[jddj]

Is the answer to this question likely to be all that meaningful?

Let's say it's 100. Unless you're confident that the lists would be identical then would we really have learned anything?

[DuskStar]

I think that if there's significant overlap - or if the top 100 companies by economic output produce a large fraction of total CO2 (say, more than 1/3) then it's just a measure of centralization, not of blame.