At Skeptical Science, they explain:

Mauna Loa is often used as an example of rising carbon dioxide levels because its the longest, continuous series of directly measured atmospheric CO₂. The reason why it's acceptable to use Mauna Loa as a proxy for global CO₂ levels is because CO₂ mixes well throughout the atmosphere.

This claim that Carbon Dioxide (CO2) mixes well in the atmosphere is repeated in other places: Example.

I am wondering if this is true and what data can prove it. I am skeptical because this fails for Ozone, for example - there are holes over Antarctica and sometimes the Arctic.

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    CO2 levels in the Artic are measured by research stations in the Arctic Circle, not Hawaii. – Oddthinking May 26 '14 at 1:49
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    This question is based on a false premise, which is unreferenced. If many people believe that the levels of CO2 in Hawaii are projected onto the Arctic, lets find a claim to that effect and we can address that. – Oddthinking May 26 '14 at 1:51
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    @Oddthinking I was led to ask by the comments in skepticalscience.com/co2-measurements-uncertainty.htm but the question is really only about in what sense CO2 mixes uniformly into the atmosphere – user19459 May 26 '14 at 1:53
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    This really belongs on the geosciences stackexchange, however the answer is "yes it is well mixed", evidence provided by the AIRS satelite mission, which shows that CO2 only varies by about 10pmmv globally (photojournal.jpl.nasa.gov/catalog/PIA11194). – Dikran Marsupial May 26 '14 at 12:39
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    The analogy with ozone is misleading: ozone doesn't concentrate in some layers of the atmosphere because of differential separation but because it is reactive. It concentrates near where it is formed. – matt_black May 26 '14 at 14:18

The NASA AIRS (Atmospheric Infrared Sounder) instrument provides satellite based measurements of global CO₂, and it shows that atmospheric CO₂ only varies by a few tens of ppm globally, which indicates that it is indeed "well mixed".

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See the description on the NASA webpage for brief explanation of some of the variability. As @user19504 suggests (+1) there is also a global network of CO₂ measurement sites (for which data are publicly available) so if CO₂ wasn't well mixed, it would be no secret.

Note the seasonal growth and die-back of vegetation results in an annual signal in CO₂ measurements that is highest in the tropic and greatly attenuated in the polar regions (where there is little annual/deciduous vegetation). Also most of the anthropogenic CO₂ is released in the northern hemisphere, and there is a delay in this propagating to the southern hemisphere of about a year, which explains the slight north/south gradient.

  • Are results less reliable at lower altitudes? – user20862 Jun 24 '14 at 14:06
  • CO2 is not well mixed near to the surface (e.g. where there can be inversion layers, industry, forests etc.), see my answer to your question about Beck's data. This is irrelevant to any discussion of the greenhouse effect, as that depends on CO2 in the upper atmosphere, absorption of IR by CO2 at the surface is largely irrelevant. – Dikran Marsupial Jun 24 '14 at 14:15

Here are a list of some of the monitoring stations for CO₂ http://co2now.org/Know-CO2/CO2-Monitoring/co2-measuring-stations.html and this is a list of all sites doing atmospheric monitoring from NOAA http://www.esrl.noaa.gov/gmd/dv/site/site_table2.php

It would be immediately obvious if CO₂ measurements were not consistent from so many different sources.

  • Welcome to Skeptics!. You suggest it would be immediately obvious... but is it? You haven't shown whether or not the CO2 values ARE consistent. – Oddthinking May 29 '14 at 14:56

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