沙漠研究 24-1, 1-4 (2014)
Ἃ₍◊✲ 24-1, 1 - 4 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Keynote Paper －㸫DT11 Refereed Paper㸫

Climate Change and CO2- Role of Terrestrial Vegetation Toshinori KOJIMA*1), 2)
Abstract: The recent status of the climate change issue is firstly addressed. Considering the increase in global population, the mostserious climate change problem should be solved together with food, energy resources and other environmental problems. The roleof terrestrial vegetation in the carbon balance is reviewed next and it is recognized that the role of terrestrial vegetation is large, and theafforestation should come after or together with the prevention of deforestation. Though biomass is one of the ways to reduce theatmospheric CO2 using renewable energy, the energy conversion efficiency is much lower than that of PV (photovoltaic). In the caseof afforestation, though CO2 reduction per unit area may be lower than biomass, necessary energy for this measure is low with highgain. The plantation should be done in areas other than agricultural lands; grass, unused, semiarid or arid land. The area of unused
land with sufficient available water is small so semiarid and arid land should come as the target of a large scale afforestation. Finallythe present status of our technology development for arid land afforestation in Western Australia is introduced. The necessity anddifficulty of its extension to other dry areas is discussed.
Key Words: Afforestation, Arid land, Carbon storage, Climate change, Terrestrial vegetation

1. Introduction
It was a very hot summer in Japan. I remember that I wasalways writing the same words every year. “Abnormalclimate” means very rare climate appearing once per three
decades or so. Therefore, the appearance of abnormal climate
itself is not abnormal, but recently the frequency of its
appearance is “abnormally” high.
In the present paper, first of all, the outline of the climatechange issue is summarized. Considering the increase inglobal population, the most serious climate change problem
should be solved together with the food, energy resources andother environmental problems. Then the role of terrestrial
vegetation in the carbon balance is reviewed (Kojima, 1998).
Finally, our trial of arid land afforestation in Western Australia
is addressed and importance and difficulty of arid landafforestation are discussed. We love to contribute to theglobal environment by this tool, though we do not have any
desert in Japan.

2. History of Climate Change Issues
2.1. Climate change as a global environmental issue
I firstly found a report on carbon dioxide concentration
increase, in a book of “The Limits to Growth” (Meadows et al.,1972), though the comment on it was just “anthropogenic”.

In 1988, IPCC (Intergovernmental Panel on Climate Change)
was established. Its reports have been published on 1990
(FAR, 1st. Assessment Report), 1995 (SAR), 2001 (TAR) and2007 (AR4). The fifth report (AR5, 5th Assessment Report)
will be completed in 2013/2014.
2.2. Kyoto Protocol
In 1992, the United Nations Framework Convention on
Climate Change (UNFCCC) was adopted at the Earth Summit
held at Rio de Janeiro. In Dec. 1997 (Dec.), Kyoto Protocol
was adopted at COP3 (3rd. Conf. Parties), Third Conference ofParties to UNFCCC. Though United States had withdrawn
from it, it became effective in Feb. 2005 by ratification byRussia. The essences of the Kyoto Protocol were as follows:a) by the period of 2008 to 2012 compared to 1990 levels(compared to 1995 levels for HFC, PFC, SF6),b) reduction in greenhouse gas emissions at least -5% of thetotal for developed countries; e.g., -8% for EU, -7% forUSA, and -6% for Japan,c) in terms of CO2-equivalent; ×21 for methane, ×310 for N2O,×1300 for HFC, ×6,500 for PFC and ×23,900 for SF6.
d) emission trading, joint implementation, and clean
development mechanism.
e) In addition to the above,inclusion of the effects of land-use
changes, namely CO2 absorption by forests establishedafter 1990 was also incorporated.
For Japan, more than half of the duty-bound reduction of* Corresponding Author: kojimaseikei@gmail.com
3-3-1, Kichijoji-Kitamachi, Musashino, Tokyo, 180-8633, Japan
1) Department of Materials and Life Science, Seikei University, Japan
2) Centre for Ecosystem Management, School of Natural Sciences, Edith Cowan University, Australia

㸦Received, September 13th, 2013; Accepted, November 27th, 2013㸧



Fig. 1. The global carbon cycle for the 1990s; fluxes by arrows in GtC/y and stocks in circles in GtC. Vales in parentheses indicate those before
1975 and others, additional ones at 1994.
Table 1. Amounts of carbon stored in various terrestrial ecosystem (Kojima, 1998).

6% had been achieved by this term. After the termination of
appointed term, now the reduction duty by Kyoto Protocol has
been extended to 2020, but Japan, the country which
experienced the devastative earthquake in 2011, has decided towithdraw from it, as has the United States.

3. Role of Terrestrial Vegetation and Desert
3.1. Role of terrestrial vegetation in the carbon cycle
Figure 1 (simplified from IPCC, 2007) shows the global
carbon cycle. The carbon accumulation in atmosphere is 3.2
Gt-c/y (6.4+1.6-2.6-2.2), which is directly calculated fromincreased CO2 concentration in the atmosphere. Between
atmosphere and land vegetation, around 120 Gt-C/y is
exchanged and it is almost globally balanced (in the level lessthan 0.1 Gt/y) before industrial revolution. Recently, 1.6 Gt/yis released (cumulatively 140 Gt until 1994) by land usechange (mainly deforestation), which is estimated by the landuse data by FAO etc., and the data given in Table 1. On theother hand, as the missing sink calculated from other sectors,
land is estimated to be absorbing 2.6 Gt/y (cumulatively 101Gt), which is explained by increase in per area biomass,Fig. 2. The cycle of materials in forest (dry organic matter basis,
Kojima, 1998).

namely the fertilization effect by increased CO2 concentration.
As shown in Figure 1, terrestrial vegetation has asignificant impact on carbon stock/cycle. Land vegetation
contains four times the carbon amount of the atmosphere.
Furthermore, twenty times more carbon dioxide is exchanged
with the atmosphere by means of photosynthesis than that
released from fossil fuels. The increased amount of CO2 in
atmosphere is twice the amount of the CO2 released fromdeforestation.
Forests are also considered to convert solar into chemicalenergy by recycling carbon as shown in Figure 2. However,Fig. 3. Forest growth and carbon fixation (Kojima, 1998).

the efficiency of solar energy use in tropical rainforests is only
0.25%, at most even when all the net primary production oforganic matter is considered as energy. Only about 20% ofthat is retained in the tree in the form of branches and trunks.
Furthermore, about 30% of that retained energy can be utilized
as generated electricity from wood. The total conversion
efficiency is less than 0.02%, which is much less than 10% of
the efficiency of a solar cell. Accordingly, the forests do nothave a large role to play when considering vegetation as a tool
for the conversion of solar energy.
3.2. Importance of arid land afforestation
Table 1 classifies each of the Terrestrial ecosystems in theworld.
It gives the sizes of the areas they cover,carbon-equivalent stock of living vegetative matter and dead
substances, density (total stock divided by the area), net
primary production (flow), and the amount of production perunit area (production density). Furthermore, the time constant(i.e. minimum time required for a complete exchange ofcarbon stock) is obtained by dividing the stock by flow; thevalue is given for both living matter and for living matter plus
dead matter combined.
From differences in the data of the amount of carbon inliving matter in tropical forests and in tropical grasslands(savanna), it was calculated that conversion of the tropicalforests into grasslands would result in the loss of about 16
Gt-C/ha.
Trends of carbon fixation rate and its cumulative value
after plantation are shown in Figure 3 (a) and (b), respectively,
when a forest is left without clearing. It is true that trees
absorb carbon dioxide and store the carbon in their body while
they are growing, but this stops after they reach maturity. The
rate of carbon fixation reaches a peak at about 15 - 20 years
after planting; and then the accumulation is virtually ceases.
In this sense, the situation can be regarded as being virtually
the same as subterranean storage (CCS: carbon capture andstorage). The difference is that in the case of afforestation it issufficient to just dig a hole in the ground and plant a sapling.
After plantation, the tree will grow on its own, and carbon willaccumulate naturally. Namely the necessary amount ofenergy for carbon fixation is small. In addition to the above

Fig. 4. Relative importance of PV, biomass and afforestation(Kojima et al., 1999).

difference, the material stocked in the tree is an organic
material not carbon dioxide, and the disadvantage of that is it
takes quite a while to achieve. However, the time required is
at most 20 to 30 years, which is sufficiently short in the context
of the carbon dioxide problem.
The other problem concerns the amount of available spaceand quantities that can be stored. The density of organic
matter in tropical and other forests is over 200 t-C/ha. If
deserts could be transformed into tropical forests, over 200
t-C/ha is accumulated, but it would be necessary to afforest
about 32 million ha each year to mitigate the annual carbon
release from fossil fuel of 6.4 Gt/y shown in Figure 1. If
considering natural sink in ocean of 2.2 Gt/y and that interrestrial vegetation of 2.6 Gt/y, and the release by
deforestation is stopped, the amount of carbon which should besequestered is reduced to a quarter of 1.6 Gt/y, with necessaryannual afforestation area of 8 million ha/y. Not completely
the same carbon amount as but comparable to the desert
afforestation is expected to be stored by changing form
agricultural land, abandoned land or grass land to the denseforest. The plantation should be done in the other areas thanagricultural land where our food is produced. Some grasslands for pastures have the same role as agricultural land.
The area of unused lands with sufficient water is limited, so,semiarid and arid lands should be the target for large scaleafforestation.
Considering the area of 4.2-4.5 billion ha of desert in Table
1, carbon sequestration by arid land afforestation can beregarded as the measure of more than 500 years.
3.3. Afforestation and biomass production
Figure 4 shows the relative role of solar, afforestation andcondition.

4. Conclusion

Fig. 5. Global distribution of arid area (Kojima and Egashira, 2011).

biomass. By introduction of PV (photovoltaic), hugeamounts of CO2 emission can be reduced by replacing fossil
fuel power generation. However in the case of PV, energy forthe production of PV modules leads to CO2 emission, so thegain is little. Furthermore, the produced electricity should betransported to its destination, and cannot be installed in thedesert area far from cities. In the case of afforestation, theamount of required energy is little, but the carbon which can bestored per unit area is little compared to CO2 emission by PVinstallation. Biomass energy production locates at themoderate place between them. We must put the right man in
the right place.
It looks promising to use the surplus biomass from theafforestation area as energy, because the CO2 emission
equivalent to the harvested wood can be reduced, if used foralternative energy such as electricity production. However,additional energy for harvesting should be minimized because
the averaged amount of carbon stock is reduced compared tothe case that the afforested area is left without clearing, as isexpected in Figure 3. According to Righelato and Spracklen(2007), much more CO2 is expected be mitigated by tropicalcropland afforestation than by bioenergy production using theland, though the present estimation of 30 years will be changed
when the evaluation term is changed.
3.4. Difficulty of arid land afforestation
Some semiarid and arid lands are said to be formed byindustrial activities, such as mining, metallurgy, ceramics
manufacturing, and farming. This means these areas are
essentially possible to be afforested if we introduce sometechnologies that guide the route from present stable but arid
vegetation to another ideal stable ecosystem with much moretrees. However, the problem is “how to get, manage andsupply sufficient water to the root area” under the arid

The colleagues of the author are now trying to develop
some technologies for afforestation of arid areas in Western
Australia and are getting some fruitful results (Kojima et al.,2006). However, considering some of deserts have very
limited annual precipitation compared to Australia as shown inFigure 5. Some strategy to extend the afforested area frommoderately dry area to severely dry area is necessary, but I
believe this should be possible from the view point of water
recycling.

References
IPCC (2007): IPCC Fourth Assessment Report: Climate
Change 2007(AR4): Working Group I: The PhysicalScience Basis, Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA., Fig. 7.3(http://www.ipcc.ch/).
Kojima T. (1998): The Carbon Dioxide Problem: Integrated
Energy and Environmental Policies for the 21th Century,
CRC Press/ISBN-13: 9789056991272/.
Kojima T., Tahara K., Inaba A. (1999): Relative importance ofsolar PV, bio-mas energy and afforestation as measures for
CO2 Problem. Proc. Intern. Conf. on Role of Renewable
Enery Technology for Rural Development, pp.81-85, Oct.
12-14, 1998, Kathmandu, Nepal.
Kojima T., Hamano H., Abe Y., Tanouchi H., Egashira Y., Saito
M., Law J., Takahashi N., Yamada K. (2006): Basic Data ofResearch Project on Large Scale Afforestation of Arid Land
for Carbon Fixation near Leonora in Western Australia.
Journal of Arid Land Studies, 16(3): 167-174.
Kojima T., Egashira Y. eds. (2011): Arid Land Afforestation
against Climate Change, Korona, Tokyo (in Japanese).
Meadows D.H., Meadows D.L., Randers J., Behrens III W.W.
(1972): The Limits to Growth. Universe Books, New York.
Righelato R., Spracklen D.V. (2007): Carbon Mitigation by
Biofuels or by Saving and Restoring Forests? Science, 317:
902.