THE LITANY OF DIRECT HEALTH IMPACTS associated with climate change is becoming well known. A rapidly warming world brings more heat-related deaths, more disease spread through contaminated food and water and by insects, and more injuries from more extreme storms. The most vulnerable individuals are the elderly, the very young and the medically infirm. And the most vulnerable people live in the poorest nations, which are least responsible for causing climate change and least able to cope with the consequences. But a pair of ailments is rising faster in rich nations than in poor ones: asthma and allergies.

These two respiratory illnesses are epidemic in the developed world, and the numbers are rising. In the U.S. alone, at least 50 million people suffer from allergies, costing $18 billion annually in health care. Asthma affects one in 14 American adults, almost one in 10 children, and is the leading cause of school absences. The more people are exposed to air pollution and pollen, the worse their symptoms are, and the more likely they are to develop additional allergies.

Climate change is measurably raising the concentrations of airborne substances that trigger such illnesses, notably ozone and pollens, and researchers are documenting a corresponding increase in cases. Ozone, the primary component of smog, is a powerful respiratory irritant that initiates wheezing in asthmatics, particularly children. Exposure to ozone during childhood can also impair normal lung growth and development and may contribute to new asthma, which can start at any age. Ozone is created when sunlight cooks pollutants in the atmosphere, some of which are from natural sources but most of which are from burning fossil fuels in vehicles, power plants and industrial processes. Of course, the more we burn, the more we produce those man-made precursor pollutants, such as nitrous oxides and so-called volatile organic compounds. Even without any increase in the precursors, hotter air driven by climate change will produce more ozone.

Pollens released by flowering plants and trees cause hay fever and can trigger asthma attacks. Many studies show that rising global temperatures have resulted in earlier and longer pollen seasons. Some studies also indicate that certain allergens, such as the pollen in ragweed, are being produced in higher quantities and have more potent allergenic components in warmer temperatures and in air with higher concentrations of carbon dioxide. Finally, studies are emerging that directly link increased ambient temperatures, longer pollen seasons and higher daily pollen counts with more doctor visits for allergic symptoms. No doubt: a warming climate promotes more respiratory suffering.

Certain interventions can reduce the aggravation. First, all asthmatics and allergy sufferers need access to health care and appropriate medication. At-risk individuals can also be taught how to understand air-quality indices and daily pollen counts and to avoid excessive outdoor time and heavy exercise when airborne contaminants are abundant. But these are only Band-Aids. Ozone and pollen will simply get worse unless nations pursue aggressive emissions controls and a rapid transition to low- or no-carbon energy systems. Perhaps an increasing number of teary-eyed, sneezing, sleep-deprived, wheezing people who are missing work and school will generate sufficient political will in the wealthiest nations to stop greenhouse gas emissions and stabilize the global climate. Gesundheit!