Um, no? Did you read the article? It is talking about a massive reforestation event due to the Native Americans dying off. This is the exact opposite of anthropogenic global warming.
He read the article. He's implying that we were on the way to anthropogenic global warming, and then Columbus and those who followed him inadvertently put a stop to it.
I think he's saying that the deforestation that had been happening before must therefore have been contributing to global warming, if ending it contributed to global cooling.
Reforestation implies prior deforestation. That the death of any number of people in the 1400's made the climate change is essentially the meaning of anthropogenic climate change. So yeah, kid, I read the article.
