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This paper examines the impact that climatic change over the last millennium has had on aggradation and degradation of permafrost peatlands and the associated change in organic matter accumulation. Permafrost reached its southernmost Holocene extent in boreal continental western Canada during the Little Ice Age with 28 800 km2 of permafrost peatland present within a sensitive zone demarcated by permafrost degradation. Subsequent degradation of permafrost has occurredin response to warming, with forested bogs changing to nonforested poor fens, associated with rising water levels. In conjunction with this ecosystem change, long-term net organic matter accumulation increases. As permafrost is in disequilibrium with climate, much of the permafrost that remains is in a relict state. Mapping of past and present permafrost distribution from peatland landforms indicates only 9% has degraded since the Little Ice Age, resulting in a 5% increase in long-term net organic matter accumulation. Of the permafrost that remains, 22% is in disequilibrium, located largely in the northern part of the sensitive zone. Additional loss of forested lands will occur inthe future in boreal continental western Canada under present-day climatic conditions as permafrost approaches equilibrium, with a further 11% increase in long-term net organic matter accumulation predicted. [ABSTRACT FROM AUTHOR]