Global Climate Change and Children's Health

Scientists¹  and governments²  concur that Earth is warming; rapid global climate change is underway, and human activities are very likely (>90% probability) the main cause. Adverse human health and ecosystem consequences are anticipated,³  and some are already being measured. Physicians have written on the projected effects of climate change on public health,^4,5  but little has been written specifically about anticipated effects of climate change on children's health.⁶ 

Children represent a particularly vulnerable group that is likely to suffer disproportionately from both direct and indirect adverse health effects of climate change.⁷  Pediatric health care professionals must understand the escalating nature of these threats, anticipate their effects on children's health, and participate as children's advocates for strong mitigation and adaptation strategies now and at all levels, from local to global.⁸  This technical report examines both direct and indirect threats to children's health and futures related to climate change.*

“Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperature, widespread melting of snow and ice, and rising global mean sea level.”¹  According to the National Climatic Data Center, all records indicate that during the past century, global surface temperatures have increased at a rate near 0.6°C per century (1.1°F per century), but the trend has been 3 times larger since 1976.⁹  The results of this warming on regional climate are not uniform. In general, land-surface temperatures are increasing faster than sea-surface temperatures.⁹  The climate in latitudes between 40°N and 70°N is warming more quickly than that in lower latitudes, and some areas (eg, the southeastern United States) are actually cooling. Changes in precipitation that occur with climate change are also nonuniform.¹⁰  Since 1900, precipitation has increased 5% globally, but it has increased 0.5% to 1% per decade in northern midlatitudes and decreased 0.3% per decade in subtropical latitudes.¹¹  In contrast, snowfall in the northern hemisphere has decreased by 10% since 1966.¹¹ 

Examples of the effects of climate change have been widely reported.¹¹  Glaciers are in rapid retreat, and Arctic sea ice is melting.¹²  As a result of thermal expansion, sea level has increased 1 to 2 mm/year over the past 100 years.¹¹  Oceans are acidifying as atmospheric carbon dioxide (CO₂) is absorbed by the marine buffer system.¹³  Ecosystems and individual species are being affected in a variety of ways.¹⁴  Changes in temperature affect the density and range of species; natural history traits such as migration, flowering, and egg laying; morphology such as body size and behavior; and genetic frequency shifts. In an analysis of 143 studies that span decades of observation,¹⁵  more than 80% of 1468 species (mollusks to mammals and grasses to trees) are currently showing significant changes in temperature-sensitive species traits.

There is strong consensus among expert scientists that Earth is undergoing rapid, global climate change,^1,16  although there remains uncertainty about how rapidly and extensively the climate will change in the future. Given the range of possibilities, the Intergovernmental Panel on Climate Change has developed a suite of scenarios for different levels of mitigation and adaptation in response to anthropogenic (man-made) global climate change; all their cases predict that temperatures and sea level will continue to rise throughout the 21st century.¹⁷  Recent analyses describe thermal inertia in Earth's climate system such that even if greenhouse gas (GHG) emissions were abruptly reduced to zero, the planet would continue to warm for decades until the energy stored in the system equilibrates.¹⁸  The possibility of reaching a tipping point at which abrupt, large, and irreversible change could be superimposed on current trends adds both urgency and further ambiguity to the situation.¹⁹  In this context, it is critical to understand that current human activities are accelerating climate change and that future human activities will affect their trajectories.²⁰ 

The greenhouse effect is necessary to life on Earth as we know it (Fig 1). Without heat-trapping GHGs such as water vapor, CO₂, and other natural components of the atmosphere, Earth would be a lifeless, frozen planet (average temperature: −18°C) instead of the diverse biosphere we know today.¹¹  Since the onset of the industrial age, however, human activity has dramatically enhanced the greenhouse effect by rapidly adding large amounts of GHGs to the atmosphere (Table 1 [note that the United States leads total country and per-capita emissions]). Three GHGs, CO₂, methane, and nitrous oxide, are responsible for approximately 88% of the anthropogenic influences that enhance the greenhouse effect and have increased 35%, 155%, and 18%, respectively, since 1750 (the beginning of the industrial era).²¹  Rates of increase in GHGs are accelerating, up 20% since 1990.

CO₂ is the most important GHG and is responsible for more than 60% of human-enhanced increases and more than 90% of rapid increase in the past decade.²¹  Most CO₂ emissions are from the burning of fossil fuels such as coal, oil, and gas. Rising CO₂ is also related, to a lesser extent, to deforestation, which eliminates an important carbon sink (carbon sinks are reservoirs that absorb or take up released carbon from another part of the carbon cycle; the 4 major sinks on the planet are the atmosphere, the terrestrial biosphere [eg, trees and freshwater systems], oceans, and sediments).²¹  Currently, the atmosphere contains approximately 370 ppm of CO₂, which is the highest concentration in 420000 years and perhaps as long as 2 million years.¹¹  Estimates of CO₂ concentrations at the end of the 21st century range from 490 to 1260 ppm, or a 75% to 350% increase above preindustrial concentrations.¹¹ 

The importance of the magnitude of GHG emissions is linked to the rate of release. In the distant geologic past, similar concentrations of atmospheric CO₂ have occurred, but they accumulated over a 10000-year period, allowing for the slow, global biogeochemical cycles to adjust to the increases. Current emissions are being added to the atmosphere at 300 times this rate.¹¹  This confluence of speed and quantity of emissions has created the current, unprecedented rapid climate change.

Human health is affected by the condition of the physical environment.²²  Because of their physical, physiologic, and cognitive immaturity, children are often most vulnerable to adverse health effects from environmental hazards.²³  As the climate changes, environmental hazards will change and often increase, and children are likely to suffer disproportionately from these changes.⁸  Anticipated health threats from climate change include extreme weather events and weather disasters, increases in certain infectious diseases, air pollution, and thermal stress. Within all of these categories, children have increased vulnerability compared with other groups. These direct health threats are discussed in this section, with an emphasis on children in the United States.²⁴  Indirect threats are discussed briefly in “Long-term and Indirect Climate Change-Associated Health Threats to Children” below.

The Intergovernmental Panel on Climate Change predicts that it is “likely” or “extremely likely” that climate change will cause increased frequency and intensity of extreme weather events and weather disasters.²⁵  Often, these events are categorized as floods, storms, and droughts. Floods represented 43% of weather-related disasters between 1992 and 2001 and are the most frequent weather-related disaster. Although less prevalent, droughts and their associated famines are the most deadly weather-related disasters.³  Developed countries such as the United States have systematically increased the risk to populations from flood events by developing coastlines and flood plains. In the United States, hurricanes and tornadoes may be the most dramatic and visible weather disasters. Evidence suggests that the frequency of category 4 and 5 hurricanes has increased over the past 30 years, but the observation period is still too short to attribute this change to increased sea-surface temperature and climate change with high confidence.²⁶ 

The health consequences associated with extreme weather events include death, injury, increases in infectious diseases, and posttraumatic mental health and behavior problems.²⁷  Few studies have specifically examined such consequences in children. Globally, 66.5 million children annually were affected by disasters between 1990 and 2000.²⁸  Children everywhere are at risk of injury and death from storms and floods.²⁹  In the developed world, infectious disease outbreaks follow natural disasters when sanitation, sewage treatment, and water-purification plants become damaged or overwhelmed, refrigeration and cooking facilities are disrupted, and people are unusually crowded in temporary shelter. These outbreaks are usually mild and well controlled, which is in contrast to the aftermath of similar catastrophes in developing nations, where disease outbreaks can be deadly.²⁴  Mosquito-borne and other vector-borne illnesses may also be increased when storms or floods create large amounts of standing water suitable for breeding. Mental and emotional distress documented for children and adolescents after weather disasters include posttraumatic stress disorder and high rates of sleep disturbance, aggressive behavior, sadness, and substance use/abuse.²⁹  Some studies have suggested that children have more persistent symptoms than adults who experience the same disaster,³⁰  but more studies specific to children's experience are required.³¹  Community support services³²  and early therapeutic intervention and postdisaster counseling^33,34  can significantly reduce the medium- and long-term mental health burden on children. Experiences with Hurricane Katrina demonstrated the difficulties with tracking children's whereabouts, keeping children and caregivers together, and special needs of hospitalized infants and children during and after major natural disasters.³⁵ 

Globally, infectious diarrhea is the second-leading cause of death in young children; water-borne gastroenteritis is projected to increase under conditions of global warming. Currently, the World Health Organization estimates that, approximately 1.62 million children younger than 5 years die of diarrhea annually, and most cases are attributable to contaminated water.³⁶  Although children in developed countries are unlikely to die of water-borne infections, they may suffer illness that is attributable indirectly to climate change. Events associated with El Nino serve as a model for global warming by altering weather for periods of several years in the direction of a hotter climate. During El Nino events, rates of hospitalizations of children for diarrhea increase.³⁷  (In 1 study, the rate of hospitalizations of children for diarrhea increased 8% per degree centigrade of temperature increase.³⁸ ) Water-borne disease outbreaks in the United States exhibit a positive correlation with excess precipitation events, which are likely to increase with climate change; over a 45-year period, 68% of water-borne illness outbreaks have been associated with precipitation above the 80th percentile.³⁹  Foodborne illness correlates positively with ambient temperature and is also likely to increase as the climate warms.^37,40,41 

Vector-borne infections are affected by climate change.⁴²  Both the hosts (eg, rodents, insects, snails) and the pathogens (eg, bacteria, viruses, parasites) can be sensitive to climatic variables such as temperature, humidity, and rainfall. The ability to predict disease rates related to climate change is complicated by a large number of additional variables such as topography, land use, urbanization, human population distribution, level of economic development, and public health infrastructure.⁴³  There is no easy formula that predicts climate change–related infection risk with confidence.

Malaria is a climate-sensitive vector-borne illness to which children are particularly vulnerable. According to the World Health Organization, malaria currently causes 350 million to 500 million illnesses annually and more than 1 million deaths.⁴⁴  Because they lack specific immunity, children experience disproportionately high levels of both morbidity and mortality from malaria; 75% of malaria deaths occur in children younger than 5 years. The young are also more susceptible to cerebral malaria, which can lead to lifelong neurologic damage in those who survive. In areas of sub-Saharan Africa, the death rate from malaria in children 0 to 4 years of age is 9.4 in 1000 vs 0.13 in 1000 in those older than 14 years.⁴⁵  More than 3 billion people live in malaria-prone areas today. Climate change is expanding the range of host mosquitoes to higher altitudes and higher latitudes, and warmer temperatures speed the development of the parasite within the host vector.⁴⁶  Small children will be most affected by the expansion of malaria zones and the success or failure of societal response to this change.

Three vector-borne diseases that affect the United States illustrate ways in which climate change can enhance disease burden: West Nile virus infection, Lyme disease, and hantavirus pulmonary syndrome.

West Nile virus infection was first reported in the United States in New York in 1999. Although it is still not known how it entered the United States, once introduced, it spread rapidly. A series of warm winters failed to kill the mosquito vectors. Warmer summers amplified the life cycle of the mosquitoes and increased the viral load. Drought and rain cycles, particularly as they affected urban landscapes, increased the contact of the bridging mosquito vectors with birds and humans.⁴⁶  Human populations with no herd immunity were highly susceptible to infection. In 1999, there were 62 human cases of West Nile virus infection, all reported from New York state. In 2003, there were 9862 human cases reported from 45 states and the District of Columbia.⁴⁷  Although this infection is primarily of concern for the elderly rather than children, the rapid spread illustrates the challenge of infection control in a warming climate.

The prevalence of Lyme disease has been increasing in the United States since it became a reportable disease in 1992.⁴⁸  The geographic distribution of Ixodes species ticks, the vectors for this bacterial infection, is expanding as well. Researchers in Sweden have documented a correlation between the expanding range for Ixodes ticks and climate change.⁴⁹  Children 5 to 14 years of age and adults 50 to 59 years of age are most likely to contract the illness. Lyme disease, although rarely fatal, occasionally causes long-term morbidity and represents another example of a disease that is likely to increase further as the climate warms.

Finally, the 1993 outbreak of hantavirus pulmonary syndrome in the southwest United States has been linked to the El Nino conditions of 1991–1992, with increased rainfall and pine nut production, which favored population growth among rodent vectors.⁵⁰  With a case fatality rate of 36%,⁵¹  it is of concern that warmer climates may enhance vector populations further. As with most infectious diseases, human adaptations can reduce exposure risk and disease burden.⁵² 

Air pollution is well established as a short-term contributor to hospital use⁵³  and premature death. Air pollutants such as fine particulates, nitrogen oxides, sulfur oxides, and ozone are likely to increase as countries adapt to hotter temperatures by using more energy to drive air conditioning and fans. The anticipated global population of 9 billion by 2050 will also be associated with increased energy demands, which, if met by burning more fossil fuels, will exacerbate both ambient air pollution and GHG emissions.⁵⁴  Children are especially vulnerable to both short-term illness and long-term damage from ambient air pollution, because their lungs are developing and growing, they breathe at a higher rate than adults, and they spend more time outdoors engaging in vigorous physical activity.⁵⁵  Air pollution (such as ozone and particulate matter) causes respiratory and asthma hospitalizations, school absences, increased respiratory symptoms, and decrements in lung function.⁵⁵  Formation of ozone, in particular, is known to increase with increasing temperature, even without increases in the precursor primary pollutants (volatile organic hydrocarbons and oxides of nitrogen).⁵⁶  Children who are active in outdoor sports in communities with high ozone are at increased risk of developing asthma.⁵⁷  In addition, high levels of particulate matter and other copollutants affect the ability of children's lungs to grow regardless of history of asthma.⁵⁸  Rates of preterm births, low birth weight, and infant mortality are increased in communities with high levels of particulate air pollution.⁵⁵ 

A second change that is being observed is the temperature-related increases in pollen production and other aeroallergens in some regions and some cities. Increased temperature causes increases in amounts of pollens produced by some plants⁵⁹  and can also affect spatial distribution and density of plants, fungi, and molds that produce aeroallergens.⁶⁰  To the extent that exposure to aeroallergens contributes to the incidence, prevalence, and severity of asthma, atopy, and other respiratory disease, climate change will affect the pattern of disease in children. Some investigators have argued that part of the current global increase in childhood asthma can be explained by increased exposure to aeroallergens driven by climate change.⁶¹ 

For all organisms, there exists a range of ideal temperature above and below which mortality increases. Humans are no exception, although temperature-mortality relationships vary significantly by latitude, climatic zone, and level of socioeconomic development.³  As ambient temperatures increase, the frequency of heat waves will increase. It is expected that there will be fewer cold-related deaths in a warmer world,⁶²  but whether this will offset the expected increase in heat-related deaths is unknown. Populations that live in temperate climates, such as in the United States and Europe, are likely to be hard hit initially, because global warming is most dramatic in these latitudes and there has been little time for populations to acclimatize to changes in temperature. Observations on heat and mortality have been reported for decades⁶³  and have gained recent attention with the heat waves of 2003 in Europe⁶⁴  and of 2006 in Europe and North America.^63,65  Heat-related deaths and hospitalizations are most common in the elderly, especially if they are ill.^66,67  One study has found that infants and young children may represent a second, albeit smaller, higher-risk group,⁶⁸  but effects on children have not been studied adequately. In addition, children spend more time outside, especially playing sports in the heat of the afternoon, which puts them at increased risk of heat stroke and heat exhaustion.⁶⁹  Increased outdoor time during hot weather may also put children at increased risk of UV radiation–related skin damage, including basal cell carcinoma and malignant melanoma.⁷⁰  Some data indicate that heat-related mortality in the United States has decreased in recent years, in part associated with increasing percentage of homes with air conditioners.⁷¹  It is currently unknown how effective adaptation and acclimatization will be in preventing excess heat-related deaths and illness.^72,73 

Long-term and indirect effects on children's health from climate change will depend on how the climate continues to change over the next decades and what sorts of mitigation and adaptation strategies are adopted now.¹⁷  How quickly and comprehensively GHG emissions can be stabilized and then reduced will have a significant effect on the rate and degree of warming, but even the most optimistic scenarios describe continued warming through the end of this century.¹⁷  Food availability may be affected as land and ocean food-productivity patterns shift.⁷⁴  Water availability may change and become much reduced in some regions, including during summer in the snow run-off–dependent American west coast.⁷⁵  Coastal populations will be forced to move because of rises in sea level, and massive forced migrations, driven by abrupt climate change, natural disaster, or political instability over resource availability, are conceivable.²⁴  In addition, world population is expected to grow by 50% to 9 billion by 2050, which would place additional stress on ecosystem services and increase the demand for energy, fresh water, and food.⁵⁴  As these changes evolve, social and political institutions will need to respond with aggressive mitigation strategies and flexible adaptation strategies to preserve and protect public health, particularly for children.

Strategies to address the effects of climate change, known as mitigation and adaptation, are concepts that parallel the focus on both primary and secondary prevention strategies in pediatric health care. These strategies are discussed briefly here. The prevention or minimization of the effects of climate change on children's health is beyond the control of an individual pediatrician. Yet, pediatricians can play important public roles as advocates by individual example and through community participation, political involvement, or collective advocacy at the local, state, and national levels.^76,77 

Broadly, mitigation policies (Table 2) for reduction of atmospheric GHG include reducing emissions through energy efficiency and use of renewable energy sources, increasing carbon sinks by forest preservation and reforestation, and development of GHG-capture and -sequestration technologies (carbon sequestration is the fixation of atmospheric CO₂ in a carbon sink through an active process). Adaptation involves developing public health strategies to minimize adverse health outcomes that are anticipated from climate change. These strategies include improved disease surveillance and reporting, improved weather forecasting and early warning systems, advanced emergency management and disaster-preparedness programs, development and dissemination of appropriate vaccines and medicines, and public health education and preparedness. Category-specific examples can be found at www.grida.no/climate/ipcc_tar/wg2/646.htm#tab18-2. These adaptation strategies include policy and legislative actions, engineering responses, and personal behavior change.

Effective implementation of mitigation and adaptation strategies must involve actions from the global to local levels by governments, corporations, communities, and individuals. Furthermore, climate change is part of generalized global change, which includes population growth, land use, economic change, and evolving technology; all have effects on individual human and public health (Fig 2). Any solutions that address climate change must be developed within the context of overall sustainable development (the use of resources by the current generation to meet current needs while ensuring that future generations will be able to meet their needs). Protecting the health of current and future generations requires a fundamental shift in thinking for health professionals⁷⁸ ; pediatricians, as advocates for children's health, can be leaders in a move away from a traditional focus on disease prevention to a broader, more integrated focus that encompasses sustainability as synonymous with health. Given the health implications for current and future generations of children, the disease-prevention role for pediatric health care professionals includes advocating for environmental sustainability.

This technical report describes the broad scientific consensus that man-made climate change has begun and is accelerating. The major cause of this change is the rapid release of CO₂ from burning of fossil fuel. All predictions indicate that climate change will continue for at least a century, but the trajectory of that change depends on human responses. There are anticipated effects on human health from extreme weather events, infectious diseases, air pollution, and heat stress. Although little research thus far has concentrated on the pediatric age group, it is likely that children will suffer disproportionately from climate change.⁶  Furthermore, the state of the world of future children is uncertain and depends on actions taken to mitigate and adapt to climate change and other global-scale trends. Pediatric health care professionals are in an ideal position to advocate for action, not only to address climate change but also, more broadly, to ensure sustainability. Specific recommendations for pediatricians and governments are enumerated in the American Academy of Pediatrics policy statement⁷⁹  on climate change and children's health, which accompanies this technical report.

Michael W. Shannon, MD, MPH, Chairperson

Dana Best, MD, MPH

Helen J. Binns, MD, MPH

Joel A. Forman, MD

Christine L. Johnson, MD

Catherine J. Karr, MD, PhD

Janice J. Kim, MD, PhD, MPH

Lynnette J. Mazur, MD, MPH

James R. Roberts, MD, MPH

Katherine M. Shea, MD, MPH

Elizabeth Blackburn, RN

US Environmental Protection Agency

Mark Anderson, MD

Centers for Disease Control and Prevention/National Center for Environmental Health

Sharon Savage, MD

National Cancer Institute

Walter Rogan, MD

National Institute of Environmental Health Sciences

Paul Spire