<p>The magnitude of these seasonal variations differ from location to location. The graph below portrays variations in CO<sub>2</sub> levels at Point Barrow Alaska (PTB), La Jolla California (LJO), Mauna Loa Observatory (MLO), Christmas Island (CHR), Samoa (SAM), and the South Pole (SPO) over the last 60 years.</p>

<p><a href="https://i.sstatic.net/XciFD.png" rel="noreferrer"><img src="https://i.sstatic.net/XciFD.png" alt="Graph portraying variations in CO2 levels at six sites over the last 60 years. All of the sites show a general increase in CO2 levels. The northern hemisphere sites also show a marked seasonal variation."></a><br>
<sup>Source: <a href="http://scrippsco2.ucsd.edu/graphics_gallery/other_stations/global_stations_co2_concentration_trends.html" rel="noreferrer">Scripps $\text{CO}_2$ Program, Global Stations $\text{CO}_2$ Concentration Trends</a>.</sup></p>

<p>Note that all sites show a general increase in $\text{CO}_2$ concentrations over those 60 years. The sites in the Northern Hemisphere (Point Barrow, La Jolla, and Mauna Loa) also show seasonal variations, with the variations being the greatest at Point Barrow. The sites in the Southern Hemisphere (Christmas Island, Samoa, and the South Pole) show a much reduced seasonal variation, essentially vanishing at Samoa and the South Pole.</p>

<p>One reason for these variations is the relatively slow mixing between the northern hemisphere and southern hemisphere atmospheres. It takes about a year for changes in the northern hemisphere atmosphere to make their way into the southern hemisphere atmosphere (and vice versa), and even longer for those northern hemisphere changes to migrate to the South Pole. This slow mixing time means that seasonal variations are confined to the hemisphere in which they occur.</p>

<p>There's a large difference between the land to ocean ratio in the northern hemisphere versus the southern hemisphere, and an even greater disparity outside the tropics. The large temperate land mass in the northern hemisphere is the primary cause of those seasonal variations in CO<sub>2</sub> levels in the northern hemisphere. Plants absorb CO<sub>2</sub> from the atmosphere in the spring and summer, and release CO<sub>2</sub> back to the atmosphere in the fall and winter.</p>

<p>References:</p>

<p><a href="https://scripps.ucsd.edu/programs/keelingcurve/2013/05/07/why-are-seasonal-co2-fluctuations-strongest-in-northern-latitudes/" rel="noreferrer">"Why are Seasonal CO<sub>2</sub> fluctuations strongest at Northern Latitudes?" Scripps Institution of Oceanography</a></p>

<p><a href="http://onlinelibrary.wiley.com/doi/10.1029/JD092iD06p06614/full" rel="noreferrer">Daniel James Jacob, et al., "Atmospheric distribution of <sup>85</sup>Kr simulated with a general circulation model," Journal of Geophysical Research 92:D6 (1987).</a></p>

CC BY-SA 3.0
2017-04-21T16:04:26.973Z
2017-04-21T16:04:26.973Z
David Hammen
<p>The respiration of plants is not evenly distributed through seasons since the northern and southern hemisphere have a different amount of land and plants.  The southern hemisphere has far less land. In the northern winter, the carbon released increases and then by ~May the northern hemisphere has enough carbon uptake (due to increased photosynthesis) to cause a dip in the $\ce{CO2}$ record.  Then summer in the north ends... autumn commences, and net $\ce{CO2}$ starts to rise again. </p>

CC BY-SA 3.0
2014-12-20T04:06:19.937Z
2014-12-20T12:02:19.093Z
2014-12-20T12:02:19.093Z
f.thorpe
<p>I'm doing some homework on the increase of $\mathrm{CO}_2$ in the atmosphere. On one of the graphs it shows the amount of $\mathrm{CO}_2$ peaks in May and has a low in November. Why is this? Shouldn't it just be constantly going up?</p>

<atmosphere><climate-change><co2><homework>
Why is there a seasonal cycle to the amount of CO2 in the atmosphere?
Shannon Torstonson
# Why is there a seasonal cycle to the amount of CO2 in the atmosphere?

(Asked by: username_0 on 2014-09-24)

I'm doing some homework on the increase of $\mathrm{CO}\_2$ in the atmosphere. On one of the graphs it shows the amount of $\mathrm{CO}\_2$ peaks in May and has a low in November. Why is this? Shouldn't it just be constantly going up?

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


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## 2 answers

### Answer by username_1 on 2017-04-21. Score: 6

The magnitude of these seasonal variations differ from location to location. The graph below portrays variations in CO2 levels at Point Barrow Alaska (PTB), La Jolla California (LJO), Mauna Loa Observatory (MLO), Christmas Island (CHR), Samoa (SAM), and the South Pole (SPO) over the last 60 years.

[![Graph portraying variations in CO2 levels at six sites over the last 60 years. All of the sites show a general increase in CO2 levels. The northern hemisphere sites also show a marked seasonal variation.](https://i.sstatic.net/XciFD.png)](https://i.sstatic.net/XciFD.png)  
Source: [Scripps $\text{CO}\_2$ Program, Global Stations $\text{CO}\_2$ Concentration Trends](http://scrippsco2.ucsd.edu/graphics_gallery/other_stations/global_stations_co2_concentration_trends.html).

Note that all sites show a general increase in $\text{CO}\_2$ concentrations over those 60 years. The sites in the Northern Hemisphere (Point Barrow, La Jolla, and Mauna Loa) also show seasonal variations, with the variations being the greatest at Point Barrow. The sites in the Southern Hemisphere (Christmas Island, Samoa, and the South Pole) show a much reduced seasonal variation, essentially vanishing at Samoa and the South Pole.

One reason for these variations is the relatively slow mixing between the northern hemisphere and southern hemisphere atmospheres. It takes about a year for changes in the northern hemisphere atmosphere to make their way into the southern hemisphere atmosphere (and vice versa), and even longer for those northern hemisphere changes to migrate to the South Pole. This slow mixing time means that seasonal variations are confined to the hemisphere in which they occur.

There's a large difference between the land to ocean ratio in the northern hemisphere versus the southern hemisphere, and an even greater disparity outside the tropics. The large temperate land mass in the northern hemisphere is the primary cause of those seasonal variations in CO2 levels in the northern hemisphere. Plants absorb CO2 from the atmosphere in the spring and summer, and release CO2 back to the atmosphere in the fall and winter.

References:

["Why are Seasonal CO2 fluctuations strongest at Northern Latitudes?" Scripps Institution of Oceanography](https://scripps.ucsd.edu/programs/keelingcurve/2013/05/07/why-are-seasonal-co2-fluctuations-strongest-in-northern-latitudes/)

[Daniel James Jacob, et al., "Atmospheric distribution of 85Kr simulated with a general circulation model," Journal of Geophysical Research 92:D6 (1987).](http://onlinelibrary.wiley.com/doi/10.1029/JD092iD06p06614/full)


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### Answer by username_2 on 2014-12-20. Score: 4

The respiration of plants is not evenly distributed through seasons since the northern and southern hemisphere have a different amount of land and plants. The southern hemisphere has far less land. In the northern winter, the carbon released increases and then by ~May the northern hemisphere has enough carbon uptake (due to increased photosynthesis) to cause a dip in the $\ce{CO2}$ record. Then summer in the north ends... autumn commences, and net $\ce{CO2}$ starts to rise again.


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