climate-l@mbnet.mb.ca
LINKING HEALTH EFFECTS TO CHANGES IN CLIMATE
New York Times
August 10, 1998
Internet:
http://www.nytimes.com/yr/mo/day/news/national/science/sci-climate-disease.html
Scientists have long theorized that climatic changes related to global
warming could unleash outbreaks of diseases like malaria, dengue fever,
cholera and heat stroke. But with the modest amount of warming
experienced so far, they have been unable to produce much hard evidence.
Now the experts have a research gift from an unlikely benefactor: El
Nino. Combined with an underlying global warming trend, say scientists
who track such things, El Nino will probably make 1998 the warmest year
in several centuries. And the heavy rains, droughts and other extreme
weather fostered by El Nino over the last year are precisely what many
scientists expect will also result from a predicted warming of the globe
in the decades ahead.
So, in the belief that 1997 and 1998 may provide a taste of what is to
come, those who pay attention to the health effects of climate are now
pulling together data about weather-related illness and death in recent
months. Though most of the evidence is circumstantial, consisting of
correlations and coincidences, it suggests that amid all the scientific
smoke there is some fire.
These are some of the clues:
. The World Health Organization reports "quantitative leaps" in the
incidence of malaria around the world, coincident with extreme weather
events associated with El Nino.
Heat and variations in rainfall affect transmission of the disease by
mosquitoes.
. Tens of thousands of people in Kenya and Somalia were afflicted by
another mosquito-borne disease, Rift Valley fever, and at least 200
died, after the heaviest rains since 1961, attributed to El Nino, fell
on the region.
. The incidence of cholera increased markedly over the last year in
Latin America, where an epidemic had already been in progress for seven
years, and parts of Africa.
In both cases the surge in cases was associated with heavy rainfall and
floods linked to El Nino.
. In the southern Rockies, a warm, wet winter brought on by El Nino has
produced abundant food and cover for deer mice, which transmit the
deadly hantavirus to humans.
The number of mice has increased, and the deaths of three people have
been ascribed to the disease. Federal disease-control agents are still
analyzing the problem.
. Forest fires in Southeast Asia, made possible by a killing drought
attributed to El Nino, subjected hundreds of thousands of people to
respiratory ailments.
While this and similar evidence is sifted and tested, scientists are
also beginning to focus more closely on the health impact of extreme
weather events quite apart from El Nino, especially in the United
States. One thing they are finding is that there is a statistically
significant association in the United States between heavy rainstorms
and outbreaks of waterborne diseases.
These include hepatitis, E. coli infections and the cryptosporidium
parasite that infected 400,000 people and killed 50 to 100 in Milwaukee
in 1993, as well as other gastrointestinal diseases caused by viruses,
bacteria and parasites.
In East Africa, Model and Portent
If the relationship between heavy rain and disease is a solid one and
climate experts are right, the country may be in for a surge of
climatically induced waterborne illness.
Analyses of the last century's weather records by the National Climatic
Data Center have found that extremely heavy rainstorms have become more
common.
For example, single rainfalls on the order of eight and nine inches each
deluged the Boston area in mid-June, the Ohio Valley in late June and
south-central Tennessee in mid-July.
Climatologists say that this is just the kind of increase in extreme
rainstorms that would be expected in a warming atmosphere, which holds
more moisture and causes more water to evaporate from the oceans. The
heavier rain that results is more likely to cause floods that not only
kill people but also overwhelm drinking-water purification systems.
"If extreme weather events are part of a changing climate," said Dr.
Paul R. Epstein, associate director of the Center for Health and the
Global Environment at Harvard Medical School, "we've seen lots of
evidence of the profound health effects associated with climate change
this year."
East Africa, he said, especially illustrates the risk to health posed by
climatic factors. There, simultaneous outbreaks of cholera, malaria and
Rift Valley fever followed heavy rains and flooding.
Dr. Epstein has long held the view that global warming will have a
serious effect on health. His group at Harvard has also made a
compilation of possible health effects of El Nino in the last year.
The view has provoked argument. In the always contentious debate over
climate change and the uncertainties that attend it, it has been
especially difficult to get a handle on the question of health and
disease. The Intergovernmental Panel on Climate Change, an international
group of scientists advising the United Nations, recognized this in its
most recent report, issued in 1995.
The panel predicted that if emissions of heat-trapping industrial waste
gases like carbon dioxide were not reduced, the average surface
temperature of the earth would rise by about 3.5 degrees Fahrenheit by
the end of the next century.
This is roughly half the amount of warming experienced since the depths
of the last ice age. About a degree of warming has taken place in the
last century, and the latest surface readings combined with tree-ring
studies made by climatologists at the University of East Anglia in
Britain indicate that 1997 was the warmest year in the last 1,000 and
that 1998 will probably be warmer still.
Some recent events, the intergovernmental panel said in 1995, might
plausibly be early signals of climate-induced changes in human health.
The panel cited a surge in heat-related deaths in India in 1995 (there
was a similar surge this year), changes in the ranges of some insect-
borne diseases and the spread of cholera along coastal areas in some
developing countries.
But the group also said it was "not possible to attribute particular,
isolated events to a change in climate or weather pattern."
The problem, said Dr. Duane Gubler, director of the division of vector-
borne infectious diseases at the Federal Centers for Disease Control and
Prevention in Atlanta, "is that we may see some correlations" between
climate and disease outbreaks, "but we don't know whether it's cause and
effect." So, he said, "we're kind of cautious" in tying climatic change
to changes in health.
More Than One Way to Kill a Mosquito
Not a few experts point out, for instance, that while a warming
atmosphere would theoretically be expected to expand the range of
mosquito-borne tropical diseases like malaria and dengue fever, reality
is not so simple.
Temperature, humidity, rainfall and other weather factors are indeed
some of the main things that influence transmission of the diseases. In
some instances, temperature increases the virulence of the disease
itself, by prompting viruses to multiply more.
Heavier rainfall creates more standing water for some kinds of
mosquitoes to breed in, and populations soar. Drought encourages people
to store water in open containers, with the same result.
But in the developed countries, experts like Dr. Gubler say, public
health pluses like pest control and better living conditions (more
tightly built houses, for example) have pretty much slammed the door on
epidemics of mosquito-borne illness. Until early this century, malaria,
dengue fever and yellow fever were common in the United States. Today,
outbreaks of those diseases are small, isolated and rare.
Usually, says Dr. Gubler, the cases have arrived from somewhere else.
This public-health success, a number of experts say, would probably stop
any climate-induced invasion by mosquito-borne diseases at the United
States border -- as indeed might have happened already: dengue fever,
resurgent in the Caribbean and Central America in recent years, has not
become a major problem in the United States, even though, Dr. Gubler
says, the temperature along the Gulf Coast is higher than in the
Caribbean.
While Texas reported only a handful of cases in 1995 and again in 1997,
said Dr. Gubler, there were thousands of cases a stone's throw away, in
Mexico.
Dr. Gubler, Dr. Epstein and many others agree that developing countries,
with less effective and in some cases nonexistent controls on
mosquitoes, would be highly vulnerable to any climatically induced surge
in diseases borne by vectors, or animals, usually insects, that carry a
disease from a host to another animal.
They also agree that efforts to improve public health measures there and
limit climatic change globally are necessary.
But the richer countries, including the United States, may not be immune
to climate-sensitive health problems.
Two big cases in point are heat waves and waterborne diseases.
Many climate experts say that heat waves are likely to become more
frequent and intense, and therefore more deadly. If they are right, what
has happened in Texas this summer may be a foretaste. More than 100
people have died there in a heat wave that saw temperatures in Dallas
rise above 100 degrees Fahrenheit for weeks on end.
It was even worse in India, where the most intense heat wave in 50 years
sent the temperature soaring above 120 degrees in some places. Nearly
1,300 people died.
Skeptics point out that people in the southern United States have become
acclimatized to heat, and argue that northerners will adapt if the
climate warms.
But Dr. Laurence S. Kalkstein of the University of Delaware, who has
long studied the subject, says that people become vulnerable to heat
whenever it reaches a certain threshold above what they are used to --
even if they are used to high temperatures. The lethal Southern and
Indian heat waves this year may provide some evidence of this.
The important unanswered question, Dr. Kalkstein said, is whether heat
waves will get hotter with the general climate.
"If New York's climate becomes more like Jacksonville's and all the days
stay about the same in the summer," he said, "I think New Yorkers will
acclimatize." But if hotter heat waves are then superimposed on top of a
generally warmer climate, "we are going to get more deaths," he said.
Skeptics also point out that cold-related deaths would probably drop in
the winter.
But Dr. Kalkstein believes that heat-related deaths will more than
offset this.
Many cold-season deaths, he explains, result from diseases like flu that
are transmitted in confined spaces in buttoned-up winter buildings.
Climate change is not likely to alter this picture much, Dr. Kalkstein
says.
Tracking Diseases Borne by Water
Experts are just beginning to get a firm handle on weather-related
outbreaks of waterborne disease in the United States.
One problem is that heavy rainfalls tend to overwhelm sewage-treatment
systems early in a flood, catching those who operate the systems
unprepared. As a result, disease organisms "ride the initial wave that
comes downstream," in the first hour or two of a storm, infecting people
before anything can be done, said Dr. Dennis Juranek, the associate
director of the division of parasitic diseases at the Centers for
Disease Control and Prevention. The difficulty is compounded by the fact
that outbreaks of diarrheal diseases, the most common waterborne
maladies, are not usually perceived as a public-health emergency -- even
though they are sometimes fatal to people whose immune systems are
depressed -- and therefore are probably underreported.
Diarrheal diseases do not "cause people to fall over or bleed out of the
eyes or mouth," Dr. Juranek said, adding, "It has to be something big
like Milwaukee" to gain attention. Even in Milwaukee, "we came within a
hair's width" of failing to find out that the cryptosporidium outbreak
of 1993 was waterborne.
Scientists at the University of South Florida, the University of
Maryland and the National Climatic Data Center are taking some of the
first steps in pinning down the cause and effect between climate and
disease. They have plotted more than 300 outbreaks of waterborne disease
over the last 50 years against the distribution of heavy rains.
Although the data are still being analyzed, "we can demonstrate
increased probability of waterborne outbreaks when there are extreme
events," said Dr. Joan Rose, a microbiologist at the University of South
Florida.
In 1982-83, the last big El Nino period before 1997-98, 60 to 70 percent
of the outbreaks were associated with extreme rainfalls, she said.