The problem in switching to measuring at a volcano is because they have shitloads of co2 just pouring out. And the graph really starts going crazy as soon as they switched places. Another problem is that we would have no idea whether the temurature rise cause higher co2 or higher co2 causes tempurature rise. Science point to it being the former. Heres a little experiment. Get a two cans of the same exact soda and put one the rifridgerator. Then open them both up at the same time in a day or something. See which one has more co2 coming out.