It's both. Despite nightwork4's idea that "we are killing our planet," when Mt. Saint Helens erupted years ago, more co2 was released than in the entire history of fossil fuel consumption. . . .so nature is a far more powerful source of the warming than we are.
I'm not saying at all here that we shouldn't be more responsible, we should be more responsible. The nightwork4 perspective is false, and based in a guilt that you and I should not have.
"We" are not killing our planet, corporations are, and mother nature is a destructive force herself.