This theory is not new.
Historian Charles Mann discusses it in his books, “1491” and “1493,” covering the Americas before and just after the arrival of Europeans.
For the record, Charles C. Mann is not an historian. He's a B.A. who writes stuff, generally at great length. A heavy-breathing, politically correct scribe who takes a lot of liberties with the truth, in my observation.
Did he explain why the Norse Greenland settlements were dying due to temperature drops 50 to 100 years befor Columbus sailed? Maybe they should blame it on the 35% drop in Europe’s population due to the Black death. With a drop in population less food was needed,less acreage cultivated,reforestation takes place.
Mann is not a historian; he writes speculative historical fiction.