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Asthma, Respiratory Allergies, and Airway Diseases

Impacts on Risk

Climate change will affect air quality through several pathways including production and allergenicity of aeroallergens such as pollen and mold spores and increases in regional ambient concentrations of ozone, fine particles, and dust. Some of these pollutants can directly cause respiratory disease or exacerbate respiratory disease in susceptible individuals.

Earlier flower blooming resulting from temperature increases and increased carbon dioxide (CO2) concentrations affects timing of distribution of aeroallergens such as pollen through plant photosynthesis and metabolism. There is also a possibility that certain aeroallergens may become more allergenic as temperatures and CO2 concentrations increase. Precipitation-affected aeroallergens such as mold spores also are of concern, as 5% of individuals are predicted to have some respiratory allergic airway symptoms from molds over their lifetime.

In the presence of certain air emissions, the rate of ozone formation increases with higher temperatures and increased sunlight, and can also be affected by changes in storm tracks, humidity, and stability of the boundary layer (lowest part of the atmosphere) Humidity and temperature also partly determine the formation of PM2.5. Research studies associate fine particles with negative cardiovascular outcomes such as heart attacks, formation of deep vein blood clots, and increased mortality from several other causes. These adverse health impacts intensify as temperatures rise.

Studies also link elevated exposure to ground-level ozone, PM2.5, coarse thoracic PM, and aeroallergens to decreased lung function, aggravation of asthma, rhinitis, exacerbations of chronic obstructive pulmonary disease, hospitalizations for respiratory and cardiovascular diseases, and premature mortality. Air pollution overcomes the mucosal barrier in lungs by inducing airway inflammation, which results in allergen-induced respiratory responses. In addition, air pollutants such as PM2.5 and ozone may alter the allergenicity of aeroallergens like pollen, thereby promoting further airway sensitization. The triggers for such adverse respiratory responses vary and include climatic factors (meteorological events, rainfall patterns, and temperature anomalies), high levels of vehicle emissions, land-use patterns, variables in the built environment, geography, and distance from roadways. Physiology also plays a significant role, as individuals with existing respiratory conditions are most vulnerable to disease exacerbations triggered by the environment. The populations most vulnerable to the increased disease risks include children, pregnant women, persons of low socioeconomic status, persons situated near high traffic zones within urban centers, and those with preexisting respiratory and cardiovascular diseases.

Other airborne exposures are also likely to worsen with climate variability and change. Changes in the hydrologic cycle with increasingly variable precipitation and more frequent drought may also lead to a global increase of airborne dust, which, when coupled with anticipated stagnant air masses and increasingly strong inversion layers, will trap ozone and other airborne pollutants near the ground causing exacerbations of respiratory disease.

Coarse thoracic PM (between 2.5 and 10 micrometers in diameter) is associated with increased risk of emergency department visits and hospitalizations for cardiovascular outcomes, especially among adults over 65 years of age. Increased incidence of wildfires in some areas can also contribute to PM concentrations. In certain areas airborne dust serves as a carrier of specific diseases, such as coccidioidomycosis, or “valley fever,” in the desert Southwest, the incidence of which has increased in recent years. Prolonged drought will lead to more dust and particulate pollution while increased rainfall will cleanse the air but may create more mold and microbial pollution. In addition, drought, declining water quality, and increased temperatures contribute to the growth of harmful algal blooms that produce toxins that can be aerosolized and exacerbate asthma and respiratory diseases. Despite strong evidence of associations between a wide range of environmental variables impacted by climate and respiratory disease, the direct impacts of climate change on asthma, respiratory allergies, and airway diseases need further study to evaluate the fraction of respiratory disease risk that can be attributed to climate change and potentially mitigated or avoided.

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