Climate change is likely to influence several aspects of indoor environmental quality (IEQ). Examples include more frequent periods of high indoor temperatures and associated heat stress, driven by more frequent outdoor heat waves, changes in indoor air pollutant levels driven by changes in outdoor air pollution, and increased indoor dampness and mold problems as a consequence of having more frequent severe storms. Also, IEQ will be affected, positively or negatively, by changes in building designs and operational practices implemented to mitigate and adapt to climate change. The magnitudes of the changes in IEQ will depend highly on the extent of climate change and on the climate change mitigation and adaption measures that are implemented.

Changes In IEQ and Health Driven by Changes in the Outdoor Environment

Thermal Stress and Deaths During Heat Waves: Longer, more severe, and more frequent heat waves are expected as the climate warms. Unless susceptible buildings are modified in a manner that prevents overheating, there will be more periods of very high indoor temperatures with associated cases of heat stress, hospitalizations, and premature death. The elderly, young children, people with poor health, and the poor who live in substandard housing and cannot afford air conditioning, are more likely to be affected. Some building energy efficiency measures and increased availability of air conditioning could mitigate these adverse effects.

Dampness and Mold From Severe Storms and Flooding: Globally, as a consequence of climate change, the frequency and intensity of heavy precipitation are expected to increase. Also, there are expected to be more frequent or more severe hurricanes in some regions of the world, and sea level will rise. These changes are expected to increase water entry into buildings through failures of the envelope and via flooding, leading to more frequent dampness and mold problems in buildings. As a consequence, adverse respiratory health effects, including cases of exacerbation of asthma, are expected unless preventative measures are taken. Possible preventative measures include changes in building envelope and foundation designs, improved envelope maintenance, and less frequent location of buildings in flood plains.

Other Effects on IEQ of Severe Storms and Flooding: Severe storms and flooding frequently lead to electrical power outages, loss of heating and cooling, and dislocation from homes. The resulting high or low indoor air temperatures impose thermal stress that can affect health. The use of backup generators increases during power outages caused by severe storms, resulting in more indoor carbon monoxide poisonings. Severe storms and floods lead to dislocations of families from their homes to temporary housing and emergency shelters where exposures to indoor-air contaminants may be increased.

Wildfires: Increased outdoor temperatures, heat waves, and droughts are expected to lead to increased wildfires. Wildfires can cause temporary large increases in outdoor airborne particles, and substantial increase in several gaseous air pollutants. A substantial portion of people's exposures to these air pollutants will occur indoors. Several, but not all, studies have documented increased adverse health effects in populations exposed to pollutants from wildfires. Health effects assessed in these studies have included hospital admissions for various causes, mortality, respiratory symptoms, and respiratory infections. These adverse health effects may be reduced by taking the following actions when air is polluted by emissions from wildfires: 1) spending more time indoors; 2) keeping windows and doors closed; and 3) operating particle filtration systems.

Humidity and Dust Mite Allergies: Climate change is expected to increase the global average moisture content of outdoor air; however, the effects of climate change on the moisture content of outdoor air and indoor air humidity, are likely to vary highly with region. The indoor air humidity affects the survival and number of house dust mites and these mites are an important source of allergens that contribute to allergic and asthmatic symptoms. The overall net effect of climate change on allergies and asthma due to allergens from house dust mites is uncertain.

Increases in Ozone: The temperature increases from climate change are expected to moderately increase ambient outdoor ozone within and near urban areas where most people live. Climate change has been projected to cause substantial increases in ozone-related respiratory health effects, hospitalizations, and deaths, although the predicted magnitudes of health effects are uncertain and vary among studies and with location. A portion of these adverse health effects will be a consequence of indoor exposures to outdoor ozone that has migrated indoors. Changes to buildings could diminish the adverse health effects of increases in ozone. Increased use of air conditioning and associated closing of windows, is likely as the climate warms and could be encouraged when ozone levels are high. Filters containing activated carbon, through which air is passed using fans, can be effective in removing ozone for an extended period. Some types of building materials can passively, i.e., without fans, remove ozone, reducing indoor air concentrations. In locations with aggressive implementation of outdoor air ozone control measures, ozone levels and associated adverse health effects may decrease, although climate change will lessen the decrease.

Particles: Outdoor air particle pollution is a major source of morbidity and mortality. Much of people's exposures to particles occurs indoors. Climate change is expected to modify outdoor particle levels via several mechanisms. At present, there is no consensus about the net effect of a changing climate on outdoor air particles; thus, the health consequences of associated changes in indoor particle concentrations are uncertain.

Pollen Allergens: Pollen allergens contribute to allergic disease and asthma. The warmer temperatures from climate change will cause the pollen season to start earlier in the 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 the potency of some pollen allergens. A portion of our exposures to these allergens occurs inside buildings, although the fraction is likely modest. Changes in building design and use may be effective in mitigating climate-related increases in indoor pollen allergens. Keeping windows closed and using air conditioning will reduce pollen allergen exposures. Increased particle filtration could reduce airborne levels of pollen fragments, although it is not likely to substantially reduce indoor concentrations of large intact pollens. More frequent or effective building cleaning may reduce the resuspension of pollens from indoor surfaces into the indoor air. Few experimental data are available to assess the effectiveness of these measures.

IEQ and Health Consequences of Adaption to and Mitigation of Climate Change

Increased Use of Air Conditioning: As climate change increases outdoor temperatures, air conditioning will more often be used to maintain comfortable indoor conditions, with both positive and negative effects on health. Increased availability of air conditioning is expected to diminish the increases in adverse health effects resulting from heat waves. When air conditioning is employed, windows are normally maintained closed, consequently, rates of building ventilation with outdoor air are often reduced. By keeping windows closed, indoor air concentrations of some outdoor air pollutants, particularly particles and ozone, from outdoor air are diminished, with associated health benefits. At the same time, indoor concentrations of pollutants from indoor sources will increase, posing health risks. For reasons that are not well understood, air conditioning is associated with increases in acute health symptoms often called sick building syndrome (SBS) symptoms, and also with respiratory health effects associated with asthma. Exposure to microbial contaminants that grow on the often-wet components of air conditioning systems are a possible explanation. Increased use of air conditioning may lead to more of the adverse health effects associated with air conditioning.

Building Energy Efficiency: To reduce future climate change it will be necessary to reduce building energy consumption; thus, broad application of energy efficiency measures in buildings is expected as climate change advances. Many energy efficiency measures for buildings will influence comfort conditions or indoor air quality positively or negatively. The net effect of building energy efficiency, motivated by climate change, on indoor environmental quality, comfort, and health cannot be predicted with confidence. It is clear that there is a potential to improve comfort and health conditions through strategic implementation of energy efficiency measures.

Indoor Biomass and Coal Stoves: Approximately 40% of the world's population employs biomass or coal stoves which are a large source of indoor air particulate matter and other health-damaging indoor pollutants. Biomass and coal-based stoves are also important sources of emissions of black carbon particles and methane to outdoors, which contribute to climate change. Consequently, use of stoves that employ other fuels, emitting less pollution, and the use of more efficient and lower-emitting biomass and coal stoves, are attractive climate change mitigation measures that could improve indoor air quality and health for a very large population.

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