04/06/2008 09:03 pm ET | Updated Nov 17, 2011

World Health Day: The Hazards of Global Warming to Your Health

By Susan Blumenthal, M.D., Yi-An Ko, Stephanie Safdi, Beth Hoffman and Julie Chen*

As thousands of people pour into emergency rooms and millions line up to be vaccinated, Brazil's public health officials and recently even its military are fighting to control vector-borne diseases. Mosquitoes are carrying illnesses like dengue and yellow fever into Brazil's largest cities, including Rio and Brasília, and the tropical disease, chikungunya, previously unheard of in Italy, was reported there last year. The two recent outbreaks in Brazil have caused a total of more than 80 deaths, 57,000 new infections, and widespread panic. As a result of global warming, mosquitoes, ticks, rodents and other vectors are expanding their geographic range and altering long-established patterns of disease. Climate changes worldwide are also causing serious problems with food and water supplies, increasing mental health concerns, and exacerbating air pollution, which elevates chronic disease risk.

Global temperature increases of 0.9°F (0.5°C) over the past century have led to an estimated 150,000 deaths and the loss of 5.5 million disability-adjusted life years (DALYs) annually, with the rates expected to double over the next several decades. The World Health Organization (WHO) has documented 39 new or re-emerging diseases since the 1960's, many linked to global warming -- an explosion of illnesses that has not been seen since the Industrial Revolution when masses of people moved to cities, increasing the spread of disease. Nevertheless, only minimal attention has been paid to one of the most significant yet least publicized hazards of climate change -- its impact on the health of people worldwide. Human health, influenced by a complex system of biological, social, economic, political and geographic factors, is particularly vulnerable to the effects of global warming and has significant humanitarian, economic and national security implications. On World Health Day, it is time to focus international attention on this critical issue.

Many infectious diseases exhibit sensitivity to climate change. Mosquitoes -- the most common disease vectors that spread illnesses such as malaria, dengue, West Nile encephalitis, and yellow fever -- thrive in wet and humid tropical environments. Currently, at least one million people die every year, including 3000 children every day, from malaria. A 3.6-5.4°F increase in global temperatures would cause malaria-carrying mosquitoes to enter new geographic areas, placing millions more people at risk of the disease. Moreover, this is not just a problem for the developing world. Malaria and dengue fever cases have been reported in the United States. West Nile encephalitis outbreaks, linked to warmer temperatures, have been on the rise in America as well. Studies also suggest that the extreme storms of El Niño increased mosquito populations, contributing to a five-fold rise in malaria rates worldwide. As global climate change produces more extreme weather events, such as hurricanes and flooding, spikes in the prevalence of other weather sensitive diseases can be expected. Furthermore, deforestation, a major contributor to global warming, has brought animals and ticks in contact with humans, resulting in the emergence of a new infectious illness, Lyme's Disease, first reported in 1975. Global warming is projected to expand the range of ticks that carry this disease.

The earth's water supply has also been profoundly affected by global warming, endangering the health of people and the planet. Water is essential to all aspects of life, yet 99% of water on Earth is unsafe or unavailable to drink. As a result of global warming, water will become even more scarce and contaminated as climate patterns change, extreme weather events occur, and glaciers melt. The 20th century has witnessed the greatest increase in temperature of any century in the past thousand years, bringing with it a change in precipitation patterns and a rise in sea levels. Global sea levels rose at an average rate of 0.07 inches per year from 1961-2003 (rising at an even greater rate of 0.12 inches per year on average from 1993-2003) reducing fresh water availability and elevating water temperatures that threaten already scarce water supplies. The 2007 Intergovernmental Panel on Climate Change Report projected that the global mean sea level is expected to rise between 7.1 to 23.2 inches by 2100. In many places, a rise in 19.7 inches would cause some beaches to be washed away, and for some islands such as the Maldives, it could mean significant portions of the land being submersed underwater. Furthermore, the combination of extreme weather events and changes in the availability of water affect agricultural food production, destroy botanical sources of natural medicines, incapacitate sewage systems, and result in widespread population displacement, leading to disruptions in acute and chronic disease management with national security implications as well. Some of the world's major conflicts have arisen over disputes concerning arable land and water and these types of tensions may become even more prevalent as resources diminish.

Changes to the earth's water supply have threatened populations around the globe with new diseases and sanitation concerns. 1.1 billion people worldwide lack safe drinking water and 2.6 billion people do not have access to adequate sanitation infrastructure. In the United States alone, more than 750,000 cases of diseases associated with unsafe drinking water occurred between 1980 and 1996. Moreover, changes in the quality and distribution of water in the aftermath of extreme weather events are linked to increased malnutrition and food poisoning, increased rates of child and infant mortality, and elevated morbidity and deaths from diarrheal diseases. Flooding, in particular, causes upsurges in rodent-borne illnesses, such as leptospirosis, tularemia, plague, viral hemorrhagic diseases and cholera. The impact on human health continues long after the waters recede - with toxic contamination of food and water and mental health problems, such as post-traumatic stress disorder and depression. Not surprisingly, developing nations bear the overwhelming burden of the health damaging effects of climate change. Of the 600,000 casualties caused by weather-related natural disasters in the 1990s, 95% occurred in the developing world. As a result of flooding in 2007 alone, 30,000 people lost their lives in Venezuela, and in China, 105 million people required immediate basic survival needs such as food, water, shelter, sanitation and medical assistance.

Scientific evidence also suggests that the noticeably hot summers of recent years may not be a coincidence. Climate change generates extremely hot weather, which threatens large population groups across the world with heat stroke and cardiac and respiratory complications. The 2003 European summer heat waves, during which temperatures reached 95° to 104°F, were associated with 35,000 deaths in a two month period. As the average global temperature rises, such heat waves can be expected to increase in severity and frequency.

Along with changes to water supplies and temperature patterns, global warming has dramatically affected the quality and safety of the very air we breathe. Air pollution is linked to 2 million deaths worldwide. Global warming enhances smog formation, which contributes to an increased risk for chronic diseases including lung cancer, heart disease, asthma and allergies (the rates of which have increased fourfold in the U.S. alone since 1980). Recent studies have found that carbon dioxide stimulates the production of pollen and of the spores of some fungi found in the soil. These allergens are carried into the lungs of humans by diesel particles found in urban areas, contributing to an increased risk for acute and chronic disease. These illnesses are further exacerbated by ground level ozone formation emanating from traffic emissions, increases in particulate matter, pollen and mold, and exposure to greenhouse gases like nitrous oxide. A study extrapolating the effects of air pollution suggests that a 1.8°F rise in temperature could increase global deaths by another 21,600 per year. Recent conditions in Beijing offer a worrisome example of the effects of air pollution on human health. In this city of over 17 million people, 2007 smog levels exceeded safety guidelines set by the World Health Organization by 400%, leaving citizens with only 65 days of acceptable breathing air and prompting public health officials to close highways and restrict air travel. These environmental problems have raised concerns by some people about the health of athletes competing in the 2008 Summer Olympics.

The profound effects of climate change demonstrate that the health of our planet and its people are inextricably entwined and underscore why action is needed now on multiple fronts to safeguard the health of people worldwide. The fight to stop global warming and reduce its health damaging effects begins with building a cleaner energy future and a more climate-conscious population. Greenhouse gas emissions must be reduced and natural resources protected through increased use of clean, efficient energy sources, developing new clean energy technologies, and encouraging individuals to make more environmentally conscious lifestyle decisions. Public health infrastructure and planning must be strengthened by advancing climate modeling and satellite monitoring, improving environmental public health tracking and disease surveillance, and increasing research into the relationship between climate change and health. Additionally, increasing health professional training and public education, developing government and private sector response plans, and building communication networks will enhance society's capacity to respond. To prevent and reduce the serious public health threats from global warming, nations in both the developed and developing world must share knowledge and best practices. A global coalition of governments, NGO's, businesses, schools, philanthropists, and individuals must collaborate across communities and countries to develop and implement lifesaving programs and innovative policies to ensure a greener and healthier world.

For a comprehensive scientific overview of the effects of global warming, see the Intergovernmental Reports on Climate Change (IPCC), available here.

This article is adapted from a commentary piece published in the Washington Times on April 6, 2008.

*Rear Admiral Susan Blumenthal, M.D. (ret.) is the Distinguished Advisor for Health and Medicine at the Center for the Study of the Presidency in Washington, D.C. and a Clinical Professor at Georgetown and Tufts University Schools of Medicine. For more than twenty years, she served in health leadership positions in the Federal government, including as Assistant Surgeon General of the United States and as the first Deputy Assistant Secretary of Women's Health in the U.S. Department of Health and Human Services, and as Chief of the Behavioral Medicine and Basic Prevention Research Branch at the National Institutes of Health. She was also a White House Advisor on health issues. Dr. Blumenthal has received numerous awards including honorary doctorates for her important contributions to improving health in the United States and globally.

Yi-An Ko, a recent graduate of Harvard University, is a health policy fellow at the Center for the Study of the Presidency in Washington D.C.

Stephanie Safdi, M.Phil, is a research assistant at the Center for the Study of the Presidency in Washington D.C. She graduated summa cum laude from Harvard University and earned her Masters Degree from Cambridge University on a Harvard-Cambridge Scholarship. Ms. Safdi served as a research fellow at the Harvard Initiative for Global Health and is the recent recipient of a Fulbright Fellowship.

Beth Hoffman, an honors graduate of Brown University, is a health policy fellow at the Center for the Study of the Presidency and will be a first year medical student at the University of Pennsylvania School of Medicine in the Fall.

Julie Chen, a senior at the University of California-Berkeley, is an intern at the Center for the Study of the Presidency in Washington D.C.