My least favourite shonky climate panacea is probably the populationist idea. Not because it's intrinsically more dangerous or less do-able than nuclear power or "clean coal" carbon sequestration. Simply because in my experience it appeals to so many people with a smug, dogmatic sense of superiority, and is more common among racists than genuine environmentalists (The group pictured, Sustainable Population Australia, do not promote racism as far as I can tell, but other "green" populationists are not so discerning).
This is not to deny there is a real debate on population growth to be had, with people who don't present population policy as a simplistic panacea. But for me, the population issue is about human rights - like access to contraception and family planning and aged care - not statistical artifices like "carrying capacity" and per-capita national averages of consumption.
And of course, we have precious little time to turn around dangerous climate change. If we wanted to do that using population control measures, the only means that might achieve it in the short time available would make the Third Reich look saintly. There is plenty written elsewhere to debunk populationist arguments, such as a good series at Climate and Capitalism. For further illustration I am providing these pictures of Sustainable Population Australia putting forward insultingly simplistic "solutions" with their hobby horse of curbing population growth.