Is that established? I believe that there are major giant cities that operate with a lower CO2 footprint than suburban and rural areas might, per capita. But there is the cost of all the CO2 that allowed that urbanization; NYC didn't get the subway without a carbon cost, all that steel in the buildings released a lot of carbon, etc..
CO2 per capita is not the only measure of absurdity.
Because it's not absurd, the advantages of city living are too numerous to count. Your premise is flawed.