33

Impact of Climate Change on Human Health in Asia and Japan
Yasushi HONDA
University of Tsukuba,
1-1-1 Tennoudai, Tsukuba 305-8577, Japan,
honda@taiiku.tsukuba.ac.jp

Abstract
Recent IPCC (Intergovernmental Panel for Climate Change) reports have recognized healthimpacts as one of the most important issues.
The health impacts of climate change in Asia are serious: the WHO (World Health Organization)
has calculated the disability adjusted life years (=DALYs) due to the climate change in 2000 (comparedwith a baseline of 1961-1990). Among the regions studied, South-East Asia-D, which includes
Bangladesh, Bhutan, India, the Maldives, Myanmar and Nepal, had the highest total DALYs mainly due
to diarrheal diseases and malnutrition.
Unlike in the rest of Asia, the health impacts in Japan have been considered to be mainly direct. To
evaluate the impact of heat stress, the relationship between daily maximum temperature and mortality
rate was examined for different prefectures. The relation was V-shaped, that is, there was shown to be an
optimum temperature (OT) at which the mortality rate is lowest, and the mortality rate is higher when
the temperature becomes either higher or lower than the OT. The V-shaped pattern was affected byclimate: The OT shifted from right to left as the area became warmer. We found that the 85-percentile ofthe daily maximum temperature best predicted the OT in Japan.
The elderly contributed most to the V-shaped temperature-mortality pattern due to compromised
adaptive capacity. As for causes of death, circulatory and respiratory diseases constituted the V-shape.
One of the potentially important issues is mortality displacement, i.e., that the decedents due toheat stress would have died anyway within several days or in a couple of months even if the heat stress
had not occurred. This phenomenon is, however, still in debate.
Key words: climate, diarrhea, elderly, heat stress, malnutrition

1. Introduction
Recent IPCC reports have recognized healthimpacts as one of the most important issues along withproblems of dwindling water resources, energy,
agriculture and biodiversity (Watson et al. eds., 1996;
McCarthy et al. eds., 2001). It is extremely difficult,however, to conduct health research with regard toclimate change, partly because we cannot conduct
experiments on possible hazards to humans, and partly
because health is related not only to climate, but also
to ecological, social, cultural and economical factors.
Another difficulty is data collection. Especially indeveloping countries, it is very hard to collectmorbidity and mortality data. Even in developed
countries this can be a difficult task. For example,
Japan has an official system for collecting these data
for some important infectious diseases, but no system
as a nation, for collecting data on heat stroke
incidence.
Despite the above difficulties, we have accumuGlobal Environmental Research
11: 33-38 (2007)
printed in Japan

lated knowledge, owing to the efforts of pioneeringresearchers. In this article, I will present the status quoof the research and its results, first from new reports
and articles with emphasis on Asia and second fromour own research in Japan.

2. Health Impacts in General
Global climate change is not a mere shift in average temperatures. It also entails increased climate
variability, i.e., more hot days, more frequent and intense floods (Milly et al., 2002). In other words, notonly will the mean increase, but so will the degree ofvariance. We need to take these two changes into
account in estimating the impact of global climatechange.
Although the data for estimating health impact is
not readily available, it is rather easy to collect the
numbers of heat stroke patients transported to hospitals by ambulance cars. This type of impact is called a“direct” impact. Other examples of direct impact are©2007 AIRIES34

Y. HONDA

injuries and drownings due to floods or typhoons.
Unlike direct impacts, indirect impacts, which
affect human health through ecological and/or social
disruptions, are very hard to estimate. An example ofan indirect impact would be malnutrition due toreduced crop yields under an altered climate. There
are only a few reports on this type of impact. Among
those is an estimation of the underfed population
under certain climate change scenarios (Parry et al.,2004).

and local land-use change (Patz et al., 2005). Partly
due to these complicated mechanisms, there has been
controversy over whether climate change would
increase the number of patients with these diseases.
Hay et al. (2002) for example, concluded that there
was no significant warming trend despite the malaria
incidence elevation, but recently, Pascual et al. (2006)
updated Hay and his coworkers’ data, reanalyzed them,and concluded that a warming trend existed. Moreinterdisciplinary research is necessary for obtaining an
uncontroversial conclusion.

3. Health Impacts in Asia
Box: Disability adjusted life years (DALYs)

Asia has wide range of countries, from the Middle
East to the Far East, and from boreal Russia to tropicalcountries such as Indonesia and Papua New Guinea.
Also, its socio-economic status varies from country tocountry, with Japan being one of the most highly
developed countries, with the world’s second largest
GDP as of 2005, whereas people in many South East
Asian countries suffer from poverty. Because of thisdiversity and lack of data for many developing countries, it is hard to describe in detail or summarize theimpact in Asia. Below are a few examples of sketches
by the WHO.
The WHO calculated, by WHO region, the disability adjusted life years (DALYs, see box) due to climate change in 2000 (compared with the baseline in
1961-1990). Among the regions, South East Asia-D(SEAR-D, which consists of Bangladesh, Bhutan,
Korea, India, the Maldives, Myanmar and Nepal) had
the highest total DALYs (Ezzati et al. eds., 2004).
Diarrheal diseases and malnutrition contributed moststrongly to the DALYs in SEAR-D. Partly because of
the large population in SEAR-D, the DALYs attributable to the climate change were about twice as large as
the DALYs of Africa-E, which had the second largest
DALYs. These facts suggests that food security andpublic health infrastructure are very important incounteracting the health hazards due to climate change,
especially in Asia.
The projected casualties due to coastal floods arealso the highest in 2030 in SEAR-D (Ezzati et al. eds.,
2004). Although Japan has a large proportion of its
population in coastal areas, the infrastructure of Japanis much better than that of SEAR-D countries, andtyphoons of similar scale may cause much smaller
numbers of casualties in Japan, compared with in
SEAR-D countries.
Other impacts to consider include vector-borne
infectious diseases. Among them, malaria and dengue
fever have been well studied. However, the epidemic
mechanisms of these diseases are complex, the important determinants of which include (i) vector survivaland reproduction, (ii) the vector’s biting rate, and (iii)the pathogen’s incubation rate within the vector organism (Patz et al., 2003). Also, there are several malaria
risk determinants such as drug resistance, humanmigration, human immune status, control programs,(See http://www.who.int/healthinfo/boddaly/en/index.html
for a more detailed explanation)

DALY is the sum of:• years of life lost due to premature death (YLL)• years of life lived with disabilities (YLD).
YLL takes into account the age at death. YLD takes into
account disease duration, age at onset, and a disability
weight reflecting the severity of the disease.

4. Health Impacts in Japan
Unlike the above-mentioned WHO estimates, it isunlikely that the most important health impact of the
global warming in Japan will be diarrheal diseases ormalnutrition. In calculating DALYs, the WHO assumed that the increase in risk in diarrheal diseases
falls to zero when the per capita GDP exceeds 6,000
US dollars per year (Ezzati et al. eds., 2004). This is
why our efforts have been mainly focused on the
direct effects. Below, I will present some results of
our analysis. However, although the effect level issmall compared with the above mentioned SEAR-D
countries, even in developed countries, diarrheal diseases or food poisoning may be associated with higher
temperatures. Sakuma et al. (2006) demonstrated thatthe number of cases of verocytotoxin-producing
Escherichia coli was associated with temperature, andBentham and Langford (2001), Kovats et al. (2004),
and D’Souza et al. (2004) demonstrated the relationship between food poisoning and high temperatures.
Sakuma et al. (2006) also pointed out that children(aged less than 15 years) and elderly (aged 65 years orolder) were at risk. Considering this, we should be
careful about infectious diarrheal diseases during very
hot days, even in developed countries.
In the following analyses, we used the mortality
data provided by the Ministry of Health and Welfareof Japan with special permission. The data included
date of birth, date of death, sex, cause of death andaddress of the decedents. The corresponding meteorological data were obtained from the Japan Meteorological Agency. Population data were obtained fromthe office of the Prime Minister. Some of the analyses
are old and only categorized temperature was used,
but in some newer analyses, we used a smoothing
spline in evaluating the relationship between tempera-

Impact of Climate Change on Human Health in Asia and Japanare concerned, relative humidity did not confound thetemperature-mortality relationship (Honda et al., 2000),
and other factors were only sporadically examined inrelated reports. Hence, I will restrict my focus to temperature as the only variable for describing weather
and climate.
The V-shaped pattern was affected by climate(Curriero et al., 2002; Honda et al., 1998) as well: The
OT shifts from right to left as the area becomes
warmer (Honda et al., 1998) as shown in Fig. 3. However, the long-term average temperature may not be agood predictor of the location of the OT; Okinawa, thesouthernmost prefecture of Japan, has a very highlong-term average temperature, and became an outlier
when the relation between OT and long-term averagetemperature was examined. Instead, we found that the85 percentile of the daily maximum temperature best
predicted the OT in Japan (Honda et al., submitted)(Fig. 4).

Mortality

ture and mortality. This nonparametric regression
method allowed us to finely evaluate the relationship.
As shown in Fig. 1, the relationship between daily
maximum temperature and the all-causes mortality
rate is V-shaped, that is, there is an optimum temperature (OT) at which the mortality rate is lowest and themortality rate is higher when the temperature becomes
either higher or lower than the OT. Figure 1 also
shows that males and females exhibit similar patterns,
with the OT for females located lower. This V-shaped
pattern can be found anywhere in the world, at least in
mid-latitude countries (Bull & Morton, 1978; Saez
et al., 1995; Curriero et al., 2002), including Lebanon(El-Zein et al., 2004). This pattern is mainly attributed
to circulatory diseases and respiratory diseases(Honda et al., 1995). Figure 2 is the visualization ofanother example.
Other meteorological factors such as humidity may
also be of interest. However, as far as Japanese data

35

Temperature

Fig. 3 Schematic presentation of the climate
effect on the temperature-mortality relationship.

–1

Mortality rate (day )Fig. 1 Temperature and mortality in Hokkaido,
Japan.

Daily maximum temperature (ºC)
Fig. 2 Relationship between daily maximum temperature (ºC) and cause-specific mortality
rate, Tokyo, Japan, 65+ years old males,
1972- 1994.

Smoothing spline curves with degree of freedom= 6. Mortality rate multiplied by 100,000,000.

Fig. 4 Relationship between 85 percentile valueof daily maximum temperature (Tmax 85)
and optimum temperature (OT).

The solid line shows the regression line, and thedotted line shows the situation OT = Tmax 85.

36

Y. HONDA

As for the magnitude of the mortality rate, elderly
people contributed to the V-shaped temperaturemortality pattern. Still, the children’s mortality rate
showed a relationship with temperature (Honda et al.,1995). Unlike the situation among the elderly, ourfurther analysis showed that the higher mortality rate
among children was attributable to accidents, as
shown in Fig. 5. The higher mortality on weekends
than weekdays in this figure suggests that the pattern
is attributable to “risk shift,” that is, for example, chil-dren going swimming, where the risk is much higher
than that in their usual life around home. Even during
weekends, the mortality rate was higher for higher
temperatures. Thus, it is possible that heat stressaffected children’s physiological strength or ability toreact to danger.
Another issue is the so-called “multiple stresses.”
As shown in Fig. 6, the effect of air-pollution cancompound the heat-stress effect (Honda et al., 2003).
This example is of carbon monoxide, and may not be
related to global warming, but the ambient ozone leveland number of days with high ozone levels would riseas global warming proceeds, and the mortality ratewould increase accordingly.
One of the potentially important issues I have notaddressed here is mortality displacement. This phenomenon refers to the situation in which the decedents
who had succumbed to heat-stress would have diedanyway within several days or in a couple of months
even if the heat-stress had not occurred. This phenomenon is, however, still under debate. Hajat et al.
(2005) reported that the situation varies among countries, and recently, Fouillet et al. (2006) reported thatno mortality displacement was observed in the 2003
Paris heat wave disaster.
Based on Japanese data and the 85 percentile
hypothesis, we projected the possible health consequence of global warming (Takahashi et al., 2007). In

Fig. 5 Relationship between daily maximum temperatureand mortalities of all external causes, Japan,
1980-1994.

Daily maximum temperature

Fig. 6 Relationship between daily maximum temperatureand mortality rate by carbon monoxide level,
Tokyo, 65+ year old males, 1976-1990.

Fig. 7 Estimated excess mortality density.

Impact of Climate Change on Human Health in Asia and Japan

this simulation we used the Atmosphere-Ocean
General Circulation Model with the world’s highest
spatial resolution at the time of the study and only
examined the impact of heat stress (i.e., an offset due
to decreased winter deaths was not considered). Other
assumptions included the following: population densities not altered in the future; no adaptation or acclimation taking place. Figure 7 shows the results for Japanand some surrounding areas. According to this projection, the impact due to heat stress will be large inJapanese metropolitan areas and the central andcoastal areas of China.

5. Useful Information for Weather Forecasting Practice
It has been shown that physiological and behavioral adaptations (McGeehin & Mirabelli, 2001) andchanges in public health preparedness (Weisskopf
et al., 2002) can reduce heat wave morbidity andmortality. Hence, along with governmental or individual measures to prepare air-conditioned shelters orhouses, it should be useful to advise people how they
can avoid heat stress and who are vulnerable.
As I showed above, heat stress may cause higher
mortalities among children and the elderly. Also,
those who already have circulatory and/or respiratory
diseases are vulnerable to heat stress. So, in weather
forecasts when the temperature becomes high during
summer, it will be advisable to warn children, the elderly and those with circulatory and respiratory diseases to be more careful than other people. Also, heatstrokes are better predicted by Wet Bulb Globe
Temperature (WBGT) than by mere maximum temperature (Committee for investigating environmental
effect due to heat island phenomenon, 2004). Thisimplies that hot days with weak wind speeds andstrong sunshine should be regarded as more dangerous
than similarly hot days with less sunshine or stronger
wind. The Japanese Society of Biometeorology is now
preparing guidelines for preventing heat stroke, andthey will be available probably in 2008. In brief, as
the WBGT or maximum temperature becomes higher,
the guidelines recommend lighter exercise or no
exercise.
Another piece of useful information is that people
living in prefectures with a lower 85 percentile valueof the daily maximum temperature are more vulnerable to the same level of heat stress, and extra caution
is necessary for them.

6. Adaptation and Mitigation
To lessen the impact of climate change, the IPCC
has classified two measures, i.e., adaptation and mitigation. Briefly, adaptation refers to efforts to reduce
the adverse responses to a certain level of global
warming, whereas mitigation refers to efforts to
reduce greenhouse gases.

37

Adaptation may occur naturally. For example,
even when the ambient temperature is 18°C in Japan,
we feel cool in autumn and warm in spring, due tophysiological changes in our bodies during winter.
Adaptation may also be achieved through technology.
For example, most of the excess deaths during the2003 European heat wave could have been prevented
if they had been in air-conditioned houses (of course,
using air-conditioners exacerbates carbon dioxide
emissions, but sometimes in some places, it may benecessary). As Kabuto et al. (2005) reported, during
summer, some residents live at warmer than adequate
temperatures even when they are in air-conditioned
rooms, so it is advisable for them to use thermometersin controlling room temperature, instead of relying on
the controller of the air-conditioner.
Unlike adaptation, which can be region-specific,
the effect of mitigation is collective: even when certain countries reduce greenhouse gases substantially,
their efforts can be overwhelmed by other countries
which increase greenhouse gases. This is why we needinternational collaboration for mitigating the effects ofclimate change.
The effects of mitigation are, however, ubiquitous,i.e., all the countries benefit from the effects (although
there are some regional variations). Also, if mitigationis completely effective, we need not adapt to global
warming. This is analogous to prevention and treatment: if you prevent a disease, you need not sufferfrom the disease. Unfortunately, the IPCC Working
Group I recently reported (2007) that the warming
trend will continue even if we stabilize the CO2 concentration at the year 2000 level, and we may have totake some adaptive actions.

7. Conclusion
We will experience heat-stress, regardless of theoccurrence of global warming, because in any case,we will have some hot summers in the future. In thissense, we need to be careful about heat-stress and try
to avoid the adverse health consequences due toheat-stress. However, global warming may exacerbate
the effect of heat-stress and may raise the all-causes
mortality rate and increase the disease burden.
We need to take actions immediately to prevent thehazards caused by global warming, because, as described above, we are already experiencing theadverse effects and the warming trend will inevitably
continue for several decades. What kind of actions
would be appropriate? Of course, mitigation is important, because the poor regions are unable to take adaptive measures except for physiological ones, which
may be weakened further by poor nutritional status.
Along with mitigation, adaptation with energyefficient measures is also important so as not to reducethe mitigation effect. To find the “best mix” of mitigation and adaptation, we need to make a comprehensive
evaluation of the effects of global warming.

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Y. HONDA

Acknowledgements
Some studies introduced in this article were fundedby the Global Environmental Research Fund (GERF)
S-4 by the Ministry of the Environment, Japan.
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