Having procreative sex is one of the most carbon expensive things we can do.
I think the OP was talking about recreative sex. B-)
Another conclusion you can draw from this article is that everyone could live very well if we would pare down the population to 2 billion.
I have to take some research to be sure, but I think that is roughly the population with access to a shelter, clean water, sanitation, health care, internet, social security...
...
Instead, we'll probably breed right up to the edge of capacity and then die in billions when something unexpected happens.
Tragic.
Perhaps, it will be a very expected thing that will happen, I mean, if that is not already happening. The main cause of conflicts in Middle East is environmental resources, like land, water, oil.
Still, I also think they are ignoring fusion and solar.
Of course, they are ignoring fusion! :P
But... adding heat energy to the planet at the rate it's been growing since the 1600's will also result in a planet with a temperature equal to boiling water in 500 years. I'm not talking about global warming- just the amount of energy used and released that has to be radiated off into space.
(This latter part I'm just quoting because it's too insightful to be left out.)