I found
this very interesting web page that deals with the idea that houses without insulation cause more CO2 to be generated for heat, while at the same time, some very highly effective forms of insulation cause the generation of large amounts of CO2 and other global warming gasses in their manufacture. And while an inch of such insulation may cut CO2 emissions by a large amount, compared to the CO2 generated in manufacturing... More foam may not offer the advantage at the same rate.
It is to determine the best insulation, and the amount, with regards to global warming that
this spreadsheet was created.
Interesting stuff.
-AC_Hacker