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Read this essay to learn about the effects of global warming on human health.
Australia’s first official assessment of the risks to public health from climate change predicts rising global temperatures will cause more Australians to become ill or die from heat, flooding and infectious diseases. According to the report, Human Health and Climate Change in Oceania, Australia is expected to become hotter and drier over the next century with annual average temperatures approximately 2 to 3°C higher over much of continent by the 2050s.
Rainfall is predicted to increase in Central Australia and the Kimberley, and to decrease by around one-third in south-west Australia. When it does rain, storms are likely to be intense. The estimated annual 1100 deaths of people aged over 65 from hot summers in capital cities each year is expected to increase by several hundred over the next 50 years. Annual flood related deaths and injuries are expected to rise by to 240% by 2020 in some regions, and the frequency and intensity of food-borne diseases is also expected to rise.
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Sea level is predicted to rise by up to 30 cm by 2030, up to nearly one metre in 100 years, and will probably drive migrations of environmental refugees. The number of people who experience flooding by the 2050s could increase by a factor of more than 50, to between 60,000 and 90,000 in a year. The impact of flooding on settlements, the impact of sea-level rise on freshwater quality and quantity is likely to be a critical threat to Pacific Island health and welfare.
The global environment is changing—with far reaching and complex consequences for human health. The poor are more vulnerable to weather related disasters caused by land clearing, deforestation and climate change. Weather related economic losses were highest in industrial countries but the human toll was far greater for developing countries. In 2002, more than 150,000 Kenyans were displaced by massive rains, while more than 800,000 Chinese struggled with the most severe drought in more than a century.
An examination of Earth’s “Vital Signs” reveals alarming trends of poverty, disease and environmental decline that threaten global stability, according to the World watch Institute’s Annual Report 2002 on trends shaping the world’s future. The report concedes that weather related disasters are likely to worsen as the climate continues to change. Last year was the second warmest since record keeping began in the late 1800s and most scientists are convinced this trend will result in more erratic weather and rising seas.
The concern that climate change would disproportionately affect the world’s poor was identified by the first International Conference on Climate Change in 1988, but the industrialized world has not heard its own warning. “Climate Change is occurring more rapidly than scientists thought,” explains Paul Epstein, associate director at Harvard Medical School’s Centre for Health and the Global Environment.
Epstein cited evidence of decreasing polar ice, warming ocean waters and increased rain at higher altitudes as well as decreased salinity in North Atlantic and extreme weather events. It is perhaps the more subtle elements of climate change—warmer winters, warmer nights and shifts in the onset of spring and winter—that pose the greatest challenge for that focussed on global health.
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Biological systems are responding to the warming of the climate and this has implications for vectors of infectious diseases. Warmer weather gives insects a much greater window. “We are seeing geographical shifts of vector borne diseases,” Paul Epstein said, citing new findings of malaria at higher elevations and the rapid spread of West Nile virus in the United States.
From coral reefs to rainforests, global warming and climate change are triggering infectious disease epidemics in living creatures around the world. A two year study by Drew Harvell of Cornell University, published recently in the journal Science, sounds a special warning for countries in temperate zones of the globe. The study says viruses, bacteria and fungi associated with disease as well as vectors such as mosquitoes, ticks and rodents become more active with slight increases in temperature and moisture.
Longer, warmer summers also mean that diseases can spread further. Traditionally, the winter snap is a limiting factor for many pathogens, reducing their numbers each year. As winters become less severe their population bottleneck may disappear. Under such conditions carriers are likely to spread into new areas and have devastating effects on wildlife previously not exposed?
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One example was that warmer temperatures since the 1960s have allowed mosquitoes to move further up on the Hawaiian Islands. This has led to a spread in avian malaria to native bird populations.
In the 1960s, mosquitoes were restricted to elevations below 762 meters, but now they have spread up to 1372 meters. The researchers said that there was also clear evidence that increased moisture in the Rift Valley due to heavy rains for El Nino was responsible for mosquito-borne Rift Valley Fever outbreaks. The last outbreak in 1998 killed thousands of people in East Africa.
Coral bleaching due to increased temperature made corals more susceptible to diseases. A group of scientists have isolated a fungus that tended to be a pathogen in immune compromised hosts. Increased temperature was also linked to the north-word movement of an oyster parasite in the U.S.
The researchers warn that infectious disease spread by vectors that are moving from tropical areas towards the poles can hit temperate zones harder. In tropical areas, there is a greater diversity of species, but smaller numbers of individuals, which means the pathogen, is diluted between species. There is a greater chance a mosquito will bite a species in which the disease does not develop. In temperate areas, however, there is lower biodiversity so vectors have fewer choices about what to bite.
The most direct effect of climate change would be the impacts of hotter temperatures themselves. Extremely hot temperatures increase the number of people who die on a given day for many reasons- People with heart problems are vulnerable because one’s cardiovascular system must work harder to keep the body cool during hot weather. Heat exhaustion and some respiratory problems increase. Higher air temperatures also increase the concentration of ozone at ground level.
The natural layer of ozone in the upper atmosphere blocks harmful ultraviolet radiation from reaching the earth’s surface; but in the lower atmosphere, ozone is a harmful pollutant. Ozone damages lung tissue, and causes particular problems for people with asthma and other lung diseases. Even modest exposure to ozone can cause healthy individuals to experience chest pains, nausea, and pulmonary congestion.
In much of the USA, a warming of 4°F could increase ozone concentrations by about 5 percent. Statistics on mortality and hospital admissions show that death rates increase during extremely hot days, particularly among very old and very young people living in cities.
In July 1995, a heat wave killed more than 700 people in the Chicago area alone. Studies based on these types of statistics estimate that in Atlanta, for example, even a warming of about 2°F would increase heat-related deaths from 78 at present to anywhere from 96 to 247 people per year. Recently, more than 2000 people in France and more than 1,500 people, mostly elderly, died due to heat wave.
Global warming may also increase the risk of some infectious diseases, particularly those diseases that only appear in warm areas. Diseases that are spread by mosquitoes and other insects could become more prevalent if warmer temperatures enabled those insects to become established farther north; such “vector-borne” diseases include malaria, dengue fever, yellow fever and encephalitis.
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Some scientists believe that algal blooms could occur more frequently as temperatures warm—particularly in areas with polluted waters—in which case diseases such a cholera that tend to accompany algal blooms could become more frequent.
Malaria, the ancient mosquito-borne disease that was rolled back to medical advances in the mid-20th century, is making a deadly comeback. Strains of the disease are becoming increasingly resistant to treatment, infecting and killing more people than ever before— sickening as many as 900 million last year. More than 1 million people of those victims died.
Only AIDS kills more people worldwide and among children malaria kills even more than AIDS. The economic cost of malaria is also high – in countries of Africa, Asia and Latin America where the disease is endemic, the World Health Organisation estimates up to $12 billion are lost annually to the disease.
Changes in climate and weather may factor into some disease outbreaks, but it is not yet possible to determine whether global warming will actually cause diseases to spread, says a new report from the National Academies’ National Research Council.
i. Studies have shown that climate variation from one season or year to the next can affect the life cycle of many pathogens and disease-carrying insects, potentially affecting the timing and intensity of disease outbreaks.
ii. A number of computer models have been developed to simulate the effects of climate change on disease incidence, but estimates of the extent to which diseases will potentially spread have varied significantly among some of the models.
iii. In addition, observational and modeling studies generally are not able to consider complex social factors—such as sanitation and public health services, population density, and travel patterns—that also play important roles in disease dynamics.
Scientists know that weather can influence where and when some epidemics occur. For instance, mosquito-borne diseases such as dengue, malaria and yellow fever are generally associated with warm weather, while influenza epidemics usually occur during cold weather, and outbreaks of intestinal illnesses caused by cryptosporidiosis are linked to heavy rainfall. However, basic public health protections such as adequate housing and sanitation, as well as the availability of vaccines and drugs, can limit the geographic distribution of diseases regardless of climate.
“There are strong indications that a disturbing change in disease patterns has begun and that global warming is contributing to them,” said Dr. Paul Epstein. According to the report, the spread of infectious diseases has accelerated not only because the world is warming, but because nighttime temperatures are rising faster than daytime temperatures. This has particularly disturbing implications for human health because chiefly nighttime temperatures limit the range of many disease-transmitting insects.
Diseases like dengue and malaria are affecting new populations as warmer conditions allow mosquitoes to survive over a wider area and at higher altitudes. Dengue fever—a flulike illness which can be fatal and for which there is no vaccine— blanketed Latin America in 1995. It has been recorded in northern Argentina and Australia and is now occurring regularly in Asia.
In fact, mosquitoes carrying dengue fever have invaded more than a third of the homes in Argentina’s most populous province. The Aedes aegypti mosquito appeared in Argentina in 1986 and is now being found in 36 percent of homes in Buenos Aires province, according to Dr. Alfredo Seijo of the Hospital Munoz. The province is home to 14 million people. Malaria currently kills up to 2 million people each year and over 2 billion people are considered at risk of contracting the disease.
Hot, humid periods in the 1990s have led to malaria cases being recorded in the United States in California, New Jersey, New York, Texas, Georgia, Florida, Michigan and Virginia, as well as in Toronto, Canada. Analyses show malaria outbreaks outside tropical regions becoming more common in the future.
Scientists and governments agree that the world has warmed by up to 0.6°C (1.1°F) this century, according to WWF. Heat waves caused thousands of additional deaths in India and hundreds in central Europe and the United States. At the same time, extreme droughts turned forests in Asia, the Mediterranean region, Mexico, Central America, Florida and California into tinderboxes.
Enormous quantities of air pollution from burning forests led to a dramatic rise in the number of cases of eye irritation, respiratory illness and cardiovascular disease—examples of the unexpected public health surprises which become more likely in a warming world. Meanwhile, floods which affected several regions of the world led to upsurges of cholera, malaria and Rift Valley fever.
Cholera also affected parts of Latin America following flooding along the Pacific Coast and southern Brazil. In developing countries, health conditions depend to a great extent on the success of the harvest. Both floods, which encourage the growth of fungi, and droughts, which promote whiteflies, locusts and rodents, have an impact on agricultural production. Half of the world’s agricultural production, worth $250 billion, is currently, lost to pests and weeds and this figure could increase with warmer and more unpredictable weather.