According to this post on MetaFilter (which in turn is a comment on this article in The Economist about the rising American population and all that implies), the average American produces as much carbon emissions as 20 average Nigerians.
However, judging by the evidence contained in my e-mail inbox, one average Nigerian produces as much scam spam as 20 average Americans.
(Of course, “average people” are complete freaks of nature. As my statistics professor used to say: “The average person has one tit and one ball.”)