finding 13.2 : key-message-13-2

Wildfire smoke degrades air quality, increasing the health risks to tens of millions of people in the United States. More frequent and severe wildfires due to climate change would further diminish air quality, increase incidences of respiratory illness from exposure to wildfire smoke, impair visibility, and disrupt outdoor recreational activities (very likely, high confidence).



This finding is from chapter 13 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

Due to limited resources and requirements imposed by the Federal Advisory Committee Act, the decision was made that this chapter would be developed using an all-federal author team. The author team was selected based on expertise in climate change impacts on air quality; several of the chapter authors were authors of the “Air Quality Impacts” chapter of the U.S. Global Change Research Program’s (USGCRP) Climate and Health Assessment.5ec155e5-8b77-438f-afa9-fbcac4d27690 This chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors via weekly teleconferences and email exchanges. The authors considered inputs and comments submitted by the public; the National Academies of Sciences, Engineering, and Medicine; and federal agencies.


Description of evidence base:

Wildfire smoke worsens air quality through its direct emissions to the atmosphere as well as through chemical reactions of those pollutants with sunlight and other pollutants. Exposure to wildfire smoke increases the risk of exacerbating respiratory illnesses in tens of millions of people in vulnerable population groups across the United States.9a222c75-5ff9-408e-9694-b7bd90a2a0ca Several studies have indicated that climate change has already led to longer wildfire seasons,e1e1f3a0-9fea-4ad2-a3af-575716f9849e increased frequency of large wildfires,d96a729a-a5db-4318-8f52-78f6031b42fd bcc07e69-1ffb-4630-b203-1d4e1bbfa04e and increased area of forest burned.de4a77df-03ba-4319-a13f-7fdefbb353a5 Additional studies project that climate change will cause wildfire frequency and burned area in North America to increase over the 21st century.a29b612b-8c28-4c93-9c18-19314babce89 b95e9226-076c-4eb5-9367-472499624084 f4daa36c-4b3f-449a-8d03-94cdd39fe1eb c0fc95a5-870b-4c25-a63f-81716351c81f 52b8c0e6-00b2-42aa-9df5-6d46fe600b7d 139442ad-69f8-452f-9c46-0dc9438ec5fb 39a8b555-de10-4244-b292-52d0b202531d f680e49e-d58f-45c2-8ad6-a7bc97c12ca0 Increased emissions from wildfires may offset the benefits of large reductions in emissions of PM2.5 precursors.a92b6912-a92c-482b-a8e7-f43d324947e3 c644739f-2708-4c5b-ba4d-a9dd0a50d3dc There is a broad and consistent evidence base leading to a high confidence conclusion that the increasing impacts of wildfire are very likely. Increases in wildfire smoke events due to climate change would reduce opportunities for outdoor recreational activities (Ch. 22: N. Great Plains, KM 3 and Ch. 24: Northwest, KM 4).

New information and remaining uncertainties:

Humans affect fire activity in many ways, including increasing ignitions as well as conducting controlled burns and fire suppression activities.415d7f4d-4e24-4cff-a9aa-c76f30dbeb42,ea8d831c-6b6b-4f8c-9b60-f17bab43660e The frequency and severity of wildfire occurrence in the future will be largely determined by forest management practices and climate adaptation measures, which are very uncertain. Housing development practices and changes in the urban–forest interface are also important factors for future wildfire occurrence and for the extent to which associated smoke emissions impair air quality and result in adverse health effects. The composition of the pollutants contained in wildfire smoke and their chemical reactions are highly dependent on a variety of environmental factors, so projecting and quantifying the effects of wildfire smoke on specific pollutants can be particularly challenging. Exposure to wildfire smoke may also increase the risk of cardiovascular illness, but additional data are required to quantify this risk.9a222c75-5ff9-408e-9694-b7bd90a2a0ca More accurate forecasting of wildfire smoke events may mitigate health impacts and reduced opportunities for outdoor recreational activities through changes in timing of those activities.

Assessment of confidence based on evidence:

There is high confidence that rising temperatures and earlier spring snowmelt will very likely result in lengthening the wildfire season in portions of the United States, leading to an increased frequency of wildfires and associated smoke. There is very high confidence that increasing exposure to wildfire smoke, which contains particulate matter, will increase adverse health impacts. It is likely that smoke from wildfires will reduce visibility and disrupt outdoor recreational activities.

References :

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