Full Circle

Bringing the deep-time series to a close — with three last pieces, and some overdue thanks.

Dean Rovang - Staying Curious · justdean.substack.com · ORCID 0009-0006-1351-5320

This series didn’t begin with a conclusion. It began with a diagram I kept redrawing until I understood what it was telling me.

I did not set out to build an equilibrium relationship spanning 66 million years. I arrived at one, slowly, by following the evidence where it led — and, just as often, by throwing out the parts that didn’t survive a closer look. Along the way I audited my own work. I traced every number back to its published source. When one of my regression fits turned out not to be reproducible from the primary data, I retired it. When a fourth paleoclimate record ran hotter than the other three, I set it aside — by a stated rule, not because it was inconvenient. What came through that scrutiny is the band you’ll see in these essays: narrower, better documented, and more honest than what I started with.

I mention this not to claim rigor as a virtue, but because it is close to the whole point. The argument these pieces make, in the end, is that you can follow the evidence in the open and show your work — that the foundation of this science is something anyone can rebuild for themselves from published sources. This series is my attempt to do exactly that, mistakes and course-corrections included.

I did not get here alone, and I want to name some of the people who helped.

I owe a particular debt to Andrew Dessler, who has been this work’s most steadfast advocate. As a scientist who has spent his career pinning down precisely how sensitive the climate is, he had every reason to hold an outsider’s diagram at arm’s length — and instead he took it seriously, encouraged me to open the work to public engagement, and lent it his attention and his standing when both mattered most. More than anyone, he is why I kept going.

Andrew Revkin, too, engaged this work and encouraged it when it was rougher than it is now; his attention helped me see which parts were worth sharpening. Raymond Pierrehumbert and Chris Colose took the deep-time framing seriously in public exchange — Pierrehumbert’s correction on how long the slow carbon drawdown actually takes changed my understanding and made the picture more honest than it had been. Mike Palin, a research geologist, brought the view from the rock record and the slow geologic carbon cycle — the machinery that governs how carbon eventually returns to stone — and offered a careful correction that kept me precise about where the tight CO₂–temperature correlation holds, and where it doesn’t; he has also put the diagram to work teaching that carbon cycle to educators. And after a conversation about reframing the problem in deep-time terms, Marcus Sarofim offered to extend his own analysis of long-term uncertainty out to the year 2300 — an act of intellectual generosity that took the reframing seriously and tested it on its own terms.

Tom Harris, separately, has helped carry these ideas to readers I would not otherwise have reached.

I should be clear about what that gratitude does and doesn’t mean. The generosity was in the engagement — the willingness to look, to correct, to take an idea seriously. That is the thing I’m thankful for, and it is also, not coincidentally, the thing this series is about.

What follows is three pieces.

The first is the audit itself — how the band was built, what I discarded and why, and how you can rebuild it yourself from primary sources.

The second is the plainest version of the picture: what the deep past shows about carbon dioxide and temperature, told for anyone.

The third is what that picture does when it meets the strongest organized case against the science — and what that case, given every resource and motive, turned out to be unwilling to contest.

Richard Feynman gave the rule its plainest form: “you must not fool yourself — and you are the easiest person to fool.” That is what the audit was for: not to prove the diagram right, but to make it harder to fool myself into believing it. Checking your own work in the open, and letting go of what won’t hold, is most of what separates science from the performance of it. These three pieces are my attempt to stay on the right side of that line. I’ll set the series down there.

“You can’t really know where you are going until you know where you have been.” — Maya Angelou