Climate Change Research Program Japanese

Core research project 1: Long-term variation mechanisms of greenhouse gas concentrations and their regional characteristics

Research Plan > Core Research Projects > Results of 2007
[Results of fiscal year 2007]

Research sites

The locations of the sites where we are carrying out this research project and their regional characteristics are shown below.
Figure 1: Observation sites and factors influencing variation in CO2 concentration
Figure 1: Observation sites and factors influencing variation in CO2 concentration

Global Carbon balance and its variation

CO2 emissions from anthropogenic sources have dramatically increased during the past few years, resulting in a considerable increase in atmospheric CO2 concentrations. In the present project, we have estimated the global carbon balance in the atmosphere by measuring oxygen concentrations and CO2 isotopes, using marine vessels (Figs. 2, 3, 4). According to these measurements, it was estimated that 30% of the average CO2 emissions (from fossil fuel and cement production) were taken up by the ocean and 10% by terrestrial eco-systems (Table 1).

The annual variation of carbon budget, estimated from carbon isotopes, was believed to be largely influenced by variation in CO2 uptake by terrestrial plants. This was also connected to temperature change, with generally decreasing CO2 uptake as temperatures increased. The variation in oceanic uptake was generally small until 2005, after which an increase in CO2 uptake was seen.

Figure 2: Locations of oceanic air sampling
Figure 2: Locations of oceanic air sampling

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Figure 3: Exchange of O2 and CO2s among the atmosphere, terrestrial plants, the ocean and human activities
Figure 3: Exchange of O2 and CO2 among the atmosphere, terrestrial plants, the ocean and human activities
Figure 4: Partitioning of oceanic and terrestrial plant CO2 uptake by oxygen concentration observation
Figure 4: Partitioning of oceanic and terrestrial plant CO2 uptake by oxygen concentration observation
Table 1: Global carbon balance
Table 1: Global carbon balance
Figure 5: CO2 uptake by terrestrial plants and the ocean estimated from isotopes
Figure 5: CO2 uptake by terrestrial plants and the ocean estimated from isotopes
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Factors influencing CO2 balance

In this project, we have studied the regional variations and mechanisms of terrestrial and oceanic CO2 uptake.

(a) Direct observation of variations in oceanic CO2 flux (Figs. 6-8)

For the past 11 years we have made measurements of the partial pressure of CO2 in the surface water of the North Pacific in order to estimate long-term variations in CO2 flux. We observed only a small variation in the carbon balance in the North Pacific, and found that an uptake of approximately 0.5Gt-C was maintained (Fig. 7). In 1998 we observed a small increase in the amount of CO2 uptake due to El Nino, but in 1999 a decrease was observed as a consequence of La Nina. This was in agreement with the global uptake pattern. An area of 30-40 degrees of latitude per hour was affected by this variation. Presently we have started observations by ship on the Japan-Oceania route.

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Figure 6: Observation routes in the North Pacific
Figure 6: Observation routes in the North Pacific

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Figure 7: Long-term variation of CO2 flux in the North Pacific area
Figure 7: Long-term variation of CO2 flux in the North Pacific area
Figure 8: Latitude-specific long-term variation of CO2 uptake
Figure 8: Latitude-specific long-term variation of CO2 uptake

(b) Observation of variations in terrestrial CO2 flux

The aim of this project was to study the regional characteristics and annual variation of terrestrial CO2 flux in the Asian region. At present, we are conducting observations in larch forests in Japan, and in the grasslands of the Tibetan Plateau which are rich in organic life. CO2 uptake in Tibet decreased in 2002/2003 and increased in 2004, whereas a reverse trend was observed in Japanese forests. We are going to further study this different response within the Asian flux observation network.

We are also conducting field experiments at five locations in Japan to study soil respiration, thought to be affected by climate change (Figure 9). Data collected from Tsukuba, Hokkaido and Hiroshima imply that the thermal response of soil respiration gets three times stronger when raising the temperature by 10 degrees C (Table 2). This is a 50% higher value compared with our model simulations predicting only a doubling of the thermal response, implying a much stronger thermal feedback than was estimated for Japanese forests. At present we are conducting laboratory experiments on incubation with soil segments sampled from all over Japan (Fig. 11).
Table 2: Increase in soil respiration rate as thermal response to global warming at three locations in Japan
Forest type
Control group
Global warming group
Observed increase in respiration
Effects of moisture
Broad-needle mixed forest (Hokkaido)
3.0
(0.79)
2.8
(1.0)
19%／1℃

None
Red pine forest
 (Kanto area)
2.9
(1.08)
2.7
(1.08)
3.5%／1℃
In summer
Evergreen forest
 (Chugoku area)
3.0
(0.70)
2.9
(0.63)

5%／1℃
In summer
Figure 9: Locations of field experiments for soil respiration
Figure 9: Locations of field experiments for soil respiration
Figure 10: Global warming experiment at Teshio
Figure 10: Global warming experiment at Teshio
Figure 11: Incubation experiment
Figure 11: Incubation experiment
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Variation in and regional characteristics of anthropogenic emissions in Asia

Greenhouse gas emissions from anthropogenic sources have been increasing in the Asian region. Increases in CO2 and halocarbons emissions have been observed in recent years at Hateruma monitoring station. In particular, increased emissions of HCFC-22, and HFC-23 in winter have been detected. It is estimated that more than half of the world’s HFC-23 emissions originate from the Asian region.
Figure 12: Variation in HFC-23 concentration observed at Hateruma
Figure 12: Variation in HFC-23 concentration observed at Hateruma

We also conduct aircraft monitoring of the vertical distribution of CO2 concentration above major airports in the world, and study their seasonal variation at different places. Combining information on terrestrial CO2 uptake and on the influence of the stratosphere, we found a large altitude-specific seasonal variation above the inland areas of the continent. However, the different pattern of seasonal variation within a 2km height above Jakarta and Bangkok might have been the result of forest fires.

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Figure 13
Figure 13: Average seasonal variation of CO2 above Northern Europe, Southern Europe, Vancouver: YVR, Incheon: ICN, Narita: NRT, Honolulu: HNL, Bangkok: BKK, Jakarta: CGK and Sydney: SYD
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Model analysis

In order to conduct simulation of high resolution data, we have developed a coupled model combining a trajectory type model and the traditional diffusion type model. Figure 14 shows a comparison between the traditional diffusion model and the newly developed coupled model. It can be seen that the subtle variations in the observations are best reproduced by the coupled model.
Figure 14: Simulation of observations made at Hateruma
Figure 14: Simulation of observations made at Hateruma
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Overall summary of findings of Core project 1 (Fiscal year 2008-2009)

1) Monitoring the atmosphere

・After monitoring the carbon balance for 10 years, it seems that 30% uptake by the ocean and 10% by terrestrial ecosystems is maintained.
・From continuous aircraft monitoring of different kinds of greenhouse gases and tracer gases, and 14C data accumulation, our knowledge of atmospheric and general circulation models has increased.
・Anthropogenic emissions in the Asian region, including China, greatly contribute to the regional distribution and variation in CO2, CO, Ozone and Halocarbons concentrations.
・We have collected data on the vertical distribution of CO2 uptake in Siberia both from aircrafts and monitoring towers.

2) Monitoring the ocean

・We have clarified the long-term variations of oceanic CO2 uptake in the North Pacific.
・With recently started monitoring of the West Pacific we have been able to cover a larger area in the Pacific.
・We have shown that there seems to be an annual variation in oxygen and CO2 release from the ocean. Whether this information can be used as an indicator for ocean water temperature and the production of living organisms is now under consideration.

3) Terrestrial monitoring

・When there is a disruption in an ecosystem, its CO2 uptake rapidly drops, and it ceases to serve as a CO2 sink for about 3 years.
・Our initial experiments on the effects of global warming on soil organic carbon decomposition suggest that soil organic carbon decomposition is accelerated by 20-30% as a result of heat, resulting in a considerable decrease in CO2 uptake.
・We have found a reverse thermal response in the short term between the flux sites of the Tibetan Plateau and those of Japanese forests.

4) Model

・Although our forward simulation model has been improved, a future task is to carry out further improved parameterization by using observational data.
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