Ice ages and interglacials: measurements, interpretation and models
Bibliographic record
Abstract
The typical description of the past 800,000 years would be that the Earth has experienced about nine major periods of glaciation ("Ice Ages") spaced at various intervals ranging from 0.9 my to 1.1 my (see Fig. 8.23).This presupposes that Ice Ages are unusual departures from normalcy.Actually, it appears as if the natural state of the Earth during this period was an Ice Age, but there were about nine interruptions of the glacial state, during which the Arctic climate was much warmer for time periods of the order of 10,000 years or so.Each Ice Age required many tens of thousands of years to develop to its maximum state of glaciation.During the last glacial maximum, some 20,000 years ago, Canada and the northern USA were blanketed by huge ice sheets, up to 4 km in thickness.In addition, there was a large ice sheet covering Scandinavia that reached down into Northern Europe.The Antarctic ice sheet was somewhat more extensive than today.Local glaciations existed in mountainous regions of North America, Europe, South America and Africa, driving the tree line down by up to 700-800 m.The temperature of Greenland was lower by up to 20 °C, but the climate was probably only a few degrees colder than normal in the tropics.Conditions were very harsh 20,000 years ago at the last glacial maximum (LGM).These ice sheets tied up so much of the Earth's water that more than 150 m of ocean was removed.As a result, the shorelines of the continents moved outward by a considerable distance.The Beringia land bridge from Siberia to Alaska was created, allowing animals and humans to cross from one continent to the other.In the upper-mid latitudes, the climates were semi-arctic and the flora shifted to tundra.Humidity was reduced, and many lands dried out.At the LGM, the CO 2 concentration dropped below 200 ppm, and this combined with cold, led to plant starvation and desertification of marginal areas.The sharp temperature discontinuity at the edges of the ice sheets generated violent winds that swept up dust and dirt from dry regions, filling the atmosphere with dust.Dust deposited on the ice sheets preceded each termination of an Ice Age, allowing much greater solar absorption and the demise of the ice sheets.This last Ice Age began to wane around 17,000 years ago and dissipated through a series of gyrating climate oscillations, ending in a comparatively benign period that has lasted for the past *10,000 years, called the Holocene.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 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".