Exactly Diuretic, there's not proof. So we should all assume that global warming is caused by humans, even if there's no proof? If was AGW alarmist that brought this about in the first place with absolutely no proof to back up their theory. They have bits of information that are still disputed by many...
The earth has heated and cooled many times before, without human help or interference. That is science and is fact...Due to this fact that the earth has heated and cooled many times before (at different rates), PROVES that this current heating trend may not be caused by humans. Until science can prove what caused heated and how fast things heated prior to human history and recorded science, then they have a hard battle in front of them.