Baudrillard in 'Simulations' talks about three successive phases of simulations. First the map describes the real. Then the map overlays the real until it is impossible to tell the difference. Finally the map destroys the real so there is a copy with no original.

So 'material existence' is destroyed leaving a socially constructed copy. There are more teddy bears than there are real bears in the wild.

For the individual, it is impossible to tell the difference between real 'material existence' and social beliefs.

This is the way knowledge works in a postmodern age. It is impossible to know what is real and what is simulation.

For climate change, how do you know the planet is getting warmer? You trust scientists who create socially constructed maps of the weather. These maps can't predict more than a few weeks out. How can they predict 50 or 100 years out? Maybe scientists are overlaying a map of the climate that is destroying the original data, and replacing it with their own social constructions. In postmodernism we just can't know.