The tree ring record shows this climate change happening long before humans had enough technological throw weight to influence what was going on. In fact, there is no reason to doubt that climates changed before there were any human beings whatsoever, or even their small mammal ancestors.
So, friends, the real question is whether or not we humans are contributing to climate change. You can argue that we probably do. You can also argue that since it can demonstrably happen without our assistance, it's likely that we aren't contributing to the change. The point is that there is really no way to know. No experiment can be undertaken to determine the cause(s) for climate change.
The scientific principle of Occam's Razor suggests that we adopt the most simple answer to a scientific question that covers the known facts. The most simple answer to the question of climate change is that, if climate is changing, it is changing for the same reasons it has always changed, whatever those reasons may be.
