Climate does change...over very very long periods of time. right now it's changing over very very short periods do directly to our actions.
I think this is just the direct result of smoothing/filtering past data. There is not evidence that past climate changed slowly and steadily, on the contrary there are studies that shows that climate can change swiftly. I remember to have seen in the '90s, so before all the mainstream fuss about climate change, a study about beetles found in peat bogs, that suggested that different beetles species alternate with other beetle species (that dwell in different climates) in short spans of times, a few decades.
From my point of view, I look at all these quasi-linear climate models very suspiciously.