(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: CO2 levels are recorded on top of Mauna Loa … a volcano! No wonder the levels are so high.

Atmospheric Carbon Dioxide
(image courtesty of Global Warming Art)

Answer: Yes, it’s true, Mauna Loa is an active volcano. In fact it’s the biggest volcano on earth! So, should we suppose that Charles Keeling didn’t know that?

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Well, no, he did know it. And using subtle scientific indicators like “wind direction,” he was even able to ensure that his readings were not contaminated by any out-gassing when it was occurring. OK, to be fair, it is not really always that simple; out-gassed CO2 can be carried far away on a favorable wind, only to return much later on an ill one. But really, these are clever people, these scientists, and while mistakes are made, they are not usually such simple ones.

A quick look at the actual levels recorded makes it pretty hard to believe there is any volcanic influence. We have a nice, slow, steady trend with a regular up and down seasonal variation. No spikes, no dips. Nothing random, as one would expect from an overwhelming volcanic influence. The record is here among other places.

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But, OK, let’s throw out Mauna Loa. There are dozens of other sampling stations scattered all over the globe, including one in the Antarctic, far from cities, SUVs, cement plants, and active volcanoes. It also shows the same rise [PDF], though the southern hemisphere tends to lag a few years behind the northern hemisphere, where the majority of the CO2 is produced. Here are eight others — same results.

Sorry, its all of us Joes, not the volcanoes.