The simulated CH<sub>4</sub> flux

<p><strong>Figure 4.</strong> The simulated CH<sub>4</sub> flux. (a) The monthly CH<sub>4</sub> fluxes from 1961 to 2080. (b) The change of the CH<sub>4</sub> flux between the recent and the future periods. Values are for the wetland fraction of the study area only.</p> <p><strong>Abstract</strong></p> <p>One major challenge to the improvement of regional climate scenarios for the northern high latitudes is to understand land surface feedbacks associated with vegetation shifts and ecosystem biogeochemical cycling. We employed a customized, Arctic version of the individual-based dynamic vegetation model LPJ-GUESS to simulate the dynamics of upland and wetland ecosystems under a regional climate model–downscaled future climate projection for the Arctic and Subarctic. The simulated vegetation distribution (1961–1990) agreed well with a composite map of actual arctic vegetation. In the future (2051–2080), a poleward advance of the forest–tundra boundary, an expansion of tall shrub tundra, and a dominance shift from deciduous to evergreen boreal conifer forest over northern Eurasia were simulated. Ecosystems continued to sink carbon for the next few decades, although the size of these sinks diminished by the late 21st century. Hot spots of increased CH<sub>4</sub> emission were identified in the peatlands near Hudson Bay and western Siberia. In terms of their net impact on regional climate forcing, positive feedbacks associated with the negative effects of tree-line, shrub cover and forest phenology changes on snow-season albedo, as well as the larger sources of CH<sub>4</sub>, may potentially dominate over negative feedbacks due to increased carbon sequestration and increased latent heat flux.</p>