This one guy in the comments section of the Aftenposten news site says that you can't trust scientific consensus because there was once a scientific consensus that the Earth was flat, that the Earth was the center of the universe, and that the sun orbited the Earth.
It's a myth that the ancients believed the Earth was flat.
As for the rest: The means of observation were limited. They are not anywhere near as limited when it comes to, say, contemporary climate science.