European colonization of Americas cooled Earth's climate (2019)

I remember far-right accounts using this story to troll on Twitter by stating that colonization was good for the environment and combatting climate change.

The spread of disease is an interesting subject. Would the same mass casualties have arisen without European colonization, if and when Europeans, Asians, or Africans had reached the shores of the Americas under different circumstances?

The claims of germ warfare, a field unknown of at the time, seem unwarranted, with only one or two confirmed cases of tainted blankets being given to Indigenous tribesmen in the hopes of killing them off. In the most famous case, due to it being documented, the smallpox blanket gift at Fort Pitt had no effect as the warring tribe already had smallpox and may have been the very ones who spread it to the Fort in the first place. The intention is clear but the reality negates it.