The carbon cycle is the means by which carbon is moved between the world’s soils, oceans, atmosphere, and living organisms. Northern tundra ecosystems play a key role in the carbon cycle because the cold, moist, and frozen soils trap rotting organic material in the soils. This very slowly decaying organic material has caused carbon to build up in the Arctic during the past thousands of years. Now warming in the Arctic is slowly causing the tundra to become warmer and dryer. As a result, the trapped carbon leaves the soil as carbon dioxide and goes into the atmosphere.