ERP is not the same thing as raw wattage 'into the waveguide'. It involves antenna gain and the transmitter output can be much smaller.
Many TV stations saw huge reductions in energy use after the digital transition. With analog, you needed a really strong signal to look good. With digital, you either get a perfect picture or no picture at all. Cell transmitters can be relatively small for this reason ( compared to an analog transmission). I wouldn't worry about RF generally except to the extent that people have a transmitter (cell phone) on their person.
