| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2014 Arctic tundra and boreal forest have accumulated a vast pool of organic carbon, twice as large as the atmospheric carbon pool and three times as large as the carbon contained by all living things. As the permafrost region warms, more of this carbon will be exposed to decomposition, combustion, and hydrologic export. This permafrost carbon feedback has been described as the largest terrestrial feedback to climate change as well as one of the most likely to occur; however, estimates of its strength vary by a factor of thirty. Models predict that some portion of this release will be offset by increased arctic and boreal biomass, but the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets with serious societal and environmental consequences. In this dissertation I investigate the potential and actual response of Arctic and boreal carbon balance to climate change. First, I present estimates from 98 permafrost-region experts of the response of circumarctic biomass, wildfire, and hydrologic carbon flux to warming over the next several centuries. Because precise estimates of the factors driving arctic and boreal carbon balance are unlikely in the near future, these qualitative estimates provide a holistic summary of current scientific understanding and provide a framework for assessing uncertainty and risk. Assessments indicate that little agreement exists on the magnitude and even sign of change in high-latitude biomass, and that end-of-the-century organic carbon release from arctic rivers and collapsing coastlines could increase three-fold while carbon loss via burning could increase seven-fold. Second, I test the impact of permafrost collapse (thermokarst) on carbon and nutrient release from upland tundra on the North Slope of Alaska. The biogeochemical consequences of thermokarst are not adequately conceptualized or characterized to incorporate into numerical models, though thermokarst ...
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