In my previous post , I addressed the issue of how many people the Earth could support, just as animals. It's a lot of people, double our current population- but we don't want to live like animals. Can the earth support the lifestyle we would prefer? That's a question of resources. Again, I'll use America as a microcosm of the Earth. So what's the first resource environmental activists warn us we're running out of? Clean water is the biggie; all others pale next to that. The common numbers quoted is that the US consumes some 408 billion gallons a day. That's a big, scary number... surely that couldn't be sustained, could it? No, it couldn't- if it were true.
We don't consume 408 billion gallons, we merely use it. What do I mean? Look at your daily life... it takes a lot of water just to wash- yourself, your clothes, your dishes. But you didn't consume that water; you just borrowed it for a few minutes, then opened the drain and put it right back into the environment. (hopefully after being treated first) Water is endlessly recyclable. Yesterday's bath water is returned to the environment and comes back as tomorrow's bath water- that 408 billion gallons isn't a consumption rate, it's the flow rate of a cycle.
But surely we keep some of it, even if only temporarily, right? Sequestered away from the environment? Certainly. In your life, you've ingested thousands of gallons of water in food and drink- depending upon your age, perhaps a hundred thousand pounds of water... how much have you kept? Your body mass, of course. At an average of 150 lbs., that's some 18 gallons. That's all- the rest was returned to the environment, as water vapor in your breath and sweat, and flushed down the toilet. That, plus what you keep in your pipes and water heater (assuming you don't have a flow-through heater), is all you're keeping out of the environment.
And even that ratio is high compared to manufacturing, because the human body is actually composed of water plus some trace elements. All told, it took hundreds of thousand of pounds of water to manufacture your car- virtually all of which was used and returned to the environment, again hopefully after treatment. (We spend tens of millions of dollars enforcing compliance with the Clean Water Act- didn't it ever occur to the government that there's an easier way to ensure compliance? Simply require that their intake pipes be downstream of the output- they'd make damn sure the output was clean then, wouldn't they? But I digress.) But after all that water usage manufacturing that car, how much was kept? The ten pounds or so in the radiator. That's all. We don't dam up the flow of rain on the plains which mainly runs to rivers which runs to oceans who evaporate and rain on the plains... we just divert a small portion of it in a different direction along the way.
So how big is that flow? The Mississippi river discharges an average 12,740 metric tons of fresh water into the ocean per second. The St Lawrence only slightly less. And there are a lot of rivers. Plus underground rivers. Plus billions of tons as clouds and atmospheric water vapor. Many times what we're currently using. I've been speaking so far of just North America; how much water is available for world use? What is easily useable is groundwater and fresh surface water- lakes and rivers. According to Wikipedia , there is 13,000,000 km³ of groundwater and 250,000 km³ of freshwater; a cubic kilometer is one billion metric tons of water.
What's that you say? Despite all my claims, there are genuine shortages out west, aquifer levels dropping, cities and states suing each other over water rights- what do I have to say about that? It's all true- but it doesn't mean the needed water doesn't exist; it merely means that it's not where they need it. You know, the Romans faced that problem a couple millennia ago, and they came up with this bizarre, counterintuitive solution: move the water from where it is to where you want it. We've proven we can do it with the vast oil pipelines around the world. The only reason they don't do it out west is economics; at this moment, it's cheaper to just dig the wells deeper and sue your neighbor over the surface water within arm's reach.
So to make a long story short, (I know, too late!), how many people do I think can the Earth sustain, at our level of civilization? To start with, the land area of the earth is 148,940,000 square kilometers; let's say only a third of that is comfortably usable. As to how to live on that land, I look to Europe- they've been civilized a long time; I'll presume they're doing things in a more or less sustainable way. The have a nice energy mix; France, for example, gets 80% of their electricity from non-polluting nuclear plants. Belgium, despite being sustainable, (as I noted in The Myth of Overpopulation Part 2 , they're a net food exporter) has an excessive population density. France, being the flattest European country, is perhaps not representative of the diverse geography of the world. So let's look at Germany- they have mountains and forests with wild animals, ocean front beaches, and farms in-between. Germany has a population density of 230/km; multiplied by a third of the land area mentioned above, that's 11.4 billion people. That's without altering our lifestyle, other than actually enforcing anti-pollution laws and using existing green energy techniques. If we went vegetarian, or nearly so, did more public transportation, all the obvious things, we could double that and still have a comfortable lifestyle.
What's your estimate?