There is no exact answer to this question. Unfortunately, our way of living encourages consumption.yet certain resources on Earth are being exhausted at a much faster rate than they can be created. The worst part is, China and India are following a similar path and their population far exceeds the United States. Also, their practices are less regulated.
Here's the issue. The human lifespan is less than 100 years (~75+/-). Considering our eating habits and lifestyles that number should be dropping but through medical advances and technology, it has remained the same. The resources we use were created on a geologic time scale which is several orders of magnitude higher than our lives (millions of years). So in essence, the value of certain natural resources is skewed. If we were to place a realistic dollar value on oil, coal, or even water, it would be insanely high. Markets dictate prices and our global society thinks we are in trouble now....not true. Future generations will be much worse off if we maintain our current route. I wish any hardworking individual success and happiness, but the American Dream is simply an INDIVIDUAL pursuit of material gain, nothing more. Happiness can't be measured on how much stuff we have, although many believe that's the case, it is a quality of life matter. The more we have, the more resources that we need to utilize.
Many think of energy resources as today's gold, and in a sense, for society to function we require energy, but the most important resource is water. Without clean potable water, human life as we know it is over. So the real question you should be asking is, when will our growing global population reach a point of consumption that exceeds our capacity to clean and replenish water supplies?
Some resources have 50 - 100 years remaining, whereas others have a few hundred or thousand years. Availability of certain things will become increasingly low in time unless we take a second to evaluate how we are operating and what we're doing to the planet. I'm a conservative person, but whatever political background you have, the status of Earth should be somewhat of a priority.
"green" is a media term - be sustainable