Declining atmospheric CO2 during the late Middle Eocene climate transition
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
The transition from the extreme greenhouse of the early Paleogene (∼52 Ma) to the present-day icehouse is the most prominent change in Earth's Cenozoic climate history. During the late Middle Eocene climate transition (42-38 Ma), which preceded the onset of long-lived, continental-scale ice sheets, there is concordant evidence for brief pulses (\<1 m.y. in length) of global warmth and ice sheet growth but few constraints on atmospheric CO~2~. Here we estimate the concentration of atmospheric CO~2~ during this critical interval using stomatal indices of fossil *Metasequoia* needles from ten levels in an exceptionally well-preserved core from the Giraffe kimberlite locality in northwestern Canada. Reconstructed CO~2~ concentrations are mainly between 700 to 1000 ppm, but include a secular decline to 450 ppm towards the top of the investigated section. Because the CO~2~ threshold for nucleating continental ice sheets at this time was ∼500 to 750 ppm, the CO~2~ decline is compatible with a rapid (\<10^4^ yrs) transition from warm, largely ice-free conditions to cooler climates with ice sheets. These fossils provide direct evidence that high-latitude deciduous forests thrived in the geological past under CO~2~ concentrations that will likely be reached within the 21^st^ century (500-1000 ppm).
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it