The ad futurum fallacy appeals for support to future, hypothetical discoveries to overcome or negate all of the presently-available contrary evidence. In abductive reasoning (which constitutes a good deal of scientific thinking) one must use the available evidence to arrive at the best explanation of it. It is fallacious to assume that future knowledge will overturn the conclusion to which present evidence leads.
An example is: “We don’t know how the universe came into existence. We’re working on that. All I know is that appealing to a god doesn’t solve anything.”