The problem with trying to state something that can only be observed on a timeline longer than one lifetime as absolute fact is that you simply can't. It doesn't make sense.

Science dictates that you need some fashion of evidence, and anything measurable within a lifetime that doesn't have DRASTIC swings -- not a minute percent of a percent -- can easily be explained away by the life cycle of the planet and the sun.

If the atmosphere were, say, 30% carbon today then yeah we'd be fucked.

But that's just not the case.