There are visible signs of the consequences of global warming everywhere you look—ice caps melting, weather patterns becoming increasingly erratic, and animals migrating because of climate changes. One slightly less visible, though just as nerve-wracking, sign is in the form of an annoying little mosquito buzzing around your ear.
Mosquitoes and other insects have long been harbingers of disease, but global warming is allowing them to venture into the newly warmer areas and spread once uncommon ailments to unfamiliar locations. The following are five diseases that, much like Al Gore’s career, have had a comeback thanks to global warming.
Dengue Fever
The Aedes mosquito, which transmits the dengue fever virus, lives primarily in tropical and subtropical climates. Frost kills mosquito larvae and adults, effectively limiting the temperature range in which it can survive. However, with warming temperatures, the mosquitoes and the disease have expanded their range.
Aedes has been detected as far north as the Netherlands. In 1995, a town in Texas experienced a small outbreak of dengue. Chikungunya, a disease with symptoms similar to dengue and carried by Aedes mosquitoes, recently caused a 300-person outbreak in a small town in Italy. According to the World Health Organization (WHO), this is the first time a disease only seen in the tropics was found in modern Europe.
As higher altitudes become warmer, the dengue-carrying mosquito is also moving to higher ground. Normally limited to elevations of 3,300 feet, in the past three decades, the mosquito has been found at 5,600 feet in Mexico and at 7,260 feet in the Andes.
Since mosquitoes thrive in stagnant water, rainstorms and flooding, induced by climate change, have caused epidemics of mosquito and water-borne diseases. When three feet of rain fell on Mumbai in one day in 2005, the flooding caused epidemics of dengue fever and malaria, as well as cholera.
Malaria
As is the case for dengue and chikungunya, rising temperatures have expanded the range of the Anopheles mosquito that carries malaria. Malaria is now found in highland regions in Africa, where it had previously not been detected; a WHO report found that warming caused malaria outbreaks in Rwanda and Tanzania and caused the disease to expand its range in Kenya. According to a report issued by the Harvard Medical School, malaria is not only circulating at higher altitudes; it is also maturing at a faster rate. At 68° F, the malarial protozoa take twenty-six days to incubate; at 77° F, they take half that time. Since Anopheles live only several weeks, warmer temperatures mean greater replication and transmission of the parasite.
Up until recently, the United States had completely eradicated malaria, but the Anopheles mosquitoes are present in the U.S. Small outbreaks of locally transmitted malaria have occurred in the past decade in Texas, Georgia, Florida, Michigan, New Jersey, and New York.
West Nile
West Nile Virus had never been documented in the Western Hemisphere until 1999, when it was determined by the Centers for Disease Control to be the cause of an encephalitis outbreak in New York. How WNV appeared in the U.S. is unknown, but extreme weather conditions can amplify virus replication in animals and birds. Drought followed by warm temperatures is a particularly favorable and common condition for outbreaks.
In 1999, a severe drought followed by a mild winter may have set the stage for WNV outbreaks. In the summer of 2002, drought and hot weather caused WNV to spread across the U.S. and into Canada, killing 304 people in North America.
Rift Valley Fever
While the mosquito that transmits West Nile can thrive in small pools of water left after drought, uncharacteristically wet weather can lead to outbreaks of Rift Valley Fever, an emerging pathogen whose rise has been attributed to changing global weather patterns. Recently, both Kenya and Madagascar have experienced outbreaks following severe rainstorms and flooding. The mosquito population, whose eggs can survive for years in dry weather and hatch to produce infected larvae in wet weather, spreads the virus to livestock, which then spreads it to humans.
If global warming continues unabated, weather patterns will become more erratic, bringing stronger storms and floods, creating ideal breeding grounds for the Rift Valley fever virus.
Lyme Disease
Warmer weather is contributing to a rise in Lyme disease in two ways: higher temperatures allow both ticks to thrive and people to stay outdoors more. A study conducted by the Center for Health and the Global Environment at Harvard Medical School found that rising temperatures during winters in North America are causing a growth in tick populations, which has led to more Lyme disease cases. Like mosquitoes, ticks are attracted to warmer conditions, so as climate change gradually increases the temperature in northern geographic areas, ticks will find new homes (and new targets).
These diseases aren’t just due to climate change—globalization, loss of predators, ecological factors, and lack of prevention play a role. But their increasing incidence and range, due in large part to warmer weather and extreme rainfall, make them seem like the canaries in our global coalmine.
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