Roger Pielke Jr., from substack.com

An important new paper published this week in Nature Communications looks at the historical record of fire in North America — A fire deficit persists across diverse North American forests despite recent increases in area burned. Reseachers find that large fires of recent decades in North America are not unprecedented:

Our study of 1851 tree-ring fire-scar sites and contemporary fire perimeters across the United States and Canada reveals a substantial, persistent fire deficit from 1984–2022 in many forest and woodland ecosystems, despite recent increases in burning. Contemporary fire occurrence is still far below historical (1600–1880) levels at NAFSN [North American tree-ring Fire-Scar Network] sites despite multiple large and ‘record-breaking’ recent fire years, such as 2020 in the western United States. Individual years with particularly widespread fire during the 1984–2022 period were not unprecedented in comparison with the active fire regimes of the historical period across most of the study region. Historically, fires in particularly active fire years were spatially more widespread and ubiquitous compared to fires burning during active contemporary years.

The authors start by asking an important question (emphasis added):

[A]verage annual area burned since the late 19th and early- to mid-20th centuries is generally less than that experienced under historical fire regimes across many North American forests, resulting in a widespread 20th century ‘fire deficit’ relative to earlier time periods. However, area burned by wildfire has increased across much of North America over the last few decades. Over this time period (mid-1980s—present), several regions have experienced individual years with exceptionally high area burned, leading to questions about whether recent fire years are unprecedented. As area burned has increased rapidly since the mid-1980s in parts of North America, is it possible that the fire deficit has been reduced or eliminated?

To answer this question they look at a novel dataset on tree-ring scars caused by fire.

It is not often that I am reading a scientific paper and encounter results that make me say — “Wow!”. This is one of those cases:

The year 2020 had the highest percent of sites recording fire in the contemporary time period, with 6% of NAFSN sites burned. This percentage is far below the 29% burned in the most widespread historical fire year (1748) and equal to the average of 6% that burned per year across NAFSN sites during the historical period.

Overall, fires occurred at a rate of only 23% of that expected based on historical fires — indicating a huge accumulated deficit.