Earth Officially Home To 7 Billion Humans

> What is the carrying capacity of Earth?

Probably depends on the quality of life people are willing to put up with.

Unless this model doesn't apply to the human population. While I'm sure it does in the general aspect, it seems likely that once the overshoot has begun, we'll be able to stave off the decline (starvation, disease, and therefore war) more effectively than other species, leading to a larger overshoot and eventually, a more drastic decline.

"If one believes that this is a reasonable model to apply to the human population on Earth,"

It almost certainly isn't. The extremely strong propensity for rich countries to have fewer-than-replacement children kills this model. Animal models have no equivalent to this.

We're headed into uncharted territory with human population. Usually this is supposed to be a sort of implicitly scary thing to say, but since the charted territory here is "guaranteed major ecological catastrophe", it's net good news. Disaster is not assured! (Of course, it's still on the table. It's always on the table.)

On the flip side, we're in thoroughly uncharted territory in terms of carrying capacity as well. On the relevant timeframes (decades, minimum), nobody can correctly predict what our technological carrying capacity will be. There's no guarantee it will continue going up, but contrary to the doommongers there's no guarantee it will stay static or go down significantly either; if in 40 years we've licked nuclear energy and cheap robots we could well be growing huge amounts of food in robot-tended greenhouses stacked into skyscrapers, powered by the nuclear energy, or growing meat in vats with chemical energy more efficiently than going through the full biological cycle. And while that may sound like sci-fi, those actually feel like conservative extrapolations of existing trends. (Just about the only prediction I won't buy is the one where we make no further progress and everything stays the same but we keep consuming resources at the same rate, but that's the one you hear most often.)

A better question should be: "What are the limits of energy production on Earth?". We are far from reaching this limit.

The difference is that with our technology and through our politics, humans can drastically effect the carrying capacity of Earth. We choose.

As another answer says, global carrying capacity depends on people's living standards. Wars normally start when there is a regression in standards. I am sympathetic to the idea that in the West this might not apply as much, i.e. regressing to 1970s living from 2011 wouldn't be a huge tragedy even if it was a loss. However, as current protests and riots in the West show, there is also a psychological element. Additionally, large portions of the world do not have that padding, and regression actually means physical pain (food shortages) rather than psychological pain. Large groups in that category are also nuclear-equipped (Russia, Pakistan, India and China) and so I guess your sine-wave of population gently dipping down from carrying capacity after briefly going over might actually be a very sharp movement downward, measured in the units of the nuclear age: megadeaths.[1]

[1]http://en.wikipedia.org/wiki/Megadeath

Humans are technological. We do not have an ecological niche as other animals do, we make our own. On the one hand we use agriculture and industry to make our own food and homes. On the other hand we choose our own behaviors based on our culture, economy, etc. That makes the idea of a simple carrying capacity meaningless. We can change our diet and the effective carrying capacity will change. Or we can change our technology, our land use, etc, etc, etc.

As far as the absolute limits, it's unlikely we're anywhere near them. If humans switched to becoming significantly more vegetarian in their diet we could support quite a lot more people with current levels of food production. Yet food production is not even remotely running up against fundamental limits at current levels.

Human societies with different development levels could be considered as different species competing for more abstract resources, such as money. Assuming the world order will remain constant for a few decades, maybe you could apply such a model.

Yet the culture of those "large family" groups will probably change if they start to dominate, putting less emphasis on large families. The societal impetus to having a large family could come from an insecurity about your cultural block (not the individual impetus mind you, which can sometimes be more important, eg. kids to take care of you in old age or extra kids to overcome infant death). That clan insecurity starts to disappear when you start to become the majority in whatever context you feel is appropriate to consider.

I'm more curious / concerned about how we'll be able to manage all the resources needed to support another billion without stripping the earth to the point that we find ourselves in a collapse because we've run out of water / food / oil / etc.

Of course, the same thing was said when the global population hit 1 billion, and so forth... thus I do agree that given we're an innovative species there is a good chance we'll survive.

I dunno if I'd definitively say it's purely distribution. Surely even with perfect distribution there's a point where scarcity becomes a factor, even assuming technological progress, unless you're talking unlimited energy and star trek replicators.

Whatever the limit is, there is a limit. Because there is a limit to the earth. Whether that limit of sustainability is 2 or 50 billion is something we haven't figured out yet but that there is a limit seems to be something you can't around.

I was expecting Gapminder to have something useful, but as cool as it is, I couldn't make anything really interesting out of the total world population. http://www.gapminder.org/world/#$majorMode=chart$is;shi=t;ly... But at least it's less "entertainment" and more straight-up data.

Luckily nobody reads articles on /. anyhow. Submissions like this are probably what led to that sort of culture on the site.

That would be a very interesting outcome. It seems rare that things that grow exponentially just level off at some point (I'm thinking of economic bubbles), or even slowly decline. I'd be happy with anything but a massive collapse.

I'm not so sure. I agree we will eventually reach a point where the global birth rate (and later population) goes down, but I don't think we're close to it yet. I suspect we'll hit 8 or 9 Billion before we start to shrink back again.

And if we continue to extend the average age, then we may never shrink in numbers (barring a major catastrophe or mass-migration).

Not in the white regions of the world.