Wasn’t HAARP a target of quite a few conspiracy theorists a few years back?
Something like mind control broadcasts or some such...
Well, it has at least been admitted to be an ionospheric heater, to the tune of millions of watts of power. So it does fit the question of this article, about what else is "heating the sky" besides the sun.
Which of course is quite enough of concern right there. But speculation about other uses abound as well.