I tinks de description is off. If you go to Ellesmere Island, you can walk the beaches in July and pick coral, the same coral that you find in Hawaii today. In order for it to grow, you need an ambient temp of roughly 80 degrees.....which would suggest to me that its not always been cold there!
But that would imply that the world is not warmer than it has ever been. Can’t have that idea getting out.