Vulnerability of Permafrost Carbon to Climate Change: Implications for the Global Carbon Cycle

H alter the global cycle of carbon (C) by burning fossil fuels and modifying the land surface. The addition of billions of tons of C greenhouse gases to the atmosphere is changing its heat-trapping capacity, which, in turn, is changing Earth’s climate (IPCC 2007). Although much of the modern increase in the atmospheric C pool results from human activities, the future trajectory of the atmosphere also depends on the response of terrestrial and ocean systems to climate change (Friedlingstein et al. 2006). Natural fluxes of C in and out of terrestrial and ocean reservoirs are an order of magnitude larger annually than the perturbation from fossil fuels and land-use change. Accordingly, relatively small changes in ocean dissolution and biological C cycling processes, such as photosynthesis and decomposition, can have large impacts on the size of the atmospheric C pool (IPCC 2007). The responses of these processes to changes in temperature, precipitation, carbon dioxide (CO2) levels, and nitrogen (N) deposition have therefore received significant attention by the scientific community (Holland et al. 1997, Nemani et al. 2003, Davidson and Janssens 2006). Recent attention has also focused on processes and pools in the global C cycle that are less well understood than photo synthesis, decomposition, and ocean dissolution, but could