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Quantifying the contribution of major carbon producers to increases in vapor pressure deficit and burned area in western US and southwestern Canadian forests [1]
['Kristina A Dahl', 'Climate', 'Energy Program', 'Union Of Concerned Scientists', 'Oakland', 'Ca', 'United States Of America', 'Http', 'John T Abatzoglou', 'Management Of Complex Systems Department']
Date: 2023-05
Over the last several decades, the western United States and southwestern Canada have experienced increases in the area burned by wildfires (Abatzoglou and Williams 2016, Hanes et al 2019, Balch et al 2022), the number of large fires (Dennison et al 2014, Westerling 2016), the length of the fire season (Westerling 2016, Kirchmeier-Young et al 2017, Goss et al 2020), the elevation at which fires burn (Alizadeh et al 2021), and the extent of forested lands that burn at high severity (Parks and Abatzoglou 2020). These trends, particularly evident in the region's forested ecosystems, coincide with a twofold increase in Canadian fire suppression costs and a more than sevenfold increase in US federal suppression costs when comparing average costs from 1985–1989 to those of 2013–2017 (Canada; Natural Resources Canada 2021) or 2017–2021 (US; National Interagency Fire Center 2022).
Significant portions of many of these trends in wildfire activity have been attributed to anthropogenic climate change (Abatzoglou and Williams 2016, Kirchmeier-Young et al 2017, Williams et al 2019, Zhuang et al 2021). Vapor pressure deficit (VPD)—a measure of atmospheric water demand defined as the difference between the amount of water vapor in the air and the amount of water vapor that air would hold at saturation—has emerged as a key metric linking climate change and burned area (BA) due to its role in regulating ecosystem water dynamics (Grossiord et al 2020, Clarke et al 2022). Through the lens of regional wildfire risk, rising VPD ultimately translates to a greater likelihood that fuels will ignite and carry fire across a landscape.
More than two-thirds of the observed summertime increase in VPD in the western US has been attributed to anthropogenic warming (Zhuang et al 2021). In turn, the increase in summertime VPD has driven increases in fuel aridity in the region, resulting in nearly a doubling of BA in western US forests during 1984–2015 (Abatzoglou and Williams 2016). Regionally, there is a strong and established interannual relationship between VPD and BA across forested subregions of the western US and southwestern Canada (Abatzoglou et al 2018, Williams et al 2019, Whitman et al 2022). In flammability-limited ecosystems like forests, area burned is exponentially related to VPD (Juang et al 2022).
The question of who bears responsibility for climate change and impacts such as increases in BA is being actively explored in both scientific and legal realms. The current global governance system to address climate change is centered on the responsibilities of nation states, but corporate actors also bear a distinct responsibility for the climate crisis. Recent research has found that carbon dioxide and methane emissions traced to major fossil fuel and cement manufacturing companies have contributed to more than 40% of rising global temperatures, 25% of global sea level rise, and 50% of ocean acidification between 1880 and the 2010s (Ekwurzel et al 2017, Licker et al 2019). However, their role in setting the stage for the increased fire extent observed in the western US and southwestern Canada in recent decades has gone unexamined.
This study establishes the role of major carbon producers in increasing wildfire risks in forested landscapes by examining two primary research questions: (a) what is the quantifiable relationship between changes in VPD in western North America and changes in global mean temperature (GMT)? and (b) given a quantified relationship between GMT and VPD, how much have emissions from major carbon producers contributed to the observed increase in VPD and the cumulative forest BA in the western United States and southwestern Canada? By addressing these questions, this study advances the source attribution literature as well as national and international dialogues around liability for climate impacts.
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[1] Url:
https://iopscience.iop.org/article/10.1088/1748-9326/acbce8#erlacbce8s3
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