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Which is the Correct Graph for Carbon Dioxide Concentrations in the Atmosphere?

The following are three graphs representing the change in parts per million of carbon dioxide (CO2) measured at the Mauna Loa Observatory in Hawaii from March 1958 through December 2015:

Parts Per Million of CO2 measured at Mauna Loa from 1958-2015, on a reference scale with the upper and lower bounds during the period

Parts Per Million of CO2 measured at Mauna Loa from 1958-2015, on a reference scale from 0 to the modern-day maximum

Parts Per Million of CO2 measured at Mauna Loa from 1958-2015, on a reference scale since the Triassic Period

All three graphs accurately represent the same data. Each is presented on a different scale. The first graph takes the upper and lower bounds of the period 1958-2015 as the appropriate Y-axis scale. This is the approach to CO2 concentration graphing taken by NOAA. The second graph features the same maximum, but offers the value 0 as a minimum for the Y-axis. The third graph puts 2,000 parts per million of CO2 as the upper limit of the axis, based on the apparent maximum CO2 concentration level between the current day and the ancient Triassic period when dinosaurs roamed the planet.

Which of the three Y-axis configurations is most appropriate, in your opinion? Why? What does that graph demonstrate that the others don’t?

3 thoughts on “Which is the Correct Graph for Carbon Dioxide Concentrations in the Atmosphere?”

  1. J Clifford says:

    You and your trick questions. I can only answer with another question: Appropriate for what political purpose?

  2. Jim Cook says:

    What do you mean by political, J. Clifford? If you mean “intervention to offset an effect,” then it’s important to consider what effect we’re talking about, which I think is different depending on the graph. People treat the zero point in a graph as natural, but in the Earth’s atmosphere it’s not clear that the zero point is reasonable. On the other hand, why treat the last 60 years as if they are the norm? Is the Triassic period a reasonable comparison point? Is there another, better frame than to reach back to the age of dinosaurs? It depends on what the bounds of reasonable climate variation might be.

    1. J Clifford says:

      By political, yes, you could say I mean “intervention to offset an effect”. More plainly, I mean political in the sense of something intended to support a particular agenda.

      If you’re a politician who wants to keep fossil fuels sales high in order to get more financial contributions from oil, coal and gas companies, then the correct graph to use is the one that makes CO2 concentrations look relatively flat.

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