Willis Eschenbach mischievously lays two charts atop one another. One being CO2 and the other being temperature. And they don’t move together. Which to be sure has been done before using various time periods. But in this case he takes the period from the birth of Christ to the present and says why doesn’t CO2 change at all and, if it doesn’t why does temperature, and throws down the gauntlet: “NOT ONE CLIMATE SCIENTIST KNOWS THE ANSWERS TO THOSE QUESTIONS.” If true, it’s a devastating indictment of the entire field. And if it’s not true, someone should say something. By which we mean the answers, not some sort of insult.

Of course there are various possible explanations of the phenomenon including that the data are flawed. Starting with the CO2 measurements. The CO2 reconstruction he’s using comes first from ice cores and then from Mauna Loa instruments. And it is famously important to beware of charts where a change in methodology creates a discontinuity. Are you listening, Michael Mann?

In this case, the specific potential pitfall is that ice cores might seem to the uninitiated, like Al Gore, to give annual readings of atmospheric CO2. But in fact the bubbles they contain take many years to form completely, sometimes many centuries (on which see for instance Chapter 6 in the Australian Institute of Public Affairs‘s new Climate Change: The Facts 2020), and so they actually present a smoothed average.

Speaking of Michael Mann, another possibility is that the temperature measurements are wrong. Perhaps in fact temperature was stable until the 20^th century and we just imagined the Little Ice Age, Roman Warm Period and so on including, of course, the Medieval Warm Period or “anomaly” or whatever they’re now calling it to try to make it go away as Mann infamously did with his hockey stick. (Or if you’re John Kerry, it has been stable “for millions of years – literally millions of years.”)

Odd as even Mann’s more modest position might seem given all that we know about, say, the Vikings settling Greenland, and a growing body of evidence that these phenomena were neither regional nor minor, one continues to encounter claims like “Before the Industrial Revolution, the Earth’s climate was, for a large amount of time, in a relatively stable, harmonious stasis where heat energy coming in to the atmosphere was equivalent to energy going out. Note that the sun brings incoming heat energy, and the Earth itself gives off outgoing energy to maintain balance.” Which you’ll notice seems to demolish not just Chartres Cathedral but that whole business of the Pleistocene glacial advances and retreats, unless “a large amount of time” does not mean what we think it means, or else “relatively stable, harmonious stasis” doesn’t.

Anyway, allow us to pick up Eschenbach’s gauntlet in order to fling it down again in the same place, harder. Is it really true that atmospheric CO2 was stable from the time of Caesar Augustus until that of Roosevelt Theodore? And if so, and CO2 drives temperature, what is the explanation for temperature fluctuating over the period from 0 to 1900 AD while CO2 did not? Or was temperature stable too, and virtually all the evidence is wrong?

If climate science can’t answer those questions, it is only settled in the same sense that the Titanic is.