A Cynical Look On the cum hoc ergo propter hoc Logical Fallacy.

The (cum hoc ergo propter hoc) or Correlation does not imply causation fallacy essentially says that because one thing has a correlation with another, it does not automatically mean that one caused the other.

And indeed a third variable could cause the problem.

As an example, Co2's relationship to global warming does not necessarily mean that Co2 is what causes global warming. Instead, global warming may actually be a result of all the hot air spewing fourth from Al Gore's overinflated head.

In any event, a problems stems from this type of logical fallacy. At it's most base level, everything falls into this category. For example, just because you see words on your computer screen does not necessarily mean that anyone wrote them. You may actually see these words because I have hit you over the head with a large blunt object, and now you are simply delusional. Also, being hit over the head with a bat may not be what caused you to be delusional, perhaps it was that moldy sandwich you found in the back of the fridge. To continue, perhaps that sandwich was not moldy because it has been in the back of the fridge for so long, but because aliens have decided to invade peoples homes and use their mold guns on random articles of food.

Starting to see a problem? This can continue on forever.

In reality, man kind can only ASSUME that any one thing causes another through enough correlative data. Any kind of statement that any one thing causes another is in fact a logical fallacy. If humanity wants to have any kind of understanding of the world, it is going to have to accept that enough correlation should at least point towards causation.