What releases greenhouse gases?

Burning fossil fuels and cutting down trees releases carbons. Fossil fuels like coal, oil and natural gas release long held carbon when we burn them in vehicles or to make electricity. Half the weight of a tree is carbon, so when the tree rots or is destroyed (to make paper, for example), it releases all its carbon.

A significant part of the atmospheric carbon inventory is recycled due to the decomposition of organic material which converts the stored carbon in dead plant and animal material to carbon dioxide or methane.