An official website of the United States government
Abstract Wildfire is an essential earth‐system process, impacting ecosystem processes and the carbon cycle. Forest fires are becoming more frequent and severe, yet gaps exist in the modeling of fire on vegetation and carbon dynamics. Strategies for reducing carbon dioxide (CO2) emissions from wildfires include increasing tree harvest, largely based on the public assumption that fires burn live forests to the ground, despite observations indicating that less than 5% of mature tree biomass is actually consumed. This misconception is also reflected though excessive combustion of live trees in models. Here, we show that regional emissions estimates using widely implemented combustion coefficients are 59%–83% higher than emissions based on field observations. Using unique field datasets from before and after wildfires and an improved ecosystem model, we provide strong evidence that these large overestimates can be reduced by using realistic biomass combustion factors and by accurately quantifying biomass in standing dead trees that decompose over decades to centuries after fire (“snags”). Most model development focuses on area burned; our results reveal that accurately representing combustion is also essential for quantifying fire impacts on ecosystems. Using our improvements, we find that western US forest fires have emitted 851 ± 228 Tg CO2(~half of alternative estimates) over the last 17 years, which is minor compared to 16,200 Tg CO2from fossil fuels across the region.
more »
« less
This content will become publicly available on December 13, 2025
Do Forest Fires or Cars Produce More CO2 Emissions?
Students act as environmental engineers to solve a problem using carbon dioxide (CO2) emissions from cars and wildfires. Wildfires are a timely topic because every year they cause people in many areas to face poor air quality. Students use Microsoft Excel to investigate CO2 emitted from two sources: highway traffic and forest fires. They estimate and graph the CO2 emitted by forest fires and from U.S. highway driving annually from 2004 to 2021. After they analyze these two pieces of data, they analyze a specific fire and evacuation that happened in Saratoga Springs in June 2020, named the Knolls Fire. Finally, using the Excel data and the Knolls Fire data, students decide whether the U.S. should spend money on reducing the number and severity of wildfires, or on reducing CO2 emissions from driving cars. The students design and create a poster based on their decision and present it to the class.
more »
« less
- PAR ID:
- 10600501
- Publisher / Repository:
- Teach Engineering
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Wildfires in humid tropical forests have become more common in recent years, increasing the rates of tree mortality in forests that have not co-evolved with fire. Estimating carbon emissions from these wildfires is complex. Current approaches rely on estimates of committed emissions based on static emission factors through time and space, yet these emissions cannot be assigned to specific years, and thus are not comparable with other temporally-explicit emission sources. Moreover, committed emissions are gross estimates, whereas the long-term consequences of wildfires require an understanding of net emissions that accounts for post-fire uptake of CO 2 . Here, using a 30 year wildfire chronosequence from across the Brazilian Amazon, we calculate net CO 2 emissions from Amazon wildfires by developing statistical models comparing post-fire changes in stem mortality, necromass decomposition and vegetation growth with unburned forest plots sampled at the same time. Over the 30 yr time period, gross emissions from combustion during the fire and subsequent tree mortality and decomposition were equivalent to 126.1 Mg CO 2 ha −1 of which 73% (92.4 Mg CO 2 ha −1 ) resulted from mortality and decomposition. These emissions were only partially offset by forest growth, with an estimated CO 2 uptake of 45.0 Mg ha −1 over the same time period. Our analysis allowed us to assign emissions and growth across years, revealing that net annual emissions peak 4 yr after forest fires. At present, Brazil’s National Determined Contribution (NDC) for emissions fails to consider forest fires as a significant source, even though these are likely to make a substantial and long-term impact on the net carbon balance of Amazonia. Considering long-term post-fire necromass decomposition and vegetation regrowth is crucial for improving global carbon budget estimates and national greenhouse gases (GHG) inventories for tropical forest countries.more » « less
-
Abstract The NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) experiment was a multi‐agency, inter‐disciplinary research effort to: (a) obtain detailed measurements of trace gas and aerosol emissions from wildfires and prescribed fires using aircraft, satellites and ground‐based instruments, (b) make extensive suborbital remote sensing measurements of fire dynamics, (c) assess local, regional, and global modeling of fires, and (d) strengthen connections to observables on the ground such as fuels and fuel consumption and satellite products such as burned area and fire radiative power. From Boise, ID western wildfires were studied with the NASA DC‐8 and two NOAA Twin Otter aircraft. The high‐altitude NASA ER‐2 was deployed from Palmdale, CA to observe some of these fires in conjunction with satellite overpasses and the other aircraft. Further research was conducted on three mobile laboratories and ground sites, and 17 different modeling forecast and analyses products for fire, fuels and air quality and climate implications. From Salina, KS the DC‐8 investigated 87 smaller fires in the Southeast with remote and in‐situ data collection. Sampling by all platforms was designed to measure emissions of trace gases and aerosols with multiple transects to capture the chemical transformation of these emissions and perform remote sensing observations of fire and smoke plumes under day and night conditions. The emissions were linked to fuels consumed and fire radiative power using orbital and suborbital remote sensing observations collected during overflights of the fires and smoke plumes and ground sampling of fuels.more » « less
-
Over the past several decades, the annual burned area in California's Sierra Nevada mountains has increased considerably, with significant social, economic, and ecosystem impacts that provide motivation for understanding how the history of forest management influences the composition of fuels and emissions in wildfires. Here, we measured the carbon concentration and radiocarbon abundance (∆14C) of fire-emitted particulate matter from the KNP Complex Fire, which burned through several groves of giant sequoia trees in the southern Sierra Nevada mountains during California’s 2021 wildfire season. Over a 26-hour sampling period, we measured the concentration of fine airborne particulate matter (PM2.5) along with carbon monoxide (CO) and methane (CH4) dry air mole fractions using a ground-based mobile laboratory. Filter samples of PM2.5 were also collected and later analyzed for carbon concentration and ∆14C. Covariation of PM2.5, CO, and CH4 time series data confirmed that our PM2.5 samples were representative of wildfire emissions. Using a Keeling plot approach, we estimated that the mean ∆14C of PM2.5 was 111.5 ± 2.3‰ (n=12), which is considerably enriched relative to that of atmospheric carbon dioxide in the northern hemisphere in 2021 (-3.4 ± 1.4‰). By combining these ∆14C data with a steady-state one-box ecosystem model, we estimated that the mean age of fuels combusted in the KNP Complex Fire was 40 ± 6 years. This multi-decadal fuel age provides evidence for emissions from woody biomass, coarse woody debris, and larger-diameter fine fuels. The combustion of these larger-size fuel classes is consistent with independent field observations that indicate high fire intensity contributed to widespread giant sequoia mortality. With the expanded use of prescribed fires planned over the next decade in California to mitigate impacts of wildfires, our measurement approach has the potential to provide regionally-integrated estimates of the effectiveness of fuel treatment programs.more » « less
-
Abstract We present emission measurements of volatile organic compounds (VOCs) for western U.S. wildland fires made on the NSF/NCAR C‐130 research aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) field campaign in summer 2018. VOCs were measured with complementary instruments onboard the C‐130, including a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and two gas chromatography (GC)‐based methods. Agreement within combined instrument uncertainties (<60%) was observed for most co‐measured VOCs. GC‐based measurements speciated the isomeric contributions to selected PTR‐ToF‐MS ion masses and generally showed little fire‐to‐fire variation. We report emission ratios (ERs) and emission factors (EFs) for 161 VOCs measured in 31 near‐fire smoke plume transects of 24 specific individual fires sampled in the afternoon when burning conditions are typically most active. Modified combustion efficiency (MCE) ranged from 0.85 to 0.94. The measured campaign‐average total VOC EF was 26.1 ± 6.9 g kg−1, approximately 67% of which is accounted for by oxygenated VOCs. The 10 most abundantly emitted species contributed more than half of the total measured VOC mass. We found that MCE alone explained nearly 70% of the observed variance for total measured VOC emissions (r2 = 0.67) and >50% for 57 individual VOC EFs representing more than half the organic carbon mass. Finally, we found little fire‐to‐fire variability for the mass fraction contributions of individual species to the total measured VOC emissions, suggesting that a single speciation profile can describe VOC emissions for the wildfires in coniferous ecosystems sampled during WE‐CAN.more » « less
