Allergies are a significant health problem in the United States, with at least 50% of the population testing positive for one or more allergens. Currently, diagnosis and treatment of allergies costs the health care system over $20 billion annually. Aeroallergies, allergies associated with inhaled allergens such as pollen and mold, are extremely common and are responsible for three common allergic diseases: asthma, allergic rhinitis (commonly known as hay fever), and atopic dermatitis (commonly known as eczema). Scientists believe there will likely be an indirect, although significant, relationship between the expected levels of future climate change and the future incidence and severity of aeroallergies.
How Aeroallergies Occur
The allergic process occurs in two stages. In the first stage, an individual is exposed and sensitized to an allergen, resulting in the formation of IgE antibodies. In the second stage, renewed and continued exposure to the allergen causes a cellular response to the now existing IgE antibodies. The cellular response is designed to fight the antibodies, creating the common symptoms of aeroallergies such as sneezing, watering eyes, congestion, or skin irritation. Respiratory allergies typically developed by two years of age in about 40% of those affected. The remaining 60% see allergies develop by age six.
Even though allergies are created by the response to the allergen, there are many other factors that determine whether an individual will develop an allergy. These factors include land use, air pollution, and individual adaptive responses. The most important factor is the individual’s underlying genetic profile. The gene/environment interface is poorly understood and creates some difficulty in anticipating which individuals will develop aeroallergies and how those allergies will to environmental changes.
How Greenhouse Gas Emissions and Global Warming Affect Plant Productivity
The most common inhaled allergens are directly related to the products produced by plants during reproductive cycles. Increased productivity leads to increased reproductive capacity and increased amounts of these products, for example, plant pollen. Both pollen and mold production are also greatly affected by pre-season temperatures and precipitation.
Carbon dioxide, CO2, is one of the primary components of greenhouse gas emissions and the predicted primary cause of impending climate change. Taking into account similar or even increased greenhouse gas emissions in the future, experts are predicting increased CO2 concentrations in the atmosphere and a corresponding one to three degree Celsius increase in temperatures in the continental United States. Increasing temperatures are predicted to increase evaporation of surface water causing a related ultimate increase in precipitation.
Scientists studying the effects of climate change on plant productivity believe that many plants may be directly affected by the increased temperature, moisture, and CO2 concentrations. Research indicates that doubling the levels of CO2 available to ragweed, a common allergen-creating plant, results in a 60 to 90 percent increase in pollen production. Ragweed is actually found to grow faster, flower earlier, and produce significantly pollen levels in urban areas than in rural areas, with urban areas typically showing higher temperatures and CO2 concentrations. For trees, a significant source of allergens, increased temperature and moisture resulted in earlier start dates for pollen production with a resulting extended pollen-producing season.
The Anticipated Allergic Reaction to Climate Change
The impact of climate change on allergies will be indirect, through the impact on plant productivity, and therefore is difficult to definitively predict. However, scientists have identified three possible climate change-induced impacts on aeroallergens that may alter the severity and prevalence of allergic disease:
- longer exposure during sensitization may result in a greater likelihood of the development of allergies,
- higher doses during sensitization may result in a greater likelihood of the development of allergies, and
- higher doses during subsequent exposures may result in an ultimately more severe allergic reaction.
Scientists cannot be sure exactly how impending climate change will affect allergies in individuals. However, based on plant productivity science alone, it is relatively certain that increased temperature, CO2 concentrations, and precipitation will have an effect.