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1. Historical Southern Hemisphere biomass burning variability inferred from ice core carbon monoxide records

   https://doi.org/10.1073/pnas.2402868121  

   Strawson, Ivo; Faïn, Xavier; Bauska, Thomas K; Muschitiello, Francesco; Vladimirova, Diana O; Tetzner, Dieter R; Humby, Jack; Thomas, Elizabeth R; Liu, Pengfei; Zhang, Bingqing; et al (August 2024, Proceedings of the National Academy of Sciences)

   Biomass burning plays an important role in climate-forcing and atmospheric chemistry. The drivers of fire activity over the past two centuries, however, are hotly debated and fueled by poor constraints on the magnitude and trends of preindustrial fire regimes. As a powerful tracer of biomass burning, reconstructions of paleoatmospheric carbon monoxide (CO) can provide valuable information on the evolution of fire activity across the preindustrial to industrial transition. Here too, however, significant disagreements between existing CO records currently allow for opposing fire histories. In this study, we reconstruct a continuous record of Antarctic ice core CO between 1821 and 1995 CE to overlap with direct atmospheric observations. Our record indicates that the Southern Hemisphere CO burden ([CO]) increased by 50% from a preindustrial mixing ratio of ca. 35 ppb to ca. 53 ppb by 1995 CE with more variability than allowed for by state-of-the-art chemistry-climate models, suggesting that historic CO dynamics have been not fully accounted for. Using a 6-troposphere box model, a 40 to 50% decrease in Southern Hemisphere biomass-burning emissions, coincident with unprecedented rates of early 20th century anthropogenic land-use change, is identified as a strong candidate for this mismatch. 

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2. Late Holocene tundra fires and linkages to climate and vegetation in Northern Alaska

   https://doi.org/10.1139/as-2025-0009  

   Frank-DePue, Lee; Chipman, Melissa L (July 2025, Arctic Science)

   Charcoal particles in lake sediments can reveal past fires and linkages to climate and vegetation change. We use analyses of charcoal accumulation rates from two lakes on the Alaskan North Slope to reconstruct past fire activity, and charcoal morphology to identify changes in fuel sources. Charcoal peak analyses were used to calculate individual fire-return intervals (FRIs; years between fire) and mean FRIs (mFRIs) with 95% confidence intervals at local and regional scales. The Lake I4 core (RTS7U2, basal age 7046 cal year B.P.) shows shorter FRIs after ∼3000 cal year B.P. based on the >90 µm charcoal size fraction (regional burning), which coincides with Neoglacial cooling and decreasing moisture. A second higher-resolution core from nearby Kirk Lake (RTS5U3, basal age 743 years) captures short FRIs (mFRI = 198 (105–133) years), suggesting frequent burning compared to the late Holocene portion of Lake I4 core (mFRI = 378 (294–455) years). mFRIs from the larger charcoal size fractions (>125 µm; local burning) at both sites overlap with modern fire cycles observed in the region over the past 82 years. However, the Kirk Lake watershed burned more frequently than other sites in the region, likely related to abundant local shrub cover. These analyses suggest that tundra fires are related to climate variability, but local-scale feedbacks with vegetation can result in heterogenous burning, with implications for ongoing Arctic greening and warming. 

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3. Arctic and boreal paleofire records reveal drivers of fire activity and departures from Holocene variability

   https://doi.org/10.1002/ecy.3096  

   Hoecker, Tyler J.; Higuera, Philip E.; Kelly, Ryan; Hu, Feng Sheng (June 2020, Ecology)

   Abstract Boreal forest and tundra biomes are key components of the Earth system because the mobilization of large carbon stocks and changes in energy balance could act as positive feedbacks to ongoing climate change. In Alaska, wildfire is a primary driver of ecosystem structure and function, and a key mechanism coupling high‐latitude ecosystems to global climate. Paleoecological records reveal sensitivity of fire regimes to climatic and vegetation change over centennial–millennial time scales, highlighting increased burning concurrent with warming or elevated landscape flammability. To quantify spatiotemporal patterns in fire‐regime variability, we synthesized 27 published sediment‐charcoal records from four Alaskan ecoregions, and compared patterns to paleoclimate and paleovegetation records. Biomass burning and fire frequency increased significantly in boreal forest ecoregions with the expansion of black spruce, ca. 6,000–4,000 years before present (yr BP). Biomass burning also increased during warm periods, particularly in the Yukon Flats ecoregion from ca. 1,000 to 500 yr BP. Increases in biomass burning concurrent with constant fire return intervals suggest increases in average fire severity (i.e., more biomass burning per fire) during warm periods. Results also indicate increases in biomass burning over the last century across much of Alaska that exceed Holocene maxima, providing important context for ongoing change. Our analysis documents the sensitivity of fire activity to broad‐scale environmental change, including climate warming and biome‐scale shifts in vegetation. The lack of widespread, prolonged fire synchrony suggests regional heterogeneity limited simultaneous fire‐regime change across our study areas during the Holocene. This finding implies broad‐scale resilience of the boreal forest to extensive fire activity, but does not preclude novel responses to 21st‐century changes. If projected increases in fire activity over the 21st century are realized, they would be unprecedented in the context of the last 8,000 yr or more. 

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4. Large changes in biomass burning over the last millennium inferred from paleoatmospheric ethane in polar ice cores

   Melinda R. Nicewonger, Murat Aydin (December 2018, Proceedings of the National Academy of Sciences of the United States of America)

   Biomass burning drives changes in greenhouse gases, climate-forcing aerosols, and global atmospheric chemistry. There is controversy about the magnitude and timing of changes in biomass burning emissions on millennial time scales from preindustrial to present and about the relative importance of climate change and human activities as the underlying cause. Biomass burning is one of two notable sources of ethane in the preindustrial atmosphere. Here, we present ice core ethane measurements from Antarctica and Greenland that contain information about changes in biomass burning emissions since 1000 CE (Common Era). The biomass burning emissions of ethane during the Medieval Period (1000-1500 CE) were higher than present day and declined sharply to a minimum during the cooler Little Ice Age (1600-1800 CE). Assuming that preindustrial atmospheric reactivity and transport were the same as in the modern atmosphere, we estimate that biomass burning emissions decreased by 30 to 45% from the Medieval Period to the Little Ice Age. The timing and magnitude of this decline in biomass burning emissions is consistent with that inferred from ice core methane stable carbon isotope ratios, but inconsistent with histories based on sedimentary charcoal and ice core carbon monoxide measurements. This study demonstrates that biomass burning emissions have exceeded modern levels in the past and may be highly sensitive to changes in climate. 

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5. Large changes in biomass burning over the last millennium inferred from paleoatmospheric ethane in polar ice cores

   https://doi.org/10.1073/pnas.1807172115  

   Nicewonger, Melinda R.; Aydin, Murat; Prather, Michael J.; Saltzman, Eric S. (November 2018, Proceedings of the National Academy of Sciences)

   Biomass burning drives changes in greenhouse gases, climate-forcing aerosols, and global atmospheric chemistry. There is controversy about the magnitude and timing of changes in biomass burning emissions on millennial time scales from preindustrial to present and about the relative importance of climate change and human activities as the underlying cause. Biomass burning is one of two notable sources of ethane in the preindustrial atmosphere. Here, we present ice core ethane measurements from Antarctica and Greenland that contain information about changes in biomass burning emissions since 1000 CE (Common Era). The biomass burning emissions of ethane during the Medieval Period (1000–1500 CE) were higher than present day and declined sharply to a minimum during the cooler Little Ice Age (1600–1800 CE). Assuming that preindustrial atmospheric reactivity and transport were the same as in the modern atmosphere, we estimate that biomass burning emissions decreased by 30 to 45% from the Medieval Period to the Little Ice Age. The timing and magnitude of this decline in biomass burning emissions is consistent with that inferred from ice core methane stable carbon isotope ratios but inconsistent with histories based on sedimentary charcoal and ice core carbon monoxide measurements. This study demonstrates that biomass burning emissions have exceeded modern levels in the past and may be highly sensitive to changes in climate. 

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