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Q: elevated CO2 and humans ( Answered 4 out of 5 stars,   1 Comment )
Subject: elevated CO2 and humans
Category: Science > Earth Sciences
Asked by: jigari-ga
List Price: $8.00
Posted: 29 Apr 2003 14:07 PDT
Expires: 29 May 2003 14:07 PDT
Question ID: 197162
What can elevating CO2 do to humans? Although increasing CO2 is
thought by many to cause global warming, I am interested in effects on
humans that are not related to climate change. That is aside from
possible climate change, how else can elevated CO2 affect us either
indirectly or directly?
Subject: Re: elevated CO2 and humans
Answered By: shivreddy-ga on 29 Apr 2003 15:38 PDT
Rated:4 out of 5 stars

Thank you very much for your question. Yes of course, the increase in
CO2 levels in the atmosphere leads to what scientists term as the
Greenhouse Effect. However as you have suspected, there are certainly
more adverse effects of elevated CO2 concentrations. Most of these
adverse effects affect human beings directly and most others are
indirect. The elevation in CO2 level is termed as Hypercapnia.

"The atmosphere's CO2 concentration is increasing at a rapid rate in
the context of both evolutionary and ontogenetic time scales.  Since
the start of the Industrial Revolution, it has risen by about 35%,
from approximately 275 ppm to 375 ppm; and it will likely continue to
rise for quite some time.  What will be the ultimate consequence of
this ubiquitous environmental change for human health?"
How Will Future CO2-Enriched Air Affect Human Health? 
Volume 5, Number 48: 27 November 2002

In point form I have listed the different effects of  elevated
concentrations of CO2 on human beings.

1) Hypercapnia lowers the shivering threshold and increases core
cooling rate in humans. Along with eucapnic hypoxia, hypercapnia hence
has intense effects on human temperature regulation. Research work,
both current and past have been done on this subject. I have found
abstracts and mentions of such research here:

"Johnston CE, DA Elias, AE Ready and GG Giesbrecht. Hypercapnia lowers
the shivering threshold and increases core cooling rate in humans.
Aviat Space Environ Med. 67: 438-444, 1996"
"V Lun, JCL Sun, GG Giesbrecht and IB Mekjavic. Shivering
thermogenesis during acute hypercapnia. Can J Physiol Pharmacol. 72:
238-242, 1994."

2) Effects of Hypoxia and Hypercapnia on Human Red Blood Cell ATP
Release. I found a mention of this as part of a project details of
which are given below:
Upstate Medical University Department of Medicine Student Research
Fellowship  Summer 1999
Mentors: Dr. Tawfic Hakim, Associate Professor, Department of Medicine
Dr. Jeffrey Freedman, Associate Professor, Department of Physiology

Details : "...conduct research with Dr. Hakim and Dr. Freedman in the
field of red blood cell physiology. I gained experience in grant
application preparation, phlebotomy, measurement and manipulation of
blood gases,  determination of ATP release and hemolysis, and data
entry and analysis..."

3) Effect of carbon dioxide on diaphragmatic function in human beings.

"...Our results show that contractility was reduced with hypercapnia
(when end-tidal carbon dioxide was 7.5 per cent or higher), although
hypocapnia (end-tidal carbon dioxide, 3 per cent) had no effect on
diaphragmatic contractility. We also studied the development of
diaphragmatic fatigue before and during carbon dioxide
breathing...Electromyographic signs of fatigue appeared at a lower
tension-time index during hypercapnia than during normocapnia,
indicating that endurance is diminished during hypercapnia."
The New England Journal of Medicine.Volume 310:874-879  April 5, 1984 
Number 14

4)  Physical effects on human beings as detailed in the extract given

"With respect to the direct health effects of CO2-enriched air, it is
known that very high concentrations of atmospheric CO2 can produce a
state of hypercapnia (Nahas et al., 1968; Brackett et al., 1969; van
Ypersele de Strihou, 1974) or an excessive amount of CO2 in the blood
that typically results in acidosis (Poyart and Nahas, 1968; Turino et
al., 1974), which is a serious and sometimes fatal condition
characterized in humans by headache, nausea and visual disturbances. 
However, several studies have indicated that these phenomena have
little to no negative impact on human health until the CO2
concentration of the air reaches approximately 15,000 ppm (Luft et
al., 1974; Schaefer, 1982), which is 40 times greater than the air's
current CO2 concentration and far higher than any concentration that
could ever be produced by the burning of fossil fuels..."
How Will Future CO2-Enriched Air Affect Human Health? 
Volume 5, Number 48: 27 November 2002

5) Sudden increase in CO2 concentration has taken its toll in the
past. While plants flourish with higher CO2 levels, most animals
struggle to breath withextremely high CO2 levels. Rapid elevation of
CO2 levels can be catastrophic (e.g., Lake Nyos) In 1986, volcanic
Lake Nyos erupted huge quantities of CO2, resulting in the deaths of
approximately 1800 people and thousands of livestock upto 25 km away.
High CO2 levels made it difficult for biota that formed
calcareous(CaCO3) shells to make their shells. High CO2in water
isessentially carbonic acid. Silica-shelled life did much better.

6) Effects on the plant life kingdom. This particular point is
important as it indirectly affects us:

"As shown by Idso and Idso (2001), Loladze (2002), and Jablonski et
al. (2002), there are bound to be certain changes in the chemical
composition of wild and agricultural plants in a CO2-enriched world of
the future; and some of the changes in plant quality, such as a
possible decline in the concentrations of essential elements, could
have negative repercussions for human health (Loladze, 2002).  So what
should be done about it? ..."
Researchers Must Pay More Attention to The Role of CO2 in Human
Nutrition and Health
Volume 5, Number 48b: 27 November 2002

Several other points can be drawn from a reading of the excellent
article, "How Will Future CO2-Enriched Air Affect Human Health?" which
I have listed above.

Additional Links and Further Reading:

1) Researchers Must Pay More Attention to The Role of CO2 in Human
Nutrition and Health
Volume 5, Number 48b: 27 November 2002

2) Health Effects of CO2 -- Summary  Center for the Study of Carbon
Dioxide and Global Change  (
3) Van Ypersele de Strihou, C.  1974.  Acid-base equilibrium in
chronic hypercapnia. In: Carbon Dioxide and Metabolic Regulations.  G.
Nahas and K.E. Schaefer (Eds.). Springer-Verlag, New York, NY, pp.

Search Strategy:

"elevated CO2" effects
"elevated CO2" effects human beings
hypercapnia human health
hypercapnia human begins

I hope I have  answered your question in detail. Thank you once again
for your query. Please do not hesistate to request any form of
clarification on the answe I have given above.
Warmest Regards, 
Shiv Reddy

Request for Answer Clarification by jigari-ga on 29 Apr 2003 16:42 PDT
Your answer claims that "Most of these adverse effects affect human
beings directly." However, most of the effects you list relate to
Hypercapnia, which is elevation of CO2 in blood, not atmosphere.
Because increase in atmospheric CO2 is modest (as you write 35%),
claiming that it causes Hypercapnia is absurd, as one needs to
increase atmospheric CO2 by 1000-5000% to have any noticeable effect
on human blood concentrations. Thus, most of your answers are
irrelevant to increase of CO2 in atmosphere. I clarify my question:
what are the effects of rising ATMOSPHERIC CO2 on humans?
Thank you for your time.

Clarification of Answer by shivreddy-ga on 29 Apr 2003 22:52 PDT

Thank you for your 'Request to Clarify'. I will be happy to explain my
answer. Hypercapnia is a condition that is abnormally caused by
shallow respiration or Hypoventilation. However, it is true that
certain ailments due to acidosis is directly related to exposures to
CO2 - rich air. In fact it is the only way atmospheric CO2 affects
human beings with such disasterous consequences. Which is why I have
chosen to list its direct consequences (on increased levels in the
blood). In all I have listed 3 points (the first three) in support of
this view. The remaining 3 points talk about other indirect

As you have already indicated that you are aware, very high
concentrations of atmospheric CO2 can produce a state of hypercapnia,
or an excessive amount of CO2 in the blood, which typically results in
acidosis, a serious and sometimes fatal condition characterized in
humans by headache, nausea and visual disturbances. This condition
will be faced by people who have abnormal breathing patterns and hence
can be sited as a direct effect on human beings of CO2-enriched air.

In all, if you ignore hypercapnia, it will shorten the list
considerably and this is because little other consequnces of elevated
CO2 levels really affect human beings directly or indirectly as the
remaining three points indicate. I will add 3 more points to make the
answer more relevant.

1) There are a certain number of  CO2-sensitive physiological
processes in humans that could well be altered due to rising CO2
levels. A study in this by Idso (1989, reference: has identified several of these processes.

Idso, C. D. and Idso, K. E. (2000). Forecasting world food supplies:
The impact of the rising atmospheric CO2 concentration. Technology 7S,
2) In fact it really is considered 'obscene' to suggest that
increasing CO2 levels in the air can adversely affect humans to a
great extent. Elevated concentrations of CO2 in the atmosphere does
indeed have its onw positive contribution as a reading of the
following editorial will demonstrate.

"We humans, as stewards of the earth, have got to get our priorities
straight.  We have got to do all that we can to preserve nature by
helping to feed humanity; and to do so successfully, we have got to
let the air's CO2 content rise.  Any policies that stand in the way of
that objective are truly obscene..."
Feeding Humanity to Help Save Natural Ecosystems:
The Role of the Rising Atmospheric CO2 Concentration 
Volume 5, Number 36: 4 September 2002

3) On the other hand the imbalance in the system due to the increase
in CO2 levels could have resulted in reduction of a number of
nutrients in plants which are common food.

"...In a recent Opinion piece published in Trends in Ecology &
Evolution, Loladze (2002) conducts what he calls a "thought
experiment," wherein he concludes that the dilution effect of the
extra plant biomass produced by the aerial fertilization effect of
atmospheric CO2 enrichment tends to reduce the concentrations of a
number of micronutrients found in plant tissues, many of which are
important to human health and are currently present in common food
plants in what are believed - by some - to be insufficient quantities.
 Being one of that believing cadre, Loladze suggests that the increase
in the atmosphere's CO2 concentration since preindustrial times may
have caused an elemental imbalance in earth's plants, contributing to
the problem of micronutrient malnutrition, which he says is harming
the health and economy of over half of the world's population..."
Has the Historical Rise in the Air's CO2 Content Negatively Impacted
Human Health? Volume 5, Number 44: 30 October 2002

In essence not much has been done to establish the effects of CO2
"...But what if something really unusual happens, so in a high-CO2
world of the future some people truly do acquire smaller amounts of
certain essential elements than they do currently?  If the truth be
told, we really do not know what the ultimate consequences would be;
for the many potential effects of elevated CO2 on human physiology
that...[I have described earlier in point 1], could possibly alleviate
or compensate for the negative effects of the CO2-induced nutrient
How Will Future CO2-Enriched Air Affect Human Health?

I will end this clarification by acknowledging that indeed, I have
chosen to list out points that were related mostly to hypercapnia. I
did this simply because it was the *only* real effect CO2 had on human
beings. The remaining consequences thereof are indirect or can be
disregarded for lack of deeper research.

"...It must be acknowledged, however, that the potential direct
effects of continuously inhaling modestly-CO2-enriched air are highly
speculative; but that fact only intensifies the need we have to study
these phenomena in greater detail..."
How Will Future CO2-Enriched Air Affect Human Health? 

I suggest you read these highly enlightening articles from the Center
for the Study of Carbon Dioxide and Global Change. They seem to answer
(or leave for want of better research) most of your questions. I find
myself repeatedly quoting them as authoritative sources.

1) Guest Editorial: Elevated CO2 Will Affect Human Nutrition 
Volume 5, Number 47: 20 November 2002

2)Has the Historical Rise in the Air's CO2 Content Negatively Impacted
Human Health? Volume 5, Number 44: 30 October 2002


I hope this completes the answer to your satisfaction. Thank you very
much for your patience.

Warmest Regards,
Shiv Reddy
jigari-ga rated this answer:4 out of 5 stars and gave an additional tip of: $1.00
Hypercapnia effects (that is direct effects of atmospheric CO2 on our
blood concentrations) are absolutely irrelevant to increasing
atmospheric CO2, because atmospheric CO2 levels are too low for that
to happen. However, your answer suggests that elevated CO2 can affect
our nutrition because it directly changes plant quality and this
change is not related to global warming. Indeed, our health can
significantly be altered if crop quality changes globally under
elevated CO2. Your answer suggests that aside from climate change,
what we should be aware of is coming changes in plant quality
worldwide. I puzzled by you repeatedly citing the Center for the Study
of Carbon Dioxide - they are known to be pro-CO2 and advocate against
any reduction in CO2 emissions. I am sure there are other scientific
sources that speak about such changes.
In any case, thank you for your help.

Subject: Re: elevated CO2 and humans
From: shivreddy-ga on 30 Apr 2003 00:10 PDT

Thank you very much for your comments. I was not aware of the
reputation that the Center for the Study of Carbon Dioxide and Global
Change had. I nevertheless found their literature logical and
interesting. I will keenly follow this area and post follow-ups if I
come across any in the future.

Shiv Reddy

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