Also "knowing" and actually knowing are different things.

There had been research done as far back as that which came to the conclusion that it causes climate change. But that doesn't mean that the governing body at that time was aware of the research and if so, really believed it or just thought that the researchers are massively exaggerating.

I know that the research was done on the behalf of the government, but that doesn't mean that everyone governing/deciding on these issues had access to/were aware of the results.