Tomorrow's Forecast: Hot and Sneezy

July 20, 2005 Update:

A study by the Agricultural Research Service in Baltimore Maryland found that ragweed grew more rapidly and with higher pollen counts in and around cities than in rural areas where temperatures and carbon dioxide levels are lower. According to the USDA, global warming may have already doubled the amount of pollen produced by ragweed. Since 2000 the USDA has acknowledged a connection between increased carbon dioxide levels and increased pollen production. More recently in Japan, researchers have found a similar pattern in pollen produced by cedar and cypress plantations. Based on the study, scientists predict the number of people suffering from hay fever in Japan will increase 40 percent by 2050. In the UK the number of allergy sufferers has increased from 10-12 percent of the population in 1965 to 15-25 percent today. Again, research suggests global warming is the culprit. Plants such as the cocksfoot and meadow foxtail are flowering earlier, so allergy season is arriving earlier and lasting longer.

In early April, after the warmest U.S. winter on record and one of the driest ever in the East, many people were seized by sneezes, runny noses, watery eyes and other allergic reactions to tree pollens nearly a month earlier than usual. They were experiencing the health effects of climate change, according to Paul Epstein, M.D., M.PH., associate director of the Center for Health and the Global Environment at Harvard Medical School. In the last 100 years, the Earth's average surface temperature has risen by about 1 degree Fahrenheit, and it may climb between 2.5 and 10 degrees higher by 2100, the Intergovernmental Panel on Climate Change (IPCC) predicts. For the estimated 50 million Americans who suffer from allergies, and the approximately 18 million with asthma, which is frequently triggered by allergens, global warming may mean more frequent and intense symptoms. "These warm winters and early springs may be a factor contributing to the rise of asthma, which has tripled in incidence in the past 20 years," Epstein says. In 1998, at least 5,438 people died of asthma in this country, and 423,000 were hospitalized for it, according to the U.S. Centers for Disease Control and Prevention. Among children, asthma increased 160 percent between 1980 and 1994. For children and adults global warming means pollen and other allergens such as molds will be more widely dispersed, more abundant, and longer lasting.

Last spring, Boston's unseasonal warmth caused birch, poplar and maple trees to bloom, releasing their pollen early and in higher than normal amounts. Along with warmth, increased levels of carbon dioxide (CO2)-the main heat-trapping "greenhouse" gas-in the air stimulate growth of plants and trees, Dr. Epstein says, adding that "CO2 in Earth's atmosphere was .03 percent since the last ice age, and in the past hundred years it's gone up to .04 percent." According to the IPCC and a 2002 report from the Environmental Protection Agency (EPA), global temperature rise in the past 50 years is largely attributable to human activities, including fossil-fuel-burning vehicles and electric power plants, which emit CO2.

A Duke University study last year showed that when CO2 was increased in the air around loblolly pine trees, it tripled the pine cones and seeds produced. The increased pollen might give loblollies a reproductive advantage as, like many species, they move north, seeking to stay within a healthy temperature range. In human health terms, Dr. Epstein says, it could mean that residents of temperate zones will have new allergens to contend with as the globe warms.

Now it's high summer, and tree pollens have long since busted out all over, but we're still not out of the woods. Ragweed, that autumn bane of allergy sufferers, may also be striking earlier and with greater force. Dr. Epstein has just completed a study on how increased CO2 accelerates and increases pollen production in ragweed, which is common throughout the U.S. and Canada.

There are many other ways in which climate change can affect human health worldwide. Projected effects include greater mortality from heat stroke, drowning, respiratory problems from air pollution, spread of diseases (see Landrigan, p. 4) and hunger due to crop loss. It's not just the heat but also increases in extreme weather that worry some scientists. "Droughts, floods and rising temperatures are what we see when we look at our projections, based on global climate models," says Cynthia Rosenzweig, Ph.D., senior scientist at the NASA Goddard Institute for Space Studies and the Columbia University Earth Institute. "The climate is becoming more variable and apparently less stable. That's the big issue right now," Dr. Epstein says. The EPA report warns that environmental consequences could be severe.

Below, a look at some health impacts.

Breathing Problems: "Hotter weather means more ozone, or smog, is produced from the burning of fossil fuels, and that will cause more respiratory effects," says Dr. Rosenzweig. Already, approximately half of all Americans live in areas with unhealthy ozone levels, the American Lung Association reported in May 2002. Cutting emissions from vehicles and smokestacks in just four cities-New York, Sao Paulo, Mexico City and Santiago-could save 64,000 lives over the next 20 years, according to a study at Carnegie Mellon University published in the August 17, 2001, issue of Science magazine.

Hunger: Last winter, the Northeast and West suffered severe droughts, among the worst in 100 years. "The drought is a hint of things to come-what we can expect if we don't reduce the rate of climate change," says Peter H. Gleick, Ph.D., director of the Pacific Institute for Studies in Development, Environment and Security, in Oakland, California. Due to drought, "large regions of the developing world may experience reduced food supplies and potential increase in malnutrition," Dr. Rosenzweig and others wrote in a 2001 report.

The flip side of climate change is too much water. In May 2002, sudden torrential rains caused flooding in Illinois, Missouri and Indiana. To those who say that heavier rains from climate change will benefit agriculture in temperate regions, Dr. Rosenzweig counters that higher temperatures and greater precipitation "are likely to result in the spread of plant pests and diseases." A 2002 study she coauthored, just released, details other negative effects of excessive rain. For instance, "If it rains for three days, you get waterlogged soil and the roots don't get enough aeration, with a negative pressure on yields. And heavy rains can flatten crops like wheat," Dr. Rosenzweig says.

Thirst: According to the United Nations, more than 1 billion people lack access to fresh drinking water, and polluted water contributes to the death of 15 million children under five every year. Increased droughts will further reduce drinking-water supplies, and floods increase water contamination and the spread of disease-causing bacteria, as powerfully demonstrated when hog and chicken waste killed fish in the Chesapeake Bay in 1995. Even in the Southeast, which gets an average of 50 inches of rainfall a year, battles over water rights among sprawling cities are under way. "Saving water makes sense, and it also saves money. Who wouldn't want to do both?" Dr. Gleick asks. The same goes for using energy more efficiently. By reducing emissions of global- warming gases, we'll contribute to less pollution, a more stable climate and better health.