Imagne twice the amount of people will just kill all other existing life. And you have a sense of that just from looking at family size in these countries. if we look at, this is Sweden as an example of a developed country. > But there's got to be a limit. dNt/dT, is equal to r max times N at that time t times K minus Nt minus tao. And, based on the models that we have today, in 2030 we should have about 345 million. So, people have tried to. high birth rate. Massachusetts Institute of Technology. New knowledge and technology raised it from the per 1820’s one billion, but new knowledge and technology can only raise it so much. How long before human numbers and activities push so many species to extinction that it begins to negatively affect the natural ecosystems we all depend upon? And this is called a density dependent response. When I first started teaching about human population growth, the projections were at 12 billion. 30 seconds . Let's replot this, because it's. We have been growing like this. Right. We cleared forests for grasslands and agriculture. up to here we are today, And, this is back in the hunter gatherer era. I believe based on our current path, we max out at 4 to 5 billion. This is also done by. We've already peaked out. And these density dependent birth rates and death rates introduce a stabilizing factor. > 1990, 250 million, and actually today, at 10:45 this morning, because I looked it up on my trusty population clock on the Web, we had 295,979, 38 people. We reached 200 million, and actually today, at 10:45 this morning, because I looked it up on, we had 295,979, 38 people. Patterns of population growthhave been studied and observed in ecology. If we don't have enough grain, we'll genetically engineer to make more grain. go chaotic for certain parameter values. just thought I would point that out. But it's just a wonderful account, analysis, if you analyze human population growth, and at the same time looking at the phenomenon in a totally objective way. And I'm not that old. So, let's just briefly, let me go back over here, and let's go back over this carrying capacity. So t or tao is the time lag between sensing environments, and, change in growth rate. And now, we're looking at the human population in the US, and this is one over N, dN/dt, and this is N in millions. 4 models. Human carrying capacity is therefore dynamic and uncertain. So the answer is one billion people. And they came up with a function that looks like this. Some of these issues have been studied by computer simulation models such as World3. Just looking at the exponential and. Great turn of phrase – ‘The fewer the people, the more destructive the elite of this world will get.’ Couldn’t agree more. As a model for population growth. And, the way we look at this, we are planning birth rates here, which is the pink one, and death rate here, which is the green one. But these models are based on something entirely much more complex now than the simple logistic equation. As a model for population growth, what's wrong with this? So far I’ve not heard it pointed out that: The rich have always known that the real value of their fortune is “how much labor will it buy?” This because almost all things humans value are merely frozen labor. So, those are bad things, not to be yada, yada, yada'd. introduce time lags into the equation, and we don't have time. This field is for validation purposes and should be left unchanged. The current population could be reduced by attrition. Oh, they're up there. Carrying capacity is the maximum number of a species an environment can support indefinitely. And death rate has gone down, but they're not matching each other at all. Maybe when we see the next slide we'll see. We're going to plot one over N. dN/dt as a function of N. If we want to rewrite the equation. And here we are with a steady, increase. Well, I guess this is the super optimistic model. just no change in human population on Earth. And we hit 6 billion in 1999. So the real trick is, in terms of trying to level off at someplace lower than 9 billion, is to get the birthrates in the developing countries to drop as fast as we can. A population of any species can live in overshoot for a while, but eventually lack of sustainability will catch up with it, causing suffering and strife. There is a limit and reproducing carelessly endangers our long-term survival and the survival of other species with whom we share the planet. from looking at family size in these countries. So, it kind of looked like exponential growth. So, they said, so they asked the, question: OK, we're modeling this population, we're saying it grows, according to the logistic equation, we can predict what the carrying, capacity in the United States for humans by simply doing a regression. And what we've been assuming, is that the carrying capacity will grow with us, OK? Like this? This one assumes that it'll do. If we don't have enough grain, we'll genetically engineer to make, more grain. It's smoothed over, and these are the greenhouse gases, concentration of greenhouse gases in the atmosphere. that they put on here. Many scientists think Earth has a maximum carrying capacity of 9 billion to 10 billion people. For most of the developed world, that would mean about one million. If we do and we want to continue our current lifestyle, I think the answer is closer to 2 billion. Marian Starkey, Senior Director of Publications. So, in this case, this is really a maximum growth rate. to double down to 1000 to 3000 years for the population to double. Did you know you could fit the entire population of humans on Earth shoulder to shoulder in Los angles. Yes, I would like to receive e-mail from Population Connection. And we don't. This is what we call carrying capacity, the amount of people that can be sustained based on the resources we have. this model is actually used in fisheries conservation for years. how about 13.8 billion , the number which the creator has given us by the age of universe? Animal populations are, on average, less than half the size they were in 1970, and we’re currently witnessing the sixth mass extinction, wiping out entire species with our destructive activities. They might have one generation that's still at the same growth rate, as it was before, before the biochemistry readjusts. off, but we've been growing like this. So, you don't have much population growth. Imagine what would happen if desperately poor people were fortunate enough to live a middle class lifestyle. And, we said we could describe this as one over the dN/dt equals some growth rate, r. And, in this case, we're talking about, let me ask that is a question. The doubling time is extending. that context, because this is an important thing. And the really important feature here is what's called a demographic transition. First of all, before we do that, I want to remind you that all of these lectures are tied together because remember this from lecture 20 when we were talking about biogeochemical cycles? Carrying capacity is the number of organisms that an ecosystem can sustainably support. But I wouldn’t try to hit that. Already, we’re consuming the Earth’s renewable resources at one and a half times the sustainable rate. I mean, this is just this little snippet of time in the history of. OK, so all right, forget that. I am just checking if the 19 thoughts are provided by readers or if they had been hand selected by the author for a school report. Even. This is just an approximation. Let me just make sure that's not, ambiguous. Absolutely right. and modern agriculture won't be able to overcome that, that our water will be polluted, that the climate will change so. tao hours or days or whatever, earlier than t, divided by K. So, what this says is that the growth rate of the population is a function, of the density up a little bit earlier, or some amount earlier than.