If climate change is man made, what caused previous climate shifts? I think global warming could well be a natural phenomenon. A lot of opinion in the area seems to be based on tracking the trends in world weather over the last few hundred years, or even less. However there is plenty of evidence that the planet has experienced extremes of climate in the distant past as well. This could not possibly have been caused by man. We don't fully understand what caused these previous climate changes so how can we be sure it is not for the same reason now?