The red line for plant death on earth is around 150 ppm (below which plants cannot sustain photosynthesis), implying a critical lower limit for CO₂ concentrations below which life would struggle to survive. The optimum CO₂ level for photosynthetic plants & algae is around 1,000 ppm, which last occurred when the first primates arose. Since then, CO₂ levels have been steadily declining.
Yet it is still significantly higher than today’s 400 ppm, after recovering from a low point of 180 ppm during the glacial optimum 26,000-20,000 years ago. CO₂ has been trending downwards from 2,750 ppm 160 million years ago, when a coral diversity explosion occurred & when CO₂ levels were significantly higher.
This downplays claims that higher CO₂ levels will damage coral reefs.
Some background
On Earth, the atmospheric carbon dioxide (CO2) level below which most plants cannot sustain photosynthesis is approximately 150 parts per million (ppm). A drop below this threshold would cause a catastrophic collapse of the biosphere, as land-based plants and the animal life that depends on them would die.
Thresholds for different photosynthetic pathways
The minimum required CO2 concentration for photosynthesis varies depending on the type of photosynthetic pathway a plant uses.
- C3 photosynthesis: This is the most common form of photosynthesis, used by roughly 85% of plant species. Plants with this pathway are the most sensitive to declining CO2 levels and effectively cease photosynthesis around 150 ppm, which also prevents them from reproducing. The CO2 compensation point for C3 plants—the concentration where carbon uptake equals carbon release from respiration—is around 50 ppm.
- C4 photosynthesis: This more efficient photosynthetic pathway, used by plants like corn and grasses, is adapted to function at much lower CO2 concentrations. C4 plants can continue to photosynthesize effectively at levels below 10 ppm, allowing a C4-based biosphere to persist longer under very low CO2 conditions.
Implications for Earth’s history
Historical data from ice cores shows that during glacial periods, or “ice ages,” atmospheric CO2 levels have dropped dangerously low, to 180 ppm of CO2.
Near-extinction: The 180 ppm CO2 level is only 30 ppm above the theoretical extinction threshold for most plant life. This demonstrates how close Earth’s biosphere came to a mass extinction event during these natural planetary cycles.
Glacial maxima: The lowest CO2 concentration recorded during the last several glacial cycles was about 180 ppm. At this level, many plants, especially C3 species, would have been severely stressed, with stunted growth and reproduction.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Really nice summary, short and sweet, no fluff. Appreciate how long it must have taken to keep it so simple and to the point.
Harold The Organic Chemist Says:
At the MLO in Hawaii, the concentration of CO2 in dry pure air is 425 ppmv. One cubic meter of this air has a mass of 1.29 kg and contains 0.84 g of CO2 at STP. Note that there is little CO2 in the air. This is why plants grow ever so slowly.
In air at 70° F and 70% RH, the concentration of H2O is 17,780 ppmv. One cubic meter of this air has a mass of 1.20 kg and contains 14.3 g of H2O and 0.78 g of CO2. To the first approximation and all things being equal, the amount of the greenhouse effect (GHE) due to H2O is given by:
GHE=moles H2O/moles H2O+moles CO2= 0.79/0.79+0.018= 0.98 or 98%
This calculation assumes that a molecule of H2O and a molecule of CO2 each absorb about the same amount of out-going long wavelength IR light. Actually H2O absorbs more IR light than CO2. Shown in Fig. 7 is the IR
absorption spectrum of a sample of Philadelphia inner city air from 400 to 4000 wavenumbers (wns). There are additional peaks for H2O in the 200 to 400 wavenumber range which is below the 400 wn cutoff the spectrometer.
The GHE active range for H2O and CO2 is from 400 to ca 700 wn. Note how narrow the CO2 peak is. CO2 is absorbing little out-going IR light.
The above empirical data and calculations falsify the claims by the IPCC that CO2 causes “global warming” and is the “control knob” for climate change. The purpose of these claims is to provide the UN the justifications for the maintenance and generous funding of the IPCC and the distribution of founds from the rich donor nations to poor nation to help them cope the effects of global warming and climate change. When the EPA issues a recission of the 2009 CO2 Endangerment Finding, the greatest scientific fraud since the Piltdown Man will finally come an end.
NB: Fig. 7 was taken from the essay: “Climate Change Reexamined” by Joel M. Kauffman. The essay is 26 pages and can be downloaded for free.
PS: If you click on the Fig. 7, it will expand and become clear. Click on the
“X” in the circle to return to comment text.
Wow, thanks Harold. I have assumed the water absorption band overlapped the CO2 band due to the fact that H2O is a more powerful CO2 absorber than water. It’s good to get clarity on this. My ignorance on display.
Harold,
Nice comment, from one Chemist to another.
Geoff S
The question is, are the 180ppm correct?
180 YEARS OF ATMOSPHERIC CO2 GAS ANALYSIS
BY CHEMICAL METHODS
by
Ernst-Georg Beck
ABSTRACT
More than 90,000 accurate chemical analyses of CO2 in air since 1812 are
summarised. The historic chemical data reveal that changes in CO2 track changes in temperature, and therefore climate in contrast to the simple, monotonically increasing CO2 trend depicted in the post-1990 literature on climate-change. Since 1812, the CO2 concentration in northern hemispheric air has fluctuated exhibiting three high level maxima around 1825, 1857 and 1942 the latter showing more than 400 ppm.
Between 1857 and 1958, the Pettenkofer process was the standard analytical method for determining atmospheric carbon dioxide levels, and usually achieved an accuracy better than 3%. These determinations were made by several scientists of Nobel Prize level distinction. Following Callendar (1938), modern climatologists have generally ignored the historic determinations of CO2, despite the techniques being standard text book procedures in several different disciplines. Chemical methods were discredited as unreliable choosing only few which fit the assumption of a climate CO2 connection.
For these people telling these measurements don’ t show background CO2 levels:
Accurate Estimation of CO2 Background Level from Near Ground Measurements at Non-Mixed Environments
Francis Massen, Ernst-Georg Beck
Abstract
Atmospheric CO2 background levels are sampled and processed according to the standards of the NOAA (National Oceanic and Atmospheric Administration) Earth System Research Laboratory mostly at marine environments to minimize the local influence of vegetation, ground or anthropogenic sources. Continental measurements usually show large diurnal and seasonal variations, which makes it difficult to estimate well mixed CO2 levels.
Well, for at least short interval of averaging (Oct to mid-Nov, 2014) NASA’s OCO-2 spacecraft provided data that world-wide variations in atmospheric concentrations of CO2 varied over only a narrow range about 387 to 403 ppm, or about +/- 2.0% about the mean. See the attached image.
I would define that as “well-mixed” in the context of global atmospheric chemistry.
Of course, there are many other more recent such images and even movies showing similar levels of uniformity of mixing as the seasons vary over the Earth’s surface . . . even considering NH vs SH.
Your definition of what constitutes a “large” variation may differ from mine.
Hmmm . . . image failed to upload as a JPG file and as a PNG file.
So, here’s the URL to the website that has posted the NASA OCO-2 imaging of worldwide atmospheric CO2 variations that I referenced above:
https://climateataglance.com/carbon-dioxide-saturation-in-the-atmosphere/
I have no idea where you see a well mixed CO2 level…
🤔
Nor do I. It looks like there is some CO2 everywhere, but it sure isn’t homogeneous.
Well mixed doesn’t mean completely uniform or homgeneous.
A 2% variation certainly qualifies as well mixed.
Mark,
People do not understand gas analysis if they quote an accuracy of +/- 2% of the mean. This is hard for big high quality lab work, not plausible for satellite work especially of this CO2 design with beams going through an ever-varying atmosphere. Geoff S
Geoff S, apparently you have overlooked how easy it is nowadays to falsify wild assertions by just searching the Web.
Here is what Google’s AI summary says when being queried about “What is the stated accuracy of the OCO-2 satellite measurement of CO2 concentration in Earth’s atmosphere?”:
“The stated accuracy for OCO-2 measurements is better than 0.3% (or approximately 1 part per million or ppm) for its XCO2 data, with recent evaluations showing absolute average biases below 0.4 ppm compared to ground-based measurements (TCCON). The mission is designed to detect CO2 with high precision to identify sources and sinks, and the team continually works to improve data quality through calibration and algorithm adjustments.”
(with linked reference to: https://ocov2.jpl.nasa.gov/whats-new-oco-2 )
You have simply confused a stated +/- 2% variation in data measurements (the variation across a data set) with a claim of measurement accuracy to +/- 2%.
Jim, at what percentage of variation do you consider chemical concentrations in Earth’s atmosphere to be “homogeneous”.
Some choices for you:
+/- 5%
+/- 1%
+/- 0.1%
+/- 0.001%
+/- 0.0001% (i.e., 1 pmm?)
Not that I’m expecting any response, of course.
Homogeneous means what it says. The same throughout a substance. The fact that you list variations means it is not homogeneous.
In that case, nothing is ever homogeneous, it is an impossible standard.
The finer the resolution, the more impossible the goal.
That’s one of the reasons why they talk of well mixed, not homogeneous.
A semiconductor substrate is supposed to be homogeneous. Impurities are added such that they are equally distributed. Of course that is darn near impossible. But it also means they are not homogeneous. There is a heterogeneous distribution. Words and definitions matter.
Uh-oh, now you’ve done it!
As MarkW correctly points out, the term “homogeneous” (like the term “heterogeneous”) is context dependent. If you take any mixture and look at it on the scale of intermolecular distances it will exhibit inhomogeneity.
Is a cubic km of the atmosphere homogeneous?
How about a cubic meter?
How about a cubic mm?
How about a cubic micron?
Does the fact that I list various volumes mean that atmospheric air in one cubic meter volume cannot possibly be considered to be homogeneous across that volume?
ROTFL.
The terms are not context oriented. Homogeneous means homogeneous. If it’s not, then it is heterogeneous. If you wish to assume that low concentrations allows one to treat the material as homogeneous, then you should say so.
BTW, I haven’t mentioned uncertainty. What is the uncertainty of these measurements? A measurement is not complete w/o an uncertainty.
And, going one step further, an uncertainty is not complete without knowing how it is developed and what measurements go into its determination and whether or not they are biased to one side of the mean (e.g., +1.7%/-0.6%). Sources of uncertainty that need to be defined:
— measuring instrument calibration accuracy and when last calibrated
— accuracy of the referenced standard
— measuring instrument drift rate
— mathematical inaccuracy resulting from statistical variation of analysis of a given data set obtained over time (can be a function of assumed trend function, e.g. linear, exponential, second-order polynomial, power law, etc.)
How many people, let alone scientists, really expect all these details to be delineated for each and every value presented in a written article or during discussions?
Example: mention that the atmospheric CO2 concentration level as measured by the NOAA Mauna Loa observatory was 424.25 ppm for the week beginning September 7, 2025. On their webpage that cites this value (https://gml.noaa.gov/ccgg/trends/weekly.html ) NOAA does not say whether this value is homogeneous or heterogeneous, nor do they cite an uncertainty associated with this published value.
“It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible.”
— attributed to Aristotle
Related to that, what lateral or vertical variance would you consider as a cutoff for something being non-homogeneous? Or, does it vary with context? You of all people should understand that nothing is perfect and there are going to be impurities and variations in the compositions of everything, even 24kt gold.
I do understand that nothing is perfect. That is why homogenous has a meaning. When I was learning about semiconductor substrates and doping for characteristics, homogeneous was the goal because impurities could ruin a whole chip. We all knew that wasn’t possible due to being unable to measure beyond a certain point. That was one of my first introductions to measurement uncertainty and quality control in production processes.
Nothing in the world is really homogeneous unless produced under very controlled conditions. The very fact that there are point sources of CO2 from anthropogenic burning means the concentrations must vary at the levels we measure temperature at. Otherwise, surface measurements and satellite measurements of temperature should agree completely.
Homogenous or well mixed means that CO2 values should be in perfect correlation among all the measuring stations at all times. The fact that there are seasonal variations means there must be areas where concentrations are higher and lower. Maybe I’m being pedantic about the descriptions used, but using averages to declare that something is homogenous just doesn’t appear to be a good assumption without adequate proof.
It depends on the purpose of the claim and the scale. At a mega-scale, the composition of a salt crystal is homogeneous. However, at an atomic scale, the crystal regularly alternates between sodium and chloride ions. However, even at the mega-scale, an in situ salt bed has inclusions of gypsum, clays, and sulfur. Whether to call it homogeneous or not probably depends on the intended use. That is, for human consumption, greater homogeneity would be required than for making blocks of salt for cattle, or as a feed-stock for a chemical process that required sodium chloride.
CO2 may not be perfectly uniform, but when compared to how water vapor varies spatially, it is very much more uniform.
I just replied to your first post about this. You are correct that it matters what the final use is. However, But in the end, one has to say something is 99.99% homogenous which is not 100%. Or you have to say it is heterogeneous at .01%.
What I’m trying to point out is that declaring CO2 well mixed at the altitudes we measure surface temperature at is an assumption that allows climate science to declare that CO2 average values is all that is needed to use CO2 as a control knob for global temperature. This along with a host of other average values such as insolation adds up to a back of the envelope calculation that his lucky to be plus or minus 50%.
The picture provided shows it.
Look at the color contour legend at the URL I posted that shows the range of CO2 concentration levels that are displayed on the world-wide color map. As I clearly stated, I consider a CO2 concentration that varies less than +/- 2% over the Earth’s surface to be “well mixed”.
Perhaps that will give you some idea.
What I see are the data min387ppm and max402 ppm, they correspond to the increase of the mean of the years 2009-2015/2016.
I have no idea what data you are looking at, but for the image I referenced that is available at https://climateataglance.com/carbon-dioxide-saturation-in-the-atmosphere/ , the image title clearly states it is the range of 387–402.5 ppm CO2 as averaged over the period of Oct 1 – Nov 11, 2014.
That’s just six weeks, not several years, and is only from year 2014.
Please look again.
Maybe my answer wasn’t clear.
I would say, that the lower limit and upper limit correspond to the respective increase of global average CO2 measured at ML fom 2009 to 2015/16
You are free to say what you want, but the fact is that the graph I referenced, with its color scale for min and max CO2 concentration values is clearly labeled to indicate it covers OCO-2 data obtained from Oct 1 to Nov 11, 2014.
Period.
So is the Mauna Loa measurement the +2% or the -2%?
Well, the monthly data from the NOAA Mauna Loa observatory (ref: https://gml.noaa.gov/webdata/ccgg/trends/co2/co2_mm_mlo.txt )—had you bothered to look—shows the following:
monthly average October 2014: 396.16 ppm CO2
monthly average November 2014: 397.40 ppm CO2
Both of these measurements are within 0.7% of the median of 394.8 ppm obtained by reference to the OCO-2 color contour plot limits I referenced for the period of Oct 1 – Nov 11, 2014.
So, maybe—just maybe— you can conclude for yourself that the agreement between OCO-2 and the NOAA observatory at Mauna Loa is better than 1% for the period in question.
You are attempting to justify the use of averages in a calculation of the effects of a continuous phenomenon. Temperature and radiation is related using an exponential function. Using averages short circuits the actual results and can mislead one into false conclusions.
If you want to claim an average value is an actual measurement, then you must also provide the variance associated with that calculation.
An average CO2 value is also a time series. What effect does auto-correlation and seasonality have on the value.
Absolutely incorrect. I have been referencing a contour graph/image of measured data (obtained from the OCO-2 spacecraft instrument designed to detect CO2 to a high level of accuracy) averaged over about a six week period. There is no “calculation of effects of a continuous phenomenon” involved.
Please look up the definitions of “measurement” and “calculation” and understand the difference.
Dude I don’t need you to “educate” me.
I have made measurements all my life. Not once have I averaged measurements of different things to obtain an “average measurement” of all of them. For an engineer, that would be unethical and probably result in failure somewhere in a project.
I have used averages for time series to make projections, those are calculations. They are tempered with uncertainty obtained from the measured estimates. And, I can assure you, averages of more and more different things does not reduce uncertainty of the mean value.
You need to read and understand what GUM F.1.1.2 means about samples of a property which is what you are talking about. Here it is so you don’t need to find it.
Your calculation of 1% has nothing to do with measurements. It assumes each value is 100% and the difference is somehow meaningful.
Well, there you have it in a nutshell! I’m at a loss to understand what “each value being at 100%” means; furthermore, if “each value is 100%” how there can be a “difference” between them.
Nevertheless, I am so happy to hear that you’ve made measurements “all your life”. We’re any of them meaningful?
P.S. I’m sure you don’t know this, but “dude” was originally a synonym for “rags” and later a derogatory Old West term for “dandy.” Thanks, but no thanks.
“Well-mixed” is whatever it is defined to be for the task at hand.
But it needs to be included as an uncertainty value when used for calculations. Simply assuming well-mixed allows climate science to allow that there is no effect due to distribution so using averages is also appropriate. It is just one more example how averages can hide pertinent information.
Well, that’s your definition.
Thank you, Krishna,
It is a travesty that poor scientist activists dismiss the Beck work. As an analytical chemist in the olden days, I have little concern about claimed inaccuracy of these older CO2 analyses. Most of them seem top class. Beck properly notes and questions some of them for stated logical reasons.
The blanket rejection of CO2 levels is mostly because the samples were taken not in the rarified isolation of Mauna Loa or the South Pole, but in normal living and working environments. This misses the point that Nature cannot tell the difference between these types of CO2. They all do the same things with the physics of radiation, raising the air temperature as CO2 rises (if you subscribe to that mechanism) whether in a German village or isolated Cape Grim.
Then there is the matter of CO2 pathways. Studies in corn fields show large CO2 variations through the day reacting to plant growth and death. What value should be adopted for modelling?
Much CO2 might live an isolated life, never travelling far enough to reach Mauna Loa. Power station CO2 emissions at high concentrations might simply travel a few km (or tens or hundreds of km) before being immobilized by dissolving in rain or lake water or trapped in new plant growth or absorbed in soils. All of the time that it is in the air as a gas, it is subject to CO2 radiative physics but is not measured. The basis of global warming estimates from Mauna Loa CO2 concentrations is wrong.
Beck must be taken seriously. His work has to be added to ways that climate sensitivity is currently calculated.
Geoff S
Well said!👍
Unfortunately H.-G. Beck died while working on his habilitation.
What matters is not the source of the CO2, but the fact that cities are major sources of CO2, and sources that changed rapidly over time. It’s like putting a temperature sensor inside a busy airport, vs putting it in a field well away from extraneous sources of heat.
Cities major sources of CO2? Not in my book. Cycling between air and ocean is immensely greater.
BTW, where you put the thermometer depends on what you seek to measure. Much action derives from people trying to validate greenhouse warming theories, so far with little success. This one-eyed research detracts from neutral studies of the overall picture of CO2 in global settings, to the detriment of the advance of science. Geoff S
Even if a lot of people cycle, the vast majority drive cars.
Then their is heaters and water heaters, as well as various businesses and their energy consumptions.
Cities are definitely major sources of CO2 and the rate of CO2 production varies dramatically depending on time of day and time of year.
Measure CO2 above the rainforest over day and night, you will wonder…
In your opinion, unless every cubic foot of atmosphere has the exact same concentration of CO2, then CO2 isn’t well mixed?
Yes, there is at least one animation produced by NASA that shows the diurnal respiration of plants over a year.
We are allways told, CO2 is well mixed worldwide, fact is, it isn’t, independent of the sources.
Nobody has provided any evidence that it isn’t.
Mark,
You need to balance emissions with captures or you argue with only half the story. Geoff S
Current content does just that.
If plants could talk.
They would say: We are hungry and starving. Give us more CO2.
Not only did primates develop when the CO2 levels were higher, the geographic distribution of primates was also much greater when the climate was WARMER.
The fossil evidence indicates that the widest distribution of primates probably coincided with the very warm period known as the Miocene Climate Optimum.
As the modern Earth exhibits higher CO2 levels and warmer temperatures – and moves closer to the ideal condition for humans and the rest of the primates, the alarmists are telling us this constitutes an existential threat to humanity?
Do they know any human physiology or basic biology at all?
Top 10 countries by Population Density:
Macau (China)
Monaco
Singapore
Hong Kong
Gibraltar
Bahrain
Vatican City
Maldives
Malta
Bangladesh
Sint Maarten (NL)
Bermuda (UK)
Palestine
No Canada, Russia or Iceland. Yes Bahrain, Bangladesh and Bermuda. Climate is clearly a factor.
Had to look up climate of Gibraltar… Reliably 50F-85F
“Red Line of Death”
-giggle-
this information is actually the straw that could bring the climate hoax to its knees
Excellent summary article, especially for noting the difference in CO2 “starvation levels” between C3 and C4 photosynthesis pathways in different plants.
FWIW,
— among the best-known C3 plants: wheat, barley, rice, oats, all forms of beans, potatoes, sweet potatoes, yams, squashes, melons, and sugar beets and most trees,
— among the best-known C4 plants: maize/corn, sugarcane, sorghum, and millets,
— grasses (a common food for horses, cattle and other grazing animals) are split about equally between C3 and C4 types,
— marine phytoplankton and algae predominantly use the C3 pathway, although most marine species have evolved CCMs (carbon concentrating processes) to use bicarbonate from seawater—much more abundant than dissolved CO2 at an ambient water pH of around 8—to increase the concentration of CO2 around the RuBisCO enzyme.
However, all plants—even C4 type—need CO2 to combine with sunlight, water, and ground- or water-based nutrients to produce carbohydrates/sugars, the basis of metabolic life on earth.
As paleoclimatology and just the last 100 years have both shown, increasing atmospheric CO2 levels to concentrations of 2000 ppm or higher is a good thing, resulting in the “greening” of Earth and more food and oxygen for all life forms.
Almost forgot to mention: the zooxanthellae—more properly classified as a class of algae than a class of plants—that inhabit marine coral in a symbiotic relationship and uses photosynthesis for energy and to produce food for its fellow animal . . . yep, also uses a C3 type of photosynthesis pathway!
The coral’s “waste” products, such as carbon dioxide and ammonia, provide essential nutrients for the zooxanthellae to perform photosynthesis and grow. In turn, the zooxanthellae products, such a sugars, fats, and proteins, provide essential nutrients for the coral polyps to build structure and grow.
The “web of life” on planet Earth, gotta love it!
Amazing, innit, how CO2 “drives climate” from behind. It’s sort of a back seat climate driver.
This is really important and needs to reported worldwide using every information outlet there is. If we can get the average guy to understand this the CAGW clowns will be told to hit the road.
I’ve been making similar comments for several years now, after reading Dr Patrick Moore (early Greenpeace member) discuss how low CO2 levels triggered multiple mass extinctions on the Earth. Additionally, I read a bit about greenhouses and found that their CO2 levels are normally 1000PPM or a bit more.
Add in the fact that the earth is in an Ice Age (we’re in the warmer glacial period) and one can see that that the entire CO2 scare is just a worldwide economic shakedown by a bunch of grifters.
A needed correction in the first line of your second paragraph:
“Add in the fact that the earth is in an Ice Age (we’re in the warmer
glacialinterglacial period) and one can see . . .”Also, it is only some greenhouse growers that choose to raise their internal greenhouse air CO2 levels to the range of 800-1200 ppm so as to maximize crop yields/growth rates. Many of the smaller greenhouse growers don’t want to spend the money to do so and are content to grow their crops just using ambient air (at about 420 ppm).
Otherwise, right on!
Thank you very much for the corrections. In my haste, I missed the ‘inter-‘
And appreciate you letting me know that many smaller greenhouses don’t want the additional expense of raising CO2 levels. In the future, I will simply state that 800-1200 is optimum for greenhouses.
I think that it should be self-evident, but rarely thought about, that organisms tend to be optimized for the prevailing environmental conditions when they first stabilize their evolutionary changes. That is, changes, such as tolerance to different conditions, lag the changes and tend to be slow if the changes go against their fundamental character.