This doctoral thesis examines the controls that climate has on natural emissions of N2O and CH4 from the terrestrial biosphere to the atmosphere, and explores the feedbacks between climate and the N2O and CH4 cycles. The development of a process-oriented global biogeochemical model for soil N2O emissions (with a 2.5 degree x 2.5 degree spatial resolution) and a more empirically based global model for wetland CH4 emissions (1 degree x 1 degree resolution) are described. The models are used to quantify the natural emission changes due to climate change and the feedback of the natural emissions onto the climate system. Two extreme climatic cases are considered: that associated with doubling current CO2 levels and that during the last glacial maximum. Climate influences, seasonal variation, spatial and temporal vegetation variations and sensitivity experiments are discussed. The emission models were coupled with MIT's 2D climate and chemistry models. Results indicate that changes in natural N2O and CH4 emissions corresponding to long term climate changes are significant. Fully interactive model runs show that there is a significant positive feedback between emissions and climate.