"No, we could have a stable outcome in which all countries converge on consumption rates considerably below the current highest levels. Americans might object: there is no way we would sacrifice our living standards for the benefit of people in the rest of the world. Nevertheless, whether we get there willingly or not, we shall soon have lower consumption rates, because our present rates are unsustainable.
Real sacrifice wouldn’t be required, however, because living standards are not tightly coupled to consumption rates. Much American consumption is wasteful and contributes little or nothing to quality of life. For example, per capita oil consumption in Western Europe is about half of ours, yet Western Europe’s standard of living is higher by any reasonable criterion, including life expectancy, health, infant mortality, access to medical care, financial security after retirement, vacation time, quality of public schools and support for the arts. Ask yourself whether Americans’ wasteful use of gasoline contributes positively to any of those measures."I gues another point that critics/optimists bring up is that Earth is able to support up t0 9 billion people. That is true but the problem is that the population in question is not 9 billion but 73 billion when measured in current consumption standards. Again from Jared Diamond,
If India as well as China were to catch up, world consumption rates would triple. If the whole developing world were suddenly to catch up, world rates would increase elevenfold. It would be as if the world population ballooned to 72 billion people (retaining present consumption rates).