Well okay, yes, there have been some minor temperature variations in the past couple of thousand years (the Little Ice Age, the Medieval Warming Period, etc.), but on the scale of temperature shifts throughout Earth's history, those were actually very minor changes (though I would like to point out that even those very minor changes ended up having a significant impact on humanity). Which, I guess all you need is a shift of a couple of degrees or so to suggest that the Earth has natural cycles, but I think you'd be the point much more effectively by pointing out things like the Ice Age and various tropical periods throughout Earth's history.