Flexi Says: Organic carbon contained in soils of the Arctic permafrost comes from biomass--the remains of plants, animals, and microbes. This biomass has built up in the frozen soil over hundreds to thousands of years because organic matter decays very slowly in the cold conditions. Arctic permafrost holds 1.5-1.6 trillion metric tons of carbon, which is almost twice as much carbon as is currently in the atmosphere. Now that the permafrost is melting, this biomass is decaying more rapidly and releasing carbon in the form of carbon dioxide (CO2) and methane (CH4) into the atmosphere. This creates a positive feedback that adds more greenhouse gases to the atmosphere as the Arctic warms.