes. The product directly contributes to elucidating the global and local carbon cycle andmonitoring the nation’s climate mitigation efforts toward the Paris Climate goal.

1
What are the trends of the concentration of GHGs in the atmosphere and global average temperature and what global emission
pathways are consistent with the goals set out in Articles 2 para 1(a) and Article 4.1?
2GOSAT is a joint project of the Japan Aerospace Exploration Agency (JAXA), the Ministry of the Environment (MOE), and theNational Institute for Environmental Studies (NIES).

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Figure 1. Monthly average CO2 changes (red).
The JAXA/GOSAT CO2 data between 70°N and 50°S are averaged for each month.

Figure 2. Monthly average CH4 changes (blue).
The JAXA/GOSAT CH4 data between 70°N and 50°S are averaged for each month.

2Table 1. A summary of the JAXA GOSAT GHG product
Items

Description

Monitored GHGs

CO2, CH4

Variables

Total, lower, and upper troposphere column concentrations

Indicator

forGHG

Solar induced fluorescence (SIF) for emissions/removals

emissions and removals(natural)Target spatial scale (s) of

Global, regional, national, and subnational (cities)

emissions and removals
PeriodJune 2009-Pressent

Frequency

Monthly

Uncertainty

2 ppm for total column CO2, 17 ppb for total column CH4

Data accesshttps://www.eorc.jaxa.jp/GOSAT/index.html

1. Methodology
1.1 Overview of GHG observations by Japan’s GOSAT satellite
Japan’s Greenhouse gases Observing SATellite (GOSAT) was launched as the first GHG-dedicatedsatellite on the 23rd of January 2009. Since then, GOSAT has monitored changes in atmosphericcarbon dioxide (CO2) and methane (CH4) to advance our understanding of the global carbon cycle andsupport climate monitoring.
The GOSAT observation concept is illustrated in the right image of Fig. 3. GOSAT observations
are based on remote sensing and measure the solar light reflected from the Earth’s surface forcollecting atmospheric CO2 and CH4 data. GOSAT carries a Thermal and Near-Infrared Sensor for
Carbon Observation Fourier-Transform Spectrometer (TANSO-FTS). The spectrometer detects gas
absorption spectra of solar radiation reflected from the Earth’s surface in the Short-Wave InfraRed(SWIR) region and the Thermal Infrared Radiation (TIR) emitted by the ground and the atmosphere.
TANSO-FTS can simultaneously measure the oxygen A band (0.76 μm), weak and strong CO2 bands(1.6 and 2.0 μm), weak CH4 bands (1.6 μm) with orthogonal polarizations, and a wide TIR band (5.5–14.3 μm) with 0.2 cm−1 spectral sampling intervals. GOSAT has accumulated global CO2 and CH4
data continuously every three days with a circular observation footprint of 10.5 km diameter from analtitude of 666 km.
GOSAT pioneered the two-axis agile pointing mechanism for implementing special target mode
observations of megacities and large power plants. This mechanism has been adopted by other stateof-the-art satellites, such as OCO-3 and GOSAT-2. The pointing system allows us to implement
multiple observation patterns tailored for target emissions and removals, such as gird observations
over land, glint observations over oceans, and target observations over megacities and large point
sources. The technical details of the GOSAT satellite are described in Kuze et al., 2009, 2016.
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1.2 JAXA/GOSAT GHG products
Several research teams have utilized GOSAT data to retrieve the column concentration of both
CO2 and CH4. While there are several retrieval methods, most focus on using the reflected sunlight
spectra in the SWIR region for retrieving the total-column information. In contrast to conventional
methods, JAXA developed a retrieval algorithm to derive vertical concentration information by usingreflected sunlight with two orthogonal polarizations and thermal emissions observed by GOSAT. The
product allows us to use concentration information for the lower and upper troposphere to assess
surface emissions better. The two-layer vertical concentration information, especially the one near thesurface, will enhance our ability to examine surface emissions and removals and advance ourunderstanding of the carbon cycle.
Figure 3 shows a schematic diagram of the satellite GHG observation concept and the difference
between conventional total-column GHG retrieval data and the JAXA/GOSAT GHG product (withtwo-layer vertical information). Due to CO2 emissions and removals at the surface, the lower
troposphere concentration should reflect surface emissions more directly than the total columnaveraged concentration. The JAXA/GOSAT GHG product includes both total and two-layer verticalconcentration to assess anthropogenic emissions better. A detailed technical overview is described inKikuchi et al., 2017.

Figure 3. A schematic diagram of the JAXA/GOSAT GHG product42. Results
The monthly averaged CO2 and CH4 changes and trends are presented in Figs. 1 and Fig.2,respectively. JAXA/GOSAT GHG data in the region between 70°N and 50°S were averaged toobtain monthly average CO2 and CH4 values. The trends in CO2 and CH4 concentrations werecalculated as the polynomial part of Eq. 1.

22𝑓𝑓(𝑡𝑡) = 𝑎𝑎0 + 𝑎𝑎1 𝑡𝑡 + 𝑎𝑎2 𝑡𝑡 + � 𝐶𝐶𝑛𝑛 [𝑠𝑠𝑠𝑠𝑠𝑠(2𝑛𝑛𝑛𝑛𝑛𝑛 + 𝜑𝜑𝑛𝑛 )]𝑛𝑛=1

Eq.1.

The trends of CO2 and CH4 clearly show the increase of atmospheric CO2 and CH4 in the last decade.
The latitudinal monthly average CO2 changes are plotted in Fig. 4 with the fit lines based on Eq.
1. As shown in Fig. 4, larger seasonal variation and higher concentrations are observed in the northernhemisphere because of the large terrestrial sinks in this region and the emissions from mostindustrialized countries.

Figure 4. Latitudinal monthly average CO2 changes with the function fit lines.
The JAXA/GOSAT CO2 data are averaged for each 20°latitudinal bin. Lines are color-coded bylatitude.
The latitudinal monthly averaged CH4 changes are plotted in Fig. 5. Like the CO2 feature, the5larger seasonal amplitudes and higher concentrations were observed in the northern hemisphere. For
CO2, the seasonal variation in the southern hemisphere is milder than in the northern hemisphere. In
contrast, the seasonal variation of CH4 in the southern hemisphere is also clearly observed with a phasedifferent from that of the northern hemisphere.

Figure 5. Latitudinal monthly average CH4 changes with the function fit lines.
The JAXA/GOSAT CH4 data are averaged for each 20°latitudinal bin. Lines are color-coded bylatitude.
As shown in Figs. 1 and 2, JAXA/GOSAT GHG products present the global CO2 and CH4
concentration changes. Features such as seasonal trends are similar to ground-based observations.
Figures 6 and 7 show the locations of ground-based in-situ observation stations and GOSAT
observation points in June 2021, respectively. Comparing the observation locations between the global
ground-based network and the satellite-based (GOSAT) observation, the GOSAT observations collect
CO2 and CH4 data over the areas where ground-based observations have not been available or aresparce. GOSAT can provide more than 100 times the number of CO2 and CH4 observation points tofill such observation gap areas.

6Figure 6. The world distribution of ground-based observation stations.

Figure 7. the GOSAT observation track in June 2021.

3. Contact Persons
Hiroshi Suto, Japan Aerospace Exploration Agency, suto.hiroshi@jaxa.jp
Akibi Tsukui, Institute for Global Environmental Strategies, tsukui@iges.or.jp

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4. References
Kuze, A., Suto, H., Nakajima, M., and Hamazaki, T.: Thermal and near infrared sensor for carbon
observation Fourier-transform spectrometer on the Greenhouse Gases Observing Satellite forgreenhousegases

monitoring,Appl.

Optics,48,

6716–6733,

https://doi.org/10.1364/AO.48.006716, 2009.
Kuze, A., Suto, H., Shiomi, K., Kawakami, S., Tanaka, M., Ueda, Y., Deguchi, A., Yoshida, J.,
Yamamoto, Y., Kataoka, F., Tay- lor, T. E., and Buijs, H. L.: Update on GOSAT TANSO- FTSperformance, operations, and data products after more than 6 years in space, Atmos. Meas. Tech.,9, 2445–2461, https://doi.org/10.5194/amt-9-2445-2016, 2016.
Kuze, A., Kikuchi, N., Kataoka, F., Suto, H., Shiomi, K., Kondo, Y.: Detection of Methane Emission
from a Local Source Using GOSAT Target Observations. Remote Sens. 2020, 12, 267.
https://doi.org/10.3390/rs12020267, 2020.
Kuze, A., Nakamura, T., Oda, T., Yoshida, J., Kikuchi, N., Kataoka, F., Suto, H., Shiomi., K.:
Examining partial-column density retrieval of lower-tropospheric CO2 from GOSAT target
observations over global megacities. (Accepted)
Kikuchi, N., Kuze, A., Kataoka, F., Shiomi, K., Hashimoto, M., Suto, H., Knuteson, R., Iraci, L.,
Yates, E., Gore, W., Tanaka T.: Three-dimensional distribution of greenhouse gas concentrations
over megacities observed by GOSAT, AGU fall meeting. 2017.

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