What evidence would show that global warming is not man made?

Are there any evidence that could emerge right now that would show that global warming is not man made?
In other words, is it possible to falsify this theory?

I'm not being anti global warming, just pointing to a small thought exercise. What scientific data would show that it is not happening, or that humans are not responsible? What evidence or events would lead to the conclusion, that it's not real?
Obviously to show that global warming is not happening, the average temperature of earth should go down, but by how much and in what time scale, so that it would not be considered temporary. What data would show that humans are not causing it?

If there isn't anything that could possibly falsify it, then the theory is not far from being a cult like thing.