709
11
Human Health: Impacts,
Adaptation, and Co-Benefits
Coordinating Lead Authors:
Kirk R. Smith (USA), Alistair Woodward (New Zealand)
Lead Authors:
Diarmid Campbell-Lendrum (WHO), Dave D. Chadee (Trinidad and Tobago), Yasushi Honda
(Japan), Qiyong Liu (China), Jane M. Olwoch (South Africa), Boris Revich (Russian Federation),
Rainer Sauerborn (Sweden)
Contributing Authors:
Clara Aranda (Mexico), Helen Berry (Australia), Colin Butler (Australia), Zoë Chafe (USA),
Lara Cushing (USA), Kristie L. Ebi (USA), Tord Kjellstrom (New Zealand), Sari Kovats (UK),
Graeme Lindsay (New Zealand), Erin Lipp (USA), Tony McMichael (Australia), Virginia Murray
(UK), Osman Sankoh (Sierra Leone), Marie O’Neill (USA), Seth B. Shonkoff (USA),
Joan Sutherland (Trinidad and Tobago), Shelby Yamamoto (Germany)
Review Editors:
Ulisses Confalonieri (Brazil), Andrew Haines (UK)
Volunteer Chapter Scientists:
Zoë Chafe (USA), Joacim Rocklov (Sweden)
This chapter should be cited as:
Smith
, K.R., A. Woodward, D. Campbell-Lendrum, D.D. Chadee, Y. Honda, Q. Liu, J.M. Olwoch, B. Revich, and
R. Sauerborn, 2014: Human health: impacts, adaptation, and co-benefits. In: Climate Change 2014: Impacts,
Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the
Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros,
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova,
B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University
Press, Cambridge, United Kingdom and New York, NY, USA, pp. 709-754.
11
710
Executive Summary ........................................................................................................................................................... 713
11.1. Introduction ............................................................................................................................................................ 715
11.1.1. Present State of Global Health ......................................................................................................................................................... 715
11.1.2. Developments Since AR4 .................................................................................................................................................................. 715
Box 11-1. Weather, Climate, and Health: A Long-Term Observational Study in African and Asian Populations .......................... 715
11.1.3. Non-Climate Health Effects of Climate-Altering Pollutants ............................................................................................................... 716
11.2. How Climate Change Affects Health ....................................................................................................................... 716
11.3. Vulnerability to Disease and Injury Due to Climate Variability and Climate Change ............................................. 717
11.3.1. Geographic Causes of Vulnerability .................................................................................................................................................. 717
11.3.2. Current Health Status ....................................................................................................................................................................... 717
11.3.3. Age and Gender ............................................................................................................................................................................... 717
11.3.4. Socioeconomic Status ....................................................................................................................................................................... 718
11.3.5. Public Health and Other Infrastructure ............................................................................................................................................. 718
11.3.6. Projections for Vulnerability .............................................................................................................................................................. 718
11.4. Direct Impacts of Climate and Weather on Health ................................................................................................. 720
11.4.1. Heat- and Cold-Related Impacts ....................................................................................................................................................... 720
11.4.1.1. Mechanisms ...................................................................................................................................................................... 720
11.4.1.2. Near-Term Future .............................................................................................................................................................. 721
11.4.2. Floods and Storms ............................................................................................................................................................................ 721
11.4.2.1. Mechanisms ...................................................................................................................................................................... 722
11.4.2.2. Near-Term Future ............................................................................................................................................................... 722
11.4.3. Ultraviolet Radiation ......................................................................................................................................................................... 722
11.5. Ecosystem-Mediated Impacts of Climate Change on Health Outcomes ................................................................. 722
11.5.1. Vector-Borne and Other Infectious Diseases ..................................................................................................................................... 722
11.5.1.1. Malaria .............................................................................................................................................................................. 722
11.5.1.2. Dengue Fever .................................................................................................................................................................... 723
Box 11-2. Case Study: An Intervention to Control Dengue Fever .................................................................................... 724
11.5.1.3. Tick-Borne Diseases ........................................................................................................................................................... 725
11.5.1.4. Other Vector-Borne Diseases ............................................................................................................................................. 725
11.5.1.5. Near-Term Future ............................................................................................................................................................... 725
11.5.2. Food- and Water-Borne Infections .................................................................................................................................................... 726
11.5.2.1. Vibrios ............................................................................................................................................................................... 726
11.5.2.2. Other Parasites, Bacteria, and Viruses ................................................................................................................................ 726
11.5.2.3. Near-Term Future ............................................................................................................................................................... 727
Table of Contents
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11
11.5.3. Air Quality ........................................................................................................................................................................................ 727
Box 11-3. Health and Economic Impacts of Climate-Altering Pollutants Other than CO
2
........................................................... 728
11.5.3.1. Long-Term Outdoor Ozone Exposures ............................................................................................................................... 728
11.5.3.2. Acute Air Pollution Episodes .............................................................................................................................................. 729
11.5.3.3. Aeroallergens .................................................................................................................................................................... 729
11.5.3.4. Near-Term Future ............................................................................................................................................................... 729
11.6. Health Impacts Heavily Mediated through Human Institutions ............................................................................. 730
11.6.1. Nutrition ........................................................................................................................................................................................... 730
11.6.1.1. Mechanisms ...................................................................................................................................................................... 730
11.6.1.2. Near-Term Future ............................................................................................................................................................... 730
11.6.2. Occupational Health ......................................................................................................................................................................... 731
11.6.2.1. Heat Strain and Heat Stroke .............................................................................................................................................. 731
11.6.2.2. Heat Exhaustion and Work Capacity Loss .......................................................................................................................... 731
11.6.2.3. Other Occupational Health Concerns ................................................................................................................................ 731
11.6.2.4. Near-Term Future ............................................................................................................................................................... 732
11.6.3. Mental Health ................................................................................................................................................................................... 732
11.6.4. Violence and Conflict ........................................................................................................................................................................ 732
11.7. Adaptation to Protect Health ................................................................................................................................. 733
11.7.1. Improving Basic Public Health and Health Care Services .................................................................................................................. 733
11.7.2. Health Adaptation Policies and Measures ......................................................................................................................................... 733
11.7.3. Early Warning Systems ...................................................................................................................................................................... 734
11.7.4. Role of Other Sectors in Health Adaptation ...................................................................................................................................... 734
11.8. Adaptation Limits Under High Levels of Warming .................................................................................................. 735
11.8.1. Physiological Limits to Human Heat Tolerance .................................................................................................................................. 736
11.8.2. Limits to Food Production and Human Nutrition .............................................................................................................................. 736
11.8.3. Thermal Tolerance of Disease Vectors ............................................................................................................................................... 736
11.8.4. Displacement and Migration Under Extreme Warming ..................................................................................................................... 736
11.8.5. Reliance on Infrastructure ................................................................................................................................................................. 736
11.9. Co-Benefits ............................................................................................................................................................. 737
11.9.1. Reduction of Co-Pollutants ............................................................................................................................................................... 737
11.9.1.1. Outdoor Sources ................................................................................................................................................................ 738
11.9.1.2. Household Sources ............................................................................................................................................................ 738
11.9.1.3. Primary Co-Pollutants ........................................................................................................................................................ 739
11.9.1.4. Secondary Co-Pollutants .................................................................................................................................................... 739
11.9.1.5. Case Studies of Co-Benefits of Air Pollution Reductions .................................................................................................... 740
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Chapter 11 Human Health: Impacts, Adaptation, and Co-Benefits
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11.9.2. Access to Reproductive Health Services ............................................................................................................................................ 740
11.9.2.1. Birth and Pregnancy Intervals ............................................................................................................................................ 740
11.9.2.2. Maternal Age at Birth ........................................................................................................................................................ 741
11.10. Key Uncertainties and Knowledge Gaps ................................................................................................................ 741
References ......................................................................................................................................................................... 743
Frequently Asked Questions
11.1: How does climate change affect human health? .............................................................................................................................. 741
11.2: Will climate change have benefits for health? .................................................................................................................................. 742
11.3: Who is most affected by climate change? ........................................................................................................................................ 742
11.4: What is the most important adaptation strategy to reduce the health impacts of climate change? ................................................. 742
11.5: What are health “co-benefits” of climate change mitigation measures? ......................................................................................... 742
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Human Health: Impacts, Adaptation, and Co-Benefits Chapter 11
Executive Summary
The health of human populations is sensitive to shifts in weather patterns and other aspects of climate change (very high
confidence). These effects occur directly, due to changes in temperature and precipitation and occurrence of heat waves, floods, droughts, and
fires. Indirectly, health may be damaged by ecological disruptions brought on by climate change (crop failures, shifting patterns of disease
vectors), or social responses to climate change (such as displacement of populations following prolonged drought). Variability in temperatures
is a risk factor in its own right, over and above the influence of average temperatures on heat-related deaths. {11.4} Biological and social
adaptation is more difficult in a highly variable climate than one that is more stable. {11.7}
Until mid-century climate change will act mainly by exacerbating health problems that already exist (very high confidence). New
conditions may emerge under climate change (low confidence), and existing diseases (e.g., food-borne infections) may extend their range into
areas that are presently unaffected (high confidence). But the largest risks will apply in populations that are currently most affected by climate-
related diseases. Thus, for example, it is expected that health losses due to climate change-induced undernutrition will occur mainly in areas
that are already food-insecure. {11.3}
In recent decades, climate change has contributed to levels of ill health (likely) though the present worldwide burden of ill health
from climate change is relatively small compared with other stressors on health and is not well quantified. Rising temperatures
have increased the risk of heat-related death and illness (likely). {11.4} Local changes in temperature and rainfall have altered distribution of
some water-borne illnesses and disease vectors, and reduced food production for some vulnerable populations (medium confidence). {11.5-6}
If climate change continues as projected across the Representative Concentration Pathway (RCP) scenarios, the major changes in ill health
compared to no climate change will occur through:
Greater risk of injury, disease, and death due to more intense heat waves and fires (very high confidence) {11.4}
Increased risk of undernutrition resulting from diminished food production in poor regions (high confidence) {11.6}
Consequences for health of lost work capacity and reduced labor productivity in vulnerable populations (high confidence) {11.6}
Increased risks of food- and water-borne diseases (very high confidence) and vector-borne diseases (medium confidence) {11.5}
Modest reductions in cold-related mortality and morbidity in some areas due to fewer cold extremes (low confidence), geographical shifts
in food production, and reduced capacity of disease-carrying vectors due to exceedance of thermal thresholds (medium confidence). These
positive effects will be increasingly outweighed, worldwide, by the magnitude and severity of the negative effects of climate change (high
confidence). {11.4-6}
Impacts on health will be reduced, but not eliminated, in populations that benefit from rapid social and economic development
(high confidence), particularly among the poorest and least healthy groups (very high confidence). {11.4, 11.6-7}
Climate change is
an impediment to continued health improvements in many parts of the world. If economic growth does not benefit the poor, the health effects
of climate change will be exacerbated.
In addition to their implications for climate change, essentially all the important climate-altering pollutants (CAPs) other than
carbon dioxide (CO
2
) have near-term health implications (very high confidence). In 2010, more than 7% of the global burden of disease
was due to inhalation of these air pollutants (high confidence). {Box 11-4}
Some parts of the world already exceed the international standard for safe work activity during the hottest months of the year.
The capacity of the human body to thermoregulate may be exceeded on a regular basis, particularly during manual labor, in parts of the world
during this century. In the highest Representative Concentration Pathway, RCP8.5, by 2100 some of the world’s land area will be experiencing
4°C to 7°C higher temperatures due to anthropogenic climate change (WGI AR5 Figure SPM.7). If this occurs, the combination of high
temperatures and high humidity will compromise normal human activities, including growing food or working outdoors in some areas for
parts of the year (high confidence). {11.8}
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The most effective measures to reduce vulnerability in the near term are programs that implement and improve basic public
health measures such as provision of clean water and sanitation, secure essential health care including vaccination and child
health services, increase capacity for disaster preparedness and response, and alleviate poverty (very high confidence). {11.7}
In addition, there has been progress since AR4 in targeted and climate-specific measures to protect health, including enhanced surveillance and
early warning systems. {11.7}
There are opportunities to achieve co-benefits from actions that reduce emissions of warming CAPs and at the same time improve health.
Among others, these include:
Reducing local emissions of health-damaging and climate-altering air pollutants from energy systems, through improved energy efficiency,
and a shift to cleaner energy sources (very high confidence) {11.9}
Providing access to reproductive health services (including modern family planning) to improve child and maternal health through birth
spacing and reduce population growth, energy use, and consequent CAP emissions over time (medium confidence) {11.9}
Shifting consumption away from animal products, especially from ruminant sources, in high-meat-consumption societies toward less CAP-
intensive healthy diets (medium confidence) {11.9}
Designing transport systems that promote active transport and reduce use of motorized vehicles, leading to lower emissions of CAPs and
better health through improved air quality and greater physical activity (high confidence). {11.9}
There are important research gaps regarding the health consequences of climate change and co-benefits actions, particularly in
low-income countries. There are now opportunities to use existing longitudinal data on population health to investigate how climate change
affects the most vulnerable populations. Another gap concerns the scientific evaluation of the health implications of adaptation measures at
community and national levels. A further challenge is to improve understanding of the extent to which taking health co-benefits into account
can offset the costs of greenhouse gas mitigation strategies.
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11.1. Introduction
This chapter examines what is known about the effects of climate
change on human health and, briefly, the more direct impacts of climate-
a
ltering pollutants (CAPs; see Glossary) on health. We review diseases
and other aspects of poor health that are sensitive to weather and
climate. We examine the factors that influence the susceptibility of
populations and individuals to ill health due to variations in weather
and climate, and describe steps that may be taken to reduce the impacts
of climate change on human health. The chapter also includes a section
on health “co-benefits.Co-benefits are positive effects on human
health that arise from interventions to reduce emissions of those CAPs
that warm the planet or vice versa.
This is a scientific assessment based on best available evidence according
to the judgment of the authors. We searched the English-language
literature up to August 2013, focusing primarily on publications since
2007. We drew primarily (but not exclusively) on peer-reviewed journals.
Literature was identified using a published protocol (Hosking and
Campbell-Lendrum, 2012) and other approaches, including extensive
consultation with technical experts in the field. We examined recent
substantial reviews (e.g., Gosling et al., 2009; Bassil and Cole, 2010;
Hajat et al., 2010; Huang et al., 2011; McMichael, 2013b; Stanke et al.,
2013) to check for any omissions of important work. In selecting citations
for the chapter, we gave priority to publications that were recent (since
AR4), comprehensive, added significant new findings to the literature,
and included areas or population groups that have not previously been
well described or were judged to be particularly policy relevant in other
respects.
We begin with an outline of measures of human health, the major driving
forces that act on health worldwide, recent trends in health status, and
health projections for the remainder of the 21st century.
11.1.1. Present State of Global Health
The Fourth Assessment Report (AR4) pointed to dramatic improvement
in life expectancy in most parts of the world in the 20th century, and
this trend has continued through the first decade of the 21st century
(Wang et al., 2012). Rapid progress in a few countries (especially China)
has dominated global averages, but most countries have benefited from
substantial reductions in mortality. There remain sizable and avoidable
inequalities in life expectancy within and between nations in terms of
education, income, and ethnicity (Beaglehole and Bonita, 2008) and in
some countries, official statistics are so patchy in quality and coverage
that it is difficult to draw firm conclusions about health trends (Byass,
2010). Years lived with disability have tended to increase in most
countries (Salomon et al., 2012).
If economic development continues as forecast, it is expected that
mortality rates will continue to fall in most countries; the World Health
Organization (WHO) estimates the global burden of disease (measured
in disability adjusted life years per capita) will decrease by 30% by 2030,
compared with 2004 (WHO, 2008a). The underlying causes of global
poor health are expected to change substantially, with much greater
prominence of chronic diseases and injury; nevertheless, the major
i
nfectious diseases of adults and children will remain important in some
regions, particularly sub-Saharan Africa and South Asia (Hughes et al.,
2011).
11.1.2. Developments Since AR4
The relevant literature has grown considerably since publication of AR4.
For instance, the annual number of MEDLINE citations on climate
change and health doubled between 2007 and 2009 (Hosking and
Campbell-Lendrum, 2012). In addition, there have been many reviews,
reports, and international assessments that do not appear in listings
such as MEDLINE but include important information nevertheless, for
instance, the World Development Report 2010 (World Bank, 2010) and
the 2011 UN Habitat report on cities and climate change (UN-HABITAT,
2011). Since AR4, there have been improvements in the methods applied
to investigate climate change and health. These include more sophisticated
modeling of possible future impacts (e.g., work linking climate change,
food security, and health outcomes; Nelson et al., 2010) and new methods
Box 11-1 | Weather, Climate, and Health:
A Long-Term Observational Study
in African and Asian Populations
Given the dearth of scientific evidence of the relationship
between weather/climate and health in low- and middle-
income countries, we report on a project that spans sub-
Saharan Africa and Asia. The INDEPTH Network currently
includes 43 surveillance sites in 20 countries. Using
standardized health and demographic surveillance systems,
member sites have collected up to 45 years of information
on births, migrations, and deaths. Currently, there are about
3.2 million people under surveillance (Sankoh and Byass,
2012).
To study relationships between weather and health, the
authors obtained daily meteorological data for 12 INDEPTH
populations between 2000 and 2009, and projected future
climate changes to 2100 under the SRES A1B, A3, and B1
scenarios (Hondula et al., 2012). The authors concluded the
health of all the populations would be challenged by the
new climatic conditions, especially later in the century. In
another study from the Network, Diboulo et al. (2012)
examined the relation between weather and all-cause
mortality data in Burkina Faso. Relations between daily
temperature and mortality were similar to those reported in
many high-income settings, and susceptibility to heat
varied by age and gender.
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Chapter 11 Human Health: Impacts, Adaptation, and Co-Benefits
11
t
o model the effects of heat on work capacity and labor productivity
(Kjellstrom et al., 2009b). Other developments include coupling of high-
quality, longitudinal mortality data sets with down-scaled meteorological
data, in low-income settings (e.g., through the INDEPTH Network; see
Box 11-1).
Since AR4, studies of the ways in which policies to reduce greenhouse
gas (GHG) emissions may affect health, or vice versa, leading to so-
called “co-benefits” in the case of positive outcomes for either climate
or health, have multiplied (Haines et al., 2009).
Much has been written on links between climate, socioeconomic
conditions, and health—for example, related to occupational heat
exposure (Kjellstrom et al., 2009b) and malaria (e.g., Gething et al., 2010;
Béguin et al., 2011). There is also growing appreciation of the social
upheaval and damage to population health that may arise from the
interaction of large-scale food insecurity, population dislocation, and
conflict (see Chapter 12).
11.1.3. Non-Climate Health Effects
of Climate-Altering Pollutants
CAPs affect health in other ways than through climate change, just
as carbon dioxide (CO
2
) creates non-climate effects such as ocean
acidification. The effects of rising CO
2
levels on calcifying marine species
a
re well documented and the risks for coral reefs are now more closely
defined than they were at the time of the AR4 (see Chapter 30). There
are potential implications for human health, such as undernutrition in
coastal populations that depend on local fish stocks, but, so far, links
between health and ocean acidification have not been closely studied
(Kite-Powell et al., 2008). CAPs such as black carbon and tropospheric
ozone have substantial, direct, negative effects on human health (Wang
et al., 2013; see Section 11.5.3 and Box 11-3). Although CO
2
is not
considered a health-damaging air pollutant at levels experienced
outside particular occupational and health-care settings, one study has
reported a reduction in mental performance at 1000 ppm and above,
within the range that all of humanity would experience in some extreme
climate scenarios by 2100 (Satish et al., 2012).
11.2. How Climate Change Affects Health
There are three basic pathways by which climate change affects health
(Figure 11-1), and these provide the organization for the chapter:
Direct impacts, which relate primarily to changes in the frequency
of extreme weather including heat, drought, and heavy rain (Section
11.4)
Effects mediated through natural systems, for example, disease
vectors, water-borne diseases, and air pollution (Section 11.5)
Effects heavily mediated by human systems, for example, occupational
impacts, undernutrition, and mental stress (Section 11.6).
Warning systems
Socioeconomic status
Health and nutrition status
Primary health care
Geography
Baseline weather
Soil/dust
Vegetation
Baseline air/water
quality
Public health capability
and adaptation
Environmental
conditions
Social infrastructure
Direct exposures
Indirect exposures
Via economic and social disruption
Food production/distribution
Mental stress
Mediated through natural systems:
Allergens
Disease vectors
Increased water/air pollution
Flood damage
Storm vulnerability
Heat stress
HEALTH IMPACTS
Undernutrition
Drowning
Heart disease
Malaria
CLIMATE CHANGE
Precipitation
Heat
Floods
Storms
Mediating factors
Figure 11-1 |
Conceptual diagram showing three primary exposure pathways by which climate change affects health: directly through weather variables such as heat and
storms; indirectly through natural systems such as disease vectors; and pathways heavily mediated through human systems such as undernutrition. The green box indicates the
moderating influences of local environmental conditions on how climate change exposure pathways are manifest in a particular population. The gray box indicates that the extent
to which the three categories of exposure translate to actual health burden is moderated by such factors as background public health and socioeconomic conditions, and
adaptation measures. The green arrows at the bottom indicate that there may be feedback mechanisms, positive or negative, between societal infrastructure, public health, and
adaptation measures and climate change itself. As discussed later in the chapter, for example, some measures to improve health also reduce emissions of climate-altering
pollutants, thus reducing the extent and/or pace of climate change as well as improving local health (courtesy of E. Garcia, UC Berkeley). The examples are indicative.
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T
he negative effects of climate change on health may be reduced by
improved health services, better disaster management, and poverty
alleviation, although the cost and effort may be considerable (Section
11.7). The consequences of large magnitude climate change beyond
2050, however, would be much more difficult to deal with (Section
11.8). Although there are exceptions, to a first approximation climate
change acts to exacerbate existing patterns of ill health, by acting on
the underlying vulnerabilities that lead to ill health even without climate
change. Thus, before pursuing the three pathways in Figure 11-1, we
summarize what is known about vulnerability to climate-induced illness
and injury.
11.3. Vulnerability to Disease and Injury Due to
Climate Variability and Climate Change
In the IPCC assessments, vulnerability is defined as the propensity or
predisposition to be adversely affected (see Chapter 19 and Glossary).
In this section, we consider causes of vulnerability to ill health
associated with climate change and climate variability, including
individual and population characteristics and factors in the physical
environment.
We have outlined the causes of vulnerability separately, but in practice
causes combine, often in a complex and place-specific manner. There are
some factors (such as education, income, health status, and responsiveness
of government) that act as generic causes of vulnerability. For example,
the quality of governance—how decisions are made and put into
practice—affects a community’s response to threats of all kinds (Bowen
et al., 2012; see Chapter 12). The background climate-related disease
rate of a population is often the best single indicator of vulnerability to
climate change—doubling of risk of disease in a low disease population
has much less absolute impact than doubling of the disease when the
background rate is high. (Note that here, and elsewhere in the chapter,
we treat “risk” in the epidemiological sense: the probability that an
event will occur.) But the precise causes of vulnerability, and therefore
the most relevant adaptation capacities, vary greatly from one setting
to another. For example, severe drought in Australia has been linked to
psychological distress—but only for those residing in rural and remote
areas (Berry et al., 2010). The link between high ambient temperatures
and increased incidence of salmonella food poisoning has been
demonstrated in many places (e.g., Zhang et al., 2010), but the lag
varies from one country to another, suggesting that the mechanisms
differ. Deficiencies in food storage may be the critical link in some
places; food handling problems may be most important elsewhere
(Kovats et al., 2004).
The 2010 World Development Report concluded that all developing
regions are vulnerable to economic and social damage resulting from
climate change—but for different reasons (World Bank, 2010). The
critical factors for sub-Saharan Africa, for example, are the current climate
stresses (in particular, droughts and floods) that may be amplified in
parts of the region under climate change, sparse infrastructure, and
high dependence on natural resources (see Chapter 22). Asia and the
Pacific, on the other hand, are distinguished by the very large number
of people living in low-lying areas prone to flooding (see Chapters 24
and 29).
11.3.1. Geographic Causes of Vulnerability
Location has an important influence on the potential for health losses
caused by climate change (Samson et al., 2011). Those working outdoors
in countries where temperatures in the hottest time of the year are
already at the limits of thermal tolerance for part of the year will be more
severely affected by further warming than workers in cooler countries
(Kjellstrom et al., 2013). The inhabitants of low-lying coral atolls are
very sensitive to flooding, contamination of freshwater reservoirs due
to sea level rise, and salination of soil, all of which may have important
effects on health (Nunn, 2009). Rural populations that rely on subsistence
farming in low rainfall areas are at high risk of undernutrition and
water-related diseases if drought occurs, although this vulnerability may
be modified strongly by local factors, such as access to markets and
irrigation facilities (Acosta-Michlik et al., 2008). Living in rural and
remote areas may confer increased risk of ill health because of limited
access to services and generally higher levels of social and economic
disadvantage (Smith, 2008). Populations that are close to the present
limits of transmission of vector-borne diseases are most vulnerable to
changes in the range of transmission as a result of rising temperatures
and altered patterns of rainfall, especially when disease control systems
are weak (Zhou et al., 2008; Lozano-Fuentes et al., 2012.). In cities, those
who live on urban heat islands are at greater risk of ill health due to
extreme heat events (Stone et al., 2010; Uejio et al., 2011).
11.3.2. Current Health Status
Climate extremes may promote the transmission of certain infectious
diseases, and the vulnerability of populations to these diseases will
depend on the baseline levels of pathogens and their vectors. In the USA,
as one example, arboviral diseases such as dengue are rarely seen after
flooding, compared with the experience in other parts of the Americas.
The explanation lies in the scarcity of dengue (and other pathogenic
viruses) circulating in the population, before the flooding (Keim, 2008). On
the other hand, the high prevalence of HIV infection in many populations
in sub-Saharan Africa will tend to multiply the health risks of climate
change, due to the interactions between chronic ill health, poverty,
extreme weather events, and undernutrition (Ramin and McMichael,
2009). Chronic diseases such as diabetes and ischemic heart disease
magnify the risk of death or severe illness associated with high ambient
temperatures (Basu and Ostro, 2008; Sokolnicki et al., 2009).
11.3.3. Age and Gender
Children, young people, and the elderly are at increased risk of climate-
related injury and illness (Perera, 2008). For example, adverse effects of
malaria, diarrhea, and undernutrition are presently concentrated among
children, for reasons of physiological susceptibility (Michon et al., 2007).
In principle, children are thought to be more vulnerable to heat-related
illnesses, owing to their small body mass to surface area ratio, but
evidence of excess heat-related mortality in this age group is mixed
(Basu and Ostro, 2008; Kovats and Hajat, 2008). Maternal antibodies
acquired in utero provide some protection against dengue fever in the
first year of life, but if infection does occur in infants it is more likely to
provoke the severe hemorrhagic form of illness (Ranjit and Kissoon,
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011). Children are generally at greater risk when food supplies are
restricted: households with children tend to have lower than average
incomes, and food insecurity is associated with a range of adverse
health outcomes among young children (Cook and Frank, 2008).
Older people are at greater risk from storms, floods, heat waves, and
other extreme events (Brunkard et al., 2008), in part because they tend
to be less mobile than younger adults and so find it more difficult to
avoid hazardous situations and also because they are more likely to live
alone in some cultures. Older people are also more likely to suffer from
health conditions that limit the body’s ability to respond to stressors
such as heat and air pollution (Gamble et al., 2013).
The relationship between gender and vulnerability is complex. Worldwide,
mortality due to natural disasters, including droughts, floods, and storms,
is higher among women than men (WHO, 2011). However, there is
variation regionally. In the USA, males are at greater risk of death
following flooding (Jonkman and Kelman, 2005). A study of the health
effects of flooding in Hunan province, China, also found an excess of
flood deaths among males, often related to rural farming (Abuaku et
al., 2009). In Canada’s Inuit population males are exposed to dangers
associated with insecure sea ice, while females may be more vulnerable
to the effects of diminished food supplies (Pearce et al., 2011). In the
Paris 2003 heat wave, excess mortality was greater among females
overall, but there were more excess deaths among men in the working
age span (25 to 64) possibly due to differential exposures to heat in
occupational settings (Fouillet et al., 2006). In Bangladesh, females
are more affected than males by a range of climate hazards, due to
differences in prevalence of poverty, undernutrition, and exposure to
water-logged environments (Neelormi et al., 2009). The effect of food
insecurity on growth and development in childhood may be more
damaging for girls than boys (Cook and Frank, 2008).
Pregnancy is a period of increased vulnerability to a wide range of
environmental hazards, including extreme heat (Strand et al., 2012) and
infectious diseases such as malaria, foodborne infections, and influenza
(Van Kerkhove et al., 2011).
11.3.4. Socioeconomic Status
The poorest countries and regions are generally most susceptible to
damage caused by climate extremes and climate variability (Malik et
al., 2012), but wealthy countries are not immune, as shown by the
deaths resulting from bushfires in Australia in 2009 (Teague et al., 2010).
Also, rapid economic development may increase the risks of climate-
related health issues. For instance, changes in Tibet Autonomous Region,
China, including new roads and substantial in-migration may explain
(along with above-average warming) the appearance and establishment
in Lhasa of Culex pipiens, a mosquito capable of transmitting the West
Nile virus (Liu et al., 2013b).
A review of global trends in tropical cyclones 1970–2009 found that
mortality risk at country-level depended most strongly on three factors:
storm intensity, quality of governance, and levels of poverty (Peduzzi et
al., 2012). Individuals and households most vulnerable to climate hazards
tend to be those with relatively low socioeconomic status (Friel et al.,
2
008). A study of the impacts of flooding in Bangladesh found that
household risk reduced with increases in both average income and
number of income sources. Poorer households were not only more
severely affected by flooding, but they also took preventive action less
often and received assistance after flooding less frequently than did
more affluent households (Brouwer et al., 2007).
In many countries, race and ethnicity are powerful markers of health
status and social disadvantage. Black Americans have been reported to
be more vulnerable to heat-related deaths than other racial groups in
the USA (Basu and Ostro, 2008). This may be due to a higher prevalence
of chronic conditions such as overweight and diabetes (Lutsey et al.,
2010), financial circumstances (e.g., lower incomes may restrict access
to air conditioning during heat-waves; Ostro et al., 2010), or community-
level characteristics such as higher local crime rates or disrupted social
networks (Browning et al., 2006). Indigenous peoples who depend
heavily on local resources, and live in parts of the world where the
climate is changing quickly, are generally at greater risk of economic
losses and poor health. Studies of the Inuit people, for example, show
that rapid warming of the Canadian Arctic is jeopardizing hunting and
many other day-to-day activities, with implications for livelihoods and
well-being (Ford, 2009).
11.3.5. Public Health and Other Infrastructure
Populations that do not have access to good quality health care and
essential public health services are more likely to be adversely affected
by climate variability and climate change (Frumkin and McMichael,
2008). Harsh economic conditions in Europe since 2008 led to cutbacks
in health services in some countries, followed by a resurgence of
climate-sensitive infectious diseases including malaria (Karanikolos et
al., 2013). The condition of the physical infrastructure that supports
human settlements also influences health risks (this includes supply of
power, provision of water for drinking and washing, waste management,
and sanitation; see Chapter 8). In Cuba, a country with a well-developed
public health system, dengue fever has been a persistent problem in
the larger cities, due in part to the lack of a constant supply of drinking
water in many neighborhoods (leading to people storing water in
containers that are suitable breeding sites for the disease vector Aedes
aegypti; Bulto et al., 2006). In New York, daily mortality spiked after a
city-wide power failure in August 2003, due in part to increased exposure
to heat (Anderson and Bell, 2012).
11.3.6. Projections for Vulnerability
Population growth is linked to climate change vulnerability. If nothing
else changes, increasing numbers of people in locations that are already
resource poor and are affected by climate risks will magnify harmful
impacts. Virtually all the projected growth in populations will occur in
urban agglomerations, mostly in large, low latitude hot countries in
which a high proportion of the workforce is deployed outdoors with little
protection from heat. About 150 million people currently live in cities
affected by chronic water shortages and by 2050, unless there are rapid
improvements in urban environments, the number will rise to almost a
billion (McDonald et al., 2011). Under a “business as usual” scenario
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Population increase factor
(2010 to 2050)
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Mid-21st century projection
Figure 11-2 |
Increasingly frequent heat extremes will combine with rapidly growing numbers of older people living in cities—who are particularly vulnerable to extreme heat. Countries are shaded according to the expected proportional
increase in urban populations aged over 65 by the year 2050. Bar graphs show how frequently the maximum daily temperature that would have occurred only once in 20 years in the late 20th century is expected to occur in the mid-21st
century, with lower numbers indicating more frequent events. Results are shown for three different Special Report on Emission Scenarios (SRES) scenarios (blue = B1; green = A1B, red = A2), as described in the IPCC Special Report on
Emissions Scenarios, and based on 12 global climate models participating in the third phase of the Coupled Model Intercomparison Project (CMIP3). Colored boxes show the range in which 50% of the model projections are contained, and
whiskers show the maximum and minimum projections from all models (WHO and WMO, 2012).
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Alaska/Northwest Canada
East Canada/Greenland/Iceland
East North America
Central North America
West North America
Central America/Mexico
Amazon
Northeast Brazil
West Coast South America
Southeast South America
South Africa
West Africa
East Africa
Sahara
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Mediterranean
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North Asia
Central Asia Tibetan Plateau East Asia
South Asia
North Australia
South Australia/New Zealand
West Asia
Central Europe
Southeast Asia
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w
ith mid-range population growth, the Organisation for Economic
Co-operation and Development (OECD) projects that about 1.4 billion
people will be without access to basic sanitation in 2050 (OECD, 2012).
The age structure of the population also has implications for vulnerability
(see Figure 11-2). The proportion aged over 60, worldwide, is projected
to increase from about 10% presently to about 32% by the end of the
century (Lutz et al., 2008). The prevalence of overweight and obesity,
which is associated with relatively poor heat tolerance, has increased
almost everywhere in the last 20 years, and in many countries the trend
continues upwards (Finucane et al., 2011). It has been pointed out that
the Sahel region of Africa may be particularly vulnerable to climate change
because it already suffers so much stress from population pressure,
chronic drought, and governmental instability (Diffenbaugh and Giorgi,
2012; Potts and Henderson, 2012).
Future trends in social and economic development are critically important
to vulnerability. For instance, countries with a higher Human Development
Index (HDI)—a composite of life expectancy, education, literacy, and gross
domestic product (GDP) per capita—are less affected by the floods,
droughts, and cyclones that take place (Patt et al., 2010). Therefore policies
that boost health, education, and economic development should reduce
future vulnerability. Overall, there have been substantial improvements
in HDI in the last 30 years, but this has been accompanied by increasing
inequalities between and within countries, and has come at the cost of
high consumption of environmental resources (UNDP, 2011).
11.4. Direct Impacts of Climate
and Weather on Health
11.4.1. Heat- and Cold-Related Impacts
Although there is ample evidence of the effects of weather and climate
on health, there are few studies of the impacts of climate change itself.
(An example: Bennett et al. (2013) reported that the ratio of summer
to winter deaths in Australia increased between 1968 and 2010, in
association with rising annual average temperatures.) The issue is scale,
as climate change is defined in decades. Robust studies require not only
extremely long-term data series on climate and disease rates, but also
information on other established or potential causative factors, coupled
with statistical analysis to apportion changes in health states to the
various contributing factors. Wherever risks are identified, health agencies
are mandated to intervene immediately, biasing long-term analyses.
Nevertheless, the connection between weather and health impacts is
often sufficiently direct to permit strong inferences about cause and
effect (Sauerborn and Ebi, 2012). Most notably, the association between
hot days (commonly defined in terms of the percentiles of daily maximum
temperature for a specified location) and increases in mortality is very
robust (Honda et al., 2013). The IPCC Special Report on Extreme Events
(SREX) concludes that it is very likely that there has been an overall
decrease in the number of cold days and nights, and an overall increase
in the number of warm days and nights, at the global scale. If there has
been an increase in daily maximum temperatures, then it follows, in our
view, that the number of heat-related deaths is likely to have also
increased. For example, Christidis et al. (2012) concluded that it is
“extremely likely (probability greater than 95%)” that anthropogenic
c
limate change at least quadrupled the risk of extreme summer heat
events in Europe in the decade 1999–2008. The 2003 heat wave was
one such record event; therefore, the probability that particular heat
wave can be attributed to climate change is 75% or more, and on this
basis it is likely the excess mortality attributed to the heat wave (about
15,000 deaths in France alone (Fouillet et al., 2008)) was caused by
anthropogenic climate change.
The rise in minimum temperatures may have contributed to a decline
in deaths associated with cold spells; however, the influence of seasonal
factors other than temperature on winter mortality suggests that the
impacts on health of more frequent heat extremes greatly outweigh
benefits of fewer cold days (Kinney et al., 2012; Ebi and Mills, 2013).
Quantification, globally, remains highly uncertain, as there are few studies
of the large developing country populations in the tropics, and these
point to effects of heat, but not cold, on mortality (Hajat et al., 2010).
There is also significant uncertainty over the degree of physiological,
social, or technological adaptation to increasing heat over long time
periods.
11.4.1.1. Mechanisms
The basic processes of human thermoregulation are well understood.
If the body temperature rises above 38°C (“heat exhaustion”), physical
and cognitive functions are impaired; above 40.6°C (“heat stroke”),
risks of organ damage, loss of consciousness, and death increase
sharply. Detailed exposure-response relationships were described long
ago (Wyndham, 1969), but the relationships in different community
settings and for different age/sex groups are not yet well established.
The early studies are supported by more recent experimental and field
studies (Ramsey and Bernard, 2000; Parsons, 2003) and meta-analysis
(Bouchama et al., 2007) that show significant effects of heat stress as
body temperatures exceed 40°C, and heightened vulnerability in
individuals with preexisting disease.
At high temperatures, displacement of blood to the surface of the body
may lead to circulatory collapse. Indoor thermal conditions, including
ventilation, humidity, radiation from walls or ceiling, and the presence
or absence of air conditioning, are important in determining whether
adverse events occur, but these variables are seldom well-measured in
epidemiological studies (Anderson et al., 2012). Biological mechanisms
are less evident for other causes of death, such as suicide, that are
sometimes related to high temperature (Page et al., 2007; Kim et al.,
2011; Likhvar et al., 2011).
Heat waves refer to a run of hot days; precisely how many days, and
how high the temperatures must rise, are defined variously (Kinney et
al., 2008). Some investigators have reported that mortality increases
more during heat waves than would be anticipated solely on the basis
of the short-term temperature mortality relationship (D’Ippoliti et al.,
2010; Anderson and Bell, 2011), although the added effect is relatively
small in some series, and most evident with prolonged heat waves
(Gasparrini and Armstrong, 2011). Because heat waves are relatively
infrequent compared with the total number of days with temperatures
greater than the optimum for that location, the effects of heat waves
are only a fraction of the total impact of heat on health. Some studies
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h
ave shown larger effects of heat and heat waves earlier in the hot
season (Anderson and Bell, 2011; Rocklov et al., 2011). This may be
testament to the importance of acclimatization and adaptive measures,
or may result from a large group in the population that is more susceptible
to heat early in the season (Rocklov et al., 2009, 2011).
The extreme heat wave in Europe in 2003 led to numerous epidemiological
studies. Reports from France (Fouillet et al., 2008) concluded that most
of the extra deaths occurred in elderly people (80% of those who died
were older than 75 years). Questions were raised at the time as to why
this event had such a devastating effect (Kosatsky, 2005). It is still not
clear, but one contributing factor may have been the relatively mild
influenza season the year before. Recent studies have found that when
the previous year’s winter mortality is low, the effect of summer heat is
increased (Rocklov and Forsberg, 2009; Ha et al., 2011) because mild
winters may leave a higher proportion of vulnerable people (Stafoggia
et al., 2009). Most studies of heat have been in high-income countries,
but there has been work recently in low- and middle-income countries,
suggesting heterogeneity in vulnerability by age groups and socioeconomic
factors similar to that seen in higher-income settings (Bell et al., 2008b;
McMichael et al., 2008; Pudpong and Hajat, 2011).
Numerous studies of temperature-related morbidity, based on hospital
admissions or emergency presentations, have reported increases in
events due to cardiovascular, respiratory, and kidney diseases (Hansen
et al., 2008; Knowlton et al., 2009; Lin and Chan, 2009) and the impact
has been related to the duration and intensity of heat (Nitschke et al.,
2011).
There is evidence now that both average levels and variability in
temperature are important influences on human health. The standard
deviation of summer temperatures was associated with survival time
in a U.S. cohort study of persons aged older than 65 years with chronic
disease who were tracked from 1985 to 2006 (Zanobetti et al., 2012).
Greater variability was associated with reduced survival. A study that
modeled separately projected increases in temperature variability and
average temperatures for six cities for 2070–2099 found that, with one
exception, variability had an effect (increased deaths) over and above
what was estimated from the rise in average temperatures (Gosling et
al., 2009). Relevant to Section 11.5, rapid changes in temperature may
also alter the balance between humans and parasites, increasing
opportunities for new and resurgent diseases. The speed with which
organisms adapt to changes in temperatures is, broadly speaking, a
function of mass, and laboratory studies have shown that microbes
respond more quickly to a highly variable climate than do their multi-
cellular hosts (Raffel et al., 2012).
Health risks during heat extremes are greater in people who are physically
active (e.g., manual laborers). This has importance for recreational
activity outdoors and it is relevant especially to the impacts of climate
change on occupational health (Kjellstrom et al., 2009a; Ebi and Mills,
2013; see also Section 11.6.2).
Heat also acts on human health through its effects, in conjunction with
low rainfall, on fire risk. In Australia in 2009, record high temperatures,
combined with long-term drought, caused fires of unprecedented
intensity and 173 deaths from burns and injury (Teague et al., 2010).
S
moke from forest fires has been linked elsewhere with increased
mortality and morbidity (Analitis et al., 2012; see Section 11.5.3.2).
11.4.1.2. Near-Term Future
The climate change scenarios modeled by WGI AR5 project rising
temperatures and an increase in frequency and intensity of heat waves
(Section 2.6.1; Chapter 1) in the near-term future, defined as roughly
midway through the 21st century, or the era of climate responsibility
(see SPM). It is uncertain how much acclimatization may mitigate the
effects on human health (Wilkinson et al., 2007a; Bi and Parton, 2008;
Baccini et al., 2011; Hanna et al., 2011; Maloney and Forbes, 2011; Peng
et al., 2011; Honda et al., 2013). In New York, it was estimated that
acclimatization may reduce the impact of added summer heat in the
2050s by roughly a quarter (Knowlton et al., 2007). In Australia, the
number of “dangerously hot” days, when core body temperatures may
increase by ≥2°C and outdoor activity is hazardous, is projected to rise
from the current 4 to 6 days per year to 33 to 45 days per year by 2070
(with SRES A1FI) for non-acclimatized people. Among acclimatized
people, an increase from 1 to 5 days per year to 5 to 14 days per year
is expected (Hanna et al., 2011).
For reasons given above, it is not clear whether winter mortality will
decrease in a warmer, but more variable, climate (Kinney et al., 2012;
Ebi and Mills, 2013). Overall, we conclude that the increase in heat-
related mortality by mid-century will outweigh gains due to fewer cold
periods, especially in tropical developing countries with limited adaptive
capacities and large exposed populations (Wilkinson et al., 2007b). A
similar pattern has been projected for temperate zones. A study of three
Quebec cities, based on SRES A2 and B2, extended to 2099, showed an
increase in summer mortality that clearly outweighed a small reduction
in autumn deaths, and only slight variations in winter and spring (Doyon
et al., 2008). Another study in Brisbane, Australia, using years of life lost
as the outcome, found the gains associated with fewer cold days were
less than the losses caused by more hot days, when warming exceeded
2°C (Huang et al., 2012).
11.4.2. Floods and Storms
Floods are the most frequently occurring type of natural disaster (Guha-
Sapir et al., 2011). In 2011, 6 of the 10 biggest natural disasters were
flood events, when considered in terms of both number affected (112
million people) and number of deaths (3140 people) (Guha-Sapir et al.,
2011). Globally, the frequency of river flood events has been increasing,
as well as economic losses, due to the expansion of population and
property in flood plains (Chapter 18). There is little information on
health trends attributable to flooding, except for mortality and there
are large differences in mortality risk between countries (UNISDR, 2011).
Mortality from flooding and storm events is generally declining, but
there is good evidence that mortality risks first increase with economic
development before declining (De Haen and Hemrich, 2007; Kellenberg
and Mobarak, 2008; Patt et al., 2010). For instance, migration to slums
in coastal cities may increase population exposure at a greater pace
than can be compensated for by mitigation measures (see Chapter 10
on urban risks). Severe damaging floods in Australia in 2010–2011 and
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Chapter 11 Human Health: Impacts, Adaptation, and Co-Benefits
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i
n the northeastern USA in 2012 indicate that high-income countries
may still be affected (Guha-Sapir et al., 2011).
11.4.2.1. Mechanisms
Flooding and windstorms adversely affect health through drowning,
injuries, hypothermia, and infectious diseases (e.g., diarrheal disease,
leptospirosis, vector-borne disease, cholera; Schnitzler et al., 2007;
Jakubicka et al., 2010). Since AR4, more evidence has emerged on the
long-term (months to years) implications of flooding for health. Flooding
and storms may have profound effects on peoplesmental health (Neria,
2012). The prevalence of mental health symptoms (psychological distress,
anxiety, and depression) was two to five times higher among individuals
who reported flood water in the home compared to non-flooded
individuals (2007 flood in England and Wales; Paranjothy et al., 2011).
In the USA, signs of hurricane-related mental illness were observed in
a follow-up of New Orleans’ residents almost 2 years after Hurricane
Katrina (Kessler et al., 2008). The attribution of deaths to flood events
is complex; most reports of flood deaths include only immediate
traumatic deaths, which means that the total mortality burden is under-
reported (Health Protection Agency, 2012). There is some uncertainty
as to whether flood events are associated with a longer-term (6 to 12
months) effect on mortality in the flooded population. No persisting
effects were observed in a study in England and Wales (Milojevic et al.,
2011), but longer-term increases in mortality were found in a rural
population in Bangladesh (Milojevic et al., 2012).
11.4.2.2. Near-Term Future