Current knowledge and uncertainties associated with the Arctic greenhouse gas budget

• The Arctic is continuing to warm faster than any other region on Earth, but key uncertainties remain in our knowledge of the Arctic carbon cycle. • We review the most current knowledge pertaining to estimates of arctic greenhouse gas components and discuss uncertainties associated with these measurements and models. • While the Arctic Ocean is consistently estimated as a carbon sink, we have yet to reach an agreement on either the magnitude or the sign of the arctic terrestrial carbon budget. • Much of the uncertainty in the arctic carbon budget is related to the extent of the amount of carbon released as permafrost thaws, the magnitude of shoulder season and winter ecosystem respiration, and the impact of rising temperature and atmospheric [CO2] on plant growth. • We cannot count on the Arctic to store as much carbon as it has in the past, and evidence indicates it will likely store much less.