A thick layer of the black spongy soil, the remnants of ancient forests, wraps the globe’s northern tier. Deeper than 15 feet in places, the peat layer extends over more than 6 million square miles across Russia, Scandinavia, China, Canada, and the United States.

Carbon that those forests absorbed from the air over thousands of years is stored in the peat and suspended in waterlogged bogs or permafrost. When it is disturbed or drained - as is happening in some areas - the peat can start to decompose and dry out, unleashing greenhouse gases.

Read More: http://www.boston.com/lifestyle/green/articles/2009/12/13/under_the_icy_north_lurks_a_carbon_bomb/