Earth would end. If all human beings disappeared from the Earth,
within 50 years all forms of life would flourish.”
― Biologist Jonas Salk
In the near future, many potential triggers could lead to a cataclysm. The 20th century gave us nuclear bombs and weaponized smallpox. The 21st will surely deliver a greater variety of bioweapons. The prospect of a natural killer like the influenza virus adapting to a globalized world of 7 billion people is worrisome. The machines we have built our civilization upon—computers, software, networks—contain the seeds of destruction for the simple fact that we have come to depend on them, and they are vulnerable to manipulation. We are always figuring out new ways of bringing apocalypse on our heads. Even climate, which we tend to think of as a slowly unfolding crisis, could conceivably bite us sooner than we think. Some researchers think that weather patterns such as the ones that bring monsoons to India and sustain glaciers in Antarctica could behave like dynamical systems, prone to sudden, unpredictable, and dangerous changes.
It’s possible—perhaps likely—that any of these factors, or several acting at the same time, could cause a plunge in the human population in this century or the next. United Nations estimates have the world population, now 7 billion, rising to 10 billion by the end of the century and then leveling off. When we consider such estimates, we tend to make a questionable assumption: that the human population will behave like no other—that, after rising with breakneck speed, it will assume a steady state precisely at its peak. Ecologists will tell you that that is not usually the way it goes. Yeast cells that rapidly fill up their culture dish generally die off suddenly and in great numbers.Could Humans Go Extinct? (Slate)
There's also a good interview with the author about his book on existential threats to humanity on Skeptically Speaking. I was struck by this point about how the hunter-gatherer way of finding food is so different from the utter dependency on cereal-based monocrops today:
Host: You looked at the Sanak food chain as an example.More info on food webs: http://www.foodwebs.org/
Fred Guterl: Yeah, this was some work that Jennifer Dunne at Santa Fe Institute and others were doing. Jennifer Dunne is part of a group that's studying ancient hunter-gatherer societies in the Aleutian Islands. And what she was doing, she was building a food web. She's trying to model in a computer how the hunter-gatherers of thousands of years ago fit in the food web in these islands. And what she found was really interesting. You think of humans as being on the top of the food pyramid, you know, we eat things that eat other things that eventually eat plants, right? Plants are the things, and algae are the things that take energy from the sun and convert it into chemical energy, and then they get eaten, and we're at the top. But we're actually in the middle. Humans are in the middle.
And hunter-gatherer societies, according to her data, are right smack in the middle. And that means that we are virtually unique. I think we're unique to the extent that we are omnivores, and we will eat things at the top of the food chain, the food web, and things at the bottom; we eat everything. We are just voracious. And one of the things that hunter-gatherer societies did, was that they would prey-switch; they would switch from one prey to another depending on availability.
If you were really into eating sea otters, you know, you were sneaking up on the sea otters and were hitting them over the head and roasting them over the fire, that was really great until one day, well, gee, I can't find any sea otters. So what do I do? Should I go extinct or should I find some other source of food? The answer is always, find some other source of food. So, well, there are a lot of mussels, so we'll gather some mussels and we'll eat those. Mussels are much farther down on the food chain. Or maybe we'll just eat a bunch of seaweed, you know, let's get the seaweed and we'll roast it over the fire. I don't know if this is what they really did, I'm just kind of making it up.
But this is the idea - we switch from one prey to the other depending on what's available. And this had a stabilizing effect on the ecosystem. So if there was some overpopulation, you could count on humans to go and chase these things down with their knives and forks, and when they became scarce, the humans would go chase something else.
Now, our modern agricultural system is not like this. Our modern agricultural system is, we have come to rely on a few staple crops. We've got these vast monocultures, and they're unstable. I mean, when you have billions of people being fed by a few different strains of wheat, of a few different strains of rice, you're leaving yourself very vulnerable to some kind of pathogen that would affect that species. And we're starting to see this with things like wheat rust. there's a really nasty strain of wheat rust that has been resistant to all treatment that's spreading eastward through Uganda and has been for a number of years. And when it gets to India, it could be very bad. It could cause a lot of pain.
When you're talking about a hunter-gatherer society in the Aleutian Islands, you have a little, self-contained ecosystem. Then when you extend it to the entire globe and you have this mass agricultural system. And then you have a huge impact of humans on habitat. And then you have the fact that we fish species to nearly extinction, say, I'm thinking maybe of the bluefin tuna. I haven't checked the prices recently but they were rising and rising and rising as the fish are getting scarcer. And biologists are worried that the bluefin tuna will be threatened with extinction.
So we're not prey switching here. We're not saying, 'oh, bluefin tuna, there aren't that many of them left, let's go an eat something else.' We're saying, 'bluefin tuna, they fetch even more money, lets do whatever we can to find whatever bluefin tuna there are and deliver them to people's dinner plates!' Our agricultural incentives and our agricultural relationship with the rest of the world is really different than it was. And I think, where if you were to devise, if you were to say, well, lets have a world where there are 10 billion people, and lets devise a way to feed them, you would not devise the current agricultural system. Because the one we have now is taking us to a place that is very precarious. So the question then is, what do we do about that.
Wikipedia on Risks to civilization, humans, and planet Earth