Human Health 

--An Overview prepared by Karen Hopfl-Harris, JD (Physicians for Social Responsibility)--
 

Climate and changes in it – regardless of their cause – matter to people, communities and businesses. Global warming is likely to bring many changes to the nation. The United States as a whole is in a strong economic position to adapt to many of these changes, but adaptation is often expensive, not always possible or successful, and during transitions ecosystems, communities, and individuals could suffer. Moreover, national impact summaries disguise local dislocations and disruptions to the ways we live, work and recreate. Climate change adds a serious stress to our already threatened resources and treasured places. Overall impact statements also mask significant opportunities. To minimize the negative changes and make the most of the positive changes we need to take a close look at how climate change will affect each region. How will global warming affect the health of our Nation? And how can we respond?

Summary
Scenarios examined in the National Assessment indicate that temperatures in the US will rise by about 5-10 °F on average in the next 100 years in the absence of measures to reduce greenhouse gas emissions worldwide.  According to the Assessment, this rise will be associated with more extreme precipitation and greater evaporation leading to more frequent extremes of both very wet and very dry conditions. Based on projections developed for the national assessment as an underlying set of assumptions, scientists expect that climate change of this magnitude would increase the number of heat-related illnesses and mortality suffered by the population. In addition, respiratory and cardiovascular illnesses may be exacerbated due to higher temperatures and poor air quality.  Should the frequency or severity of extreme weather events increase, the number of direct injuries suffered and people displaced from their homes could rise, and the health care systems could be interrupted or even overburdened at times. Changes in temperature, precipitation and weather patterns may also encourage a growth in rodent and/or insect populations that can carry disease and affect the proliferation of water and food-borne diseases. 
Patterns of illness and death vary substantially by socioeconomic status, geographic region, age, race and sex. Certain populations in the U.S., namely the elderly, the poor, children, infants and those already suffering from illness, may be more vulnerable to many of the health risks that may be exacerbated by climate change. The proportion of elderly in the population is expected to rise in coming decades. Age is accompanied by multiple chronic illnesses that may result in increased vulnerability to infectious disease and environmental stresses such as heat.  The proportion of children is also expected to rise.  Children are more vulnerable to the impacts of climate change due to their size, behavior and their constant state of growth and development. Poverty also adds to these vulnerabilities.

Key Findings
Climate change may be accompanied by a variety of health effects.  Some are direct and others involve intermediate and multiple pathways. The Health Assessment looks at the current health status of the American population, other health stresses in the environment, the population’s capacity to adapt and knowledge gaps. The Assessment identifies five categories of health outcomes that are most likely to be affected by climate change because they are associated with weather and/or climate variables: temperature related morbidity and mortality; the health effects of extreme weather events; air-pollution-related health effects; water and food-borne diseases; and vector and rodent-borne diseases.

Temperature related morbidity and mortality
Heat and heat waves are projected to increase in severity and frequency with increasing global mean temperatures.  Studies of heat waves in urban areas, which already are extremely vulnerable to health problems related to heat, have shown an association between increases in heat and increases in mortality. Other heat-related health effects include heat cramps, heat exhaustion and heat stroke.  Models of weather-mortality relationships indicate that populations in the northeast and mid-western U.S. may experience the greatest number of heat-related illnesses and death in response to changes in summer temperatures.  The most sensitive regions are those where extremely high temperatures occur infrequently or irregularly. 
Milder winters may result in fewer deaths in winter months. However, many winter deaths are due to respiratory infections such as influenza, and it is unclear as of yet how influenza transmission would be affected by warmer winter temperatures.

Extreme weather events
Scientific evidence indicates that increases in heavy precipitation have occurred over the last 20 years and that this trend may continue in the future. Climate change is projected to increase the frequency of extreme precipitation events. Model projections are unable yet, however, to predict changes in the frequency, severity, timing, or duration of extreme events like storms, tornadoes and hurricanes.  Injury and death are associated with these weather events. Severe storms caused 600 deaths and 3,799 reported injuries in 1997 alone.  Floods are the most frequent natural disaster and the leading cause of death from natural disasters in the U.S. Other health effects from extreme weather include bacterial proliferation and drinking water contamination, as well as post-traumatic stress disorder.

Air pollution and health
Weather and air pollution levels are connected. The anthropogenic greenhouse gas emissions that contribute to global climate change are also air pollutants, for example, nitrogen oxides are potent heat-trapping gases as well as ingredients of smog. Protecting against increased heat by an increased use of air conditioning, as one possible adaptive response, would lead to increased fuel combustion for power generation and hence greater emissions. 
Heat can also increase ozone formation. Ground level ozone can exacerbate respiratory diseases by damaging lung tissue, reducing lung function and sensitizing the lungs to other irritants. Drops in lung function are accompanied by chest pain, coughing and pulmonary congestion. Exposure to particulate matter can aggravate existing respiratory and cardiovascular diseases, and lead to cancer or premature death. Those who suffer from asthma are especially vulnerable.  Climate change may also play a role in exposure to airborne allergens by affecting pollen production and the time spent indoors in summer and outdoors in winter.

Water and food borne diseases
Changes in precipitation, temperature, humidity, salinity and wind can affect the quality of water used for drinking, recreational, and commercial use, and the habitat of fish and shellfish. Direct weather associations have been documented for waterborne disease agents including harmful algal blooms. Toxic red tides proliferate as seawater temperatures rise. As many as nine million annual cases of waterborne disease have been estimated in the U.S. Cases range from mild gastrointestinal illnesses to more severe outcomes including chronic and/or fatal diseases and infections. One can ingest waterborne agents through contaminated water, fish or produce that has been irrigated or washed with contaminated water. Contact with contaminated water through fishing or swimming is also possible. Diseases include cryptosporidosis and giardiasis. In 1993, 400,000 cases resulted from a crytosporidum outbreak in Milwaukee. A contributing factor in the contamination was heavy rainfall and runoff resulting in poor water quality.  High soil saturation levels may also contribute to waterborne disease outbreaks in well water such as the largest recorded E. Coli outbreak in New York in September 1999 that occurred after a period of heavy rainfall.

Vector and rodent borne diseases
Climate change may affect the conditions that allow disease-carrying insects and rodents to thrive. Diseases include encephalitis, malaria, Lyme disease, hantavirus and flea-borne plague. For example, flea-borne plague incidence increased in conjunction with increasing rodent populations after an unusual winter-spring precipitation in New Mexico. Most vector-borne diseases exhibit a distinct seasonal pattern that suggests that they are weather-sensitive. Rainfall, temperature, and other weather variables affect both the vectors and the pathogens they transmit. Climate conditions may both increase a vector’s ability to survive in some cases and decrease it in others.  For example, dry conditions may eliminate smaller breeding sites, and create new productive habitats as river flow diminishes.

Adapting to the Impacts of Global Warming
 

Climate scientists agree that further climate change may be inevitable and will therefore require adaptation, although most scientists also think that the pace of climate change can be slowed by substantially reducing greenhouse gas emissions. This would give governments, businesses, and ecosystems around the world more time to respond and adapt to climate change as well as reducing the overall severity of climate change-related impacts, thereby buying "insurance" for an uncertain future.  Another way to buy insurance now is to incorporate climate change into all long-term decisions about natural resources, thereby providing greater resilience.

While much of the U.S. population is protected against adverse health outcomes associated with weather and climate, certain demographic and geographic populations are at increased risk.  Adaptations for preventing water-borne disease include improved water safety criteria, monitoring requirements and health surveillance. Future adaptation to higher temperatures is possible. However, education of the population and improved heat emergency and warning plans are essential. While populations may adapt to gradual temperature increases, adaptation during extreme heat events is unlikely. Many heat-related illnesses and deaths are preventable through the use of air conditioning and increased water intake. 
Other adaptive measures include improved disease surveillance, use of air and water filtering systems, distribution of air cooling systems to the poor and elderly, better use of weather forecasting systems, implementation of health warning outreach during times of extreme heat or poor air quality, and improved and expanded disaster preparedness, emergency management and public education programs.
Disaster preparedness in a community is key to a population’s ability to minimize potential health effects associated with extreme weather events or conditions.  This includes warning systems, evacuation plans, relief efforts, building codes and aids to recovery. 

Where do we go from here?

Vigilance in the maintenance and improvement of public health systems and government monitoring programs and their responsiveness to changing climate conditions, air pollution levels and addressing the needs of vulnerable sub-populations are essential to protect the population from any adverse health outcomes of climate change. While projections of the type and extent of potential health impacts of climate change can be made, there is still uncertainty, especially regarding the impact in specific regions.  In addition, there is only limited information regarding the sensitivity of human health to weather and climate. We do know, however, that the vulnerability of a population to any health risk varies considerably depending on population density, economics, local environmental conditions, pre-existing health status, quality and availability of health care and public health infrastructure. Understanding what groups may be most affected by climate change is critical to effective targeting of prevention or adaptation strategies.  

Additional Information
To speak to an author of the Health Sector assessment, please contact:

Dr. Jonathan A. Patz, MD, MPH, Department of Environmental Health Sciences, JohnsHopkins School of Public Health
 Tel: (410) 955-4195 Email: jpatz@jhsph.edu

For additional information on the potential impacts of global warming on health, please contact:

Karen Hopfl-Harris, JD, Associate Director, Environment and Health, Physicians for 
Social Responsibility
 Tel.: (202) 898-0150   Email: khopfl@psr.org

For related information see also http://www.psr.org/.