HEALTH IN THE HOT ZONE:
How would global warming affect humans?
By Richard Monastersky (April, 1996)
Paul R. Epstein, a specialist in tropical public health, knows too well
the kinds of diseases plaguing the tropical latitudes of this planet.
While working in Mozambique during the late 1970s, the physician endured a
withering bout of cholera that he caught by eating infected shellfish.
During the same trip, his wife and two children came down with malaria,
even though they were taking prophylactic drugs.
What concerns Epstein, a researcher and clinician at the Harvard School
of Public Health in Boston, is that many millions of uninitiated people
will endure similar lessons, as cholera, malaria, and other scourges
spread in the coming decades. The unwanted education would come courtesy
of global warming, which could allow diseases to reach into previously
unscathed areas.
"I think climate change is a very big threat," says Epstein.
"It's a major wakeup call. Climate change is already a factor in
terms of the distributions of malaria, dengue fever, and cholera. They are
changing their distributions right now."
Epstein is not alone. In a soon-to-bereleased report, the United
Nation's World Health Organization examines the health effects of global
warming—the predicted planetary fever caused by emissions of carbon
dioxide and other heat-trapping gases. The report calls climate change one
of the largest pubic health challenges for the upcoming century. Last
year, the Intergovernmental Panel on Climate Change (IPCC) reached a
similar conclusion, finding that "climate change is likely to have
wide-ranging and mostly adverse impacts on human health, with significant
loss of life."
The issue extends beyond tropical illnesses. Deaths caused directly by
heat would increase during the ever more oppressive summers. Dwindling
agricultural yields in the tropics could leave tens of millions more
people facing hunger and starvation.
Armed with such alarming forecasts, Epstein and his colleagues have
taken their information on the road. They have sounded the alert at dozens
of conferences in the last 2 years.
The new focus on health could bolster the message of climatologists,
whose warnings have received a cool reception from the public recently.
Global warming predictions have tended to be abstract and easily ignored.
Scientists speak of globally averaged temperature and worldwide sea level
rise, factors removed from everyday life. The concern about health threats
may put a human face on climate change.
Temperature and mortality
For evidence that heat can kill, one need look no farther than Chicago.
When a summer heat wave hit the eastern and midwestern United States last
year, it left more than 500 dead in that city alone.
By matching daily summertime temperatures with mortality records in
different cities, Laurence S. Kalkstein of the University of Delaware in
Newark has shown that heat waves raise death rates. Although people may
cope with gradually climbing summer temperatures, most climate models also
predict increased intensity and frequency of heat waves. Kalkstein
therefore anticipates an upward spiral in the number of heat-related
deaths.
The problem is expected to strike most severely in large urban centers
located in the midlatitudes. By the middle of the next century, giant
cities like Shanghai and New York could face several thousand extra heat
casualties each year, he wrote in the Sept. 30, 1995 LANCET.
During winter, however, warming could have the opposite effect in some
regions. One British study, cited in the IPCC report, concluded that by
2050, warming of 2° to 2.5°C will save 9,000 lives each year in England
and Wales. Most of these people would otherwise have died from heart
disease and stroke, problems exacerbated by blood's tendency to clot in
colder temperatures. The lives saved would more than balance the increase
in deaths from Britain's relatively mild heat waves, says Anthony J.
McMichael, lead author of the IPCC chapter on human health and a research
er at the London School of Hygiene and Tropical Medicine.
The United States, though, should not bank on comparable benefits from
global warming. The country's large size—with most regions situated far
from any coastline—makes it more susceptible to extreme hot spells.
"Scientists in the United States expect that there will be more
losses in the summer than gains in the winter," says McMichael.
Tropical trouble
Though heat can kill directly, global warming is expected to claim even
more of its victims through an indirect influence on disease, particularly
on vector borne microbes, which hitch a ride inside insects and other
organisms.
"Many diseases are extremely sensitive to climate," says
Jonathan Patz of the Johns Hopkins School of Hygiene and Public Health in
Baltimore. "Now that the climatology community says that climate
change is real, we know that there are going to be shifts in the
distribution of many diseases."
In the Jan. 17 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, Patz,
Epstein, and their colleagues reviewed how globe warming could encourage
emerging infectious diseases to spread. Malaria, the, note, generally does
not afflict regions with annual average temperatures below 16°C, because
lower temperatures inhibit the parasite. As minimum temperatures climb,
the disease could spread into previously malaria free regions.
At present, 45 percent of the world has conditions that permit malaria
transmission. The IPCC estimates that warming of 3° to 5°C could expand
the zone of potential transmission to include 60 percent of the globe.
Temperatures will reach this point sometime in the 22nd century, according
to model forecasts. The IPCC predictions call for global average
temperatures to rise 1° to 3.5°C by 2100.
Although malaria has the potential to envelop large parts of the world,
the IPCC panel found it unlikely that the disease will run rampant through
the United States and other developed countries. These nations have the
infrastructure to combat malaria, both by eliminating mosquito breeding
sites and by treating cases. Although many parts of the United States and
Europe already have climates that could support malaria, the disease was
wiped out in these areas in the 19th century.
The predicted consequences of global warming would fall most heavily on
tropical regions, where malaria could spread in both latitude and
altitude. "A relatively small increase in winter (minimum)
temperature would likely facilitate the spread of malaria into large urban
highland populations that are currently malaria free and immunologically
naive, such as Nairobi, Kenya, and Harare, Zimbabwe," Patz and his
colleagues contend in their recent article. Because residents of Nairobi
and Harare have little immunity to the disease, malaria would claim an
inordinately large number of people in such cities.
One study by researchers in the Netherlands estimates that climate
change will cause 1 million extra malaria deaths per year by the middle of
the next century. But such numbers represent little more than a guess,
warn researchers. Epstein points out that the ongoing spread of drugresistant
malarial strains is likely to make the situation worse than current
expectations.
Other vector borne diseases also have the potential to expand their
ranges in a warmer world. Dengue fever has already shown its ability to
respond to changing conditions. In Mexico during a heat wave in 1988, the
mosquito species Aedes aegypti carried dengue fever from an altitude of
1,000 meters up to 1,700 meters.
Recent warming helped spark an outbreak of dengue that burned through
Latin America this summer. By the end of September, the disease had
infected 140,000 people from Argentina all the way through South and
Central America, eventually reaching into Texas. More than 4,000 people
died. "This was a hell of a summer. It was quite a massive
epidemic," says Epstein.
Waterborne scourges
Future trouble will also come from the seas. According to the IPCC,
global warming should make the oceans a more hospitable home for cholera
and harmful algal blooms.
In 1991, cholera emerged in Peru for the first time this century. The
waterborne illness spread through coastal cities and waterways, eventually
reaching most countries in South America. In its first 18 months, the
epidemic infected 500,000 people and caused 5,000 deaths.
The cholera plague struck while an El Nino was warming the waters of
the equatorial Pacific, a correlation not lost on researchers interested
in health and climate change.
Scientists know that water temperature affects the spread of cholera.
The bacterium that causes the disease often hitches a ride inside tiny
marine animals called copepods, which feed on algae. When the water warms,
algae bloom and copepod populations soar. The whole chain leads to an
outbreak of cholera. In Bangladesh, for instance, the incidence of cholera
tends to rise when water temperatures do.
Scientists can't prove that the 1991 El Nino triggered the South
American cholera outbreak, but climate change is likely to encourage
epidemics in the next century, says Epstein.
Harmful algae also find favor in warmer seas. In the past few years,
scientists have tracked a global epidemic in coastal blooms of toxic
plankton that can afflict humans who consume fish or shellfish.
"Given that many of these harmful algae [thrive at higher
temperatures], warming trends and global climate change will promote
increased activity and also cause them to continue to expand and extend
their ranges," says JoAnn Burkholder of North Carolina State
University in Raleigh.
Greenhouse warming will work together with other factors that are
currently contributing to the algal invasion. Sewage and agricultural
fertilizers abet these plankton by pouring nitrogen into coastal waters,
stimulating the growth of plants. Over harvesting reduces the fish
populations that keep algae in check
Threats such as cholera and malaria, however, may pale in comparison to
the risk of food shortages caused by global warming. Although increasing
concentrations of carbon dioxide might actually boost global food
production in the near future, prolonged warming and precipitation shifts
will probably lower agricultural yields in many developing countries,
according to the IPCC. Such countries have fewer resources to adapt to
changing conditions, and their climates are already marginal for certain
crops.
One recent study predicted that climate change will put 40 million to
300 million extra people at risk of hunger in 2060. This population would
join the 640 million others expected to face food shortages by that date
even without climate change.
Beyond climate concerns
As the vast range in hunger estimates demonstrates, scientists are only
taking their first steps toward assessing how greenhouse warming will
actually affect people. In its report, the IPCC admits that its health
forecasts are fraught with uncertainty, notably, how much the climate will
change, exactly how diseases will respond, and to what extent various
countries will be able to protect against future risks.
Complicating the picture even further are the myriad other threats to
health, especially in developing countries. Increasingly crowded cities,
poor sanitation, limited supplies of potable water, and violence all cause
major harm today and will continue to do so for the foreseeable future.
In fact, some public health researchers worry that the growing emphasis
on global warming could dilute appreciation of some more important, but
perhaps less provocative, factors currently eroding health around the
world.
"My concern is that you can be distracted by what is in
fashion," says Vilma Santana, an epidemiologist at the Federal
University of Bahia in Salvador, Brazil. "I think the major issue is
poverty. One of the most consistent findings of epidemiological research
is that poverty is positively associated with disease."
Others echo Santana's concern. "Most of my colleagues in Africa
feel that in the face of populations without water, toilets, basic access
to education, and jobs, global warming is the least threat," says
epidemiologist Carolyn Stephens, a colleague of McMichael's.
Those concerned about global warming counter that climate will interact
with and exacerbate many of these seemingly unrelated problems. For
instance, shifts in rainfall may displace rural populations, thus
squeezing even more people into crowded cities, where infectious diseases
thrive. More frequent droughts would make water even scarcer than it is
today.
"My argument is that climate change is making a bad situation even
worse," says Patz.
He and Stephens agree, however, that climate change will
disproportionately burden developing countries. In this way, warming will
exact the greatest price from populations that can afford it least.
From: SCIENCE NEWS, published by Science Service Inc., 1719 N. St.
N.W., Washington, D.C. 20036. Phone: 202-785-255 Source = DieOff.org
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