Dropped 46%, and yet recent studies in South America have revealed that most of the “Rain Forest” there post-dates the various MesoAmerican cultures i.e. a lot of Central and South America was deforested by the MayIncAztecs and *grew back*.
So right there I have to doubt their numbers. They’re probably also counting the desertification of the Sahara which roughly correlates to the appearance of protohominids, which they have “deemed” the start of “human” civilization.
They compared it to satellite photos from 1000bce.