The algae on the right side of tree trunk is a symbiotic example of mutualism due to the fact that the algae and the tree are benefiting. This is because the algae needs the tree to live, and the tree is receiving protection.
Greenhouse gases grab thermal radiation, echo some of it back down to the warm ground, and ultimately, the heat gets trapped. Thick clouds reflect the sunlight back into space, but thin clouds trap the sunlight just like greenhouse gases.
If we don't do anything about our constantly emitted greenhouse gases, we could and up like Venus, a greenhouse disaster.
I think that if we don't stop this disaster in the making, I don't even want to think about the suicides that would take place, the deaths of plants that wouldn't be able to stand the weather, and ultimately, the end.
http://www.livescience.com/common/media/video/player.php?videoRef=GoldilocksGreen