Carbon neutrality is a flawed statistic IMO and can be doctored with a lot - e.g. if Google pays a company X to plant an amount of trees, who's to say that neutralizes carbon?
Keep it simple, just publish how much power they're using and what the sources are.
I’m not sure what you mean by publish “what the power sources are.” Data centers are grid connected and are therefore connected to a lot of different generators—including coal, natural gas, wind, solar, and hydro. All generators on the grid contribute to the grid. It’s really tough to single out a generation source for a particular user.
I remember walking by a google data centre on the Columbia river years ago and being told that it was sighted there so that it could use the power from the dam.
Personally, I don’t understand carbon neutrality. How deep does this rabbit hole go? If Google only buys and uses fully electric cars for street view and use only solar and wind to power them is that good enough? Does the manufacture of the car, batteries, solar panels also have to be carbon neutral? If not, can a company become carbon neutral by simply letting another company do the dirty work?
Keep it simple, just publish how much power they're using and what the sources are.