Various versions of chemtrail conspiracy theory have circulated through internet websites and talk radio programs. In some of the accounts, the chemicals are described as barium and aluminum salts, polymer fibers, thorium, or silicon carbide. In other accounts its alleged the skies are being seeded with electrical conductive materials as part of a massive electromagnetic superweapons program based around the High Frequency Active Auroral Research Program (HAARP). The reasons given by those who believe in the conspiracy vary widely as well between military weapons testing, chemical population control, or measures to mitigate global warming. Federal agencies and scientists have consistently denied these claims, insisting the sky tracks are simple contrails. As the chemtrail conspiracy theory spread, federal officials were flooded with angry calls and letters. A multi-agency response to dispel the rumors was published in a 2000 fact sheet by the Environmental Protection Agency (EPA), the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), a step many chemtrail believers interpeted as further evidence of the existence of a government cover-up.