<p>The file you provided do not have metadata nor context, which make it pretty much useless as it is.</p>

<p>But, by reading the title and as you suggested, we can assume that the unit used in the sheet is mole fraction of <span class="math-container">$CO_2$</span> in air.</p>

<p>Also the value of the data is fitting the range of the <span class="math-container">$CO_2$</span> historic measurements on Earth.</p>

<p>By definition, a mole fraction is the ratio of mole of a given component (solute) over the total mole count in a target solution. In our case, this mean:</p>

<p><span class="math-container">$mole\:fraction\:of\:CO_2= \frac{measured\:CO_2}{total\:mole\:in\:the\:sample\:solution}$</span></p>

<p>This is well expressed and explained <a href="https://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm" rel="nofollow noreferrer">here</a> in the section titled: <strong>Parts per Million by Volume (or mole) in Air</strong></p>

<blockquote>
  <p>In air pollution literature ppm applied to a gas, <strong>always means parts per million by volume or by mole</strong>. These are identical for an ideal gas, and practically identical for most gases of air pollution interest at 1 atm. Another way of expressing this value is ppmv. One part per million (by volume) is equal to a volume of a given gas mixed in a million volumes of air:
  <span class="math-container">$1\:ppm = \frac{1\:gas\:volume}{1\:million\:air\:volume}$</span> at 1 atmosphere pressure.</p>
</blockquote>

<p>Thus a simple conversion can be applied and the equation solved, knowing the weight of a mole of <span class="math-container">$CO_2$</span> and the typical weight of air. To answer your question, mole and volume are interchangeable in this context.</p>

<p>This would be my honest take, considering the limited available information.</p>

<p>About the downward tendency during the 1600: This was around the time when the Little Ice Age began; There was the Maunder minimum (first low) due to a solar spot low and then a small peak and then the Dalton minimum (second low) before the present peak. Here is <a href="https://www.britannica.com/science/Dalton-minimum" rel="nofollow noreferrer">an example</a> of how low the sunspot activity was at that time (especially Maunder) from Britannica.com</p>

<p><a href="https://i.sstatic.net/c78I7.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/c78I7.jpg" alt="Sunspots"></a></p>

<p>Consequences of those two events, detectable already during Maunder was a trend of global cooling and a diminution of the atmospheric <span class="math-container">$CO_2$</span>.</p>

CC BY-SA 4.0
2019-12-16T13:23:10.197Z
Thank you so much for your answer.
Rico1990
CC BY-SA 4.0
2019-12-16T16:30:01.460Z
@Rico1990 - my pleasure ! If this answer your question you are welcome to choose it as an answer, or discuss about anything you would like to clarify.
marsisalie
CC BY-SA 4.0
2019-12-17T19:17:47.117Z
I plotted the data with Excel, to see developments. So now my question, is it plausible to have that downward tendency about 1600 and if why?
Rico1990
CC BY-SA 4.0
2019-12-17T22:01:32.453Z
This was around the time of the Little Ice Age isn't it? You got the Maunder minimum (first low) due to a solar spot low and then a small peak and then the Dalton minimum (second low) before the present peak. Not too much space to explain in length in comments
marsisalie
CC BY-SA 4.0
2019-12-18T05:56:54.213Z
Thank you for that explanation, I‘ll post that as question hat arose out of this threat. Have a good day.
Rico1990
CC BY-SA 4.0
2019-12-19T16:31:39.843Z
Thank you for that edited answer.
Rico1990
CC BY-SA 4.0
2019-12-15T14:15:45.250Z
2019-12-18T15:14:58.087Z
2019-12-18T15:14:58.087Z
marsisalie
<p>I discovered <a href="ftp://data.iac.ethz.ch/CMIP6/input4MIPs/UoM/GHGConc/CMIP/yr/atmos/UoM-CMIP-1-1-0/GHGConc/gr3-GMNHSH/v20160701/mole_fraction_of_carbon_dioxide_in_air_input4MIPs_GHGConcentrations_CMIP_UoM-CMIP-1-1-0_gr3-GMNHSH_0000-2014.csv" rel="nofollow noreferrer">here</a> a set of yearly historical atmospherical CO2-concentrations from year 0 - 2014. Since they haven't mentioned which measure they used, I'm not sure whether it is right to talk about ppm by volume. The name of the file contains the following "mole_fraction_of_carbon_dioxide_in_air_input4MIPs" which leads me to think of ppm by mole. </p>

<p>Do you think  I'm right? </p>

<p>This leading to: is it plausible to have that downward tendency about 1600 and if why?</p>

<p>Thank you in advance for your help.</p>

<p>Edit:</p>

<p>I plotted the data with Excel:</p>

<p><a href="https://i.sstatic.net/YPtXk.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YPtXk.png" alt="enter image description here"></a></p>

<atmosphere><climate-change><co2>
Reference units for CO2 concentration in the atmosphere and meaning of a slight downward tendancy during the 1600
Rico1990
# Reference units for CO2 concentration in the atmosphere and meaning of a slight downward tendancy during the 1600

(Asked by: username_0 on 2019-12-15)

I discovered [here](ftp://data.iac.ethz.ch/CMIP6/input4MIPs/UoM/GHGConc/CMIP/yr/atmos/UoM-CMIP-1-1-0/GHGConc/gr3-GMNHSH/v20160701/mole_fraction_of_carbon_dioxide_in_air_input4MIPs_GHGConcentrations_CMIP_UoM-CMIP-1-1-0_gr3-GMNHSH_0000-2014.csv) a set of yearly historical atmospherical CO2-concentrations from year 0 - 2014. Since they haven't mentioned which measure they used, I'm not sure whether it is right to talk about ppm by volume. The name of the file contains the following "mole\_fraction\_of\_carbon\_dioxide\_in\_air\_input4MIPs" which leads me to think of ppm by mole.

Do you think I'm right?

This leading to: is it plausible to have that downward tendency about 1600 and if why?

Thank you in advance for your help.

Edit:

I plotted the data with Excel:

[![enter image description here](https://i.sstatic.net/YPtXk.png)](https://i.sstatic.net/YPtXk.png)

**Tags:** atmosphere, climate-change, co2


---

## 1 answers

### Answer by username_1 on 2019-12-15. Score: 4 | Accepted answer

The file you provided do not have metadata nor context, which make it pretty much useless as it is.

But, by reading the title and as you suggested, we can assume that the unit used in the sheet is mole fraction of $CO\_2$ in air.

Also the value of the data is fitting the range of the $CO\_2$ historic measurements on Earth.

By definition, a mole fraction is the ratio of mole of a given component (solute) over the total mole count in a target solution. In our case, this mean:

$mole\:fraction\:of\:CO\_2= \frac{measured\:CO\_2}{total\:mole\:in\:the\:sample\:solution}$

This is well expressed and explained [here](https://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm) in the section titled: **Parts per Million by Volume (or mole) in Air**

> In air pollution literature ppm applied to a gas, **always means parts per million by volume or by mole**. These are identical for an ideal gas, and practically identical for most gases of air pollution interest at 1 atm. Another way of expressing this value is ppmv. One part per million (by volume) is equal to a volume of a given gas mixed in a million volumes of air:
> $1\:ppm = \frac{1\:gas\:volume}{1\:million\:air\:volume}$ at 1 atmosphere pressure.

Thus a simple conversion can be applied and the equation solved, knowing the weight of a mole of $CO\_2$ and the typical weight of air. To answer your question, mole and volume are interchangeable in this context.

This would be my honest take, considering the limited available information.

About the downward tendency during the 1600: This was around the time when the Little Ice Age began; There was the Maunder minimum (first low) due to a solar spot low and then a small peak and then the Dalton minimum (second low) before the present peak. Here is [an example](https://www.britannica.com/science/Dalton-minimum) of how low the sunspot activity was at that time (especially Maunder) from Britannica.com

[![Sunspots](https://i.sstatic.net/c78I7.jpg)](https://i.sstatic.net/c78I7.jpg)

Consequences of those two events, detectable already during Maunder was a trend of global cooling and a diminution of the atmospheric $CO\_2$.

> **Comments:**
> **username_0**: Thank you so much for your answer.  
> **username_1**: @username_0 - my pleasure ! If this answer your question you are welcome to choose it as an answer, or discuss about anything you would like to clarify.  
> **username_0**: I plotted the data with Excel, to see developments. So now my question, is it plausible to have that downward tendency about 1600 and if why?  
> **username_1**: This was around the time of the Little Ice Age isn't it? You got the Maunder minimum (first low) due to a solar spot low and then a small peak and then the Dalton minimum (second low) before the present peak. Not too much space to explain in length in comments  
> **username_0**: Thank you for that explanation, I‘ll post that as question hat arose out of this threat. Have a good day.  
> **username_0**: Thank you for that edited answer.  

---

