To produce its food, a tree absorbs and locks away carbon dioxide in the wood, roots, and leaves. Carbon dioxide is a "greenhouse gas" that is understood by a consensus of world scientists to be a major cause of global warming and climate change. A forest is a carbon storage area or a "sink" that can lock up as much carbon as it produces. This locking-up process "stores" carbon as wood so it is not available in the atmosphere as a greenhouse gas.