Health

For decades scientists have predicted that global warming will lead to a rise in the number of extreme weather events such as hurricanes, floods, heatwaves, and droughts. Indeed, in the last few years we have witnessed events that have had unprecedented impacts on human health and human life.

Over 400,000 people were infected with cryptosporidium - a gastrointestinal illness - after the Mississippi River flooded Milwaukee’s public water supply in 1993. Hurricane Mitch in 1998 dumped six feet of rain on Honduras in three days and left epidemics of malaria, dengue fever and cholera along with more than 11,000 dead. In Venezuela in 1999 severe rains led to outbreaks of brain infections called encephalitis, and landslides killed tens of thousands.

Heatwaves have become even more extreme and more frequent. The high temperatures in 1993 killed 750 people in Chicago and hospitalized thousands more. In 2003 the heatwave that hit Europe killed more than 30,000 people and destroyed agricultural crops. During a heatwave in the summer of 2005 in the United States over 200 cities recorded new record high temperatures. Eight of the ten warmest years on record occurred in the last decade.

Prolonged droughts and changes in climate have played a role in the emergence of new diseases such as Hantavirus, as seen in the Southwestern United States in 1993. Hantavirus emerged when rodent populations blossomed in response to heavy rainfalls following a six-year drought.

Increased weather variability also contributed to the spread of West Nile Virus infecting over 200 species of animals across the United States during the hot dry summer of 2002. The disease was virtually unknown in the U.S. until 1999, but is now found in 47 states and has been responsible for more than 1,700 deaths.

Lyme disease is carried and transmitted by ticks. It is already endemic in many parts of the world and models predict that rising temperatures from global warming will allow the ticks to thrive and affect people in new areas. For example, as winters have warmed, disease-bearing ticks in Sweden are moving northward and similar shifts are predicted in North America.

Rising temperatures also have expanded the range of mosquitoes that carry malaria, and have exposed new populations to infection. Malaria is one of the most deadly infectious diseases in the world - killing more than 2 million people each year. Warmer temperatures also prolong the breeding seasons and boost biting and reproductive rates of mosquitoes that carry malaria. United Nations scientists project that malaria-carrying mosquitoes will spread north and south from the tropics and to higher elevations. Global warming could put as much as 65 percent of the world’s population at risk of infection by malaria.

Gradual increases in temperature across the globe also are having great impacts on human health by increasing respiratory irritants that lead to asthma and hay fever. The prevalence of asthma has quadrupled in the US over the past twenty years - thought due in part to climate related factors. Elevated carbon dioxide levels, for instance, lead to increased pollen production from ragweed, which triggers asthma and allergies.

Storms, heatwaves, and droughts cause deaths and injuries directly, but more importantly, they can displace large populations of people, disrupt food supplies, contaminate water sources, and increase the rates of many infectious diseases.

In 2002, the World Health Organization estimated that climate change contributes to more than 160,000 deaths each year, and this figure is likely conservative given the intensity of recent storms and events.

A report commissioned by the Pentagon in 2003 calculated that extreme weather events could lead to major disruptions in food and water supplies and have profound effects upon the health and well-being of our society. The authors of the report concluded that the risks from climate change “should be elevated beyond a scientific debate to a U.S. national security concern.”

A female mosquito feeds on a human host. A recent report says global warming will increase the range of disease-carrying mosquitoes, spawning outbreaks of malaria, West Nile virus, and other illnesses.

Photograph by James Gathany/CDC


“There is growing evidence that changes in the global climate will have profound effects on the health and well-being of citizens in countries throughout the world.”

Dr Kerstin Leitner,
WHO Assistant Director-General for Sustainable,
Development and Healthy Environments.