American ragweed spreading through Europe.
- From: Jake <jcbepstein@xxxxxxxxxxx>
- Date: 5 May 2007 03:44:02 -0700
"Over the past few years, ragweed has begun spreading through Europe.
Barely seen on the Continent a decade ago, ragweed can now be found in
Eastern Europe, especially in Hungary, and also in France, Italy, the
Netherlands and Scandinavia."
Global warming may be spurring allergy, asthma
Beltsville scientist says CO2 brings more ragweed woes
AM NAIK, The Wall Street Journal
There's growing scientific evidence that global climate change is
linked to the dramatic rise in allergies and asthma in the Western
world.
Studies have found that a higher level of carbon dioxide turbocharges
the growth of plants whose pollen trigger allergies. In 2001 Lewis
Ziska planted ragweed - the main cause of hay fever in the fall - at
urban, suburban and rural sites near Baltimore. The plots had the same
seeds and soil and were watered in the same way. Yet the downtown
plants soon exploded in size, flowering earlier and producing twice
the pollen of rural plants. The city pollen was a lot more toxic, too.
The likely cause? The city plants experienced warmer temperatures and
20 percent more carbon dioxide, the effect of more cars and pollution.
"We can see the changes now, and they already have implications for
public health," says Dr. Ziska, a plant physiologist at the U.S.
Department of Agriculture. Allergies and asthma are closely linked;
more than 70 percent of asthma sufferers also have allergies.
The Intergovernmental Panel on Climate Change, a group of the world's
leading climate researchers, will address the issue in its August
report. According to Bettina Menne, a doctor at the World Health
Organization and a lead author of the chapter on climate change and
health, the report will say that higher temperatures and carbon
dioxide levels have increased the abundance of pollen, known to
trigger allergies and worsen asthma. It will also conclude that
spring, when allergy-causing tree pollen are at peak levels, has been
arriving 10 to 15 days earlier over the past three decades, a trend
expected to continue in coming years.
"We can assume that allergic disorders are starting earlier because
the pollen season starts earlier," Dr. Menne says. "Climate change
contributes to the problem, but we don't exactly know by what amount."
The upcoming IPCC report remains inconclusive on whether pollen is
becoming more toxic.
For years, scientists have tried to explain the big increase in
allergies and asthma in Western countries. Today, roughly 35 million
Americans have seasonal hay-fever allergies and about 20 million
suffer from asthma. Even though the air in many cities is much cleaner
than in the past, the prevalence of hay fever has increased in the
U.S. over the past few decades. In 2004, asthma affected more than 6
percent of the American population, up from a little over 3 percent in
1980, according to the U.S. Centers for Disease Control and Prevention
in Atlanta.
Childhood asthma is increasing at an even-faster rate. The percentage
of children with asthma jumped to 9 percent in 2005 from 3.6 percent
in 1980, according to the CDC.
In 2004, a Harvard Medical School study linked the childhood asthma
"epidemic" among inner-city youths to climate change. Stating that
higher carbon-dioxide levels in cities promote pollen production in
plants, fungal growth, and opportunistic weeds, the study noted that
asthma among preschool children grew 160 percent between 1980 and
1994, more than double the increase for the overall U.S. population.
Much research remains to be done. No one has measured populations of
allergy-inducing plant populations nationwide to establish how pollen
levels have changed over the years.
The climate-change connection is "an interesting hypothesis that
deserves further research," says Darryl Zeldin, a senior scientist at
the National Institute of Environmental Health Sciences, part of the
National Institutes of Health. "All the data isn't in."
Some scientists blame dust mites, mold, and other indoor allergens.
Others point to specific pollutants in the air, changed diets, genetic
susceptibility and higher obesity rates. Another idea, called the
"hygiene hypothesis," argues that people today suffer from more
allergies because they faced less exposure to infectious agents in
childhood.
"I do think that climate change contributes" to the rise in allergies
and asthma, "but it's not the only answer," says Christopher Randolph,
an allergist and clinical professor at Yale University.
The links between climate change, allergies and asthma are
multilayered. Higher carbon-dioxide levels, the result of human
activity, are believed to warm the atmosphere, which in turn affects
the geographic location and growing season of allergy-producing
plants. A higher level of carbon dioxide separately spurs the growth
of ragweed and other allergy culprits. Studies indicate it may make
pollen more potent as well. Over the longer term, other potential
impacts of global climate change - more or less precipitation, more
intense hurricanes - could affect the growth of molds, which also
cause allergies, or affect how far plant pollens are dispersed.
In recent years, pollen counts have hit record levels in many urban
areas. A pollen count of 150 grains per cubic meter or more is very
high; many U.S. and European cities sometimes show counts in the
thousands. The season for birch - a major hay-fever nuisance in
Western Europe - has arrived five days earlier each decade over the
past 30 years.
It isn't surprising that rising carbon-dioxide levels and warming
climes will alter the biology, chemistry and geographical distribution
of plants. After all, many plants thrive when there's more carbon
dioxide in the air, or when it's warmer.
But the latest research has found that such shifts especially boost
invasive plants, including allergy culprits like ragweed. "No one had
thought in the 1990s that higher carbon-dioxide levels would have a
disproportionate effect on weeds," says Paul Epstein, associate
director of the Center for Health and the Global Environment at
Harvard Medical School. "It came as a surprise."
In the U.S., about three-quarters of the 35 million people who suffer
nasal allergies are primarily allergic to the pollen of ragweed, whose
season extends from mid-August to October. Common ragweed is a gray-
green plant that can attain a height of about 3 feet. A North American
native, it often erupts along roadsides, river banks and in urban lots
disturbed by construction or digging.
Over the past few years, ragweed has begun spreading through Europe.
Barely seen on the Continent a decade ago, ragweed can now be found in
Eastern Europe, especially in Hungary, and also in France, Italy, the
Netherlands and Scandinavia.
"It's a good example of a plant changing its distribution because of
climate change," says Jean Emberlin, director of the National Pollen
and Aerobiology Research Unit in Britain.
A host of independent studies draw a link between higher carbon
dioxide levels and weed growth. A paper published in 2002 by Harvard's
Dr. Epstein and his colleagues showed that a single ragweed plant,
which normally produces one billion pollen grains per season, produces
61 percent more when its exposure to carbon dioxide is doubled in a
lab setting.
At the Jasper Ridge Biological Preserve in the eastern foothills of
California's Santa Cruz mountains, scientists from Stanford University
mimic future global-warming conditions by using artificial heaters and
bombarding plants with carbon-dioxide emissions. Their key finding:
Higher amounts of the gas fuel weed growth, and drive out native
flora.
Some of the most dramatic results have been obtained by Dr. Ziska. A
researcher at the USDA's Crop Systems and Global Change lab in
Beltsville, Md., Dr. Ziska spent several years trying to draw
attention to how changing concentrations of carbon dioxide were likely
to affect crop and plant life. No one seemed interested. In early 1999
Dr. Ziska, who suffers from ragweed allergies and asthma himself, had
an idea: Would people pay more attention if he could show that rising
carbon-dioxide levels affected their health?
Wearing a face mask to protect himself from the pollen, Dr. Ziska
began to cultivate ragweed in large aluminum chambers at three
different levels of carbon-dioxide concentrations. The first was 280
parts per million of air, the level that existed before
industrialization. For the present era, he set the level to 370 parts
per million. He also experimented with 600 parts per million, a
conservative estimate for the carbon-dioxide concentration expected by
the end of the century.
Over the course of a year, Dr. Ziska found that each ragweed plant
produced 21 grams of pollen at the end-of-century level - almost twice
that produced at the present-day level and more than four times that
produced at the "pre-industrial" setting. Also, the higher the dose of
carbon dioxide, the bigger the plant.
Dr. Ziska then decided he needed a "real world" setting. Driving
around one day, he noticed large clumps of ragweed growing in empty
lots and along the sides of the road. He realized that he had a ready-
made setting for his experiment: Baltimore itself.
Cities are subject to the "heat island" effect - a dome of higher
temperatures caused by the warmth absorbed, then reflected, by
structures and pavement. Moreover, the greater number of cars means
urban areas have more carbon dioxide than outlying ones. Dr. Ziska
figured that if he could measure how ragweed and about 35 other plants
grew in downtown Baltimore versus a suburban and rural plot, it would
provide clues about how they might compete in a warmer, carbon dioxide-
richer world.
Through his field experiment, Dr. Ziska found that ragweed seed
emerged three or four days earlier at the urban site than at the rural
one, which is 40 miles away. Plus, the plants were huge, weighing
nearly 190 percent more at the city location compared with the rural
spot. A lot more pollen was produced in Baltimore as well.
In 2005, two years after that study was published, Dr. Ziska and other
scientists published research about a pollen protein that triggers an
allergic reaction to ragweed. Chemical analysis showed that there was
far more of the protein on the pollen of plants bathed in higher
levels of carbon dioxide - thus making it a lot more potent - compared
with pollen of plants exposed to lower amounts of the gas.
One recent afternoon, Dr. Ziska visited the rural site, near
Buckeystown, Md. He strode over to a 12-foot-tall metal tripod, hung
with a solar panel and electronic instruments, and checked several
measurements. The carbon dioxide level was 395 parts per million and
the temperature was 47 degrees Fahrenheit.
In the experimental plots of land, each about 5 square yards, several
plants were starting to come up. But some of the most prominent were 3-
foot-tall saplings of oak, astor and Norway maple, each of which can
also trigger severe nasal allergies.
An hour later, Dr. Ziska was at the urban site, a fenced-off area in
Baltimore's downtown science museum. Here, the instruments told a
different story: The temperature was 53 degrees Fahrenheit and the
carbon-dioxide level was a much higher 477 parts per million - not far
from the 500-level in the overall atmosphere expected by 2050, based
on a conservative estimate.
Resilient as ragweed is, other plants can be tougher in the long run.
After five years of running the Baltimore field experiments, Dr. Ziska
has found that the amount of ragweed growing in the urban location
declined as hardier plants take over. Eventually, pollen-bearing trees
- the main source of spring allergies - emerge dominant.
These trees are also flourishing. The saplings here were at least
twice the size of the plants at the rural site, and already sprouting
large leaves. Last year, one of the plants at the urban site, a weed
called ailanthus, had become a 20-foot giant and had to be chopped
down. Even now, the plants at the museum site are at least five years
ahead in their growth compared with their counterparts at the rural
location.
Then Dr. Ziska bent down and pointed to a handful of half-inch
seedlings sprouting in one of the beds. "That's where ragweed came up
last year," he said. "Looks like it's coming up again."
.
- Prev by Date: Top Websites Resources for Obesity Information, Tips & Guidelines
- Next by Date: Re: Evolution and the Hand of God
- Previous by thread: Top Websites Resources for Obesity Information, Tips & Guidelines
- Next by thread: Can Caffeine Hurt Athletic Performance
- Index(es):
Relevant Pages
|
