Volcanoes do not spew as much CO2 into the air as power plants and cars and such. They may spew a lot, but compare that to huge coal power plants and hundreds of millions of cars. They may spew a lot of other stuff, more so than humans, like ash and soot. Volcanoes also have the effect of cooling the earth down temporarily, as their ash blocks the sun, this effect was most evident after Krakatoa.
I said people who say global warming doesn't exist are uneducated about global warming, I didn't say anything about any other formal or informal education, or education in general.
As for coal consists, again there is the question of era. Today most everything coal and intermodal are unit trains, while many years ago there were carload and local trains that could have anything in them, coal included. I am sure there are exceptions to this, but unit trains seem to be the general trend in railroading. A big factor in coal is that essentially no small consumers use coal. Businesses and homes use natural gas or oil or whatnot, while the only consumers of coal need a unit train, like a steel mill or, more often, a power plant. Thus, unit trains are run, as they are quite efficient compared to carload freight, when one entity needs a lot of something at the same time.