We really should call a spade a spade. A post fact world is one of lies, spin, hype and ignorance as bliss. While science isn't perfect (it's done by finite and fallen humans), it does reveal things about the world. The relentless pursuit of the Socratic method in a systematic way yield results about cause and effect in the real world.
I think post modernism has something to answer for in eroding ideas of truth, but plain Machiavellian political cynicism, conservatism and fear of change seem to dominate politics in the West. This means climate change is given the poor treatment we see in the US and Australia. It is an 'inconvenient truth' for Donald Trump, a pragmatic, business minded demagogue.
When we understand something to be true, anything as Paul understands in Philippians (see my blog on Philippians 4:8 here), we need to weigh up how important it is. It is true that the capital of England is London, but most of the time that isn't all that important to me. That God exists or that human beings are warming the climate are far more pressing, worldview informing truths than mere facts.
The church are meant to be truth seekers, truth speakers - not giving false testimony. It is nice to see that the US political system hasn't given up on that yet, with California Governor Jerry Brown recently saying to climate scientists:
“It’ll be up to you as truth-tellers, truth seekers to mobilize all your efforts to fight back,” the governor said. “This is not a battle of one day or one election. This is a long-term slog into the future and you are there, the foot soldiers of change and understanding and scientific collaboration.”
Christians are also committed to the future. Given the hope for global transformation then, our work now is to try and transform our politics, science, economy and ecology as we wait for that future. Don't give up on truth.