Updated: 80% of world CO2 emissions are related to population levels.

[muriel_volestrangler]

5. Isn't this just 'CO2 emission has gone up a bit more than population, but a lot less than GWP'?

CO2 emission ratio 2009/1970 = 1.55/0.74 = 2.09
Population: 1.39/0.76 = 1.71
GWP: 2.23/0.58 = 3.84

0.85*1.71 + 0.15*3.84 = 2.03

But this doesn't mean "we would be much better served by attacking climate change through population reduction rather than consumption reduction". What you've showed is that each value has grown, on average, at different rates. The CO2 rate being close to the population rate is not an indication it is mainly caused by the population rate. If I found another amount that had grown about 2.1 times from 1970 to 2009, then your method would say "it's all due to this new amount, and nothing to do with either population or GWP/steel&cement".

Population reduction can only happen gradually (without actually killing people, that is). But material 'consumption' is neither Gross World Product, nor steel/cement consumption. What the difference in growth of GWP/steel & cement use and CO2 emissions shows is that we have managed to produce less CO2 per GWP than we used to. We have become more efficient - through more efficient vehicles or generators, use of renewable energy, use of gas rather than coal, better insulation, more efficient electrical devices, and so on. To say "it should be about population reduction rather than consumption reduction" is to ignore the success we'd had so far, and to pretend that our alternatives are only "cut the population" or "make us poorer, on average". We don't have to cut CO2 emissions by purely cutting economic activity; we can look for more efficiencies, from a CO2 producing point of view.