Thawing permafrost is affecting climate, but it's unclear by how much

Boreal forests and Arctic tundra are underlain by millions of square kilometers of permafrost, and scientists are still unsure of how the thawing of this long-frozen soil will affect the climate. Soils and vegetation in the region have historically held large stocks of carbon and nitrogen, both of which are components of greenhouse gases. As the ground thaws, an as-yet-undetermined portion of these elements will return to the atmosphere as greenhouse gases.