finding 8.6 : key-finding-8-6

The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s (high confidence) and is projected to further increase in those regions as the climate warms with profound changes to certain ecosystems (medium confidence). 

This finding is from chapter 8 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: Wildfires have increased over parts of the western United States and Alaska in recent decades and are projected to continue to increase as a result of climate change. As a result, shifts in certain ecosystem types may occur.

Description of evidence base: Studies by Dennison et al. (western United States)bcc07e69-1ffb-4630-b203-1d4e1bbfa04e and Kasischke and Turetsky (Alaska)f3ae636d-6cf8-4d68-b928-1888dba5ff5e document the observed increases in fire statistics. Projections of Westerling et al. (western United States)b95e9226-076c-4eb5-9367-472499624084 and Young et al.47b02899-c6eb-45b3-914d-b124e6b038f4 and others (Alaska) indicate increased fire risk. These observations and projections are consistent with drying due to warmer temperatures leading to increased flammability and longer fire seasons.

New information and remaining uncertainties: Analyses of other regions of the United States, which also could be subject to increased fire risk, do not seem to be readily available. Likewise, projections of the western U.S. fire risk are of limited areas. In terms of attribution, there is still some uncertainty as to how well non-climatic confounding factors such as forestry management and fire suppression practices have been accounted for, particularly for the western United States. Other climate change factors, such as increased water deficits and insect infestations, could reduce fuel loads, tending towards reducing fire frequency and/or intensity.

Assessment of confidence based on evidence: Confidence is high in the observations due to solid observational evidence. Confidence in projections would be higher if there were more available studies covering a broader area of the United States and a wider range of ecosystems.

This finding was derived from figure -.2: Confidence / Likelihood

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