63

Agro-climatological Aspects of the Global Warming and
Its Impact on Paddy Rice Cultivation in East Asia
Yousay HAYASHI
Graduate School of Life and Environmental Sciences,
University of Tsukuba
1-1-1 Tennoudai, Tsukuba-shi, Ibaraki 305-8572, Japanhayyou@geoenv.tuskuba.ac.jp

Abstract
Agriculture is one of the sectors having a very close relation to global warming. Intergovernmental
Panel on Climate Change (IPCC) shows ranges of percentage changes in crop yields with adaptive climatechange scenarios for geographic location of the growing area. For rice of temperate Asia, only a clear
increment is expected with an adaptation by shift of cultivation season. However, these estimations do notinclude variability of weather conditions which is getting more and more obvious. Actually, in the record
observed, cold-weather damages occurred even under the global warming conditions. It will need to observe
carefully the past and future agro-climatological events, because we need a long period of time before
mitigation technology begin to work.
Key words: agro-climatology, cold damage, East Asia, global warming, paddy rice

1. Introduction
The first commitment period of the Kyoto Protocol
finally started in 2008. In the five years from 2008 to
2012, Japan has to reduce its emission of greenhousegases by 6% below 1990 levels. Thus we have entered
the age when we should recognize the need to prevent
global warming in all of the areas of our life.
The problem of global warming is a new type ofenvironmental issue where the study and forecast ofnatural scientific phenomena and the introduction ofsystems and policies affecting social norms are closely
linked with each other. This problem greatly differsfrom traditional problem-solving type issues althoughscience and technology have developed so further that it
is now possible for us to predict the future, it isconsidered that we are still unable to examine thepredicted result fully at the time when we begin to takemeasures for the problem. Preventing global warming
contains some difficulties; for example, you may have todepend on an apparently uncertain forecast of the futurewhen you request the public to change even the qualityof their daily life.
This is related to the provisions of Article 2 of the
Framework Convention on Climate Change, on which
the Kyoto Protocol is based: “The ultimate objective of
this Convention is to achieve stabilization of greenhousegas concentrations in the atmosphere at a level thatwould prevent dangerous anthropogenic interference
Global Environmental Research
13/2009: 63-68
printed in Japan

with the climate system.” These provisions mean that it
is important to identify the dangerous level of global
warming and the threshold on which global warming
starts to have impact on climate change and that there is
the need not only to study uncertain factors but also torecognize the impact of global warming as a risk.
The present report discusses recent understanding
about global warming impacts on agriculture. Agriculture is one of the sectors having a very close relation to
global warming. While the food production activities ofagriculture generate greenhouse gases, its cultivation
environment is affected by global warming caused bythese gases. Especially, the latter aspect is described as
the subject.

2. Cause of Temperature Rise
The composition of the atmosphere and the ecosystem on the earth have changed while they have closely
been linked with each other. The gases contained in theatmosphere are, in order of the volume at present, nitrogen (approx. 78%), oxygen (21%), argon (0.9%), carbon
dioxide (0.038%) and other minor ones. Of them, thecontent of carbon dioxide (CO2) is very low, but this gas
differs from the other gases in some respects. Once
generated, CO2 stays in the atmosphere in a relatively
stable state, and this gas is one of the greenhouse gases.
Here let’s take a look at the temperatures on the earth.
The average annual temperature on the earth at present©2009 AIRIES64

Y. HAYASHI(approx. 15°C) has been kept just because a certain levelof CO2 has existed. It is relatively easy to estimate theheat budget of the earth when no CO2 exists; the resultis –19°C. The average temperature on the earth atpresent is higher than this by 34°C. This means that only
because there exist greenhouse gases, including CO2, on
the earth, certain levels of high temperatures aremaintained there. This is due to greenhouse effects.
From this fact we can say that CO2 and other greenhouse gases are indispensable substances for oursurvival. However, a massive amount of fossil fuels has
been consumed for human activities since the Industrial
Revolution, rapidly raising the concentration of greenhouse gases in the atmosphere. This is the main cause of
global warming.
The physical and chemical process in which the increasing concentration of greenhouse gases causes thetemperature on the earth to rise was well known fromold times. During and after the Industrial Revolution
period, as the fact was found that the concentration ofgreenhouse gases in the atmosphere suddenly increased

and that the temperature rose, observation was started
and then consensus began to develop about the fact thathuman activities accelerated global warming. This was a
relatively recent event; the Third Assessment Report(2001) of the Intergovernmental Panel on Climate
Change (IPCC) played a role in this issue.

3. International Trends Concerning Global
Warming
Table 1 summarizes the main events relating to
global warming. The crisis of global warming was firstrecognized in 1985, 24 years ago, at the Villach Conference. This conference adopted the declaration that temperature increases in the world in the first half of thenext century would be such large ones as the humanrace never experienced. Then in 1988, three years after
the Villach Conference, the IPCC was founded and hassince played an important part in addressing climatechange problems.
The first Assessment Report published in 1990 by

Table 1 Main events concerning global warming in the world.
Year
Event
1962 R.L. Carson, “Silent Spring”
1972 Club of Rome, “The Limit to Growth”
1977 United Nations Convention to Combat Desertification (UNCCD)
1979 The World Meteorological Organization (WMO) warned global warming caused by greenhouse effects.
1980 The U.S. government, “The Earth in the Year of 2000”
October: Villach Conference (international conference for summarizing scientific knowledge about climate change);
1985
Vienna Conference (on the protection of ozone layers)
1987 “Montreal Protocol”
1988 November: IPCC established
Conference of Environmental Ministers on Air Pollution and Climate Change (Noordwijk Conference); the1989 November:
Noordwijk Declaration; the world recognized the need to stabilize the emission of greenhouse gases.
IPCC’s first Assessment Report (which predicted that the average temperature on the earth would rise by 3°C by
1990 August:2100.)The Intergovernmental Negotiating Committee started negotiations about the UN Framework Convention on Climate
1991 Change.
(UNFCCC)
June: The UNFCCC was adopted (in New York); the aim was to keep the concentration of greenhouse gases in the
1992 atmosphere on a level not adversely affecting the climate on the earth; the UN Conference on Environment and Development
held the Global Environment Summit (that adopted the Agenda 21 and the Rio Declaration.)
The Organization of Economic Cooperation and Development (OECD) created the joint special subcommittee on
1993 “agriculture
and the environment.”
1994 March: The UNFCCC came into force; Lester Brown (Worldwatch Institute) founded the State of the World series.
March: First Conference of Parties to the U.N. Framework Convention on Climate Change (COP1) was held in Berlin,
1995 Germany; December: IPCC’s second Assessment Report (which stated that there is the evidence that global warming alreadyoccurred.)1996 Theo Colborn, et al., “Our Stolen Future”
December: COP3 (Third Conference of Parties to the U.N. Convention on Climate Change) adopted the “Kyoto Protocol;”1997 industrial countries would reduce their total emission of greenhouse gases in the period 2008 to 2012 by 5.2% below the1990 level.
March: The U.S. withdrew from the Kyoto Protocol; IPCC’s third Assessment Report; July: the final agreement on the rules
2001 ofthe protocol operation reached at the COP6 for the second time.
June:
Japan ratified the Kyoto Protocol; the Japanese government formulated the “General Rules on the Promotion of
2002 Measuresagainst Global Warming.”
2003 The third World Water Forum held; Lester Brown (Earth Policy Institute), “Plan B”
2004 November: Russia ratified the Kyoto Protocol; December: COP10 (in Buenos Aires, Argentina)
The Kyoto Protocol came into force; July: Global warming was the main item of the agenda of the Summit
2005 February:
Meeting (G8 Summit).
Gore, “An Inconvenient Truth”; the Stern Review suggested that the measures to be taken in 20 to 30 years from now
2006 Alwould have dramatic effects on the climate up to the 22nd century.
2007 IPCC’s fourth Assessment Report.
2008 The first commitment period of the Kyoto Protocol started.

Agro-climatological Aspects of the Global Warming and Its Impact on Paddy Rice Cultivation

the IPCC pointed out that the average temperature on
the earth would rise by 3°C by 2100. In 1991,
negotiations for a framework convention on climatechange were started for the purpose of reflecting scientific knowledge about global warming on policies. Thenthe IPCC’s second Assessment Report released in 1995
stated that there was the evidence that global warming
already occurred. As the situation of global warming
was thus known more and more, the COP3 (Third
Conference of Parties to the U.N. Framework Convention on Climate Change) held in 1997 adopted the
Kyoto Protocol. The period until about that time can be
regarded as Phase 1 of the problems of global warming.
While in about ten years of Phase 1, the conditions
and problems of global warming and public recognition
about these were made clear and became greater rapidly.
As long as eight years were spent until the Kyoto
Protocol finally went into effect in 2005 after thewithdrawal of the U.S. and the ratification by Russia.
We might have sympathized with the subtle change inthe view of the world at the end of the century. But wehave to find now how wasteful those years were when
we were trifled with by the opinions of the big powers.
Thus in 2007, the IPCC’s fourth Assessment Report was
published and then in 2008, the first commitment periodof the Kyoto Protocol started. The period until this may
be regarded as Phase 2. We have just entered Phase 3,
when we should take concrete steps to stabilize theconcentration of carbon dioxide.

4. Scientific Bases
The scenario of how greenhouse gases will be emitted in the future is determined by the four story lines(IPCC, 2007). The four story lines here mean the four
quadrants formed on a plane by the two coordinate axes:
the axis of nature-oriented society – developmentoriented society and that of regionalistic society –globalization society. That is, the story lines include thecase where the social structure in the future tends tohead in a development-oriented and globalization direction or where it goes in a nature-oriented and regionalistic direction, and so on. The forecast of global warming
is greatly affected not only by these scenarios for greenhouse gas emission but also by the numerical model
used for the forecast. Because of this, it has been therule to specify the symbol of the scenario adopted andthe name of the numerical model used on each of theforecast results.
The scientific bases for global warming stated in the
IPCC’s fourth Assessment Report can be summarized asfollows: (1) There is no doubt about the occurrence of
global warming; the average temperature increase in theworld was 0.74°C according to the observation data in
the 100 years from 1906 to 2005; (2) From 1961 to 2003,
the average level of sea surfaces in the world rose by
about 1.8mm a year, and it is highly likely that themelting of ice sheets in Greenland and on the South Pole
has contributed to this; (3) Glaciers and snow in themountains have decreased both in the Northern and

65Southern Hemispheres; (4) The frequency of heavy rains
has increased in many land areas; and (5) While thenumber of cold and frosty days has decreased, that ofhot days and heat waves has grown.
The report forecasts future climate conditions as follows: (1) Temperature: The temperature will rise by
about 0.2°C per decade in the 20 years from now. The
average annual temperature in the world at the end of
the 21st century will be higher than the annual averagefor the 1980-1999 period by 1.1-6.4°C; (2) Oceans: The
normal value of the average level of sea surfaces in theworld in the 2090-2099 period will be higher than thatin the 1980-1999 period by 0.18-0.50m. An increase in
the concentration of carbon dioxide in the atmosphere
will cause the acidification of oceans, and the world
average pH of surface layers of the ocean will lower by
0.14 to 0.35 late in the 21st century; (3) Precipitation:
While in high-altitude areas, the average annual
precipitation is highly likely to increase, the precipitation will decrease in many sub-tropical zones; and(4) Changes in the polar regions: Especially greatchanges are expected in these regions; regardless of the
scenario for greenhouse gas emission, the sea ice in the
North and South Pole regions will decrease. In particular,
the sea ice in the North Pole region in late summer willalmost all disappear by the second half of the 21st
century.

5. Impact of Global Warming on Paddy Rice
Cultivation in Japan
5.1 Reduction of yield and quality
Rice accounts for about 20% of the calories consumed by the entire world population. Some researchpredicts that rice production must be increased byaround 50% by 2025 in order to meet increasing populations living on rice. Countries in the monsoon Asian
region maintain relatively stable production, due toabundant precipitation and adequate irrigation facilities.
However, production from rain-fed paddy fields andupland rice fields, that account for one third of theworld’s rice growing area, is severely affected by theannual climate.
About 10 million tons of rice is produced in about
2 million hectares in Japan. What kind of impact will
global warming have on paddy rice cultivation in Japan?
The lowering of the crop index of rice, which is considered to be due to high temperatures in the ripening
period, has recently been observed mainly in Kyushu.
To deal with this problem, the Ministry of Agriculture,
Forestry and Fisheries (MAFF) has started full-scale
investigation. These publications describe the situationof impact of high temperatures and climate change not
only on rice but also on wheat, soybean, vegetables,
fruit trees, tea and other products and the estimatedeffects in future.
It has been known that decline in the quality becomes more remarkable when the average temperature
after the heading stage exceeds a given level. In thesituation where temperatures during the cultivation

66

Y. HAYASHI

period have risen, in the areas within the jurisdiction of
the Kanto Regional Agricultural Administration Office,a guideline describing the standard method of growing
the “Koshihikari” brand rice has been distributed to
growers, in which farmers are encouraged to transplant
rice seedlings in the beginning of May and later. The
guideline also recommends transplanting some otherrice varieties as late as in the late May to early June. The
aim is to avoid poor ripening due to too high temperatures through the ripening stage by delaying the cultivation period.
Global warming will generally increase production
in relatively high latitude regions and cause growth
disorder due to high temperatures in low latitude regions.
The cultivation period must be advanced in the
Hokkaido and Tohoku regions and delayed in otherregions, especially over the southern part of theJapanese Islands, in order to maintain a yield comparable to the current yield (Seino, 1995, Hayashi et al.,
2001; Hayashi et al., 2005; Iizumi et al., 2006). The
quality of rice falls due to an increase in milky whitecolored rice kernels. From an agro-climatological pointof view, by use of recent 26 years data, Okada (2009)
discussed that insolation reduction was a primary causeof quality decline of paddy rice as compared withtemperature rise.
5.2 Multiple effect of temperature and solar
radiation
Recently, an understanding relating reduction of
paddy rice production was highlighted. Through thisseveral years, especially in the southern part of Japan,
paddy rice production has been under an average of theyield index even with an otherwise near normal level ofproduction in overall Japan. Quality of the rice has also
declined remarkably. The cause is concealed under aclimate with higher temperature after heading stage
associated with low sunshine condition apparent in thatarea.
It is known that, in the growth process of paddy riceculture in Japan, the average temperature during theheading season has risen by +0.5°C compared with thatof two decades ago. The highest temperature rise inJapan was marked in the Kyushu area, where is thesouthwestern prefecture in Japan, at 1.2°C (Ministry ofAgriculture, Forestry and Fisheries, 2006 and 2007). In
addition, the regional annual changes in the rice yieldindex, which is an index for the rice grain yield with theaverage year’s yield defined as 100, indicates that the
Kyushu area had more years with yields lower than its
yield index than other areas during the past 20 years.
Furthermore, as a result of four consecutive years of
unfavorable crop conditions below the yield index of
100 from 2003 to 2006.
On the other hand, earlier studies reported that thegrain yield (ton/ha) is closely related to growing-season
temperature. The study by Peng et al. (2004) revealed
that the rice grain yield is negatively correlated withdaily minimum temperature with little correlation withdaily maximum temperature. In addition, the study by

Yoshida and Hara (1977) indicated that the ripening
grade (grain weight percentage of filled grains) of rice
varies according to a combination of temperature andlight conditions during the heading season.
Thus, it is known that the temperature and sunshine
during the heading season are climate factors affecting
the rice grain yield. However, there have been few studies analyzing the recent fluctuations in the rice grain
yield in the warmer climate regions from the aspect of
the correlations of the yield with the temperature andsunshine. That being the case, with the objective ofclarifying the correlations of the temperature andsunshine with the rice grain yield by investigating therecent fluctuations in the temperature and sunshine
during the heading season in the southern part of Japan,
Murakami (2009) discussed the factors which had
negative effects on the yield from the aspects of thetemperature and sunshine.
In terms of correlations of low-yield years with thetemperature and the sunshine duration during the heading season over the years, while low-yield years before
the middle of 1990s indicated correlativity with the lowtemperature and lower sunshine, low-yield years fromthe middle of 1990s onward indicated correlativity withthe high temperature and poor sunshine. Given thecontribution of the high temperature to the low yields inaddition to the effects of the lower sunshine, it issuggested that the low yields caused by the temperature
had shifted toward the high temperature side with the
middle of 1990s as a turning point (Hayashi & Masuya,2008). It is estimated that the frequency of low yield
years due to the high temperature and lower sunshine
will continue to increase in the future. As an
indispensable measure for these analyses, Okada et al.
(2009) has developed a set of the new climate scenario
of Japan, which will be utilized for future projection
covering a wide range of impact assessment.

6. Projection of China’s Paddy Rice
Production
Changes in agricultural water demands and soilmoisture levels had corresponding impacts on soilmoisture deficit, and consequently on agricultural
production. This is one of the most important aspects tounderstand the future impact of global warming on agriculture in China. Trends toward agricultural water demands increasing and soil drying are found on the
Northeast China Plain (Tao et al., 2003). This drying has
had significant impacts on agricultural production. In
South China, due to the more spatially diverse climate
and cropping system, the trends in agricultural water
demands and soil-moisture change were more spatiallydiverse.
To reduce the uncertainty in the projection, sophisticated treatment of statistical assessment using objectified point of view is required. Tao et al. (2008)
developed a probabilistic technique to deal with theuncertainty in climate change scenarios and CO2 emission scenarios and to provide a probabilistic assessment

Agro-climatological Aspects of the Global Warming and Its Impact on Paddy Rice Cultivationof how changes in rice production and water use in
China could vary with increases in the global mean temperature by 1, 2 and 3°C. Introduction of this concept
representing probabilistic status for the assessment
especially on negative impact under ongoing global
warming was the first trying by Tao et al. (2008). This
concept is highly expected to increase in the years ahead.
They found that the projected regional climate changes
have quite a wide range. Under this condition, period ofrice growing was reduced together with reduction inyield in future. Consequently, the median values of rice
yield decrease range from about 6% to 19%, 14% to
32% and 24% to 40% for temperature change of 1, 2
and 3°C, respectively.

yield was roughly the same as that in 1993. The possible
factor behind such phenomenon is the recent situation
where the cultivation of Koshihikari and other brandname rice in the areas with relatively low temperatures
is increasing and the range of temperature changes is
growing broader year by year.
Besides, Iizumi et al. (2007) indicated that, in thecool summer year after global warming, the monthly
mean temperature increased by 1.0 to 4.5°C throughout
Japan. And the daily accumulated solar radiation slightly
increases in the summer season, whereas it decreases innorthern Japan in June and July. These trendy patterns
will disturb the orthogenetic idea of the impacts andrequire the important aspect of risk assessment in the
future.
Although there have been a lot of reports (Wu, 1997;
Zhang & Wang, 1995; Zhao & Qin, 2004) on theimpacts of the global warming on the rice yield, there
are very few relevant research on the cool climate conditions in Heilongjiang Province, the Northeast China
Plain, where rather favorable effects will be expected.
Jiao et al. (2007) discussed that, despite the fact that theclimate is exhibiting a global warming trend, in the critical period which the paddy rice is cultivated, the frequency of a temperature which is lower than a value of
the Cold Damage Index does not show any sigh ofdeclining in Heilongjiang Province.

7. Risk of Low Temperature Damages Occurs
Even in the Global Warming
The yearly changes in temperature and the yield ofrice in Japan are shown by Fig. 1. The increase ratio of
temperatures for the 1898 to 2004 was 1.1°C per
100 years, which shown in broken lines in this figure.
The data of temperatures used here are those of the areas
where heat island effects were not very serious. Therefore, the straight line shown in the figure represents therate of global warming in Japan; the rate for Japan isabout twice the increasing rate of temperatures in theworld, which supports the phenomenon of temperature
increases occurring in a relatively large scale inhigh-altitude areas.
In the record observed, Fig. 1 indicates the yield ofrice in each year (solid lines) and the years whencold-weather damage occurred (black dots), too. The
cool summer damage in 1993 and 2003 is fresh in ourmemory and indicates that we cannot say that the frequency of cold-weather damage has recently decreased
due to global warming. A close observation of thisfigure tells us that the yield of rice in 1993 dropped to
367 kg/10a, while no cool summer damage occurred in
the three years before and after 1956, when the average

In the age when solar energy was the main resource
for agriculture, sustainable human activities were possible thanks to the ability of the global ecosystem to restore itself. However, it is said that as the consumptionof fossil fuels increased at a more and more rapid pace,
the ecosystem can no longer remain in a stable condition.
In other words, it is now considered that human activities have exceeded the carrying capacity of the earth.
From an economical point of view, Stern (2006)
pointed out as follows: Even if we take measures against
1.2

y = 2.8429x - 5179.6
2
R = 0.8995○ Yield of paddy rice× Annual temperature anomaly
The linear regression equation representingchanges in the yield of rice
The equation representing temperature changes● Cold-weather damage occurred

500

0.7

400

－0.2

300

－0.3

200

－0.8

y = 0.0106x - 21.113
R2 = 0.4127

Fig. 1 Yearly changes in the yield of rice and the average annual temperature.

2003

1998

1993

1988

1983

1978

1973

1968

1963

1958

1953

1948

1943

1938

1933

1928

1923

1918

1913

1908

1903

－1.8
1898

0
1893

－1.3

1888

100

1883

Yield of rice (kg/10a)8. Afterword

Deviation from the average annual
temperature (°C)

600

67

68

Y. HAYASHI

future climate change right now, it will need a long
period of time before such measures begin to work. The
steps we are now taking will have very limited effects
on the climate over 40 to 50 years after. However, themeasures we take in 20 to 30 years from now would
have dramatic effects on the climate in the second halfof the 21st century and in the 22nd century. It is
impossible to precisely estimate the impact of climatechange. But we can well understand the risk of ill effects
resulting from climate change. Measures to reduce theseeffects (measures to reduce the emission of greenhousegases) can be regarded as investment in the future. If wemake such investment wisely, it will not only help us
control our expenditure within a reasonable range but
also provide us with an opportunity for growth anddevelopment. When we plan these measures, we mustlay emphasis on improving the health of agriculture,
overcoming failures and minimizing possible risks.

Acknowledgement
This study was supported by the Global Environment
Research Fund (S-4) of the Ministry of the Environment,
Japan. We are grateful to Dr. Iriki who is a Professor
Emeritus of Yamanashi University for useful suggestions and thank the staffs of Food Production Prediction
Team, National Institute for Agro-Environmental
Sciences, Japan for their active support to the field
investigation.
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Yousay HAYASHI
Yousay Hayashi is a professor of Graduate
School of Life and Environmental
Sciences at University of Tsukuba. He has
been engaged in studies of the global
warming impacts on agricultural and ecosystems. Recently, he and his group aretackling a vulnerability assessment of
paddy rice cultivation in Heilongjian, thenorthernmost province of P.R. China,
under a framework of the Global Environment Bureau, Ministry of theEnvironment. He has served also as a member of a council managed under
the Ministry of Agriculture, Forestry and Fisheries. Additionally, he has
drawn on practical opinion relating countermeasures toward negative
impacts of the global warming, from ordinary industrialists, when joining
a committee steering by the Japan Agricultural Development and Extension Association. At this moment, his greatest concern is how to standagainst the present environmental issues.

(Received 30 January 2009, Accepted 24 March 2009)