How bad for you is CO2?
August 13, 2016 10:43 AM   Subscribe

What are the direct effects of elevated levels of carbon dioxide on human health in the long term?

I've been getting concerned about something, and I was hoping the science brigade here on AskMeFi could let me know if my concerns are justified.

We've released an enormous amount of CO2 into the atmosphere. We hear a lot about how that's causing global temperatures to rise.

My point is, hold on, you skipped a step. We've been releasing massive amounts of carbon dioxide into the atmosphere. Isn't carbon dioxide, like, you know, poison? Sure, it's only low levels, but it's low-level exposure over an entire lifetime; that has to have some effect.

We know it's playing havoc with shellfish, with plants and plankton, but what about us? The amount of CO2 in the atmosphere has skyrocketed in my lifetime, when it barely budged the needle for much longer than we've been around as a species.

So I started looking into it, and here's what I found:

Chronic respiratory carbon dioxide toxicity: a serious unapprehended health risk of climate change

The effects of elevated carbon dioxide on our health

Chronic Exposure to Moderately Elevated CO2 during Long-Duration Space Flight (NASA)

Just how ‘Sapiens’ in the world of high CO2 concentrations?

Health effects of increase in concentration of carbon dioxide in the atmosphere

I'd really appreciate some feedback on the ideas in those papers. A couple of them come to some very scary conclusions, and I'm really hoping they're wrong.

We could easily see concentrations as high as 800ppm by the end of the century.

What sort of health effects can we expect to see as the CO2 rises?
posted by MrVisible to Science & Nature (18 answers total) 3 users marked this as a favorite
Plants will grow better, you may have to moan your lawn more oftern. -> Higher risk of injury.
(Based on your links I am half serious with this answer).
posted by yoyo_nyc at 11:45 AM on August 13, 2016

IANAD, but even people with hypercapnia and respiratory acidosis don't die from CO2 poisoning, they die of suffocation.
posted by rhizome at 12:12 PM on August 13, 2016

Calling CO2 a "poison" is misleading. You could call water a poison if you drank enough of it. CO2 is a exhaled in every breath you take at a concentration of about 50,000 parts per million. The air you inhale is 400 parts per billion. There is more than a factor of 100 difference between the two. Changing the inhaled air by a few hundred parts per million is a tiny effect. Your body automatically compensates by breathing a little more quickly such that you wouldn't even notice.

Indoor air is commonly 1000 parts per million. Are you choking yet? In the spacecraft article you cited they are talking about 7000 parts per million. The atmospheric effects you are talking about are an increase of a couple of parts per million per year. It will be at least a couple of centuries or more, if nothing is done, before humans would notice much difference.

Humans are highly adaptable to a very wide range of CO2 in the air, at least a factor of 10. There are other things more important to worry about than CO2 "poisoning."
posted by JackFlash at 12:12 PM on August 13, 2016 [19 favorites]

Just a quick correction, atmospheric CO2 is 400 parts per million, not billion. I'm sure that's what JackFlash meant to write, but just for clarity's sake.
posted by Anticipation Of A New Lover's Arrival, The at 12:18 PM on August 13, 2016 [1 favorite]

Thanks for the correction. All numbers above are in the same units of parts per million to make easier comparison.
posted by JackFlash at 12:22 PM on August 13, 2016

A while back someone did an experiment growing cassava (a staple in the tropics) in a greenhouse with CO2 set at anticipated levels, and found that it stored less starch in its roots by quite a bit.

This was a surprise, and it's not clear how that would generalize to other root crops, but if, say, a general strategy of starch storage is fueling more rapid growth during certain phases than direct absorption of CO2 from the atmosphere could sustain, root crop agriculture could be in trouble.
posted by jamjam at 12:24 PM on August 13, 2016

JackFlash, there seems to be a huge difference between being exposed to high levels of CO2 on a temporary basis, and being exposed to persistent ambient levels of elevated CO2 over a lifetime. Please read these links:

Chronic respiratory carbon dioxide toxicity: a serious unapprehended health risk of climate change

Health effects of increase in concentration of carbon dioxide in the atmosphere
posted by MrVisible at 12:47 PM on August 13, 2016 [1 favorite]

A study out of Harvard published in 2016 shows that indoor levels of CO2 previously thought to be completely benign actually impair cognition:
Significantly, the Harvard study confirms the findings of a little-publicized 2012 Lawrence Berkeley National Laboratory (LBNL) study, “Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance.” That study found “statistically significant and meaningful reductions in decision-making performance” in test subjects as CO2 levels rose from a baseline of 600 parts per million (ppm) to 1000 ppm and 2500 ppm.
The new study, led by Dr. Joe Allen, Director of Harvard’s Healthy Buildings program, and Dr. John Spengler, Professor of Environmental Health and Human Habitation at Harvard, used a lower CO2 baseline than the earlier study. They found that, on average, a typical participant’s cognitive scores dropped 21 percent with a 400 ppm increase in CO2. Here are their astonishing findings for four of the nine cognitive functions scored in a double-blind test of the impact of elevated CO2 levels:
posted by jamjam at 12:54 PM on August 13, 2016 [2 favorites]

there seems to be a huge difference between being exposed to high levels of CO2 on a temporary basis, and being exposed to persistent ambient levels of elevated CO2 over a lifetime. Please read these links:

Believe what you like, but your sources are not particularly credible as physiology experts. Frankly they read as extremist cranks. Both are emeritus geologists.

The body adapts easily to a range of CO2 inputs within the few hundred parts per million you are talking about.
posted by JackFlash at 1:40 PM on August 13, 2016 [5 favorites]

I'd love to not believe those papers. But from what I can tell, their points make sense. I've written this piece specifically to ask for counter-arguments.
posted by MrVisible at 2:33 PM on August 13, 2016

I'd love to not believe those papers. But from what I can tell, their points make sense.

So do these arguments against dihydrogen monoxide. But as with the studies you linked, the science isn't credible.
posted by DarlingBri at 3:50 PM on August 13, 2016 [2 favorites]

I'd love to not believe those papers. But from what I can tell, their points make sense.

You will find life much more fulfilling if you seek proof to validate your beliefs rather than seeking proof to invalidate them. You should also not mix up a believable hypothesis with one that has been proven. It's far to easy to postulate something that is hard to disprove - science is based on the simplest argument that someone can prove.

That said - given what was described above, their points really do not make scientific sense...even if a causal observer who does not understand the concentrations involved might think they are feasible.
posted by NoDef at 6:51 PM on August 13, 2016 [5 favorites]

The Harvard study and the discussion of it I link to claim that an increase in indoor CO2 concentration from 500 ppm (~100 ppm above current outdoor levels) to 930 ppm (130 ppm above the outdoor level MrVisible says is credibly projected for the end of this century) causes significant cognitive impairment.
posted by jamjam at 7:58 PM on August 13, 2016 [1 favorite]

The Harvard study and the discussion of it I link to claim that an increase in indoor CO2 concentration from 500 ppm (~100 ppm above current outdoor levels) to 930 ppm ... causes significant cognitive impairment.

Given that the typical CO2 in most homes, offices and public buildings is 1000 parts per million, you would have to conclude that billions of people have been cognitively impaired for more than a century since people lived primarily indoors. I'm not buying it without more research.
posted by JackFlash at 8:14 PM on August 13, 2016 [1 favorite]

It surprises me; however, the Harvard study is more research, research which tends to confirm and extends the earlier research from Lawrence Berkeley National Laboratory -- and those are both credible institutions.
posted by jamjam at 8:35 PM on August 13, 2016 [3 favorites]

There's been some research possibly showing a correlation between rising CO2 and Obesity rates - info here
posted by bottlebrushtree at 11:54 PM on August 13, 2016 [2 favorites]

The Harvard study is a good start, but it's flawed on several levels not the least of which is the sensationalized movement to a 21%/400pm slope when many of the quantities described are not linear. It's a shame, it looks like the work was well done, but the data analysis and messaging is poorly thought out.

First it's clear the cognitive measure they use is not linear (i.e. if you are a 1 and I am a .5 you are not twice as smart as I am) This is particularly clear if you extend some of these lines and see by increasing the level of CO2 they are reducing individuals to 1/10 the cognitive capacity of a normal human.

Second, they aren't using a normative group, they are taking their sample of <2>
It seems relatively clear there should be a measurable effect of high concentrations of CO2. Just like I would expect a measurable positive effect of high concentrations of O2. In my opinion, if you wanted to create a credible scientific paper on the subject you would need to define a baseline cognitive measure, establish the scale of variations in this measure (changes due to lack of sleep, caffeine intake, serious brain trauma, etc) as well as variations across different individuals. And then run a series of tests to establish the functional form of the impact of CO2 on the measure. The result would be an indication that 400 ppm impacts your cognitive ability similar to missing 2 hours of sleep, or drinking one glass of wine, etc. which would provide a grounding to the work missing in the current paper - rather than drawing a line between 3 points and extrapolating...
posted by NoDef at 6:55 AM on August 14, 2016 [1 favorite]

You've already gotten some good answers here. I haven't had enough time to read all of the papers cited in all the papers linked, at least one paper referenced another paper (Zhang et al, 2016) which implied that it wasn't CO2, but rather other human effluents which were causing problems. But you said early on that CO2 was poison. If it is poison, it's a poison you emit, just like you emit methane.

Also, you mention how the CO2 is messing up other organisms. But that's not really quite correct - and the sources you link are actually fairly specific. CO2 doesn't harm the shellfish directly, it's the fact that the ocean is acidifying. I realize this may sound like a nitpick, but it's important to point out that acidification can be caused by other compounds, not just CO2. Similarly, the other issues for plants are caused by other problems - acid rain, knock-on effects caused by the CO2. And the plankton aren't harmed at all; the problem is the ecological issues caused by their blooms enabled by CO2. The point I'm getting at is that it's quite unlikely that CO2 is, in and of itself, the cause of anything we would call toxicity at these exposure levels. It didn't seem like the papers I had time to read had experimentally confirmed that there were no other potential sources of air pollution OTHER than CO2. The NASA paper mentioned 0.66% CO2 as a problem, but that's 6,600 ppm. That's pretty high.

I work in air monitoring and air sampling, and frankly, we always measure in parts per million or parts per billion. Seeing a concentration in the % range for anything we test for is alarming (and has also never happened to me personally), and I'm also pretty sure that no human intervention can get CO2, or any other compound, to % levels in the air anytime soon. Not only that, but with the commonly available (expensive!) gas monitors, particularly equipment that tests to federal reference methods, can be tough to calibrate and get working to the point where you can confirm there are no other sources of pollutants or compounds that might confound your results. I didn't have a chance to read deeply enough - perhaps someone else can correct me here - but I didn't see enough to confirm that there was ZERO contamination of other air pollutants. Keep in mind that it's common to encounter, among other things, Nitrogen oxides (NOx), Sulfur Dioxides (SOx), Ozone (O3), Carbon Monoxide (CO), allergens, Volatile Organic Compounds (VOCs), Semi Volatile Organic Compounds (SVOCs), aldehydes, metals in the particulate dust...the list goes on and on and you can't necessarily monitor for all of them accurately in real time, and a lot of the commonly available equipment isn't even necessarily that good at it.

I'm not saying these papers are categorically wrong, just that I have more questions than answers about their experimental procedures and interpretations, like other posting. It's pretty easy to get air stuff wrong.

But here's a good rule of thumb for you, personally. Worrying about CO2 is laughably pointless. Every time you smell gasoline or diesel, you're being exposed to far more harm. Every time you smell paint drying, car exhaust, etc., etc. Industrial pollutants are incredibly common, and they're everywhere around you. When I used to sample air in New Jersey, the questionnaire form (for VOCs sampling only) required me to ask building occupants if there was any dry cleaning in the building, if there was an attached garage, gasoline storage cans, new carpet, new furniture, any painting or pesticide application, and a few other things.

That was JUST for the 75 compounds tested on the TO-15 list. You are surrounded by air pollutants literally every day if you live in western society. You have far more clear and present danger from everything that is NOT CO2. If you're going to worry (and I wouldn't unless you work with them industrially or in traffic all day), worry about those first. CO2 is beyond your ability to control or test for effectively as an individual, anyway.
posted by Strudel at 8:33 AM on August 14, 2016 [6 favorites]

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