also known as the Milankovich Cycle, slow climate changes resulting from changes in the tilt of the Earth's axis and shape of the orbit ("forcing" signifies a physical process that affects the Earth's climate, because the changes of the orbital shape influence the total amount of sunlight reaching the Earth).

an allotrope of oxygen with the formula O3, has damaging effects on animal respiratory systems at ground level, is a greenhouse gas in the upper troposphere, and in the upper atmosphere protects living organisms by preventing damaging ultraviolet light from reaching the Earth's surface.