Climate Denial funding is untraceable. WHY use Black Money if you have a solid case?

http://ringoffireradio.com/2015/01/money-funding-climate-change-denial-efforts-is-basically-untraceable/

A study from Drexel University shows that much of the money funding the effort to deny climate change is coming from conservative foundations funded with “dark money,” meaning it comes from concealed donors, Scientific American reported.
The study, the first to examine the “organizational underpinnings and funding behind the climate denial movement,” found that money coming from these foundations whose funding cannot be traced has “risen dramatically over the past five years.”
And while the amount of “dark money” continues to grow, the traceable cash sources, like donations from Koch Industries, have all but dried up.