A lot of people say it’s too late to debate this claim, especially in the policy arena. The fossil fuel industry, they insist, should rally round the white flag, admit their product destroys the planet then ask for permission to send it through pipelines anyway. (And then look stunned when the answer is invariably “No, you mad fools.”) But here’s the weird thing. Well, one of them anyway. There’s very little evidence that CO2 drives temperature when you look closely. You may be tempted to say good grief, that ship has sailed, we know rising CO2 correlated with rising temperatures in the 20th century. But have you checked? Someone or something on YouTube called “Philosophical Investigator” just did, and rather than assuming what he set out to prove, programmed a computer to test the hypothesis, asking it to list times when they moved together and times when they did not. And guess what? The nays have it. Even after 1750 they move together 15% of the time, and apart the rest of the time.
This result is remarkable. And the analysis didn’t begin with Henry Ford, or even James Watt. It went back thousands of years. Almost as if the spirit of scientific inquiry were alive and well. And here’s what it found.
From 7500 BC on, and especially about 4800 BC until 1500 AD, CO2 and temperature, or the proxies we hope represent them, moved in opposite directions for thousands of years. How can it be, if CO2 is the “Principal Control Knob Governing Earth’s Temperature“?
OK, one possibility is that it’s wired backwards. Because the simple fact is that if you came to the warming debate cold, and looked at that data, you’d conclude that CO2 reduced temperature. Weird, huh? But of course that was then, as in, back when we didn’t even know why CO2 was rising except we knew it wasn’t human beings. But NB that the claim that CO2 drives temperature does not depend on there being two kinds, one natural that does not and one man-made that does. The theory stands or falls by whether CO2 of any sort drives temperature. And historically it does not. (Nor does it prehistorically.)
Once we get to 1750 the picture becomes less speculative. For instance we know, or think we know, why atmospheric CO2 started rising: Humans were releasing enough to drive the increase. Or to be exact we think we know why the rate of increase began to increase, since it had been rising anyway. But what of temperature? Well, from 1750 to 1850, using IPCC WG1AR5, PI says temperature kept falling. And even Michael Mann agrees.
Wait. There’s another 100 years of rising CO2 and falling temperature? Yes. Again there are minor fluctuations and it would be unreasonable to rely on the proxies to capture them all. But basically from the invention of agriculture until the invention of the telegraph, the planet saw rising CO2 and falling temperature. So where did this idea that CO2 even correlates with temperature increase, let alone causes it, come from?
Perhaps the more recent past? After 1850 we have even better data, in the form of direct if very patchy and incomplete thermometer temperature records, and some direct CO2 data too. And from 1850 to 2019, from a distance, you seem to see something like a hockey stick. Aha? Not really. Because again, PI had the computer search that period for stretches when temperature does not rise (negative or neutral) and one such period is… 1850 to 1929. What? The first 80 years of the confirmatory era don’t confirm it? Then what does?
Good question. Because the first 180 years of post-Industrial Revolution CO2 and temperature data do not, even though according to the widely accepted notion of ECS, namely that every doubling of atmospheric CO2 produces the same absolute increase in temperature, we should see the climate more sensitive to rising CO2 when it’s at lower absolute levels. And we don’t.
Yeah yeah yeah. Ancient history. Pre-television. What about the hot and bothered 20th century? Well, from 1930 to 1944 CO2 rises and so does temperature. Gotcha! Except from 1945 to 1980 CO2 keeps rising but temperature does not. It is basically flat (the data say slightly negative but we dispute the precision).
All this evidence is pretty bad. For the theory we mean, though also in its precision. But to the extent that we believe it, from 8000 BC to 1980 AD there’s no reason, outside one anomalous 15-year interval, to think rising CO2 means rising temperature. So where did the idea come from?
Well, of course from 1981 to 2000 both rose, and the AGW movement was born and grew into a giant in that brief period. At the hands of people with severely restricted and self-centred time horizons, what Oliver Wendell Holmes Sr. called “one-storey intellects” who cannot see past their own limited historical period. But even inside that cramped world-view there’s a problem: the hiatus.
From 2001 to 2012, CO2 surged onward and… temperature stalled again. Even though CO2 was now rising faster than between 1981 and 2000. Strange.
Mind you from 2013 to 2019 CO2 kept rising, naturally. Or rather unnaturally. And even faster. And temperature rose. Gotcha 2.0!
No. From 10,000 years of data, much of it speculative, we have 42 years with CO2 and temperature rising together and over 9900 years without. There are lots of very clever explanations of how CO2 increases temperature. But if it doesn’t they’re not worth the storage media they’re written on.
As PI notes, that CO2 causes warming is a theory that can be subjected to the key scientific test, an effort to falsify it by looking at the data. And by his count it was falsified four times and corroborated three times. And it gets worse because those tests are not evenly weighted chronologically. Even looking just at 1750-2019, it was falsified for 228 years and corroborated for 42. Which comes out to 84.45% vs 15.55%. Not a bet you’d take with $100, let alone your whole economy, is it?
PI notes that if we just use 1850 to 2019, discarding data we don’t like or possibly just don’t trust, overall both rise. But even in that stretch, there’s only 42 years of positive relation and 127 without. And in case you think well, none of that matters, we’re now facing runaway temperatures, Christopher Monckton reminds us that if instead of measuring from 2013 to 2019, you look at 2016-2021, you find… another hiatus. Five years and seven months with rising CO2 and no warming.
Almost as if the evidence were telling us what it seems to be, that… nah, can’t be. Mustn’t be.