GreyICE: Thank you for the counter arguments. Without them there wouldn't be a good discussion!
I can't believe that you did not know I was not literally talking about running out of atoms. I grant that it is technically possible given enough time, labor, energy, and know how to replace almost any resources, or material, or whatever you would prefer to call them. However it is also possible that our ability to do this is limited or problematic.
1. If we can replace the resources, but at a rate less than consumption, we still have a problem.
2. If we can replace the resources, but to do so requires excessive costs (whether in the form of labor, other resources, harmful environmental effects, etc)
Let me try stating my case a different way. Everything in the universe works based upon sets of rules. Our planet is a giant system of such rules. Fortunately for us, and everything else that is alive, this system regulates itself and mediates damage to continue conditions appropriate for life to continue to exist. However like all systems there are limits. This means there is a limit to the amount of food we can grow. There is a limit to the amount of land we can destroy or change before it set off adverse affects upon other areas of the system. There is a limit to the amount of clean drinkable water we can consume regularly. There is a limit to the amount we can pollute the system before it can no longer repair itself. We have seen the damage that we can do to smaller areas of this system and how long it can take for the system to repair itself. Therefor it is entirely feasible that continuing to increase population and resource use without mitigating this issue can have serious consequences.
The idea that we shouldn't convert to a more environmentally friendly and sustainable way of living because global warming isn't real, or it'll hurt our economy, or we aren't running out of resources seems flawed. You mention stuff like recycling, and better utilizing the suns energy, which is exactly what I suggest needs to be done so it seems we agree to some extent.
Now there is always the opinion, one that I certainly hope ends up being true, that technology will solve everything. Unfortunately when technology makes it possible for us to get more for less (like improved engine efficiency in cars to increase ave. mpg) we simply use/require more and either negate the improvement or use even more resources than we did before. I'm going off of memory from an article I read so hopefully this is all correct (or close enough) but if not please correct me. In the 70's engine efficiency was improved and the cars then had better gas mileage than today. This isn't because today's engines are worse than those of the 70's but because we keep getting bigger, heavier vehicles with more features that have ultimately reduced our mpg to less than what it was 30+ years ago.
I'm not entirely convinced we are doomed, or that technology can't solve these problem. In fact I think it will be very interesting to see what happens in the next 50 years. But as you've said we need to start planning, and there is no time like the present to figure out a long term solution.