[Bored chemist]

It's fairly strongly acidic, It's enough to mess up blood chemistry at concentrations well below those which cause suffocation.
And the thing about drinking carbonated drinks is a red herring too.
The stomach puts up with quite a high concentration of HCl,
but it's bad news to breathe it.
(not to mention the fact that much of the CO2 in cola is burped out)

[damocles]

From Bored chemist:

Quote from: MoreCarbonOK on Today at 05:19:44
henry@bored chemist

sorry
I thought all European chemists knew what I meant
it is Roempps Chemie Lexicon,
(Germany)
it has all the chemical properties of any known substance.


Not all European chemists speak German.
Even Google doesn't recognise it.
Did you mean "Rompp Chemie Lexikon"
(It's a bit useless unless you have log-on credentials and read German)
and, if I am looking for information about human health I will look at the journals that cover that field, like the BMJ, rather than one that specialises in chemistry.

In the meantime, it's good to know that these people didn't really die.
http://www.dailymail.co.uk/news/article-1083623/Two-French-wine-makers-suffocated-carbon-dioxide-fumes-grapes-treading.html

Sorry BC, but I have to side with henry on the subject of CO2 toxicity.

• First there is the issue of Rompp/Roempp -- these are two alternative renderings of the German o with an umlaut. English does not have any accents over letters, so there are two alternative renderings of Schrodinger/Schroedinger, etc. However Roempps Chemie Lexicon is a printed volume dating from the 1970s (when I started my career as a chemistry researcher/teacher) and climate science has moved on a long way from then. But if henry is only quoting Roempps values for LD50 there would not be too much wrong with them.

• There is also the fact that most urban dwellers are breathing air containing up to 1% CO2 most of the time. The fact that CO2 levels decrease from the source is in fact one of the main points that helps us to unravel the carbon cycle. It is also the reason why the readings for CO2 levels in places like Bulgaria are elevated, and should not be used as the basis of any argument that CO2 levels have exceeded 400 ppm many times in the recent past. There are certain "remote location" monitoring stations which are effectively controlled for CO2 levels: these include Mauna Loa (Hawaii), Cape Grim (NW Tasmania), Amundsen-Scott (South Pole), American Samoa, etc.

• It is also a fact that levels of 400 ppm have no toxic effects on humans. When we get to levels of 10% and above then we need to consider the possibility. At lower levels it is unlikely that there are any chronic effects of toxicity, and is there not some evidence that CO2 helps the breathing reflex?

• The French wine makers who were unfortunately killed almost certainly met their deaths as the result of "pooling". A gas that is heavier than air will accumulate under the influence of gravity while it remains unmixed into the air. Once mixed, it will not "unmix", but until it mixes in it can form pools in low lying areas or near strong sources, and exclude the oxygen.

[MoreCarbonOK]

Thank you, Damocles, for coming to my help there. I appreciate. I rely on my Roempps more than Wiki, which I often find "adapted" and "controlled" to fit in with general opinion. It won't be long and we will be back to like it was in German Nazi time, with all information being controlled (by the anti-christ).

Did you perhaps catch my argument here:

we have seen in my posts that the increase in CO2 from 0.03% 0.04% has caused a change in the biosphere:it has started booming. That is why we started adding CO2 in real greenhouses: you want big fruit & vegetable.

What is the logical consequence of this increase of the greening of earth?
What I have noted from my analyses of weather stations from all over the world is that where the change
in vegetation was dramatic, like in Las Vegas, which changed from a desert into a green paradise, in a relative short period of time, some heat gets trapped. Exactly the opposite happened in Tandil (ARG), where deforestation was noted. (If you want to see my tables, ask Imatfaal to approve links to my blog)
In the end, what I concluded from my tables is that
earth is warmed by
1) the sun, mostly
2) by itself (volcanic, core, lunar etc.), a little
3) by the increase in vegetation, a very little bit, due to entrapment of heat

Seeing that I also could see from my tables that the sun is going to take a nap (a figure of speech) I decided that more CO2 and more vegetation is good, to help us against the common (coming) cold....

Follow the results on my blog and you will begin to realize that we are only 6 or 7 years away from the droughts that became known in history as the Dust Bowl droughts 1932-1939 (USA). I think we will not be able to stop that from re-occurring.

Do you understand me now?

You are probably going to argue that this does not prove that CO2 on its own also does not trap heat, so how can I be sure?
Well, I did investigate that matter, at the very first beginning when I started to look at this problem. Here in Pretoria we get a lot of inversion, during winter times. In winter, also, people start burning fossil fuels for heating. So in winter there is elevated CO₂ in the air. What I did was checking the rate of the trend in warming in winter months and compared it to the rate of the trend in warming in the summer months (in Pretoria) from 1973 to present (2011, at that time). There was no difference. If anything, the reverse was true. It is a pity that I lost my own report on that, when they made changes to my blog, so I cannot give you a reference. However, I think we can repeat the statistical analysis.

[damocles]

henry I am very much afraid that you are not listening nor reading carefully. You are also being very repetitive with your arguments. If you fail to convince people the first time you put a particular argument you are not likely to do anything other than annoy them by repeating it. I cannot really be bothered to point out all of your misconceptions, many of which would be eliminated if you were to read a bit of chemical thermodynamics, which I would hope would not be part of a conspiracy theory!

henry from reply #35 and repeated in reply #42

In the end, what I concluded from my tables is that
earth is warmed by
1) the sun, mostly
2) by itself (volcanic, core, lunar etc.), a little
3) by the increase in vegetation, a very little bit, due to entrapment of heat

If most of the Earth's warmth comes from the sun, then there is a very simple radiation balance equation that can be performed to calculate an equilibrium temperature at a planet whose distance from the sun is the same as the Earth's. The result is that the average temperature at the Earth's surface "should be" –20°C. In fact, fortunately for us, the average temperature is actually +15°C. Is something wrong with the model? Well, no, because we can observe the moon, which qualifies as a planet the same distance from the sun as the Earth, and we find an average temperature of –20°C.
The Earth's internal heat generation can account for at most about 1°C. (I have no idea what the third source of heat can be but I note that you say that it is even smaller than the geothermal contribution). So what is missing from the model? The greenhouse effect, which is around 90% due to water vapour and around 10% due to carbon dioxide. So if there is a natural greenhouse effect contributing around 35°C and human activity is putting more greenhouse gases into the atmosphere, there would at least be a prima facie expectation of an increasing temperature.

henry from reply #42:

I rely on my Roempps more than Wiki, which I often find "adapted" and "controlled" to fit in with general opinion.

damocles from reply #41:

However Roempps Chemie Lexicon is a printed volume dating from the 1970s (when I started my career as a chemistry researcher/teacher) and climate science has moved on a long way from then. But if henry is only quoting Roempps values for LD50 there would not be too much wrong with them.

The fact is that Roempps on anything to do with climate science is about 40 years behind the latest research, while wikipedia is right up with it.

henry from reply #1:

Any (good) chemist knows that there are giga tons and giga tons of bi-carbonates dissolved in the oceans and that (any type of) warming would cause it to be released:

HCO3- + heat => CO2 (g) + OH-.

This is the actual reason we are alive today.

Damocles in reply #41 pointed out that urban air typically contains rather more CO2 than remote location air. This indicates strong sources of CO2 in or near major cities rather than CO2 being emitted from the oceans (even if the latter were not clearly ludicrous for good reasons of chemical thermodynamics).

And finally henry tried to use figures from 2 stations in Eastern Europe that were not in the network of remote location stations to indicate that CO2 levels had exceeded 400 ppm in the recent past -- undoubtedly they had indeed indicated this, but that is only because they were close to sources, and the daily readings would depend on which way the wind was blowing.

[MoreCarbonOK]

henry@damocles

You are not good at providing actual (measured) results (from tests) that prove your position, like I do. No word on my results here on Pretoria where elevated CO2 during winter does not cause any change in the difference of Tmax- Tmin compared to summer months. It is you who keeps on referring to calculations that are based on misconceptions. For example, we know that at TOA the TSI is reasonably constant but incoming at sea level is what varies. In this respect, Trenberth simply forgot that besides ozone, the E-UV from the sun also produces peroxides and nitric oxides that also back radiate. The oceans (SH, mostly) then get less F-UV. Incoming UV is immediately transferred to heat, due to the strong absorptivity of water in the UV.
If you go back to that solar spectrum that I showed you, and to Trenberth's papers,  you can see that the peroxides and nitric oxides are not mentioned.
So, on 1) there is a large unknown factor, also known as Trenberth's missing energy. I think I found it. My results suggest that earth is most likely on an 88 year A-C wave, the so-called Gleissberg solar/weather cycle, with ca. 44 years of warming followed by 44 years of cooling.
On 2) you have no specific values because nobody has
On 3) we can say from the results that (more) vegetation does trap some (extra) heat, but it won't be such a lot. Rompps does report some values for this in 1974, (sonnenenergie) and it is not so much. Either way, it is not up to date. I could not find any other up to date values. Note that there has been a big increase in greenery over the past 40 years.

[Bored chemist]

From Bored chemist:

Quote from: MoreCarbonOK on Today at 05:19:44
henry@bored chemist

sorry
I thought all European chemists knew what I meant
it is Roempps Chemie Lexicon,
(Germany)
it has all the chemical properties of any known substance.


Not all European chemists speak German.
Even Google doesn't recognise it.
Did you mean "Rompp Chemie Lexikon"
(It's a bit useless unless you have log-on credentials and read German)
and, if I am looking for information about human health I will look at the journals that cover that field, like the BMJ, rather than one that specialises in chemistry.

In the meantime, it's good to know that these people didn't really die.
http://www.dailymail.co.uk/news/article-1083623/Two-French-wine-makers-suffocated-carbon-dioxide-fumes-grapes-treading.html

Sorry BC, but I have to side with henry on the subject of CO2 toxicity.



• There is also the fact that most urban dwellers are breathing air containing up to 1% CO2 most of the time. The fact that CO2 levels decrease from the source is in fact one of the main points that helps us to unravel the carbon cycle. It is also the reason why the readings for CO2 levels in places like Bulgaria are elevated, and should not be used as the basis of any argument that CO2 levels have exceeded 400 ppm many times in the recent past. There are certain "remote location" monitoring stations which are effectively controlled for CO2 levels: these include Mauna Loa (Hawaii), Cape Grim (NW Tasmania), Amundsen-Scott (South Pole), American Samoa, etc.

• It is also a fact that levels of 400 ppm have no toxic effects on humans.

.
Where are these urban dwellers who get 1% CO2?
The levels I have seen are about 500 ppm at the most.
http://www.ars.usda.gov/SP2UserFiles/ad_hoc/12755100FullTextPublicationspdf/Publications/sookim/ElevatedAtmosphericCO2ConcentrationandTemperatureAcrossanUrbanRuralTransect.pdf

http://digitalarchive.gsu.edu/cgi/viewcontent.cgi?article=1032&context=geosciences_theses

(Page 31 to save you time.)
LD50 is about lethality.
Do you understand that things can cause toxicity at levels that don't kill half the population?
And, since nobody said that 400 ppm would kill (or harm) anyone, it's a red herring.

And I still maintain that a book that most people can't read isn't the best thing to cite.
(BTW, how old are the data)

[damocles]

Where are these urban dwellers who get 1% CO2?

Indoors, mostly.
From wikipedia article on indoor air quality

Carbon dioxide
Carbon dioxide (CO2) is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. Humans are the main indoor source of carbon dioxide. Indoor levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity. To eliminate most Indoor Air Quality complaints, total indoor carbon dioxide should be reduced to a difference of less than 600 ppm above outdoor levels. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation. ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.[17] The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks. European standards limit carbon dioxide to 3500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.

LD50 is about lethality.
Do you understand that things can cause toxicity at levels that don't kill half the population?

Yes

And, since nobody said that 400 ppm would kill (or harm) anyone, it's a red herring.

umm ... Is it not a red herring that you dragged in?

And I still maintain that a book that most people can't read isn't the best thing to cite.

Agreed. It is a comfortable reference for henry though, because it dates from a time when we had a much poorer understanding of climate science, and the issue of global warming had not been recognized.

(BTW, how old are the data)

As far as most of the content of the reference is concerned, 40 years plus. As far as LD50 is concerned, anything up to 100 years. But that is not really important because an old measurement of LD50 is likely to be just as reliable as a recent measurement.

[damocles]

I said:

Quote
And, since nobody said that 400 ppm would kill (or harm) anyone, it's a red herring.
umm ... Is it not a red herring that you dragged in?

 My apologies, BC. On re-reading carefully through the thread I find that in fact it was henry who introduced the red herring.

bored chemist says
Also, at levels greater than a few % it is plainly toxic.

henry says
who uses wiki for reference?
roempps suggests that maybe at a few % it becomes a bit uncomfortable, but never toxic.
everything at high concentration becomes toxic eventually, even sugar or salt.
Anyway, we are talking about a few hundredth of a %, not one or two %
...{snip}...

[MoreCarbonOK]

To summarize, we do not know that (more) CO2 causes (more) warming. If it does, probably only very indirectly so, by causing the biosphere to boom. Namely if you look at my tables at Las Vegas, that used to be a desert, you will see the difference Tmax – Tmin decreasing whereas in Tandil (ARG) where they hacked all the trees down, you see Tmax – Tmin rising.
From the beginning I figured that we must rather look at the average change from the average in a specific period of time at a certain place (weather station). To do that you need linear regression.So all of the (black) figures you are looking at in my tables, are the result of a linear regression.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[link to my tables has been removed to please Imatfaal}

My sample of weather stations was balanced by latitude and 70/30 sea/land. I looked at average yearly temps. so that the influence of longitude is cancelled out.
How do I know my tables are right? First of all, if you look at the table for means, you will see that we warmed by about 0.013 or 0.014 degrees C/annum over the past 32 years. A similar result is reported by Spencer and he looked at data from the satellites. Others also reported the same result. So we warmed by about 0.4 K over the past 32 years, on average.
This warming is an average, taking over time. Obviously the speed of warming in each year is different. This is best seen in my first table, on the bottom, where we can see a gradual drop in maximum temperatures that seemed to follow a binomial distribution. In the end, I decided it must be an A-C wave. I hope it is, because if it is not, I am not sure where we will end up.
So, don’t tell me statistics does not work. It works!! And it tells everything you want to know. I am stunned that nobody has yet been able to reproduce my results.They are all just lazy, or they rather do not want to know what the figures are telling us.
[The average temperature data from the stations were obtained from http://www.tutiempo.net.
I tried to avoid stations with many missing data. Nevertheless, it is very difficult finding weather stations that have no missing data at all. If a month’s data was found missing or if I found that the average for a month was based on less than 15 days of that month’s data, I looked at the average temperatures of that month of the preceding- and following year, averaged these, and in this way estimated the temperatures of that particular month’s missing data]
Based on my results, we can see that by 2040 we will be back to where we were in 1950, more or less.

[Bored chemist]

OK, The original assertion from Henry was
 "Wake up out of your dream worlds. More CO2 is better. I hope you at least agree with me on that."
Now whether you think CO2 is only a problem at 65% (according to some rats) and above or about 0.5% (according to OSHA)
or above 300 ppm according to the environment, the point is that more that that cut off (whichever one you choose) is a bad thing so .
Henry's original assertion is wrong above 65%, wrong  above 0.5% or wrong above 300 ppm.
The only question is not if it's wrong, but just how wrong it is.

There is also a ridiculous level of difference between saying that
"most urban dwellers are breathing air containing up to 1% CO2 most of the time."
(1% is 10,000 ppm) and reality saying "Air Quality complaints, total indoor carbon dioxide should be reduced to a difference of less than 600 ppm above outdoor levels. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation. ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.[17] The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks. European standards limit carbon dioxide to 3500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes."

Do the maths- only one of those figures is over 1% and they say that a level like that should only be tolerated for 15 mins or less.

So the assertion that "most urban dwellers are breathing air containing up to 1% CO2 most of the time"
is flatly and obviously false except in the trivial sense that 500 ppm is "up to 1%" because it's massively less than 1%.

"Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. "
Is a statement of the toxic effects of CO2 so can we stop pretending that it's not toxic?

[MoreCarbonOK]

BC says
So the assertion that "most urban dwellers are breathing air containing up to 1% CO2 most of the time"
is flatly and obviously false except

Henry says
how do you know? Typically, they have these concentrations in green houses in Holland where they grow tomatoes.
In submarines they let it go up to 4000 ppm with no effect.
If the place of work is in downtown New York with high rises in the street and lots of traffic, I can imagine that the CO2 gets higher than 1%, especially if there is little or no wind. This is because it is heavy. We have already seen that the danger of the CO2 is not its poisonous nature, but that it is heavy. It takes some time to mix in and diffuse. The benefit of more CO2 in the air is a booming biosphere and this may help us a bit as we are entering a time of global cooling, by (the extra vegetation) trapping some heat. So anything that can help us to stay warm is good. That is good for life.
More carbon is OK.

[Bored chemist]

Thank you for providing me with the data which shows that you are wrong.
"In submarines they let it go up to 4000 ppm with no effect."
Why don't they let it go up further?
Obviously, because it does have an effect (and, equally obviously, not a good effect)
Also, it may shock you to learn that most urban dwellers don't live in Dutch greenhouses.

"We have already seen that the danger of the CO2 is not its poisonous nature, but that it is heavy."
Stop denying reality.
The drowsiness + headaches that were discussed earlier are evidence of a toxic effect.
"I can imagine that the CO2 gets higher than 1%, especially if there is little or no wind. "
Who cares what you can imagine?
I already posted some measurements.
Why do you think your imagination is more important that the truth?


Learn some physics
"(the extra vegetation) trapping some heat".
Plants transpire, in doing so they evaporate a lot of water. Doing that takes energy.
They cool their environment rather than trapping heat.

"More carbon is OK"
True, the problem is that people keep burning it and making CO2.

[MoreCarbonOK]

bored chemist says
Why don't they let it go up further?

henry says
you demonstrate that you still don't understand it.
We have shown to you that CO2 is not poisonous. For pete's sake, you have it in your blood.
Smokers do not die (immediately) from inhaling  near 100% CO2

Obviously, any substance becomes toxic at very high concentrations, even sugar and salt.

However, the rabbits would not die at 65% CO2,  PROVIDED oxygen was kept at 21%
There is the problem. As soon as CO2 goes up, other components of the air go down, especially oxygen, if you are burning something.
And that creates the  problem (of inconvenience) , especially for people with breathing problems.
For people that suffer from hyper ventilation, CO2 is a miracle cure.....
Wiki is not right there, again.

Now go along, ask your doctor or GP , what he writes on the death certificate in the case of a suicide by a person who gasses himself in a car with exhaust fumes.
Hint: it will not be:  CO2 poisening.
CO2 poisening does not exist. You will die of lack of oxygen before you die of CO2 poisening....

Best wishes
MoreCarbonOK

[Bored chemist]

"We have shown to you that CO2 is not poisonous. "
No.
You have cited evidence that, even at fairly low concentrations, it's toxic- for example it causes headaches. These are not due to oxygen deficiency.
If breathing or combustion added 1000 ppm of CO2 to the air then it would remover 1000 ppm of oxygen.
That does reduce the amount of oxygen available, but so does a drop in air pressure caused by the weather.
The changes caused by the weather are rather bigger than those caused by the conversion to CO2
So, it's not the drop in oxygen concentrations which causes the headaches and so on, it's the toxic effect of CO2

Is it that you don't think a headache is a toxic effect or are you labouring under the misunderstanding that the headache is due to oxygen deprivation?

"For pete's sake, you have it in your blood."
For Paracelsus's sake there's lead and cyanide in my blood- but at levels which are not toxic.

"Smokers do not die (immediately) from inhaling  near 100% CO2"
No, but they would die from the nuclear radiation that would need to be produced from converting the nitrogen in the air to CO2.
Would it be better if you understood what you are talking about, before you made comments like that?


"For people that suffer from hyper ventilation, CO2 is a miracle cure....."
Miracle is overstating it- the science is well known- though not, it seems, by you.
However, at least you have accepted that CO2 has a physiological effect that's not just oxygen deprivation.

Taken to excess and in the absence of initial hyperventilation, that physiological effect is, of course, toxic.

"Now go along, ask your doctor or GP , what he writes on the death certificate in the case of a suicide by a person who gasses himself in a car with exhaust fumes.
Hint: it will not be:  CO2 poisening. "
Indeed, it will be carbon monoxide poisoning, because, unlike you, he knows what he's talking about.
Here's a video of a man who is suffering from CO2 poisoning.
http://www.hse.gov.uk/diving/video/co2video.htm

You will probably try to say that it's oxygen deficiency.
No, it's CO2 toxicity.
The sorbent in the rebreather failed, but the oxygen delivery system was working fine. It will have maintained the O2 levels as they should be.

What would it take to get you to realise that you have already cited evidence that CO2 is toxic- you just haven't understood it.

[damocles]

OK then,

First I am owing BC another apology because I said "... the fact that most urban dwellers are breathing air containing up to 1% CO2 most of the time."

I should have said "... the fact that many urban dwellers are breathing air containing up to 0.15% CO2 much of the time."

(Certainly my original statement is a fact in the "trivial" sense pointed out by BC, but I was focussed on the lower limit on the toxicity of CO2 rather than the offence I might have been causing another poster that I was criticizing)

To get a bit of authority into the subject, I am just going to quote a few wikipedia articles about CO2 toxicity. Sorry that you do not recognise that wikipedia articles are authoritative henry, but you should not complain too much because they largely support your side of the story.

From https://en.wikipedia.org/wiki/Carbon_dioxide

Toxicity [edit]
See also: Carbon dioxide poisoning
...{ at this point in the original there is a figure showing the main symptoms of CO2 toxicity. It is colour coded with levels ~1%, ~3%, ~5%, and ~8% . The only toxic effect at ~1% is drowsiness, which the text indicates is both mild and reversible. Some of the indicated effects at the higher levels, 5% and 8%, are quite drastic, however.}...
Main symptoms of carbon dioxide toxicity, by increasing volume percent in air. [79]
Carbon dioxide content in fresh air (averaged between sea-level and 10 kPa level, i.e., about 30 km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location.[80]
CO2 is an asphyxiant gas and not classified as toxic or harmful in accordance with Globally Harmonized System of Classification and Labelling of Chemicals standards of United Nations Economic Commission for Europe by using the OECD Guidelines for the Testing of Chemicals. In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy.[79] Concentrations of 7% to 10% may cause suffocation, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.[81]
Because it's heavier than air, in locations where the gas seeps from the ground (due to sub-surface volcanic or geothermal activity) in relatively high levels, without the dispersing effects of wind, it can collect in sheltered/pocketed locations below average ground level, causing animals located therein to be suffocated. Carrion feeders attracted to the carcasses are then also killed. For example, children have been killed the in same way near the city of Goma due to nearby volcanic Mt. Nyiragongo.[82] The Swahili term for this phenomena is 'mazuku'.
Adaptation to increased levels of CO2 occurs in humans. Continuous inhalation of CO2 can be tolerated at three percent inspired concentrations for at least one month and four percent inspired concentrations for over a week. It was suggested that 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a submarine) since the adaptation is physiological and reversible. Decrement in performance or in normal physical activity does not happen at this level.[83][84] However, it should be noted that submarines have carbon dioxide scrubbers which reduce a significant amount of the CO2 present.[85].

My interpretation of this is that you do not need to worry about chronically toxic effects of CO2 until the level gets to around 2%, and that both BC and henry are overstating their cases. It is also fairly clear that most if not all of the effects attributed to acute toxicity of high levels of CO2 are the result of asphyxiation via removal of the oxygen supply
From en.wikipedia.org/wiki/Indoor_air_quality

Carbon dioxide [edit]
Carbon dioxide (CO2) is a surrogate for indoor pollutants emitted by humans and correlates with human metabolic activity. Carbon dioxide at levels that are unusually high indoors may cause occupants to grow drowsy, get headaches, or function at lower activity levels. Humans are the main indoor source of carbon dioxide. Indoor levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity. To eliminate most Indoor Air Quality complaints, total indoor carbon dioxide should be reduced to a difference of less than 600 ppm above outdoor levels. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation. ...

My interpretation of this is that elevated indoor CO2 levels are indicative of poor ventilation and elevated levels of other more toxic gases, most notably formaldehyde and carbon monoxide, and that some of the reported effects of CO2 toxicity at lower levels should be reattributed.
I know that both BC and henry are likely to want to come back and scoff at "My interpretation of this is ..." but I would really appreciate it if they produce new evidence of why my interpretations of the articles is ridiculous when they do.

[CliffordK (OP)]

Apparently the target for Spacecraft is less than 0.5% CO₂.  However, Apollo 13 got up to about 2% which was considered critical.

"Neurological impairment" was considered to start at about 3%.

http://www.nap.edu/openbook.php?record_id=12529&page=112

Anyway, we are no where near those levels, at least in the typical outdoor environment.  If levels were slowly increased to say 5% over a period of 1000 years, most species would likely adapt (except perhaps some crustaceans).  Although, if things like migraines don't limit the human ability to procreate, potentially humanity would suffer more than other species.

I think the problem is that we are considering Earth, and all our progeny as one large experiment, without knowing the outcome. 

If we get it right, some plants will experience greater growth, and perhaps longer growing seasons.  Potentially we will never see a return of glacial periods.  Possibly enlarged tropical climates, and more pleasant temperatures in northerly climates.  Species may be shifting, and for some, the changes may be too rapid for them to fully adapt.

If we get it wrong, we'll be battling flooding along all the coasts, and `perhaps enlarged arid areas.  Or, if the impact is over-estimated, we will be spending millions or billions of dollars to fix, or put a band-aid over problems that don't exist.

The prudent course of action would be be invest in conservation.

[JP]

I dug this up on wikipedia: 
http://en.wikipedia.org/wiki/Hypercapnia

According to the table it has no significant effects until ~2% concentration in air.  The table comes from an article here:
http://archive.rubicon-foundation.org/xmlui/handle/123456789/3861

To quote from the abstract of that article,

Inhaled carbon dioxide produces the same physiological effects as does carbon dioxide produced metabolically. These effects appear to result from the acidosis induced by carbon dioxide reaction with water, rather than by the CO2 molecule itself. Toxic effects of CO2 do occur when such high concentrations of CO2 are inhaled that severe and disruptive cellular acidosis occurs. This acidosis and its effects are alleviated by lowering the inhaled concentration of CO2.

[Bored chemist]

All this talk of concentrations is beside the point.
Henry said  "More CO2 is better."
It's not.

Incidentally, NASA is in a position to be sure that the people exposed are fit and healthy and also that they are only exposed for a relatively short time.
Using their figures as a potential "target" for atmospheric concentrations would condemn quite a lot of the elderly, the very young, and those with respiratory problems to death. Personally, I don't see that as acceptable morally or in terms of common sense. Killing (even some of) your own young isn't clever.

Also, you may wish to consider that the last time the earth's CO2 levels were regularly above 400 ppm the sea levels were (IIRC) about 5 to 40 m higher.
That wipes out a lot of cities.

[evan_au]

The rebreather accident video shows that as well as having O₂ sensors, the rebreather computer should have CO₂ sensors.
Then they could set off an alarm when the CO₂ levels in the rebreather air get dangerously high.

[Bored chemist]

The rebreather accident video shows that as well as having O₂ sensors, the rebreather computer should have CO₂ sensors.
Then they could set off an alarm when the CO₂ levels in the rebreather air get dangerously high.

In reality, yes: but in Henry's world. no. Because CO2 isn't toxic.
He says  "More CO2 is better."
I think he's wrong.