Abstract. Tundra environments are experiencing elevated levels of wildfire, and the frequency is expected to keep increasing due to accelerating climate change in the Arctic. Tundra wildfires can release globally significant amounts of greenhouse gasses that influence the Earth’s radiative balance. Here we develop a novel method for estimating carbon loss and the resulting radiative forcings of gaseous and aerosol emissions from 2015 tundra wildfires in the Yukon-Kuskokwim Delta (YKD), AK. We paired burn depth measurements using two vegetative reference points that survived the fire event —Sphagnum fuscum and Dicranum spp.— with measurements of local organic matter and soil carbon properties to estimate total ecosystem organic matter and carbon loss. We used remotely-sensed data of fire severity from Landsat 8 to scale our measured losses to the entire fire-affected area, with an estimated total loss of 2.04 Tg of organic matter and 0.91 Tg of carbon, and an average loss of 3.76 kg m-2 of organic matter and 1.68 kg m-2 of carbon in the 2015 YKD wildfires. To demonstrate the impact of these fires on Earth’s radiation budget, we developed a simple but comprehensive framework to estimate the radiative forcing from Arctic wildfires. We synthesized existing research on the lifetime and radiative forcings of gaseous and aerosol emissions of CO2, N2O, CH4, O3 and its precursors, and fire aerosols. The model shows a net positive cumulative mean radiative forcing of 3.67 W m-2 using RCP 4.5 and 3.37 W m-2 using RCP 8.5 at 80 years post-fire, which was dominated by CO2 emissions. Our results highlight the climate impact of tundra wildfires, which positively reinforce climate warming and increased fire frequency through the radiative forcings of their gaseous emissions.
Abstract. Fires in the boreal forests of North America are generally stand-replacing, killing the majority of trees and initiating succession that may last over a century. Functional variation during succession can affect local surface energy budgets and, potentially, regional climate. Burn area across Alaska and Canada has increased in the last few decades and is projected to be substantially higher by the end of the 21st century because of a warmer climate with longer growing seasons. Here we simulated changes in forest composition due to altered burn area using a stochastic model of fire occurrence, historical fire data from national inventories, and succession trajectories derived from remote sensing. When coupled to an Earth system model, younger vegetation from increased burning cooled the high-latitude atmosphere, primarily in the winter and spring, with noticeable feedbacks from the ocean and sea ice. Results from multiple scenarios suggest that a doubling of burn area would cool the surface by 0.23 ± 0.09 °C across boreal North America during winter and spring months (December through May). This could provide a negative feedback to winter warming on the order of 3–5% for a doubling, and 14–23% for a quadrupling, of burn area. Maximum cooling occurs in the areas of greatest burning, and between February and April when albedo changes are largest and solar insolation is moderate. Further work is needed to integrate all the climate drivers from boreal forest fires, including aerosols and greenhouse gasses.
Abstract Deciduous tree cover is expected to increase in North American boreal forests with climate warming and wildfire occurrence. This shift in composition can generate biophysical cooling effects via increased land surface albedo. Here we use newly derived maps of continuous tree canopy and fractional deciduous cover to assess change over recent decades. We find on average a small net decrease in deciduous fraction cover from 2000 to 2015 across boreal North America, and from 1992 to 2015 across Canada, despite extensive fire disturbance that locally increased deciduous vegetation. We further find a near-neutral net biophysical change in radiative forcing across the domain due to relatively small net changes in albedo. Thus, while there have been widespread changes in forest composition over the past several decades across the domain, the net changes in composition and associated post-fire radiative forcing have not yet induced systematic negative feedbacks to climate warming.
Spruce forests have dominated Interior Alaska for millennia, generally self-replacing after wildfires.However, contemporary climate change has been linked to an increase in fire severity and frequency, promoting alternative successional trajectories and conversion to permanent deciduous forests.Because wildfire is the primary recent disturbance in interior Alaska, intensifying fire regimes have the potential to convert evergreen to deciduous-dominated landscapes.Compared to evergreen forests, deciduous forests exhibit large differences in carbon and nitrogen storage and turnover.The absence of moss cover in deciduous forests is also associated with an increase in soil temperature and deepening of the active layer compared to evergreen forests, which provide a microclimate and biochemical setting conducive to thick moss development.It is therefore critical for biosphere models to represent the biochemical and structural differences associated with boreal evergreen and deciduous forests to represent the long-term implications of climate warming and increasing fires on successional trajectories, regional carbon balance, and permafrost dynamics.In this study, we use a biosphere model developed for high latitude ecosystems to conduct a sensitivity analysis to (1) investigate the capacity of biosphere models to represent the differences in ecosystem structure and functions characterizing spruce and birch forests, (2) evaluate the differences in responses of ecosystem carbon balance and permafrost dynamics to projected climate change between these two ecosystems, and (3) evaluate the important ecological processes driving carbon and permafrost dynamics at two neighboring experimental sites representing typical black spruce dominated and birch dominated mid-successional stands.Findings will further our understanding of the impact of Arctic warming on long-term permafrost dynamics, over the next several decades. 1
GIEMS2 represents the minimum extents of northern wetlands.**GLWD provides a representation of the maximum extent of northern wetlands.***These numbers are derived from CT natural microbial emissions, which include emissions from wetlands, river/lake/pond systems, and possibly wild animals (despite the small amount).
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