An average human breathes out roughly 1kg of carbon dioxide a day | Hacker News Reader

An average human breathes out roughly 1kg of carbon dioxide a day

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36 pointstosh55 comments

I love how he ends it with “thinking about space habitats” as I immediately thought: “well, if you can trap it and compress it, you’ll have enough briquettes for a weekly bbq”.

He obviously knows this too. Dealing with human waste/by-product is a real challenge. Far more so in space than on an ocean or in an RV.

We humans need to learn to use everything and not let anything go to waste. Else we have nothing left to waste.

Luckily there are these things that take in CO2 and turn it into polymer structures with many uses such as food, fuel, and construction.

Not to mention the oxygen we breathe to stay alive.

If only we could turn that CO2 into food (C chains) and oxygen (O2) via some self sustainable self healing reproducing system that has an extremely low starting mass. A "co2 food producing seed" or something.

I love this idea. If in some way the system produced more of the "seeds", and each of those "seeds" resulted in slightly different carbon chains, we could increase the diversity of the food in interesting ways.

And if the system is large enough, and could be made beautiful, one could take a walk through the system. Call it a "forest".

And it would be mad if these "forests" would grow on a planet-sized spaceship with atmosphere and plenty of water, how cool and scifi would be that!

We already have a (kinda magical) device which does that. It's also clean to build, can self-build and self-copy, is edible.

It's called a vegetable.

Most veggies are mostly water by weight/volume so it wouldn't be a good deal. They also have very little actual calories.

What you want is actually cereal. They probably absorb a bit let CO2 than trees but at least you can eat them so that's more useful.

> if you can trap it and compress it, you’ll have enough briquettes for a weekly bbq

Compressing CO2 will not create briquettes of combustible charcoal. You still need a way to chemically remove the oxygen from CO2.

Yes, electrolysis, which would be readily available with solar and batteries up there in space…

James Miller from Arizona State University’s Global Institute of Sustainability and Innovation is working on just such a thing.

I recently picked up a video game called Oxygen Not Included. Obviously it's a fantastical game not a simulation, but you're managing a colony in an asteroid and it makes you deal with all sorts of waste including CO2.

It’s a good game ;)

A related fun fact is that you generally lose weight by exhaling, generally while you sleep. Sweating, defecating, etc. is all temporary. If you're trying to lose weight, make sure you're sleeping enough!

edit: see my followup comment, didn't mean to mislead here. I'm not a scientist and sleep and food science is both pretty hard to trust.

Why would you lose more weight with exhalations from relatively low sleeping metabolism than being awake? Not being contrary, genuinely curious.

If I were to guess, the metabolism generates waste during activity that gets processed and exhaled as CO2 during sleep.

Bad guess, I am not sure what OP really intends (perhaps you don’t consume whilst you sleep?!) because as you probably are starting to remember from primary school your body maintains homeostasis by continually respiring. It doesn’t suddenly decide to take a dump.

Ok, it does, but even when it does that, in order to do that it has been continually maintaining homeostasis

Doesn't the CO2 get exhaled during activity rather than sleep?

You exhale more CO2 during activity because metabolism increases. Burning glucose and fat produces CO2.

It doesn't make sense that you would lose more weight by sleeping only considering metabolism.

I can see an argument around sleeping always being a net loss, since you're never consuming food while sleeping. Sleeping more thus means you may eat less.

Sorry, my phrasing was not clear. Your metabolic rate is generally lower during sleep than during the day; you definitely lose more weight overall during the day than while asleep. But, while you're sleeping, you don't eat anything. And quality sleep is necessary to maintain overall metabolic function. I'm not a scientist and didn't mean to make any strong claims!

Two short articles I was basing this off of:

- "When somebody loses weight, where does the fat go?" https://www.bmj.com/content/349/bmj.g7257

- "Sleep and Metabolism: An Overview" https://pmc.ncbi.nlm.nih.gov/articles/PMC2929498/

Isn't the main reason because you're not eating?

Yes. Sleep by itself does nothing unique. In fact, you have a slightly lower rate of metabolism than even the "basal" metabolic rate.

Eh? That isn't right. The metabolic rate while asleep is even lower than the basal average. The only reason there's a net loss after sleep is because you're not regularly consuming food or water as you would when you're awake, not anything special about sleeping by itself. You're burning fewer calories than usual at that time!

At standard temperature and pressure 1 kg of CO2 has a volume of around 500 l.

Exhaled air contains about 4% CO2, so you would have to exhale 12500 l of air to put out 500 l of CO2.

At 0.5 l per exhalation that's 25,000 breaths, which seems rather on the high side: 17 breaths per minute, round the clock.

It seems like a bit of a high estimate; could be true for people who are very physically active during parts of every 24 h period.

Similarly, burning a gallon of gasoline emits about 20 pounds of CO2. (2.3 kg/l). So daily human exhalations are equivalent to driving a couple of miles or so.

True, but the gasoline is carbon taken from the air millions of years ago and sequestered underground and now being returned to the air, while the carbon I breathe out was all taken from the air by plants comparatively recently.

There was lots of diesel burned planting, harvesting and transporting those plants. Producing fertilizer also emits a lot of CO2.

But none of that carbon comes out in my breath.

A couple weeks ago mosquitos were at their peak in my yard. I started thinking about adult mosquito traps, but I don't love the idea of using propane as a CO2 source like most commercial solutions do. I casually looked into solar powered direct air capture of CO2, but that would not scale down. Then I realized maybe I could just capture my own exhalations for 30 minutes a day to use in a trap. Not sure I'll ever actually implement it.

How about a tealight?

We breathe in about 21 lbs. of air each day. This is much more than we eat each day! Important thing to think about in terms of how clean that air is.

21 lbs -> 9.5 kg For those not working for the empire ;)

Thanks! I live in the empire and was born here. I still need metric measurements because I need to relate the numbers to real uses.

I wrote about this some time ago ... the calculations are here:

https://www.solipsys.co.uk/new/CountingCarbonCalories.html?y...

I'll submit that as a separate item ...

Here: https://news.ycombinator.com/item?id=44605555

For comparison, a small ICE car produces around 100g of CO2/km, so with the same carbon budget you could drive 10km.

That comparison makes no sense because the ICE car is releasing carbon taken (mostly) from petroleum while the human is releasing carbon taken (mostly) from the atmosphere via plants and animals.

Well, years ago, I was running my indirectly injected diesel straight off sunflower oil, so that was plant based too.

But your point is valid. Comparison is still useful for getting a grasp of the quantities involved.

But only after you discard your mortal flash and upload your mind to a shiny Tesla-cloud. At which point you can probably afford to not care much about all the carbon problems anyway.

without javascript: https://xcancel.com/ID_AA_Carmack/status/1945948569246027934

That's a lie, that page uses Javascript.

Does anyone know how to reduce this? I’m worried about creating climate change.

Eat less. But don't worry.

Don't worry, the government already has plans in store for this particular issue.

Breed less

Only one sure way!

https://youtube.com/watch?v=FhyfggpI_fA

You exhaling carbon isn't causing climate change. Those carbon atoms came from your food, or from your food's food, which was a plant, and the plant got the carbon from CO2 in the air. You breathe it out, it goes to the plant, you eat the plant, and you breathe it out again. This is the carbon cycle.

The reason we have climate change is the we're extracting carbon from geologic formations where it's been trapped for millions of years. There is no carbon cycle: It gets extracted, burned, the CO2 goes into the air and stays there (maybe in 10 million years more oil and coal will form, but there are reasons to believe these processes are no longer occurring.)

> “thinking about space habitats”

I think Carmack is a genius and admire his work ethic, but I can't understand what interests smart people like him about human space travel.

Might be able to get more people excited about maintaining our amazing ecosystem if we talked about "Spaceship Earth" more.

And plants love it!

Yes, sad times when you have to explain to people how photosynthesis works.

It's got what plants crave.

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