In An Inconvenient Truth, all of the following are at fault for releasing too much greenhouse gas except trees.
In fact, the existence of trees in our planet help reduce the amount of greenhouse gases in the environment since they absorb it as an ingredient for their photosynthetic process and produce clean oxygen as well as h2o as the final result of the whole process.
On the other hand, industries, technology and modern lifetyle are the current culptit for the release of an increasing amount of greenhouse gas.