CO<sub>2</sub> levels required for deglaciation of a “near‐snowball” Earth
Bibliographic record
Abstract
Geologic evidence suggests that in the Late Neoproterozoic (∼600 Ma) almost all land masses were glaciated, with sea‐level glaciation existing even at the equator. A recent modeling study has shown that it is possible to simulate an ice‐covered Earth glaciation with a coupled climate/ice‐sheet model. However, separate general circulation model experiments suggest that a second solution may exist with a substantial area of ice free ocean in the tropics. Although 0.1 to 0.3 of an atmosphere of CO 2 (∼300 to 1000 X) is required for deglaciation of a “Snowball Earth,” the “exit” CO 2 levels for an open water solution could be significantly less. In this paper we utilize a coupled climate/ice sheet model to demonstrate four points: (1) the open water solution can be simulated in the coupled model if the sea ice parameter is adjusted slightly; (2) a major reduction in ice volume from the open water/equatorial ice solution occurs at a CO 2 level of about 4X present values—about two orders of magnitude less than required for exit from the “hard” snowball initial state; (3) additional CO 2 increases are required to get fuller meltback of the ice; and (4) the open water solution exhibits hysteresis properties, such that climates with the same level of CO 2 may evolve into either the snowball, open water, or a warmer world solution, with the trajectory depending on initial conditions. These results set useful targets for geochemical calculations of CO 2 changes associated with the open‐water solution.
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How this classification was reachedexpand
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 | 0.001 | 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 | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".