With material prosperity less dependent upon physical materials, wealth exploded in the industrial countries and spread to most of the poorer countries.
Costs for coal are highly dependent on the cost of gasoline, and the costs for wind are highly dependent on material costs like steel and concrete as wind requires about 10 times the amount of steel, concrete and copper per kWhr than any other energy source.
This is because the degree of carbonisation of organic material as measured with electron spin resonance is dependent only upon the amount of carbon and not on the time material has been heated for.