This figure would only be interesting if it were anywhere near the cost of the internet not existing. Without the internet there would, for example, be more car trips to shops which is a less effective use of energy. I am sure there are many other examples of a net saving in energy.
So, in other words it's essentially nothing: $4.5B is about 0.3 promille of US GDP.
Or for example, just Apple alone could power a complete web US infrastructure for ~7.5 years with its current cash reserves.