Assessing Interactions of Future Climate Change, Wildfires, and Terrestrial Biogeochemical Feedbacks

Rising anthropogenic emissions of radiatively active greenhouse gases and particulate matter (PM) are altering Earth’s climate, increasing human and ecosystem health risks, and inducing feedbacks from terrestrial and marine ecosystems on future atmospheric carbon dioxide (CO2) levels and PM concentrations. Process-based Earth system models (ESMs) and regional climate and chemistry transport models offer the best approach for quantifying these feedbacks and their uncertainties, projecting future atmospheric CO2 levels and resulting temperature increases and wildfire risks, predicting hazardous PM concentrations and human health risks, and understanding the impacts of potential mitigation efforts. In this dissertation, I address these globally significant environmental issues through three studies designed to highlight biases in global ESM vegetation distributions, investigate terrestrial carbon cycle feedbacks from solar radiation management (SRM) climate change mitigation, and explore impacts of future regional wildfire emissions on ozone (O3) and fine (≤2.5 micrometers) particulate matter (PM2.5) due to unmitigated climate change.In the first study, I analyzed CO2 mole fraction-driven simulations of ESMs from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and found that ESMs exhibited large biases in forest distribution, fraction, and biomass in leaves, wood, and roots. These biases induced an uncertainty of −20 Pg C to 135 Pg C in forest total biomass estimates over northern extratropical regions in ESMs, influencing estimates of carbon cycle feedbacks, fuel loads and distributions, and, thus, wildfire risk. In the second study, I found terrestrial ecosystems became a stronger carbon sink, adding 79 Pg C stored on land, under a SRM strategy designed to maintain global surface temperature at 2020 levels for the remainder of the twenty-first century. While fuel loads were increased, wildfire risks were reduced by mitigating increases in global temperature. In the third study, I found, by employing global climate and chemistry-transport model output to force the Community Multiscale Air Quality model, increased fire intensity between contemporary (2003–2010) and future years (2050–2059) had little effect on atmospheric O3 concentrations in the Western United States, but projected PM2.5 concentrations induced by fire could be as much as 21 times higher in future years in this region.