Sorry chiming in from the peanut gallery here... in the new movie Cowspiracy, they say that all burning of fossil fuels actually only makes up less than 15% of contribution to global warming, its actually being caused mostly by our diet. its animal agriculture releasing methane run off that's causing climate change.
Crazy as that sounds off hand, it is technically not all that crazy in a back-of-the-envelope sort of way. Imagine the weight of the gas in a can that one puts into a car daily. Imagine picking up the amount of grass that a cow munches down on a per-day basis. Comes down to the number's count. But before one goes into a panic, note that the grass (or alternate plant which WILL be growing there) is not destined to become a carbon rich fossil absent the cow. It would rot and 'pollute' the atmosphere with carbon anyway.
I've heard that among the largest contributors to CH4 are termites and beavers. The latter due primarily to environmental impacts which create 'wetlands'. The former hosts more or less the same microbes which can break down cellulose as do ruminates.
This comes back to the suggestion I made earlier that we humans probably made our greatest contribution to global atmospheric carbon about 100,000 years or so ago when we started lighting environments on fire.
It's worth note that the impacts of any greenhouse gas is not linear. The higher the concentration (of various constituents), the greater the 'atmospheric opacity'. The analogy I uses earlier is that if one is already behind a sheet of bullet-proof glass, strapping on some body armor is not going to make that much difference since something else will already have stopped the bullet. I'd have to look again, but I recall methane, while being a 'powerful greenhouse gas', is also especially prone to this principle. Water vapor has already absorbed most of the energy on the spectra in which methane is most active. The same principle applies to CO2 but just not as much.
But with our population growing exponentially our farts have to be considered too. Its our farts and poop plus all land animals on earth which includes all our food. At some point wouldn't it start to penetrate the glass in your analogy? or is that like only after a million years of growth? (asking because i honestly don't know the math)
Sure. Overpopulation of anything will 'harm' the environment and/or result in harm to one another. It's a perfectly valid argument that even at our current population levels humans already have crossed that point, but to have this argument one must agree on the meaning of 'harm' among other things. This seems to me to be the point where many of the 'scientists' often start to become quite 'religious' in their definitions. More like high priests than like rational engineers, and more and more that is how they are marketed to the plebs.
The way I see it 'we' still have plenty of time to figure out reasonable ways to modulate human population before 'the danger' becomes to great. Again though, this is simply a values judgement involving my own personal ethics and what-not. The proposals put forth by 'sustainability' crowd vis-a-vis energy use are flat out genocidal in practice by my estimation, and I think it is a refection of the values judgement of others which differ from my own.
Again, it is beyond absurd that CO2 from human fossil fuel use will be the big problem, but there are plenty of other things that will rupture at certain critical population densities.