The Arctic has experienced much greater warming than the global average in recent decades. Current climate models project that this Arctic warming trend will continue in this century. At present, more than 15% its land is underlain with permafrost and contains a large amount of vulnerable carbon. Further, the region accounts for about one half of the world’s wetlands and has large area of aquatic ecosystems including lakes and ponds, which are a major source of atmospheric methane (CH4). Permafrost degradation has been observed in the region. With thawing permafrost, in dry areas of terrestrial ecosystems under well-drained conditions, soil decomposition is dominated by aerobic reactions, leading to carbon dioxide (CO2) release, while in wet areas under poorly-drained conditions, more CH4 is produced through methanogenesis process. In addition, thawing lakes and ponds have also been observed as a major CH4 emission source. This session calls for either field investigations or modeling studies that focus on elucidating processes of and controls to carbon cycling and quantifying CO2 and CH4 emissions from land and aquatic ecosystems and their impacts on the global climate system.