Many pollens from plants are allergens. Pollen allergens contribute to allergic disease and asthma [56, 57]. There is a general agreement that the warmer temperatures from climate change will cause the pollen season to start earlier in the year [100-102]. Also, temperature increases will enable plants to survive in higher latitudes, changing the pollens present and may extend the pollen season for some plants [100, 101]. Between 1995 and 2013, the ragweed pollen season increased in 10 of 11 central U.S. and Canadian cities by 1 -27 days per year and decreased in the 11th city by 1 day per year . Higher temperatures and the higher carbon dioxide levels that play a large role in driving climate change are linked to increased plant biomass, potentially yielding more pollen production . There is also some evidence that increased carbon dioxide levels will increase potency for some allergens [10, 101, 102].
A portion of our exposures to these allergens occurs inside buildings. Pollen grains can enter through open windows and doors, be tracked into buildings, or carried in on clothes. Because of their large size, pollen grains will rapidly settle on indoor surfaces [34, 103], reducing inhalation exposures. However, when disturbed, they can be resuspended into air. Also, some pollens such as those from grass and birch can break into small fragments [104-107] that can remain suspended in air for hours. Consequently, without changes to buildings indoor exposures to allergens that contribute to allergic disease will be affected by climate change. At a minimum, the exposures will occur earlier in the year. It appears likely that exposures to pollen allergens will also increase.
Changes in building design might be effective in mitigating climate-related increases in indoor pollen allergens. Keeping windows closed and using air conditioning will reduce pollen allergen exposures. Air conditioning was associated with a reduction in asthma incidence in a Canadian study , although the reduction was not statistically significant. However, several other studies, detailed in the section on air conditioning point to respiratory health benefits and risks of air conditioning. More airtight building envelopes will reduce penetration of pollens or pollen fragments to the indoors with air that leaks in through cracks and holes. Increased particle filtration, using filters in heating and cooling systems or portable air filtration systems, could reduce airborne levels of pollen fragments, although filtration is not likely to substantially reduce indoor concentrations of large intact pollens. Filtration of the incoming mechanically supplied outdoor air, when present, may be particularly effective. More frequent or effective building cleaning may reduce adventitious resuspension of pollens that have settled on indoor surfaces. By and large, however, experimental data are not available to assess the effectiveness of these measures.