Agreed, it doesn't mean those things. But I think that when we say we'll be "screwed" it doesn't necessarily mean the earth will be fundamentally different after the screwing is completed. The dinosaurs got screwed, and so did the Neanderthals, and in the end all that did was make room for us, the latest species about whom the Earth cares not at all.
That humans will impact the planet is a certainty. Like all species, it's constantly "screwing" the environment. The missing link is that, in turn, the environment "screws back". This exogenous will force humans into adaptation - only failing that comes the extinction scenario.
So it's not like we have a choice. Unless the entire species subscribes to nihilism (which I doubt it's at our core, or we wouldn't be here today), we have to adapt.
