Columbus arrives in 1492. The Little Ice Age begins approximately 8 years later. So, in 8 years 70 million people die and the land they previously farmed is reforested enough that it aborbs amounts of carbon which are adequately large to cool the earth and kick off the Little Ice Age.
First the alarmists try to make us believe that natural variations in gobal temperatures, like the Little Ice Age and the Medieval Warming Period either did not exist or were not truly gobal in nature. When it is shown that their methods of doing so (the Mann hockey stick and tree ring data) are rigged to arrive at the result they desire, they are now saying that, yes, the variations did exist and were global, but at least one of them (the Little Ice Age) was the result of humams causing a decrease in carbon dioxide in the atmosphere. The alarmists truly are a bunch of one trick ponies.
Actually, that estimation of 70-80 million people is for all the Americas prior to 1500. The highest estimate I've seen for just North America (at the time of Columbus coming to America) is 10-12 million [18 million at the very tops]. Some have even estimated that the Indian population in 1500 for North America to be 5 million or less.
So in that 8 years, the Europeans would had to have also been responsible for the deaths of 80-90% of Central and South Americans. Talk about total genocide in a short period of time. I think these scientists need to find a new line of work.