Mike, Unfortunately, I can't remember where I originally read the article containing the calculations (somewhat like yours) which came to the conclusion that the maximum carrying capacity of the world without oil was around 2 billion, though this seems to be a very common conclusion in a number of studies. (e.g.)
"World population will have to adjust to lesser food supplies by a reduction in population. Pimentel and Pimentel (1996) state: ... the nations of the world must develop a plan to reduce the global population from near 6 billion to about 2 billion. If humans do not control their numbers, nature will." Because stopping and then turning around the freight train of population growth can only be done gradually, this is a project which should be started now (Cohen, 1995). If it is not done, famine on a large scale is likely to ensue." These studies are summed up in the survey article at: http://www.ilea.org/leaf/richard2002.html Note that all the 4 studies mentioned that base their carrying capacity estimates on sustainable energy supplies (Pimetel et al. (2), Daily et al and Ferguson) all come to an estimated capacity of 1 to 3 billion based on standard of living with a median estimate of approximately 2 billion. For a more general discussion of the relation between overpopulation and sustainable food supplies, see: http://peakoil.blogspot.com/2005/07/threats-of-peak-oil-to-global-food.html Paul Phillips mike wrote: >> Yet the scientists tell us that, without oil, there is only >> enough sunlight to produce sufficient food to feed 2 to 3 billion >> people. This is a scientific ratio between energy received and food >> calories produced and is independent of productivity or technological >> change. >> >> >> > > I'm curious who these scientists are. This doesn't seem to work out: > granted that photosynthesizing and then eating is not a very efficient > way to get energy, but the total available energy from the sun is > absolutely enormous, and should more than compensate for this process. > > > given: > assume we have 10 billion people, and each consumes 2000 Calories / day. > (those are actually kilo-calories, so its really 2m calories/day) > 1 calorie = 1.163*10^−3 watt-hours > so that works out to 10*10^9 * 2*10^6 * 1.163*10^-3 = 2.326*10^13 > watt-hours used per day. > > The earth absorbs 89PW of energy, excluding what is reflected back into space. > That works out to 2.136*10^18 watt-hours > Assuming that only 30% is land, and that %20 of the earth's land is > arable, 6% of that energy is falling on potential cropland. > (We of course aren't using 100% of arable land for food production, > but it is potentially available to use, so I included all of it here. > 30% of total land area is forests, for example, and I'm not sure if > that is considered "arable" in its current state or not. Also, some > portion of the world's food-energy comes from the sea, but I counted > all of the sea as unused.) > > I'm less certain about these figures, but let's assume that the > efficiency of photosynthesis for crops overall is 3%, and that the > ratio of useful food to other inedible plant matter at harvest time is > 20%. (I'm not sure on either of these, but they seem low-ish > reasonable estimates from a bit of googling. They also seem to be > highly dependent on the crop and farming technique.) > So, that works out to 2.136*10^18 * 0.3 * 0.2 * 0.03 * 0.2 = 7.689*10^14 > > 2.326*10^13 / (7.689*10^14) = 0.030 > > So, even at 10 billion people, we'd be using 3% of the total available > food capacity, viewing things strictly as energy. > > This is actually a lot closer than I expected, but its hardly a > Malthusian doomsday scenario. (I would have initially guessed > somewhere around 0.1% or less.) This is actually close enough that > using more of the available capacity, and using it better, may be a > concern if the population gets into the tens of billions. But of > course the more immediate concern is the economics involved in all of > this, which is the reason people are hungry now, instead of > hypothetically hungry if there were "too many" of us. > > --Mike I. > (an engineer, not even an "real" scientist.) > _______________________________________________ > pen-l mailing list > [email protected] > https://lists.csuchico.edu/mailman/listinfo/pen-l > > > -- Paul Phillips Professor Emertus, Economics University of Manitoba Home and Office: 3806 - 36A st., Vernon BC, Canada. ViT 6E9 tel: 1 (250) 558-0830 email: [EMAIL PROTECTED] _______________________________________________ pen-l mailing list [email protected] https://lists.csuchico.edu/mailman/listinfo/pen-l
