Northern forest soils, unlike tropical forest soils, are immense storehouses of carbon. It has always been understood that a warming planet will dry the forests of most of the world. This dryness will cause the liberation, or oxidation of much of the northern forests soils carbon. This carbon has been placed there over the millennia and even 10s of millennia as root material, decaying leaf and needle litter, peat in the form of partially decomposed plant material and carbon compounds incorporated into the soil through the many reactions and interactions of microorganisms. Northern forest of the world in fact store almost twice as much carbon as tropical forests. And the big threat is that northern climates are affected by the polar amplification effect. Significant climate change is already happening in the north. Climate models in the past have miscalculated the possible carbon response from northern forest soils as the world warms and dries. The authors say that their results suggest that there is an increased risk of a positive feedback to climate change related to the soil carbon cycle.
Temperature sensitivity of soil carbon fractions in boreal forest soil,” by Kristiina Karhu, Hannu Fritze, Kai Hämäläinen, Pekka Vanhala, Högne Jungner, Markku Oinonen, Eloni Sonninen, Mikko Tuomi, Peter Spetz, Veikko Kitunen, and Jari Liski, Ecology 91(2), February 2010.