It's a pollutant in quantities such as emitted by human activities, always orders of magnitude more than what any terrestrial life form emits through respiration.
This GHG is emitted (alongside methane, by the way), by humans, in such quantities that it severely impacts the thermal balance of the planet, and threatens an extinction-event comparable to what only large asteroids are usually capable of.
This GHG is emitted (alongside methane, by the way), by humans, in such quantities that it severely impacts the thermal balance of the planet, and threatens an extinction-event comparable to what only large asteroids are usually capable of.