>We need to live in harmony with Nature. This kind of awareness (hard metrics) has to be fed back into our decision making to do it. I believe we can support current population
There does also exist other means of reaching this goal -- a lot of low hanging fruit, actually.
Public policy could do a lot more to provide incentives which reward for increasing sustainability, and punish for decreasing it.
For example, when I go camping here in the States, especially now in the summer months, I see a lot of people running generators, and sometimes this is even to run AC units.
I look at their rigs: A white roof could reduce heat. Generators and fuel adds weight to haul on the road, decreasing MPGs. Solar panels could add charge at reduced weight. It would be massively more efficient to have the solar panels that are located at solar powerstations, located on top of someone's RV, instead, but we don't do this.
The reason that does not happen is because the incentives for consumers don't line up. Fuel is cheap, and solar panels are expensive. Energy production must be subsidized with taxpayer dollars and heavy handed regulation to create solar generation facilities that then lose power as current is transmitted over the grid.
Still, the difference is close enough that a nudge from effective public policy would make a big difference. Some people do own their own panels. I own one that can charge my laptop and smart phone. It's great, actually.
The correct answer is not a system of carbon credits and tax incentives, creating more heavy handed regulation, bureaucracy, and power to government -- exactly what politicians want. The right answer is to do what America will never vote for: tax gasoline.
If gas taxes actually accounted for the externalities they produce: local pollution, global warming, noise, etc., people would think twice about investing in that solar panel. And the rest of us wouldn't have to live with the externalities.
Taxes will net you less of what you are taxing. Perhaps that doesn't sound so illuminating, but a person from another planet visiting earth would scratch their head looking at our choice to heavily tax things we always desperately want more of (employment), and to subsidize through world policy and military expenditure things we want less of (oil).
Just getting the economics of public policy right can have a big impact on our ability to live in better harmony with nature.