If southern hemisphere seasons are less severe than northern hemisphere seasons, do you think it's always been that way during the past 200 million years? Why or why not?

No, it has not been so.

Explanation:

This is because, before we have present day continents, many years ago, they was a big Large supercontinent called Pangaea consisting of modern day continents as North America, Europe and Asia. The climate conditions was not so before, it was after the splitting of the supercontinent that this change in climate happened.

they use tree rings to figure out weather patters.