Tundra burning in Alaska: Linkages to climatic change and sea ice retreat

Abstract

[1] Recent climatic warming has resulted in pronounced environmental changes in the Arctic, including shrub cover expansion and sea ice shrinkage. These changes foreshadow more dramatic impacts that will occur if the warming trend continues. Among the major challenges in anticipating these impacts are "surprises" stemming from changes in system components that have remained relatively stable in the historic record. Tundra burning is potentially one such component. Here we report paleoecological evidence showing that recent tundra burning is unprecedented in the central Alaskan Arctic within the last 5000 years. Analysis of lake sediment cores reveals peak values of charcoal accumulation corresponding to the Anaktuvuk River Fire in 2007, with no evidence of other fire events throughout the past five millennia in that area. Atmospheric reanalysis suggests that the fire was favored by exceptionally warm and dry weather conditions in summer and early autumn. Boosted regression tree modeling shows that such conditions also explain 95% of the interannual variability in tundra area burned throughout Alaska over the past 60 years and that the response of tundra burning to climatic warming is nonlinear. These results contribute to an emerging body of evidence suggesting that tundra ecosystems can burn more frequently under suitable climatic and fuel conditions. The Anaktuvuk River Fire coincides with extreme sea ice retreat, and tundra area burned in Alaska is moderately correlated with sea ice extent from 1979 to 2009 (r = −0.43, p = 0.02). Recurrences of large tundra fires as a result of sea ice disappearance may represent a novel manifestation of coupled marine-terrestrial responses to climatic warming.

Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra

“…This pan-Arctic tundra vegetation greening is associated with increases in summer warmth [2,10] that are, in large-part, driven by summer sea-ice retreat along arctic coasts based on observational [13][14][15][16] and modeling studies [17][18][19]. Impacts of sea-ice decline on tundra vegetation productivity have been shown to weaken with distance from the coast in Eurasia [16] and to increase tundra-fire frequency in northern Alaska [20]. Since 80% of arctic tundra is within 100-km of the coast, the link between this coastal vegetation biome and sea ice is not unexpected [21].…”

Recent burning of boreal forests exceeds fire regime limits of the past 10,000 years

“…Such prognoses join a burgeoning list of exceptional changes in high-latitude ecosystems in response to ongoing climate warming (39). These changes include extensive permafrost thaw (40) and associated thermokarst formation (41), treeline (42) and shrub (43) expansion, increased tundra burning (44), and loss of Arctic sea ice (45). Given that fire is the dominant process controlling carbon cycling in boreal ecosystems (4) and that increased biomass burning is already linked to carbon losses in Alaska (46), the unprecedented fire regime shift suggested by our data is potentially an important driver shaping the trajectory of high-latitude ecosystem changes.…”

Vegetation shifts observed in arctic tundra 17 years after fire

“…However, in the near to intermediate future, global warming trends are likely to reduce vegetation and soil moisture levels and the resistance of tundra to wildfire (Serreze et al 2000, ACIA 2004, Hinzman et al 2005, Mcguire et al 2006. At the end of an uncommonly hot and dry summer in 2007, an anomalously large tundra fire was recorded on the North Slope in an area that had not experienced fire for at least 5000 years (Jones et al 2009, Hu et al 2010. Tundra fires have profound effects on the surface and atmospheric carbon and energy exchange, with important implications for the entire arctic system (Mack et al 2011, Rocha et al 2011a.…”

“…Although areas such as the Seward Peninsula and Noatak region of Alaska experience burning once every few years, tundra fires in western Alaska and the North Slope are generally smaller and less frequent (Hu et al 2010). However, in the near to intermediate future, global warming trends are likely to reduce vegetation and soil moisture levels and the resistance of tundra to wildfire (Serreze et al 2000, ACIA 2004, Hinzman et al 2005, Mcguire et al 2006.…”