I committed my first act of climate dishonesty by omission.
I stood at the front of lecture halls and projected the same graph every instructor uses: temperatures essentially flat for a thousand years, then a sharp blade upward beginning around 1900. The hockey stick.
Clean. Causal. Irrefutable.
I never showed the slides that should have come immediately before it.
The one with vineyards flourishing in Yorkshire, England. And the slide with Viking cattle grazing on grasslands that are tundra today. And the one with alpine passes so reliably snow-free that medieval merchants scheduled deliveries across them in February.
I did not show it because it would have complicated the story I was paid to deliver.
Not complicated because the data were wrong; complicated because they were inconvenient.
In 1086, the book Domesday England documented 38 commercial vineyards in England, many of them well north of London, several near York. Today, with modern hybrids, canopy management, and a warming climate, the viable limit for high-quality wine production sits about 1° north of Hadrian’s Wall. Eight centuries ago, with none of those advantages, they were making money growing grapes in York.
In Greenland, Erik the Red’s descendants were not just surviving. Archaeological digs at sites such as Brattahlíð and Garðar show large stone barns, byres that once held dozens of cattle, sheep, and goats. These animals require summer pasture. The pastures are gone now, locked under permafrost. The barns stand as ruins in a landscape that has not supported cattle in 600 years.
By the early 1300s, the English vineyards were dead. By 1450, the Norse settlements in Greenland were abandoned. The Thames froze so regularly that “frost fairs” became a London tradition for two centuries.
No one was burning coal. Atmospheric CO₂ sat stubbornly around 280 parts per million. Yet the Northern Hemisphere experienced a climatic shift large enough to redraw the map of what was possible agriculturally.
This is not fringe history.
It is documented in tax records, harvest dates recorded by monasteries, ship logs, tree rings, ice cores, and sediment varves. Hubert Lamb, founder of the Climatic Research Unit at East Anglia, published meticulous reconstructions in the 1960s showing parts of the North Atlantic region between roughly 1000–1200 as warm or warmer than the mid-20th-century baseline. His term “Medieval Warm Period” (MWP) is still used in every paleoclimate textbook.
What is no longer shown in introductory textbooks (and few policy summaries) is the amplitude of that warmth.
I learned to skip that slide because the next logical question from a bright undergraduate is lethal to the narrative we are asked to teach:
“If the climate could change this much before humans emitted meaningful CO2, how confident can we be that the changes of today are unnatural?”
That discomforting question is not meant to be asked.
Instead, we jump straight into Michael Mann’s hockey stick, which used a particular set of tree-ring proxies and statistical centring choices that had the convenient property of flattening everything before 1900 into a nearly straight line. These proxies have been widely refuted and corrected. The method was debated fiercely (the National Academies review in 2006 acknowledged “significant uncertainties”), yet the graph survived because it was rhetorically perfect.
Nobel Prizes were awarded to the Intergovernmental Panel on Climate Change and former U.S. vice-president Al Gore in 2007.
It is a questionable award with no provision for revocation. The story brings to mind the Lindy effect.
I do not claim Mann committed fraud. I claim that the graph told the story that policymakers wanted told: a stable pre-industrial climate shattered by human sin. Natural variability shuffled off as a minor footnote.
Over time, the footnote disappeared entirely.
I watched it happen. I participated. In grant applications, in faculty meetings, in curriculum reviews, the message was consistent and unspoken: keep the handle of the stick straight. Emphasize attribution certainty. Do not dwell on the centuries in which York grew grapes.
The money flows smoother that way.
I can no longer square that with intellectual honesty: none of the medieval evidence has been disproved. The vineyards are still in the Domesday book. The Norse barns are still there. Lamb’s papers are still in the library. GISP2 ice cores still show centennial swings of 2–3C during the Holocene, revealing solar and ocean-driven MWP/Little Ice Age patterns.
The data did not vanish because they were wrong.
They vanished because they raise the attribution question.
That does not mean human emissions are innocent. Greenhouse physics are real; the radiative forcing calculations appear solid. What it does mean is that the climate system has always been capable of large, rapid, entirely natural shifts on the timescales that we worry about today.
Any honest accounting of how much warming is anthropogenic must begin with an honest accounting of how much is not.
I used to end my lectures with policy slides. I would now begin with a different one: a map of 11th-century English vineyards and a photograph of a stone cattle barn on frozen Greenland soil. Only then would I show the modern temperature record with the appropriate resolution and fidelity.
Not omission.
Science that cannot survive the medieval warmth probably cannot survive the truth.
In my next article, I will explain what happened when I started asking how much of recent warming might be natural recovery from the Little Ice Age rather than entirely our fault and why certain colleagues reacted as if I had defaced a cathedral.
Some questions are more dangerous than others.
(Richard LeBlanc, BIG Media Ltd., 2025)
