The oxygen level would rapidly increase above the upper explosive level, and the carbon dioxide would rapidly be depleted. Once the O2 level were high enough, just about anything could set off an explosion - lightning, most likely, and the fireball would be fed and fueled by all oxygen (unless the atmosphere was saturated, then the explosion wouldn't be able to happen) ... and the entire surface of the planet would be purged by explosive fire.
We would become vegetarians. :P
mark as best plzz..