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I believe the climate changes regularly and naturally. How much is 'man made' is what I have reservations on.
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No Climate Scientists would disagree with the first part, at all. The point however is that there are clear sources, which are fairly regular, that can be identified for such natural changes. These include, but aren't limited to: variations in Earth's orbit (characteristic time scale greater than 10,000 years); natural emissions from volcanic eruptions, and so on (which are essentially constant, or at least fluctuate around a stable average); and, at the other side, re-absorption of CO2 by plant life (again, broadly constant).
Barring any major disruptions, then, the natural cycles on which climate change occurs are relatively slow, measured over millennia at least. Compared to that, a rapid change taking place over timescales measured in decades, which happens to correlate with changes in human activity, is readily isolated as a signal from the natural background.