How much of global warming can be blamed on humans?

Answer 1

Here we are speaking of the increase in average global temperatures since the beginning of the Industrial Age. The rise in temperatures is consistent with the rise in greenhouse gas levels, which in turn is consistent with carbon dioxide emissions from human activities. However climate scientists cautiously say that human activities are "substantially" the cause of this global warming, leaving open the possibility that a much less substantial contribution could be found from natural causes. Thus the cautious answer could be that most, if not all, the recent global warming effect is due to human activities.