So... what does it mean?
It's actually quite simple:
Global warming has happened before without human influence, both before 'civilization' (end of the ice ages) and during (the new data). This means that there exists a reason (or several reasons) for this to occur that isn't human-related.
It does not mean that human activity cannot cause global warming.
It does mean that if we believe we currently observe signs of global warming, there's at least one more still unknown cause for it. It may be irrelevant today or it may be entirely false if the both the signs of past global warming as well as the current signs are false positives and the global climate didn't change - not then, not now.
Some say that it doesn't hurt to be on the safe side and that we shouldn't take any risks when it comes to the global climate. That's all fine and good and if these people chose to live like that, fine. It's their life and they can live it how they chose.
The problems come when they turn it into a religion (more like a cult) and enforce their beliefs on others, especially policy-makers. This is wrong on several levels, both the cult aspects (brainwashing, name calling, peer pressure etc.) and the fact that policy is based on more or less guesswork. Add to that, the 'fixes' include massive expenditures, a significant drop in the options for transport and energy, and our way of life. And it's still based on guesswork. It's actually a lot like the Holy Inquisition: Convert and pay taxes to The Church - or else!
Yes, it is possible that humans cause global warming. We're just far from being able to justify that, let alone prove it. Even proof of the fact that global warming is happening doesn't change anything because we simply don't know why. There is a unknown cause out there, and as long as we don't know what and understand its part in the big picture, we cannot say that "humans caused everything". The unknown cause may explain everything on it's own, be partially to blame or have no influence at all today. We just don't know.