> 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.)
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