1. The entire world could live in the state of Texas at the density of current cities.
One hundred years ago, men offered similar advice regarding the supply of hay to feed horses (and the resulting waste-product, poop). We won't ever "run out" of anything -- prices will simply rise as less of any resource is available. Higher prices for horse-feed leads to better ways to travel (without horse feed). The world was "full" if measured one hundred years ago in exactly the same way. There was a finite amount of grass for horses.
Today is no different except that we now use different fuel sources. Did we "run out" of grass for horses? No? How is that possible? The growth in grass consumption and horse ownership was completely unsustainable. But here we are, today, still thriving.
It's not a logical way to look at the problem. If you are running out of garden-onions each summer; what is the solution? There are many. Plant more. Plants that grow closer together. Use garlic instead. But fuel on earth, be it grass or crude oil, is no more limited than what your garden can produce.
Even if we run out of oil tomorrow, we can create more, using plant oils. It will just cost more. And if that isn't enough, we can use bacterial fermentation to create fuel. It's only a matter of cost. Even if that becomes impossible, we can always use solar, wind, water, and nuclear power. They'll just cost more. That's all. And if they cost too much, we simply return to living in dirt-floored huts and using animal dung-fires to cook our meals. Nothing is ever used up. Matter is only converted to energy and vice versa.
2. Technology was not "adapting at the pace required to solve it" when we were running out of horse food either. That's the thing -- no one can see the future of innovation. We can't see the next generation of transport any more than a guy living in 1868 could see modern automobiles in the future of mankind.
It's ridiculous to claim that one can see the future. It's silly to demand changes from others based on naked speculation--especially if those changes are occurring at a pace that suits most people already. If it were not suitable, people would choose other forms of transportation even though their cost is higher. Most people today value a working car and are reasonably sure that climate change will not be as harmful as alarmists are apt to believe.
3. I can't see the future better than anyone else. And that's why I am not advocating changes for other people based on my vision of the future. I think we are all fairly blind to what the distant future will look like, but we can all predict the future of our own lives much better than anyone else--which is why it is foolish, IMO, to imply otherwise. It is foolish to imply that you know what other people should be doing unless you are a god.
If "we have the solutions, and we know what to do," why does anyone imagine that we will not do these things and implement these solutions as the prices of old habits rise? Do you imagine that the world will simply come to a screeching halt if we do not follow the directives of people who claim to "see the future," and can make these miraculous calculations regarding the earth's capacity for human life? Claiming that the earth is "full" is so laughably meaningless that I cannot fathom why anyone would be naive enough to believe it.
If you and another person are on a deserted island, and agree that one half is yours and the other half is his; does it mean that the island is "full" if he begins chopping down trees to build a home? After all, the previous rate of tree-felling was 0% per year. Now it is rising at such an unsustainable rate that if one compares the rate of tree destruction to new tree-growth, the conclusion at which one must arrive is that all tree-cutting must be halted, lest all of the trees be destroyed in the future.
Clearly, this is not how the real world works. This is how the world works to idiots that are apt to aggregate numbers out of context, imagine that they know everything about tree harvesting, home building, and the motives, desires, and future plans for both people on the island, and erroneously conclude that the man on one side will not stop cutting trees until every one of them is dead.
The reality is that he has calculated how many to cut, how many to plant, and how many to use for his own house on his own side of the island. It has nothing to do with your side, and it is not any more reasonable to see his tree-cutting rate and assume you know what the inevitable result will be than it is reasonable to claim that you know that the earth is "full" or that at the current rate of natural resource usage we are headed for disaster.
It's just completely bonkers, irrational, and induces an unnecessary fear of the future in the general public. And it does so by assuming that everyone with a piece of land will simply rape it to death and leave it a desert wasteland, and it assumes that all financial wealth comes at the direct expense of natural resources. It does not.
If you write a digitally distributed book on your computer, where did that piece of financial wealth (the book) come from? Which natural resources did it destroy in order to create that book? If everyone on earth writes a book, would the resulting plethora of book-wealth be an indicator of "unsustainable" financial growth? If you create a poem and keep it memorized in your head, offering to sell it for a dollar to anyone who wants to hear it, did the new poem (a form of wealth) harm anyone? Were natural resources depleted in its creation?
Creating wealth is a process of intelligently organizing the world to make it a better place for human beings. It is not a destructive, careless, or unsustainable tyrant that will eat you alive in your sleep. Creating wealth is a beautiful thing, and it is extremely depressing to see so many people that are so wildly ignorant of the process that they imagine a world where no one can be happy unless the earth implodes upon itself as baby seals drown in shallow pools of industrial waste and crude oil.