Why was it warmer during the Viking era? Was it CO2 from burning villages?
In any case, what are they saying to the Chinese, who are filling the air with dirty coal smoke? Nada, nada, nada. Fact is that in 1930, the air in New York and other east coast cities was full of soot. That was because they heated with coal. By 1970, after switching to heating oil, they had clean air.