"There is, quite literally, not enough oxygen being produced through photosynthesis to sustain many more people."
Where is there proof, in science, of this statement? This is one I have never heard. This one sounds like it is coming from the same "scientists" who are inventing man MADE climate change.
There is no scientific proof of that statement, because the statement is hogwash based on something other than science, or even observed reality. There is science that shows exactly how much oxygen is needed to sustain people, and the number of people it will sustain.
This article (
The Flow of Energy: Primary Production) is a rather dry read, and requires some homework, but it's all there. It's also an article that uses irrefutable data that gives global climate change folks fits.
The article is about with the
Net Primary Production (NPP) of CO[SUB]2[/SUB] in the world related to human consumption. NPP is the amount of CO[SUB]2[/SUB] that is "fixed" (
i.e., processed) by plants through photosynthesis minus the amount of CO[SUB]2[/SUB] that is produced by organisms through respiration. Therefore, to simplify things, the higher the NPP the lower the amount of CO[SUB]2[/SUB] in the atmosphere. The article cites the following table from Atjay
et al. 1979 and De Vooys 1979 which breaks down NPP by the type of ecosystem:
(The numbers in the table are amount of surface area on Earth in km[SUP]2[/SUP] x 10[SUP]6[/SUP] and the second number is the NPP in petagrams.)
- Forest: 31 / 48.7
- Woodland, grassland, and savanna: 37 / 52.1
- Deserts: 30 / 3.1
- Arctic-alpine: 25 / 2.1
- Cultivated land: 16 / 15.0
- Human area: 2 / 0.4
- Other terrestrial (chapparral, bogs, swamps, marshes): 6 / 10.7
- Lakes and streams: 2 / 0.8
- Marine: 361 / 91.6
The article uses these figures to calculate the amount of NPP that is currently co-opted for human consumption. For example, they assume that all of the NPP associated with cultivated land goes toward human consumption. They conclude that 30.7% of the terrestrial NPP and only 2.2% of the aquatic NPP is co-opted by humans. These numbers are of course based off of ~30 year old studies, but they have been updated and confirmed several times, and it's clear to conclude that there's still room for more human-based CO[SUB]2[/SUB] production before NPP goes to zero.
According to
this 2002 study by Randerson, terrestrial heterotrophs (
i.e., organisms that need to breathe oxygen, like humans) produce 82–95% of the CO[SUB]2[/SUB] represented by the NPP. Stay conservative and assume the higher amount: 95% NPP. That means that as long as the forests account for fewer than 5% of the total NPP then we should be fine. The forests produce 48.7 Pg, however, which is a little under 22% of the total NPP.
However, 13.6 Pg of NPP associated with forests is co-opted for human consumption (getting wood for building houses, etc
.). If we were to get rid of all of the forests we'd also get rid of that percentage that has already been co-opted. Therefore, if we were to get rid of all of the forests there would be a net loss of 48.7 Pg - 13.6 Pg = 35.1 Pg, which is about 16% of total NPP. That's
just low enough to meet the lower bound of 82% CO[SUB]2[/SUB] production.
Therefore, there is a small chance that there will be enough NPP after getting rid of all of the trees for human consumption, but it is likely not the case. Furthermore, if we were to get rid of all NPP producers other than grass there would certainly not be enough NPP for human survival.
It's also important to note that, by far, the most productive producers of NPP are the open ocean, tropical rainforest, and temperate forest, so by deforesting as opposed to de-grassing we would be greatly reducing the efficiency of the global ecosystem. Also, there is also the matter of carbon storage. Trees store a good amount of the carbon from the CO[SUB]2[/SUB] they process in their trunks where it stays for a long time. Grass, on the other hand, releases its carbon back into the system shortly after it dies and rots away. Therefore, even if grass does produce enough oxygen for life, it probably wouldn't have the same greenhouse gas reducing capabilities as trees.
But what all this means is, with the current level of plants and trees in the ecosystem, the amount of oxygen produced by photosynthesis and the NPP is enough to sustain roughly 90 billion people.
However, there are many more factors to consider than just the NPP and the amount of oxygen produced. It's more complicated than trying to predict the weather, and considerably more complicated than trying to predict climate change. Other immediate things to consider are things like the nitrogen cycle and the availability of phosphorus, because these have a direct effect on not only how much fresh water is available, but also in how much food can be produced to feed the population.
If things continue the way they are, including cutting down trees which are the primary factor of NPP, then the current world population of about 7 billion (not 9 billion) has little room to grow, and will max out, when you factor in both NPP and the ability to feed the population, somewhere between 9 and 10 billion. And between 9 and 10 billion is just about the place where the population will stabilize. As Dave's link noted, populations are already slowing down. UN estimates of global population trends show that families are getting smaller. Empirical data from 230 countries since 1950 shows that the great majority have fertility declines, in fact.
Globally, the fertility rate is falling to the "replacement level," which 2.1 children per woman, the rate at which children replace their parents (and make up for those who die young). If the global fertility rate does indeed reach replacement level by the end of the century, then the human population will stabilize between 9 billion and 10 billion.
The thing is, if the fertility rate doesn't fall to the replacement level, it'll still almost certainly end up stabilizing at between 9 ans 10 billion, so sayeth the Earth, because while there will be plenty of oxygen to support far more, there won't be enough fresh water or food to feed them, even if we all started eating Soylent Green.
