Large Parts of Arctic No Longer Carbon Storage, Now Net Source of Emissions Climate change is transforming large parts of the Arctic region from a carbon sink to a net carbon emitter, a new study published inNatureconcludes. Up to 40 percent of the region’s tundra, boreal forests, and wetlands now release more CO2 than they absorb. Data gaps, especially in Siberia, hamper the understanding of the carbon dynamics.