<blockquote>
<p>So what am I missing in this analysis?</p>
</blockquote>
<p>The linked data says 2017 CH<sub>4</sub> was about 1850 <strong>ppb</strong>, not 1850 <strong>ppm</strong>. Dividing parts per billion (ppb) by 1000 results in parts per million (ppm).  In other words, the atmospheric methane concentration was about 1.850 ppm in 2017. Assuming an exponential decay with a half life of 9 years means that about 0.14 ppm <span class="math-container">$\left(1850*(1-2^{-1/9}\,)\right)$</span> of the 2.4 ppm increase in the 2017 to 2018 CO<sub>2</sub> concentration was due to  methane decomposition. That's a small but not insignificant portion of the increase.</p>

CC BY-SA 4.0
2022-02-08T22:06:46.403Z
That makes so much more sense. It's not 100% insignificant but like 99% insignificant then. If methane decays relatively quickly, and it's tiny compared to the amount of CO2, it seems to me it shouldn't be much of a concern.
Some Guy
CC BY-SA 4.0
2022-02-08T14:11:22.543Z
2022-02-08T14:11:22.543Z
David Hammen
<p>I am trying to understand the atmospheric ppm data, specifically around how CH<sub>4</sub> decays to CO<sub>2</sub>.</p>
<p>This data says 2017 CH<sub>4</sub> is about 1850ppm, and 2017 CO<sub>2</sub> is 402ppm increasing about 3ppm/year. (<a href="https://www.eea.europa.eu/data-and-maps/daviz/atmospheric-concentration-of-carbon-dioxide-5" rel="nofollow noreferrer">https://www.eea.europa.eu/data-and-maps/daviz/atmospheric-concentration-of-carbon-dioxide-5</a>)</p>
<p>I've also read that CH<sub>4</sub> has a half-life in the atmosphere of about 9 years, decaying with the chemical equation CH<sub>4</sub> + O<sub>2</sub> → CO<sub>2</sub> + H<sub>4</sub></p>
<p>So if you'd expect methane's 1850ppm to decay to 925ppm over 9 years, that means you'd also expect to see an increase of 925ppm of CO<sub>2</sub>, or about 100ppm/yr just from methane decay. That'd be insanely high. But the data I linked earlier shows an increase of 3ppm.</p>
<p>So what am I missing in this analysis?</p>

CC BY-SA 4.0
2022-02-08T08:33:39.610Z
Reread your source. The CH4 (methane) numbers are in parts per billion while CO2 is in parts per million.
David Hammen
CC BY-SA 4.0
2022-02-09T03:44:23.163Z
Methane emissions are far from as quantitative as CO2 emissions. Annual CO2 emissions were around 34 Billion tons.
Annual methane emissions are 570 million tons, or 1.6% as much
decomposition reaction: CH4 + O2 → CO2 + H4
LazyReader
<atmosphere><atmospheric-chemistry><carbon><methane>
If methane decays to $\small\sf{CO_2}$ in the atmosphere, shouldn't there be much more $\small\sf{CO_2}$?
Some Guy
# If methane decays to $\small\sf{CO_2}$ in the atmosphere, shouldn't there be much more $\small\sf{CO_2}$?

(Asked by: username_0 on 2022-02-08)

I am trying to understand the atmospheric ppm data, specifically around how CH4 decays to CO2.

This data says 2017 CH4 is about 1850ppm, and 2017 CO2 is 402ppm increasing about 3ppm/year. (<https://www.eea.europa.eu/data-and-maps/daviz/atmospheric-concentration-of-carbon-dioxide-5>)

I've also read that CH4 has a half-life in the atmosphere of about 9 years, decaying with the chemical equation CH4 + O2 → CO2 + H4

So if you'd expect methane's 1850ppm to decay to 925ppm over 9 years, that means you'd also expect to see an increase of 925ppm of CO2, or about 100ppm/yr just from methane decay. That'd be insanely high. But the data I linked earlier shows an increase of 3ppm.

So what am I missing in this analysis?

**Tags:** atmosphere, atmospheric-chemistry, carbon, methane

> **Comments:**
> **username_1**: Reread your source. The CH4 (methane) numbers are in parts per billion while CO2 is in parts per million.  
> **username_2**: Methane emissions are far from as quantitative as CO2 emissions. Annual CO2 emissions were around 34 Billion tons. Annual methane emissions are 570 million tons, or 1.6% as much decomposition reaction: CH4 + O2 → CO2 + H4  

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## 1 answers

### Answer by username_1 on 2022-02-08. Score: 6 | Accepted answer

> So what am I missing in this analysis?

The linked data says 2017 CH4 was about 1850 **ppb**, not 1850 **ppm**. Dividing parts per billion (ppb) by 1000 results in parts per million (ppm). In other words, the atmospheric methane concentration was about 1.850 ppm in 2017. Assuming an exponential decay with a half life of 9 years means that about 0.14 ppm $\left(1850\*(1-2^{-1/9}\,)\right)$ of the 2.4 ppm increase in the 2017 to 2018 CO2 concentration was due to methane decomposition. That's a small but not insignificant portion of the increase.

> **Comments:**
> **username_0**: That makes so much more sense. It's not 100% insignificant but like 99% insignificant then. If methane decays relatively quickly, and it's tiny compared to the amount of CO2, it seems to me it shouldn't be much of a concern.  

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