GreenHouse Gases Project

With Ethan finishing off his 2 week school project on Greenhouse gases. Mother Earth will expel those responsible for her suffering... Mankind mainly. Ethan and I have had a long I depth conversation on whether or not the greenhouse gases die? We know the layer grows because mankind is adding to it, but once we stop adding to it - will it start to decrease? If it does, will that mean that earth will survive? (Mankind having gone long ago). If she did, all replenished and revitalised...her thoughts would be....
"remind me not to evolutionise the ape again!"