Just saw this and thought I'd share it.
Under-15 population declines for 31st straight year
Kyodo
The number of kids under 15 in Japan dropped for the 31st straight year, standing at a record-low 16.6 million as of April 1, down 120,000 from a year earlier, the government said Friday.
The ratio of children in the age group to the overall population fell for the 38th straight year, falling to a record-low 13 percent, the Internal Affairs and Communications Ministry said.
By dividing the children into three-year age brackets, those aged between 12 and 14 were the largest group, at 3.5 million, while the youngest group newborns to 2-year-olds was the smallest, at 3.1 million, the ministry said.
The Ministry of Health, Labor and Welfare's estimate showed earlier that the number of newborns in 2011 came to a record-low 1,057,000, indicating the downtrend in the birthrate is accelerating...
http://www.japantimes.co.jp/text/nn20120504x3.html
I don't understand your point about a waste-heat problem. Yes, there would be a heat stream going into the the environment. But as I'm interpreting the hypothetical we have a free clean unlimited source of energy that is producing it. That means the energy budget for sequestering carbon is irrelevant if the reversal of the greenhouse effect exceeds the thermal output of the energy source required to achieve it. I'm reasonably certain that if the efficiency numbers of Mr. Fusion are at least as good as conventional thermal generation we would easily meet that condition.