Increased population is the cause of global warming

. . .or so a colleague claims. His stance is that the increased number of humans on the planet, all basically 98.6 degree heat generators, has increased the world temperature and thus causing the shrinkage of the polar ice pack. He claims that all this heat can’t be dissipated, so the climate is changing. He also claims that the scientific theory of emissions causing global warming is bunk. It sounds suspiciously like bobblehead radio nonsense, but I’m not a scientist.

I have two questions:

  1. Is his postulation even remotely plausible and why/why not.

  2. If not, please give me a cogent argument to refute it, as I would like to be able to debunk it.

What exactly does he think is causing the heat to be unable to dissipate?

Oh, wow. Okay, for starters, try pointing out to him that passenger pigeons used to exist in tremendous flocks, and their internal temperature was 41-42 degrees celcius, compared to human temperatures of 37 degrees celcius. And passenger pigeons alone numbered around 6 billion. Humans wiped them all out. Shouldn’t the earth have experienced a dramatic cooling trend at that point?

Of course not, because that’s ridiculous. But maybe that’ll get him seeing the silliness of the argument.

Daniel

I’ve always wondered about the spread of urban areas. Aren’t urban areas generally “hotter” than the surrounding surface?

He’s very vague about that; he sort of mumbles something about the planet not being able to absorb all that heat (apparently, he thinks our atmosphere is impenetrable). Oh, and he also makes a “point” that all these human bodies, which are multiplying by the millions, are not just one-time heat generators. They keep putting out 98.6 until they die. It’s just loopy enough to be difficult to refute, which is why I’ve come here for answers.

To be more specific with my earlier post, he needs to be able to do some things for us:

  1. Show how much energy is converted to heat by humans; and
  2. Show how to total heat generated by human biomass compares to the heat generated by nonhuman biomass; and
  3. Show how total biomass has changed with human population surges.

I’m not exactly sure, but I believe that overfishing, deforestation, and erosion have been depleting total biomass. This does have an effect on global warming, inasmuch as forests act as carbon sinks, and the burning or decay of a forest releases carbon dioxide; however, the effect is not from an increased or decreased release of heat from organisms.

Overall, he’s treating human heat as far more important than it really is compared to heat from all organisms on earth.

Daniel

And don’t forget the heat from the sun. I’m thinking the total heat put out by human beings, whatever that might be, completely pales in comparison to that burning yellow eye.

Related thread: Mammal body heat and local or global climate
At 125 watts per person, the 6 billion or so of us put out 725 billion watts worth of heat. That’s small compared to world energy production of around 14 terrawatts.

And the Earth receives 84 terrawatts per day of solar energy at ground level; from the figures in the link, I calculate that another 40 terrawatts or so are absorbed directyl by the atmosphere. So the amount of heat contributed directly by humans is trivial.

It’s sounding to me like human procreation is a contributing factor to global warming, albeit an extremely small one. So his theory holds some water (heh), but as for humans being the sole source of global warming, he’s way off base considering the huge biomass that contributes to the problem.

Squink: thanks for the numbers.

I don’t even think that this is true. Organisms, whether endotherms or ectotherms (“warm-blooded” or "cold-blooded) generate heat when they burn food through respiration. I don’t think there is much evidence that the total amount of living biomass producing heat on the Earth is going up; I would suspect it has gone down as forests have been cut. (Herds of large wild herbivores have also disappeared, but I am not sure to what extent this has been balanced by the increase of domestic animals.)

But all organisms ultimately derive their energy from sunlight through photosynthesis, including animals by the consumption of plants or of plant-eating animals. Without a net increase in this energy input over the long run, there can’t be a net increase in the output. (There can, however, be short-term changes due to changes the amount of solar energy stored in the form of biomass or as fossil fuels.)

So 725 billion watts into 84 terawatts–am I correct in thinking this means that
humans put 0.86% as much heat into our system as the sun does (excluding for the moment that we’re really just re-releasing stored energy originally derived from the sun)? That seems phenomenally high to me. I’m probably doing my calculations wrong.

Daniel

Serves me right for linking to a site that misspelled terawatt. Checking around, it seems to me that the solar energy received is more on the order of petawatts (1000 terawatts), but sites differ in figures quoted.

This site gives the Earth’s “energy budget,” mostly solar, as 174,000 terawatts, and human energy use as c. 10 terawatts.

Your friend has himself what we call a hypothesis – nothing more.

He made observations and has drawn some conclusions, now the burden is on him to conduct deeper investigation/test/study. This is the trickiest part, where one needs to control for a variety of factors. Often, there is a cause/effect interpretation when not done properly.

Correct me If I am wrong, everyone, but people who stumble around the hypothesis and then draw conclusions based on the convenience are just begging the question.

Seems he is saying, “People generate heat, the planet/environment is getting hotter, so people are causing it.”

Don’t discount his hypothesis out of hand, but help him figure it out. It’s how you can debunk his claim.

Okay, but energy use isn’t the same thing as heat output, is it? I’m guessing that a significant amount of our energy use is transformed into movement of cars, light, and so forth. And even then, I read this (and granted I’ve got zero background in physics) as saying that humans consume this much energy, not that human body heat equals 10 terawatts.

If we take the previous 785 gigawatts (is that the right term) as human body heat output, and the “energy budget” as being sunlight’s contribution to earth’s temperature, then we’re dividing 785 gigawatts by 174,000,000 gigawatts, I think. That means that humans contribute 0.00045% as much heat to the earth’s system from body heat as the sun contributes, if I’m doing the calculation right.

And that’s before we get into the question of whether human biomass is replacing nonhuman biomass.

Daniel

Yes, that figure is the amount of energy used by humans for vehicles, lighting, etc, not the amount of body heat.

I just noticed that the 125 watts/person figure is an hourly figure. The “energy budget” figure is, I believe, based on an annual budget (although it’s unclear). So maybe my figure is still off.

Daniel

No, it’s a power figure. Power per hour would be a most peculiar sort of unit, which I don’t think would have any sort of practical meaning. Power is already a per-time quantity, so 125 watts/person means that each person puts out 125 Joules of energy per second.

And human energy consumption is essentially identical to human heat production. Yes, we use some of our energy to move things around, but what do you think happens to that energy afterwards? Ultimately, everything ends up as heat, and it doesn’t even usually take all that long.

The sugars and starches that humans grow (grains, potatoes, cane etc) and then burn up, absorb insolation via photosynthesis. Part of this light would otherwise be converted to heat. So wouldn’t these crops be cooling the planet down by locking up energy - temporarily.

If humans were not the eating the sugars and starches that humans eat, then something else, such as bacteria, would. In this case the bacteria would be putting out the heat.