I was discussing global warming and carbon sinks with my brother, and he asserted that the increasing human population must be having an effect on the environment. By this he meant not the things humans do, but the mere fact that there are so many of them alive and breathing all at once. I think that this is a trivial matter compared to the other things we do, like burn fossil fuels, but I’m at a loss as to whether the biomass of animals on Earth has changed much over the last few centuries. Sure, there are more humans standing around breathing, but fewer buffalo, passenger pigeons, or Tasmanian tigers, and those Stephens Island Wrens sure did absorb oxygen while they were around. Does anybody out there have any surmises on how much the biomass of oxygen breathers has changed over the centuries?
On a related matter, if you put all the Chinese into a cube and removed the space between them, how big would the cube be, and how heavy? How fast would it be growing, or is it still growing now that demographics there have been shifting? (Please feel free to use average weights and heights rather than actually weighing and measuring all the people in China - it would take a fair amount of time, and some of the ones you weighed first would have gone on diets or gained weight by the time you totaled it up.) For “China”, let’s use Mainland China exclusively, not including Taiwanese or overseas Chinese - no need to make things complicated. Or maybe there is - how big would it be if everybody on Earth was there except me? (I want to stand outside so I can get a good picture of the cube.) Thanks to anybody who can help…
This one is easy. There are about 1.5 billion people in China, right? Let’s assume that the average Chinese masses 66 kg (this is a low mass for a human, but some of those are children, and some probably aren’t eating as much as they ought). That gives us a nice round 100 billion kilograms, or 100 million tons. The human body, like most organic material, is approximately the same density as water, and water is one ton per cubic meter, so we have 100 million cubic meters. Taking the cube root, that gives us about 460 meters per side.
I’m sure someone will beat me to it, but hear goes. There are 1.3B Chinese. If they average 50 KG, that is 65B KG. People are close to the same denisty as water, so that is a cube that is 8.66 km per side.
To answer the first question, the mere existence of humans adds absolutely nothing to global temperatures. Human body heat is generated entirely by the oxidation of plant matter. Whether humans existed or not that plant matter would still have existed and it would still have been oxidised, producing the same amount of heat.
I assume that his misunderstanding comes from an assumption that “cold blooded” organisms like plants or reptiles produce no heat. Of course that isn’t true. They produce just as much heat per calorie consumed, they just consume far fewer calories.
I think he thinks that the ratio between plants and animals in the biosphere is changing, and that global warming is exacerbated by that change. I’m not entirely sure - it was a comment during an early morning car trip, when I was half awake, and I didn’t press him.
Regarding the two estimates of the size of the cube, there seems to be a slight variation here - 460 meters vs. 8.66 km. This seems to be slightly outside the acceptable statistical error…
The ratio of plants and animals probably is changing, but so what? Plants still oxidise plant biomass for their energy. The heat generated is still the same. Perhaps the point he is missing is that biomass is basically just an entropy dam. It just stores energy from the sun temporarily, it doesn’t create any energy.