Changes in climate, specifically rising temperatures, altered precipitation patterns, and increasing concentrations of atmospheric carbon dioxide, are expected to contribute to increases in the levels of some airborne allergens and associated increases in asthma episodes and other allergic illnesses [High Confidence].

This finding is from chapter 3 of The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.

Process for developing key messages: The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops, teleconferences, and email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, and Federal agencies. For additional information on the overall report process, see Appendices 2–3.

In addition, the author team held an all-day meeting at the U.S. Environmental Protection Agency National Center for Environmental Assessment in Crystal City, Virginia, on October 15, 2014, to discuss the chapter and develop initial drafts of the Key Findings. A quorum of the authors participated and represented each of the three sections of the chapter—outdoor air quality, aeroallergens, and indoor air quality. These discussions were informed by the results of the literature review as well as the research highlights focused on outdoor air quality and indoor air quality. The team developed Key Finding 2 in response to comments from the National Research Council review panel and the general public.

The Key Findings for outdoor ozone, wildfires, and aeroallergen impacts reflect strong empirical evidence linking changes in climate to these outcomes. When characterizing the human health impacts from outdoor ozone, the team considered the strength of the toxicological, clinical, and epidemiological evidence evaluated in the Ozone Integrated Science Assessment.e00fb4e2-6406-40be-90f8-071dfc43cca3 Because there is increasing evidence that climate change will increase the frequency and intensity of wildfire events, this outcome was included as a key finding, despite the inability to quantify this impact with the available tools and data. Because altered patterns of precipitation and increasing levels of CO₂ are anticipated to promote the level of aeroallergens, this outcome is also included as a Key Finding. Finally, because the empirical evidence linking climate change to indoor air quality was more equivocal, we identified this topic as an emerging issue.

Description of evidence base: There is a large body of evidence supporting the observation that climate change will alter the production, allergenicity, distribution, and timing of aeroallergens. Historical trends show that climate change has led to changes in the length of the growing season for certain allergenic pollens. Climate change also contributes to changes in allergic illnesses as greater concentrations of CO₂, together with higher temperatures and changes in precipitation, extend the start or duration of the growing season, increase the quantity and allergenicity of pollen, and expand the spatial distribution of pollens.c60ed28e-5ec3-4b9b-8b41-c6c29e4fda70 14835bc7-3df6-4fac-9e9a-2863c09e800a fa0649b9-2a09-43a3-a2ce-b57dbe0080a7 aac0f087-3ed8-49a3-b1c9-07ce3fdf7f24 7dff169a-bb19-4f80-bdc9-9aae8d13a86f While the role of weather on the initiation or exacerbation of allergic symptoms in sensitive persons is not entirely understood,7eaad122-f1a7-4062-bbfc-c4c9ad7d3078 a033e39f-2028-453b-b37b-ec698f155b25 increases in intensity and frequency of rainfall and storminess over the coming decades is expected to be associated with spikes in aeroallergen concentrations and the potential for related increases in the number and severity of allergic illnesses.025515fc-f83a-47ff-b547-92ade9513c15 713cd919-826b-426d-bf51-761a58ec7f22

These changes in exposure to aeroallergens contribute to the severity and prevalence of allergic disease in humans. Given that aeroallergen exposure is not the sole, or even necessarily the most significant, factor associated with allergic illnesses, that relationship is part of a complex pathway that links exposure to aeroallergens to the prevalence of allergic illnesses.b9370347-fe7c-4b6f-9d49-af723ed931a4 There is consistent and robust evidence that aeroallergen exposure contributes significantly to the occurrence of asthma episodes, hay fever, sinusitis, conjunctivitis, hives, and anaphylaxis.c60ed28e-5ec3-4b9b-8b41-c6c29e4fda70 f89543d6-09bf-436c-8f7e-c0f908473457 There is also compelling evidence that allergic diseases develop in response to complex and multiple interactions among both genetic and non-genetic factors, including a developing immune system, environmental exposures (such as ambient air pollution or weather conditions), and socioeconomic and demographic factors.49a88ae9-9f4c-4a99-92fa-3da34bf2a70f 7eaad122-f1a7-4062-bbfc-c4c9ad7d3078 d9f760b1-0caa-450c-a807-e65c2097c0fb Finally, there is evidence that potential non-linear interactions between aeroallergens and ambient air pollutants is likely to increase health risks for people who are simultaneously exposed.d9f760b1-0caa-450c-a807-e65c2097c0fb f89543d6-09bf-436c-8f7e-c0f908473457 036ba27d-8341-4f6d-ad66-1288e53dee65 025515fc-f83a-47ff-b547-92ade9513c15 a5b5448f-6f88-4e74-a3a9-2f34aab42ecb 6d18401d-b332-4805-8b3b-07e4f6e01d13 a52668d8-0468-4b90-9b62-c32a86cae478 203adb04-2d0d-4b2e-ac47-bbaeb3befedd 98a7b7be-a84e-4adf-bbe0-72f34256c87f

New information and remaining uncertainties: The interrelationships between climate variability and change and exposure to aeroallergens are complex. Where they exist, differences in findings from across the relevant scientific literature may be due to study designs, references to certain species of pollen, geographic characteristics, climate variables, and degree of allergy sensitization.b1d1a01e-78e1-4b26-a8b4-513c43a7240c There are also uncertainties with respect to the role of climate change and the extent and nature of its effects as they contribute to aeroallergen-related diseases, especially asthma.14835bc7-3df6-4fac-9e9a-2863c09e800a Existing uncertainties can be addressed through the development of standardized approaches for measuring exposures and tracking outcomes across a range of allergic illnesses, vulnerable populations, and geographic proximity to exposures.9d0046a1-8cd1-4a6d-a8c1-ab853fd1fb2a

Assessment of confidence based on evidence: The scientific literature suggests that there is high confidence that changes in climate, including rising temperatures and altered precipitation patterns, will affect the concentration, allergenicity, season length, and spatial distribution of a number of aeroallergens, and these changes are expected to impact the prevalence of some allergic diseases, including asthma attacks.

References :

• Projections of the effects of climate change on allergic asthma: The contribution of aerobiology (025515fc)
• Climate change and allergic disease (036ba27d)
• Impacts of climate change on aeroallergens: Past and future (14835bc7)
• Role of outdoor aeroallergens in asthma exacerbations: Epidemiological evidence (203adb04)
• webpage Allergy Statistics (49a88ae9)
• Environmental urban factors (air pollution and allergens) and the rising trends in allergic respiratory diseases (6d18401d)
• Thunderstorm-asthma and pollen allergy (713cd919)
• Projected carbon dioxide to increase grass pollen and allergen exposure despite higher ozone levels (7dff169a)
• Relationship between climate, pollen concentrations of Ambrosia and medical consultations for allergic rhinitis in Montreal, 1994–2002 (7eaad122)
• Analysis of short-term influences of ambient aeroallergens on pediatric asthma hospital visits (98a7b7be)
• Induction of asthma and the environment: What we know and need to know (9d0046a1)
• Urban air pollution and climate change as environmental risk factors of respiratory allergy: An update (a033e39f)
• Environmental risk factors and allergic bronchial asthma (a52668d8)
• The role of outdoor air pollution and climatic changes on the rising trends in respiratory allergy (a5b5448f)
• Climate change, air pollution and extreme events leading to increasing prevalence of allergic respiratory diseases (aac0f087)
• Effects of climate change on environmental factors in respiratory allergic diseases (b1d1a01e)
• Aeroallergens, Allergic Disease, and Climate Change: Impacts and Adaptation (b9370347)
• Climate change and allergic disease (c60ed28e)
• Air pollution and allergens (d9f760b1)
• Integrated Science Assessment for Ozone and Related Photochemical Oxidants (e00fb4e2)
• Anthropogenic climate change and allergic diseases (f89543d6)
• Is the global rise of asthma an early impact of anthropogenic climate change? (fa0649b9)