Boreal and arctic regions are predicted to warm faster and more strongly than temperate latitudes. Peatlands in these regions contain large stocks of soil carbon in frozen soil and these may effect a strong positive feedback on climate change. We modelled the predicted effects of climate change and wildfire on permafrost in organic soils using a peatland-specific soil thermal model to simulate soil temperatures. We evaluated the model at a lowland black spruce site in Alaska and a sedge-dominated Canadian arctic fen. We estimated the response of soil temperatures and the active layer thickness (AcLTh) under several climate change scenarios. With surface soil temperatures increased by 4.4 °C-5.4 °C, soil temperatures at 100 cm depth increased by 3.6 °C-4.3 °C, the AcLTh increased by 12-30 cm, the zone of partially thawed soil increased, and the number of thaw days increased by 17-26 %. Wildfire caused AcLTh to increase by 26-48 % in the year following fire; AcLTh differences in 2091-2100 were significant (8 cm) at one site. By 2100, climate change effects on AcLTh were larger than wildfire effects suggesting that persistent temperature increases will have a more substantial effect on permafrost than the transient effects of disturbance. © 2013 International Mire Conservation Group and International Peat Society.