Klimaspirale Part 4: CO₂, and What Was Under the Post – Simply Explained
The project sat still for a few weeks. When I opened the page again, the last big piece went in.
What the spiral cannot answer
The spiral shows what happened: it is getting warmer. The most common objection to a picture like that asks about the why. Namely: isn’t this just natural variation?
A temperature curve has no answer to that. However cleanly it is calculated, it shows the effect. About the cause it says nothing.
So a second curve now runs alongside it, on the same time axis: the CO₂ content of the air. The temperature is the effect, the CO₂ is the driver.
CO₂ is measured in ppm, parts per million. 429 ppm means: out of every million particles of air, 429 are CO₂.
That sounds like almost nothing, and the number alone is not the point. The point is the movement. Over the same span the spiral unwinds, the value went from roughly 290 to roughly 429. Just under half again.
Air out of the ice
Except there is no single series of measurements covering 146 years of CO₂. Direct measurement only starts in 1958, up on a mountain in Hawaii.
For the time before that, there is air from the past. When snow turns into ice under the pressure of new layers, tiny bubbles of air stay trapped inside. Drill an ice core out in Antarctica and you have air samples with a date on them.
An ice core is a bit like a shelf full of preserving jars. The oldest air at the bottom, the newest at the top, each jar sealed in the year it closed.
The visible seam
Two sources in one curve, and that is exactly where the honesty work begins.
The older part, from the ice, is drawn as a dashed line. The newer measured series is solid. At the switchover point a small jump stays in. It could be smoothed away, but it stays visible so you can tell where one source ends and the other begins.
The two sources overlap for a few decades, and in that window you can check whether they agree. They don’t, quite. The measuring station on the mountain almost always reads a little higher than the ice core.
That is not an error in the data. The station lies in the north, close to the regions where most CO₂ is emitted. The ice core lies deep in the south. And the air needs time to mix its way around the globe.
That is exactly why the curve switches at the seam instead of blending. A mean of north and south would be a number nobody actually measured at either place.
An early draft of the explainer text claimed the opposite: that the two series track each other in the overlap window. That was wrong. The measurement disproved it, and the text was corrected.
Then the same objection from Part 3, on a new object. Because the spiral is tilted, the CO₂ curve appears stretched at the top. Against that there is now a side view in which the distortion disappears.
The data-as-of date
Before the launch I had Claude check the data against the sources once more. Something unexpected came out of that: several months in the past had shifted slightly, after the fact.
We are talking hundredths of a degree. In the spiral they change nothing visible. They do change something about the sentence “these are the NASA data”, because without a point in time that claim cannot be checked.
The reason is harmless. Measuring stations file their values late, and the most recent months of a series still get refined. So next to the sources it now also says what day the data is from, the same date in every version.
What was under the post
For this text I went back to the beginning, to the post the clip ran in. Two things were there that nobody knew about while building.
The first is the video’s opening frame. It shows three reference circles: at minus 1, at 0, and at plus 1 degree. No reference to a climate target. No statement of which period it compares against.
So the video that set off the idea did not have the very problem that later cost the most work. It never made the claim.
The second is the comment section. It reads like the checklist I ordered for myself weeks later.
One comment brought up natural cycles and the point that 150 years is a tiny sample. The CO₂ curve stands against that today. Another asked what had happened in one particular year; the reply below it named El Niño. The markers in the spiral stand against that today.
One described the calculation method behind the numbers entirely correctly, and concluded the video was a lie. The explainer page stands against that today. And one noticed that in the picture the distance from the middle and the colour both mean the same thing. That is the objection from Part 3, weeks before my reviewer put it into words. The question of why the series starts in 1880 was there too.
Not every point has something built against it. One comment held that you can make out the two world wars as warmer years in the spiral. A reply below it explained that this hangs above all on how sea temperatures used to be recorded back then. It stands here because a spiral invites pattern-hunting, and not every pattern in it says something about the climate.
Four weeks of work on comparison periods, markers, explainer texts and a CO₂ curve. And the list for it had been sitting under the video that supplied the idea from the start. I read it while I was writing this text.
The post itself has since been removed by a moderator. The thing that set the project off no longer exists at its address, while what came out of it is going online right now.
What is online now
The spiral runs at climate.aeternalabs.io: bilingual, with the global series, to turn and tip. A Europe view was planned but came back out before the launch. Plus the markers, the CO₂ curve, the explainer page, and an export in portrait format for your phone. And video versions in high resolution.
Under all of it stand the sources and the date the data is from.
One thing is deliberately missing: the yearly updating of the data, all by itself. The sentence the project started with was “it’s automatable after all”. Delivering on it only after the launch turns it into a built proof instead of an announcement.
Part 4 of 4 in the Klimaspirale series.