Yes, global warming triggered by human activity is a myth. And cigarettes don't cause cancer, and the holocaust never happened...
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As for the science involved in this, I'm reminded of the argument that since most road accidents involve people who haven't been drinking, there's no point in trying to stop people driving when they've been drinking.

It's very likely true that increased temperature does cause an increase in carbon dioxide. But that just makes things even more critical. It's as certain as certain can be that increased carbon dioxide, from whatever source, does cause increased temperatures. If a consequence of the rise in temperature causing is that still more carbon dioxide is released, so leading to still greater increases in temperature, we're in even worse trouble than ever.

When you're in a hole the thing to do is stop digging - even if the hole was there before you fell into it.