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review article

global health

Globalization, Climate Change, and Human Health

Anthony J. McMichael, M.B., B.S., Ph.D.

From the National Centre for Epidemiol- ogy and Population Health, Australian Na- tional University, Canberra, ACT, Australia. Address reprint requests to Dr. McMichael at the National Centre for Epidemiology and Population Health, Australian National University, Canberra, ACT 0200, Australia, or at [email protected].

The global scale, interconnectedness, and economic intensity of contemporary human activity are historically unprecedented,1 as are many of the consequent environmental and social changes. These global changes fundamentally influence patterns of human health, international health care, and public health activities.2 They constitute a syndrome, not a set of separate changes, that reflects the interrelated pressures, stresses, and tensions arising from an over- ly large world population, the pervasive and increasingly systemic environmental impact of many economic activities, urbanization, the spread of consumerism, and the widening gap between rich and poor both within and between countries.

In recent decades, international connectivity has increased on many fronts, in- cluding the flow of information, movements of people, trading patterns, the flow of capital, regulatory systems, and cultural diffusion. These exponential increases in demographic, economic, commercial, and environmental indexes have been labeled the Great Acceleration.3 Remarkably, the resultant environmental effects are now altering major components of the Earth system.4,5 The current geologic epoch is being called the Anthropocene (successor to the Holocene epoch)5,6 in recognition of the global force that Homo sapiens has become, pushing or distorting Earth’s great natural global systems beyond boundaries considered to be safe for continued human social and biologic well-being.4,7 The loss of biodiversity, the greatly amplified global circulation of bioactive nitrogen compounds, and human- induced climate change have already reached levels that are apparently unsafe.4

These changes pose fundamental threats to human well-being and health.4,7 For example, a positive relationship has been observed between regional trends in climate (rising temperatures and declining rainfall) and childhood stunting in Kenya since 1975, indicating that as projected warming and drying continue to occur along with population growth, food yields and nutritional health will be impaired.8 These human-induced climatic changes often act in concert with environ- mental, demographic, and social stressors that variously influence regional food yields, nutrition, and health. Furthermore, at the current level of global connected- ness and interdependence, the environmental impact of human activity has a wider geographic range, although its influence may be offset somewhat by more effective global alerts and more rapid distribution of food aid. The extreme heat and wild- fires in western Russia in the summer of 2010 destroyed one third of that coun- try’s wheat yield, and the subsequent ban on exported grain contributed to a rise in the price of wheat worldwide, exacerbating hunger in Russia (where flour prices increased by 20%) and in low-income urban populations in countries such as Pakistan and Egypt.9,10 On the economic front, the recent global financial crisis has underscored the domino-like interdependence of national economies.

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E f f e c t s o f G l o b a l i z a t i o n o n P o p u l a t i o n H e a l t h

Global influences on population health such as those described above transcend the more spe- cific, focused frame within which international health issues are addressed.2 The processes of global change are more systemic, involving dis- ruption or depletion (not merely local pollution). Remediating or adapting to these changes re- quires an understanding of dynamic systems, their complexity and associated uncertainties, and coordinated policy responses across relevant sectors. The relationships between these perva-

sive processes of change and human health are shown in Figure 1.

Demographic Changes

Population growth is often overlooked in the dis- course on global change, including its relation to the mitigation (abatement) of climate change, to which the contribution of global emissions is obvious.11 The projections by the United Nations that today’s population of 7 billion will increase to 9.3 billion by 205012 should reactivate the de- bate about whether we can succeed in pursuing realistic objectives for a healthy climate without curtailing the actual number of humans pressing on the environment. Furthermore, the negative- feedback loop of excessive population pressure on regional environments (involving soil exhaus- tion, water depletion, and the loss of various wild animal and plant food species) not only exacer- bates various ongoing worldwide environmental and ecologic changes but also entrenches condi- tions of poverty and disadvantage. In these latter circumstances, fertility rates tend to remain high.

Some additional increase in the world popu- lation is inevitable in countries with high fertil- ity rates, given the demographic flywheel momen- tum of populations weighted toward the young. Meanwhile, moderate gains have been made in facilitating education for girls, although progress in this, as well as in the provision of adequate education about reproduction and reproductive choice, remains slow in many low-income coun- tries.13 Where unplanned pregnancy rates remain high (e.g., Timor-Leste and Nigeria), so do risks to maternal and child health.

Social Changes and Economic Activity

Many other aspects of globalization inf luence population health,2 including the accelerated emergence of new infectious diseases,14,15 the near-ubiquitous rise in the rates of obesity and associated noncommunicable diseases as daily bodily energy budgets (food energy input vs. physical energy output) shift into surplus,16 the spread of cigarette marketing, the effects of cli- mate change,17,18 increases in resistance to anti- microbial agents, and health risks in the work- place due to the deregulation of international labor markets.2 Looming large in the background as additional determinants of health are the per- sistent, even increasing, disparities in wealth, education, autonomy, and social inclusion.19 There are, of course, certain aspects of globalization

Globalization and Global Changes

Large-Scale and Systemic Environmental Impacts

Degradation of land and water Depletion of resources

Ecosystem disturbances Disruption of biogeophysical

systems (e.g., climate system)

Economic Activity Trade and capital mobility

Labor conditions Wealth creation and distribution

International aid: financial and health care

Demographic Changes

Population growth Urbanization, increased density

Aging Increased mobility Family structures Social Changes

Institutions, governance, international codes Cultural diffusion

Impacts on Population

Health

Increases in interpopulation connectivity and increases in scale and intensity of action and impact

Figure 1. Inf luence on Human Health of Changes Related to Globalization.

The figure is a schematic representation of the three major domains — social, economic, and environmental — within which globalizing processes and changes are occurring. Shown are their main components, the two-way inter- actions between them, and the central fact that all three domains influence the conditions for and levels of population health. In particular, changes in population size, distribution, mobility, levels and types of economic activity, and global flows of capital and labor all have consequences for the environ- ment, including the recent rapid increase in greenhouse-gas emissions as the primary cause of current climate change. Those great contemporary environmental changes have diverse and far-reaching consequences for human health.

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that are beneficial to health, such as the en- hanced flow of information, improvements in internationally coordinated vaccination programs and systems to respond to infectious diseases, and a greater capacity for long-distance responses to disasters.

Adverse global influences on health, such as rising food prices and extended ranges of some infectious diseases, have also impeded attain- ment of the United Nations Millennium Devel- opment Goals.20 Future global health goals must be better integrated with the fundamental in- f luences of poverty, inequity, illiteracy, climate change, land-use patterns, and food insecurity on health. After the Rio+20 Conference (2012), the Millennium Development Goals are to be replaced by Sustainable Development Goals in 2016, ref lecting the principle set forth at the original Rio Declaration on Environment and Development (1992) that concern for humans must be at the center of sustainable develop- ment. Nevertheless, concern for human health is not yet near that center. This reflects the con- tinuing misperception of what health means and the dominance of a narrow, clinically based view that seemingly does not take into account the fundamental need, in improving population health, to address the poor fit between environ- mental and sociocultural conditions and basic human biologic and psychological needs.

Environmental and Ecologic Changes

The deep-seated, essentially ecologic risks to pop- ulation health cannot be countered effectively at the local level alone. Climate change induced by human activities, for example, is due to the glob- ally aggregated excess of greenhouse emissions. Primary prevention of health problems arising from such global environmental and sociodemo- graphic changes therefore requires coordinated international policy, supplemented by more local policy-making and action. For example, the World Trade Organization should give greater priority to averting the adverse health and environmental effects of international free trade.21 There is also a need for instruments similar to the WHO Framework Convention on Tobacco Control1,22 and the WHO Global Outbreak Alert and Re- sponse Network, in relation to the emergence of infectious diseases,23 as well as the United Na- tions Environmental Programme Montreal Proto- col to protect the ozone layer.24

The following four examples describe other

environmental and ecologic changes on a global scale that will increasingly influence the world’s health. First, the probability that new strains of influenza virus will emerge is increasing, particu- larly in the rural villages of Southeast Asia and East Asia.14,25 The risk increases with population growth; the juxtaposition of traditional backyard pig, chicken, and duck farming with intensified commercial poultry production; and environmen- tal changes that affect the flight paths of mi- grating wild birds.

Second, the decline in available seafood pro- tein (which is important for many low-income coastal populations) is a threat to health and reflects the unprecedented combination of ocean warming, acidification (due to increased uptake of carbon dioxide), deoxygenation,26 destruction of coastal fish nurseries, and overfishing.27

Third, diverse health risks are posed by the deprivation, displacement, and conflict that re- sult from shortages of fresh water.8,28 Many populations, such as those in Bangladesh, Viet- nam, Egypt, and Iraq, live downstream on great rivers that traverse several countries. In many cases, river f lows are threatened by the loss of glacier mass and snowpack due to global warm- ing and by the increased diversion of f low by neighbors upstream.

Finally, the need to maintain food supplies and adequate nutrition for the increasing world population presents a major challenge.29 Global food production also faces pressures as a result of reduced yield due to land degradation, water shortages, and climate change and the rising demand for animal foods among middle-income populations. Furthermore, agriculture (especially livestock production) accounts for around one fourth of global greenhouse-gas emissions.30 Thus, there are growing pressures to transform food production (e.g., more mixed cropping and inclusion of acceptable genetically modified crops), distribution, and consumption. Since the environmental, particularly climatic, effects of producing red meat from methane-producing ruminants (e.g., cattle, sheep, and goats) are so great, thought needs to be given to the question of whether production of this protein source will need to be curtailed — while allowing a suffi- cient increase to ensure safe childhood nutrition in the many poorer populations, which currently consume levels of red meat that are lower than those in the overconsuming rich populations by a factor of 10.30 The global food security issue is

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further complicated by the ongoing land grab in eastern Africa and elsewhere by richer countries seeking investment opportunities and self-insur- ance against future land, food, and biofuel short- ages (e.g., Middle Eastern oil-producing states, China, and South Korea).31

These four examples also confirm that, in a world of global and systemic changes, these indi- vidual changes for the most part do not impinge on population health in isolation; instead, they typically act jointly and often interact. Specific examples are discussed in the next section, which reviews the health risks posed by climate change.

G l o b a l C l i m a t e C h a n g e

Global climate change is part of the larger Anthro- pocene syndrome of human-induced global envi- ronmental changes. These include land degrada- tion, ocean acidification, and disruptions and depletions of the stratospheric ozone concentra- tion, soil fertility, fresh-water resources, biodiver- sity stocks and ecosystem functioning, and global nitrogen and phosphorus cycles.4 Greenhouse emissions from fossil fuel–based power genera- tion and transport and from the agriculture and mining sectors increase the heat-retaining capac- ity of the lower atmosphere, resulting in global warming (see the interactive graphic at NEJM .org). In addition, deforestation and ocean satu- ration have added to greenhouse warming by re- ducing the capacity of terrestrial and marine en- vironments to absorb extra carbon dioxide (the main greenhouse gas) from the atmosphere. Also contributing to such warming are any ongoing natural variations in climate caused by cosmo- logic and geologic influences.32

Most of the global warming since 1950 (an increase of 0.7°C) has been the result of human activity.32 Annual global emissions of carbon diox- ide have increased over the past decade, as have the rates of sea-level rise, the loss of Arctic sea ice, and the number of extreme weather events.33 Without substantial and prompt international ac- tion to abate these emissions, average global tem- peratures (relative to the year 2000) are likely to rise by 1 to 2°C by 2050 and by 3 to 4°C by 2100, including increases of up to 6 to 7°C at high northern latitudes.33,34 Additional warming of an- other 0.7°C is locked in from the extra radiative energy already absorbed by the lower atmosphere and, in turn, by the oceans, though not yet mani- fested as surface warming. An average rise of 4°C would return Earth’s temperature to a level not experienced for 10 million to 20 million years.35

Rainfall patterns will also change, with rain- fall increasing in some regions and seasons and decreasing in others. Modeling consistently pro- jects an increase in regional aridity, and in the geographic range and severity of droughts, dur- ing this century.36 The frequency, and perhaps intensity, of extreme weather events is also ex- pected to increase in most regions — and may well have already begun to do so.37

E f f e c t s o f C l i m a t e C h a n g e o n H u m a n H e a l t h

The complex nature of climate change and its environmental and social manifestations results in diverse risks to human health.17,18,38 A three- way classification of these risks and causal path- ways is shown in Table 1.39

Our current, rather skewed knowledge of climate–health relationships has come from epi- demiologic studies of health risks in relation to differences and extremes in temperature and from quasicyclical climatic events such as the El Niño–Southern Oscillation phenomenon. How- ever, most of the health risks will arise from climatic influences on environmental systems and social conditions that affect food yields, water supplies, the stability of infectious disease patterns, and the integrity of natural and human- built protection against natural disasters (in- cluding forest cover, windbreaks, mangroves, vulnerable constructed seawalls, and urban water- drainage systems) and from the adverse health consequences of social disruption, displacement of communities, and conflict situations.18,38

Table 1. Categories of Climate-Change Risks to Health, According to Causal Pathway.

Risk Category Causal Pathway

Primary Direct biologic consequences of heat waves, extreme weather events, and temperature-enhanced levels of urban air pollutants

Secondary Risks mediated by changes in biophysically and ecologically based processes and systems, particularly food yields, water flows, infectious-disease vectors, and (for zoonotic diseases) intermediate-host ecology

Tertiary More diffuse effects (e.g., mental health problems in failing farm communities, displaced groups, disadvantaged indigenous and minority ethnic groups)

Consequences of tension and conflict owing to climate change– related declines in basic resources (water, food, timber, living space)

An interactive graphic showing

global temperature trends is available

at NEJM.org

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Key examples of these types of causal paths are shown in Figure 2. Many of the indirect ef- fects of climate change will be simultaneously inf luenced by other global changes and socio- demographic pressures that act in conjunction with climate change. Food yields and, hence, nutritional status ref lect changes not only in

climate40 but also in water supplies, soil fertility, nitrogen levels, biodiversity (e.g., pollinators and pest predators), and the health and vitality of farm workers.

It is not surprising that the health effects of climate change will be predominantly adverse.38 After all, human biology, domesticated food

Injury, death, postevent traumatic stress and

disease risk

Glacier loss, sea- level rise

Altered surface water

Reduced food yields

Food prices and availability

Microbial ecology (host

animals, vectors,

pathogen multipli- cation)

Physical hazards, risk

of death

Relocation of people

Fresh water

availability

Community and family

morale; mental health

problems

Nutrition; child devel-

opment (and life-

course adult health)

Infectious- disease

risks

Depression after event

Hygiene, homegrown

food

Conflicts, displacement

Ecosystem damage

Property loss

Infra- structure damage

Tourism and

recreation

Climate Change Changes in mean climatic conditions Increased variability, including extreme weather events

and heat waves

Primary Environmental and Social Impacts

Indirect Health Impacts

Loss of Jobs, Livelihoods

Shortages, Price

Changes

Other systemic environmental changes acting and interacting

with climate change

Direct Health Impacts

Figure 2. Processes and Pathways through Which Climate Change Inf luences Human Health.

The direct health impacts of climate change are shown in the upper right part of the figure, most of them due to amplified extreme weather events. All the other, less direct health impacts, shown in the lower part of the figure, are mediated by the primary environmen- tal and social impacts of climate change. These include the five categories of indirect health impacts and the tertiary effects on health and survival that arise from more diffuse disruptions, dislocations, and conflicts, which are likely to increase in future decades and are indicated by upward-pointing arrows.

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sources, and culture in general have evolved over many millennia within the usual prevailing cli- mate. Furthermore, populations everywhere will be vulnerable to increasingly severe extreme weather events.

Some beneficial health effects are expected to occur, at least in the earlier stages of climate change.38 In some temperate zones, milder win- ters may lead to fewer wintertime deaths from myocardial infarction and stroke, and in some low-latitude regions, hotter and drier conditions may reduce mosquito survival and, hence, mos- quito-borne infection.

Populations living in diverse social, economic, and physical conditions will be affected differ- ently by climate changes.18,38 Low-income and remote populations are more vulnerable to phys- ical hazards, undernutrition, diarrheal and other infectious diseases, and the health consequences of displacement. Populations on low-lying islands and in coastal areas, such as Bangladesh, are vulnerable to increased storm surges and flood- ing as the sea level rises. In Arctic circumpolar regions, communities may undergo enforced changes in diet as land and marine animal populations migrate or decline and as access to traditional food sources becomes physically more difficult.41

The likely future effects of climate change on various health outcomes have been modeled with the use of plausible scenarios of future climate change that have been agreed on internationally. For example, in temperate countries, as summers become hotter and heat waves more severe, modeling indicates that, from around mid-cen- tury, additional heat-related deaths will progres-

sively overwhelm the number of deaths averted as a result of milder winters.42,43 Such estimates of the extreme effects of weather will improve as the modeling of changes in climatic variability under climate-change conditions improves and as researchers take better account of physiologi- cal, behavioral, and technological adaptation by populations over time.

In China, the modeling of medium-scenario warming indicates that the transmission zone of freshwater snail–mediated schistosomiasis will extend northward, putting another 20 million people at risk by 2050.44 Such model-based esti- mation of the direction and approximate extent of likely change in health risks is an important re- source for decision-making about both climate- change abatement and localized adaptation.

Meanwhile, an important research task is to identify ongoing changes in health risks and outcomes that can be reasonably attributed to recent climate change. Given the multivariate causation of most human health outcomes, at- tribution is rarely simple.45 Nevertheless, over the past decade, observed changes in some health outcomes, viewed collectively, suggest a climate signal (Table 2).18,38,46

H e a l t h R i s k s a n d B e n e f i t s o f C l i m a t e - C h a n g e M i t i g a t i o n

a n d A d a p t a t i o n

The mitigation of climate change is a crucial first-order task for the world. However, while governments continue to wrestle with this un- precedented, complex political and ethical task, the more immediate challenge for the health sec- tor is to identify the main regional health threats posed by climate change and ensure the develop- ment of risk-lessening adaptations.

Adaptation Strategies

Adaptation capacities and strategies will differ greatly among populations. They will be particu- larly important where the rates of preexisting disease (e.g., childhood diarrhea and malnutri- tion) are already high and therefore, in absolute terms, would become considerably higher be- cause of the multiplier effects of climate change. Effective adaptive strategies will mostly require collaboration among diverse government sectors, research disciplines, and communities.

During heat waves, deaths and hospitaliza- tions predominate among the elderly, patients

Table 2. Indicators of Early Health Effects of Climate Change.

Increases in annual numbers of deaths and hospitaliza- tions due to extreme heat, observed in a range of high-income and low-income countries

Increases in rates of injuries and deaths due to the rising frequency of weather disasters in many regions

Extensions in the geographic range of several vector-borne infectious diseases or their vectors, including tick- borne encephalitis in Sweden, the tick vector of Lyme disease in eastern Canada, and malaria in the western Kenyan highlands

Although less certain, increases in the tempo of coastal outbreaks of cholera relative to the warming of coastal waters and El Niño events

Increases in the price of some staple foods, especially in vulnerable, food- insecure regions, leading to nutri- tional deprivation in low-income households

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with chronic cardiorespiratory disease, and per- sons living in low-grade housing. Early heat wave–warning systems, community caregiver schemes for vulnerable persons, well-insulated housing, and educational advice from primary health care providers would lower this risk. Mean- while, longer-term planning is needed to climate- proof urban residential areas.47

Health Benefits of Climate-Change Mitigation

One favorable aspect of efforts to mitigate climate change is that local health gains will quickly ac- crue to populations that undertake such efforts.48 Awareness of this potential health dividend — in addition to the longer-term global health benefits — should strengthen support for such actions.

Health benefits will result from mitigating ac- tions that address modes of transport, housing- design standards, energy generation, and agri- cultural systems (including livestock production). In many poor populations, improvements in

environment-related technologies will help to replace indoor-polluting cooking fuels with low- carbon fuels, and improvements in reproductive literacy will lead to fewer, better-spaced preg- nancies; both types of improvement reduce pres- sures on the climate system.11 All these actions will directly reduce well-known risk factors for disease and premature death (e.g., air pollution, sedentary living, and dietary excesses).48 Innova- tive urban design can have wide-ranging positive effects with regard to energy use, greenhouse- gas emissions, the effects of urban heat islands, patterns of physical activity, social relations, and community cohesion.

C h a l l e n g e s f o r t h e H e a l t h S e c t o r

The health sector has important roles to play in relation to climate-change abatement and adap- tation strategies for lessening unavoidable risks

Table 3. Role of the Health Sector in Climate-Change Mitigation (Primary Prevention) and Adaptation (Preparedness, or Secondary Prevention).*

Goal and Generic Action Suggested Strategies

Mitigation of climate change

Carry out health impact assessment of miti- gation strategies

Conduct epidemiologic research to estimate and document changes in health outcomes that result directly from mitigation actions

Limit the carbon (and other environmental) footprint related to the health care system

Design buildings, transport services, and facilities to achieve energy efficiency, in terms of energy sources and use, and to minimize waste

Enlist health professional organizations and government health departments

Educate the public about risks to health from climate change and explain that mitigating actions can confer additional, local health benefits

Include physicians and other health care workers as citizens

Participate in wider public discussion and moderate personal behaviors

Adaptation to lessen health risks

Provide adequate health care facilities and services

Improve facilities for handling increased patient volume resulting from extreme weather events and ensure adequate stocks of vaccine

Anticipate necessary surge capacity (e.g., for major heat waves, fires, epidemics)

Coordinate with emergency-services agencies and ambulance facilities and consider morgue capacity

Reinforce and extend public health programs to provide a foundation for dealing with most types of climate-related health effects

Develop early-warning systems (e.g., for heat waves, floods, and possible epidemics); programs for infectious-disease surveillance and analysis, vaccination, and vector control (e.g., mosquitoes, ticks); support for vulnerable communities; and mental health services (e.g., for postevent trauma and depression)

Educate and train the health workforce Develop programs that prepare health care workers to contribute to public education and to be on the alert for unexpected diagnoses

Engage in broader collaboration with other sectors

Institute policies for creating green spaces in cities (to promote physical and mental health); develop housing design and insula- tion to optimize health protection; consider livestock and wild animals as possible risks for infection

* The listed adaptation activities are intended to reduce health risks on the local and regional levels.

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to health (Table 3).49,50 Such strategies would in- clude the “greening” of health care institutions and participation in national health impact as- sessments and in intersectoral planning of sus- tainable energy systems, transportation, and ur- ban design. National delegations to international policymaking meetings that address global trends and threats (e.g., the annual conferences convened under the United Nations Framework Convention on Climate Change) should include representatives from, or at least substantive brief- ing by, the formal health sector.

C o n c l u s i o n s

Rapid globalization has brought new, large-scale influences to bear on patterns of human health. Various global-scale changes — economic, social, demographic, and environmental (particularly climatic) — are linked, for example, to the in- creased prevalence of obesity, changes in regional

food yields, the emergence of infectious diseases, the spread of cigarette smoking, and the persis- tence of health disparities.

Undertaking primary prevention at the source to reduce health risks resulting from these global influences is a formidable challenge. It requires conceptual insights beyond the conven- tional understanding of causation and prevention, as well as political will, trust, and resources. The complexities of policies to mitigate human- induced climate change are clear. Meanwhile, additional resources and strategies will be need- ed to reduce the health risks related to global change that have already arisen or are now un- avoidable. For populations to live sustainably and with good long-term health, the health sec- tor must work with other sectors in reshaping how human societies plan, build, move, produce, consume, share, and generate energy.

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