As we’ve said before, Roger Pielke Jr. is more interesting even when wrong than a great many people are even when right. For instance in a recent Substack post “The Legacy of Al Gore’s ‘An Inconvenient Truth’ 20 Years Later” he mentions its numerous scientific blunders before saying “the far more important anniversary story is not about the accuracy of any of Gore’s individual claims, but rather what the film helped to unleash in the scientific community: a decisive turn to bringing partisan politics into the institutions of science.” Indeed. On that point we agree. But RPJ, in his scrupulous effort to be fair-minded, or to avoid being cast as a MAGA troll, also insists that “Gore did get many of the basics correct” including that “Humans are warming the planet” and “that Arctic summer sea ice was in decline with human influences playing an important role.” And we won’t ask how Gore thought he knew because he was not a climate scientist, a term here referring not to formal credentials but to using the scientific method. In that sense Pielke Jr. is, of course. So we will ask how he, or anyone, could think they know either of these things. The big problem being that to detect the human influence on that ice, or the planet generally, in the last, say, century, you have to think you can say with considerable certainty what would have happened absent that influence. And if what you say is “no warming rebound from the Little Ice Age” you’re on… thin ice.
Arctic ice is particularly on our minds because we just returned from a trip to… the Arctic to see the melting ice. Which does not seem to be melting as that term is normally used, and it’s hard to see what it could mean to attribute something that isn’t happening at all to human influence. Short-term trends appear to show melting from 1979 through 2006, and nothing since, and if human-emitted CO2 had played an important role in the 1979-2006 melt, and has continued to rise since (which it has) it is a mystery why the melting stopped.
It gets worse. A lot worse. And it gets worse first because anyone pointing to the behaviour of the ice over these relatively short periods (27 in the first case, 20 in the second) as indicative of anything at all has to be able to show that such behaviour is unusual and of course they cannot because we simply don’t have sufficient data before 1979, and especially before 1900, to know whether a period of melting is unusual or whether a period of no melting is. Including a period of melting during a longer period of no melting, or of an increase, as well as a period of increase during a longer period of melting.
We do of course know that early in the 20th century the ice decreased, then from the 1940s on it increased to the peak in 1979 before declining again. Which certainly makes it odd to blame that last decline on humans and nothing else. But it is the latter point about previous longer cycles that makes it far worse.
We actually do know, and surely “we” here includes RPJ, that there was a long period of declining ice, a very long period, from the Dark Ages cold period through the Medieval Warm Period including the famous Viking voyages of discovery. And then we know there was a long period of accumulating ice from the MWP through the Little Ice Age. (And, if you’re keeping score, of increasingly foul North Atlantic weather.) But we do not know whether, during that warming, there were decades-long periods of ice increasing, nor whether, during the subsequent cooling, there were decades-long periods of ice decreasing. And so we cannot possibly point to the most recent period as proof of anything.
Yes, it gets worse. Because our knowledge of the broad contours of the longer warming-cooling cycles, the ones that seem to operate on roughly a thousand-year cycle, from the Minoan Warm Period through the Iron Age cold centuries to the Roman Warm Period to the Dark Ages cold centuries to the Medieval Warm Period to the Little Ice Age, the coldest period since the last glaciation, surely tell us that had there been no Industrial Revolution the planet would nevertheless have warmed, and warmed considerably, in the centuries after 1850. And so any effort to maintain that “Humans are warming the planet” requires you to demonstrate not only how much it would have warmed since early Victorian times absent human influence, so you can then show a residue that is presumptively due to human influence, but how you think you know.
Well, how? At CDN we do not believe climate models can tell us anything of value. And we recognize that natural variability is variable on every scale from weekly to millennial, cycles on cycles and all fractal. But if you want to maintain that after cycling down, up and down again from the Holocene Climatic Optimum on, even given the ominous tendency for the downs to exceed the ups, the global temperature was going to flatline after 1850 or even go back down instead of rebounding, it’s up to you to explain why the clear large-scale pattern was going to be disrupted. And if not, you need to have some better reason than not seeming uncool for maintaining that there is a human “signal” amid the natural “noise” of post-1850, or post-1900 warming, how large you think it is, and how you know.
It’s a debate worth having and perhaps Pielke Jr. will answer us on this point. But it has to be argued not just asserted.
