Conspiracy theories and the Koch boys aren't needed, all one needs is soot from the industrial revolution and sunlight:
https://science.nasa.gov/scien...nasa/2013/03sep_soot
https://visibleearth.nasa.gov/view.php?id=41854
https://www.nasa.gov/centers/g...3/1223blacksoot.html
Add the fact that in the last 40 years people in North America and Europe put scrubbers on most large smokestacks, the air has become clearer and the melt will increase.