Phosphorus is the 11th most common element in the earth's crust. Let that sink in for a while. It running out makes about as much sense as the humanity running out of hydrogen. Deposits economically extractable at present market prices will run out within a few decades. This doesn't mean we run out of phosphorus, it just means that the market price will rise until other extraction methods provide enough supply. It will not have to rise far, given just how common the element is.
> Now we are running out of ... energy
We are not running out of energy. Nuclear and solar each provides the capability to run for effectively forever -- fracking provides the short-term supply to build them out.
The idea of resource depletion is completely anachronistic. Today, we can produce or substitute absolutely everything we need, given input of common elements and energy. And we have sources of energy that do not depend on scarce resources. The time when the economy was based on extraction of limited resources has passed.
Like I said, we are reached peak phosphorous as we mine it currently, and reaching peak energy as we currently use mostly fossil fuels.
And like I said, I believe we can use new technologies (like, solar power... or underwater phosphorous mining) to fix it.
There's a book that was written back in the early 90s called The Ultimate Resource, by Julian Simon. A fair amount of it is typical libertarian wishful thinking, but he very strongly makes the point that in a free society, there is no such thing as a peak. There are always alternatives, and if a resource becomes more expensive, we will start switching to them. If need be, we will also change our behavior to accommodate these alternatives.
To take a great example, look at gasoline prices. There is no shortage of gasoline in the United States. The price goes up, and suddenly fuel efficiency becomes much more important. As a result, economy cars are much more common, as are hybrids and electric cars. Consumption then goes down.
This would be the case even if gasoline were ten dollars or even twenty dollars a gallon. People would simply take the alternative options, which become more and more attractive as the "default" becomes more expensive.
In the US, formerly marginalized groups like Catholics (Irish/Italian/polish) and eastern european Jewish immigrant came to wield considerable power in the mid 20th century, owing largely to burgeoning numbers. The Catholics actively organized colleges, universities and fraternal organizations that brought young Catholics into the civil service ranks.
Huh? Care to explain how did Mexico come into the picture when talking about Al-Qaeda?
These folks are very much in the fringe, and I shouldn't have mentioned it,
First, regarding absolute human numbers, we do have too much, mostly because we are rapidly using up fossil resources (not only fuel, but also fertilizers), and some important ones already peaked (phosphorous for example).
But I don't believe that making your population decline fixes things, it only create other problems, the solution for the problem that I mentioned last, is develop more technology.
Malthus was right on his diagnostic, wrong in the solution (please, stop blabbering that Malthus is some stupid dude that is wrong, even on school I heard that, more than once, by several different teachers in several different grades), Malthus was absolutely correct in his calculations, he only did not accounted for the mining of phosphorous (that is one of the major enablers of green revolution).
Now we are running out of phosphorous and energy, and our food will return to levels Malthus calculated, unless we figure new tech, I hope someone does so soon.
Now regarding declining fertility levels... This is a problem too.
In history, there are several accounts of prosperous civilizations that had declining fertility, and all of them collapsed (usually when fertility reached around 1.3 per women). Several of the current western world problems are related to that, the need of external wars to keep some income flow (alright, no major powers are at war... between themselves, but how much wars US, France, etc... are involved with other smaller countries and forces? Even Brazil that is not developed is currently participating in a occupation force in Haiti and in civil war, although the media refuse to count the latter), debt problems, specially coming from welfare programs and wars, economies that are following their population numbers (thus we have Japan for example with economy declining with the same speed that their population is), and a increase in far right and far left party powers (example: brazillian military dictatorship apologists never been stronger, Greek far-right went from having no votes in parliament to 7%, and a estimated 35% in next election, Japan also has a new far-right nationalist party that got some respectable votes, the rise of Tea Party in US and Democrats steering leftward...)
And some groups, know of all this, and have a plan to take over when they can... The most famous one being Al Quaeda (that is the Arab translation of the name of Isaac Asimov books The Foundation, and it was known that Bin Laden was fan of the series). Al Quaeda is clearly aiming to teach their followers to keep a high fertility rate, so that they can conquer developed nations when they collapse under their own bureaucracy and population decline.
All those advocating that to fix the first problem I mentioned (peek resources), don't realize that by doing that, other nations still have population increasing, some of them will collapse because of it and cause further problems for everyone (and most likely will ignore the attempts of developed nations to stop their own population decline), and other nations are increasing in population on purpose, knowing well of its military effects, and will use it against any fool that voluntarily decline his population and ends struggling to keep itself up.