Ruddiman's text, Chapter 6, Greenhouse Earth
Fig. 6-1, p. 130 (1st edition)
The world 100 million years ago -- What was climate like at that time? Why was so much continental mass innundated?
Evidence of Greenhouse warmth 100 Myr ago
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These warm-loving flora & fauna lived above the Arctic & Antarctic Circles 100 million years ago -- supporting the hypothesis of a greenhouse world where no permanent ice existed even at the Poles.
Besides the fossil record and geochemical evidence, what other evidence is used to reconstruct the probable global climate of 100 million years ago?
The 100 million year ago curve is based on geologic evidence input to a curve indicating mean zonal (temperatures. This is compared with modern mean temperature variations with latitude. How would you explain the results on this diagram?
Why is Antarctica so much colder today? Compared with the Arctic?
What explains this difference in temperatures with latitude 100 million years ago compared with today?
Low latitudes were a few degrees warmer than present.
High latitudes were as much as 20 to 40 degrees C warmer than present!
Sea levels were 200 meters higher than present.
Diagram of estimated minimum and maximum temperatures with latitude during the Cretaceous (Broad colored band).
Modeled scenarios test likely changes in temperature with latitude based on (1) Changes in geography -- land-sea distribution and elevation (mountains); and (2) changes in geography plus changes in CO2 content of the atmosphere (4 times pre-industrial percentages).
Which is closer to the paleoenvironmental record? Why do the models overestimate tropical temperatures and underestimate polar temperatures?
Possible reasons for Mismatch:
1. Fossil plants and animals are not good proxies for climate 100 million years ago --
They have evolved to be less tolerant of cold now than they were then.
Is this likely? Based on Uniformitarianism?
2. Misinterpretation of organic proxies
3. Alteration of materials in the geologic record after they were deposited (particularly geochemical proxies such as oxygen isotope ratios.
Changes in Ocean Deep Water Formation, based on distribution of contintental masses?
Differences in Ocean Salinities during Cretaceous, due to different continental mass distributions relative to latitude ...
Sea Level changes -- marine transgressions and regressions, especially along continental shelves -- How do these affect regional and global temperatures?
Sea Level over the past 100 million years
