The goal of the project is to explore the dynamics of high latitude carbon balance to (1) understand the processes driving the decay of permafrost carbon; (2) quantify tipping point uncertainties; (3) partition between CO2 and CH4 fluxes; and (4) estimate changes in atmospheric CO2 and CH4 concentration. The project has two parts: a model evaluation in the 20th century driven by the NCEP reanalysis and multiple 21st century projections driven by selected Intergovernmental Panel on Climate Change scenarios. The 20th century evaluation will compare model results against observations to ensure reasonably reproduction of current conditions. An analysis of the ensemble of 21st century projections will quantify mean values and uncertainty in the tipping point, partitioning between CO2 and CH4, and atmospheric CO2 and CH4 concentrations. The Simple Biosphere/Carnegie-Ames-Stanford Approach (SiBCASA) model will be used to represent the terrestrial carbon cycle, the Walter Wetland Model (WWM) to estimate CH4 emissions from wetlands, and the TM5 chemical tracer transport model to predict atmospheric concentrations of CO2 and CH4.