Phanerozoic CO2 levels and global temperatures inferred from changing paleogeography
Published:January 01, 1994
Thomas R. Worsley, Thomas L. Moore, Carmen M. Fraticelli, Christopher R. Scotese, 1994. "Phanerozoic CO2 levels and global temperatures inferred from changing paleogeography", Pangea: Paleoclimate, Tectonics, and Sedimentation During Accretion, Zenith, and Breakup of a Supercontinent, George O. Klein
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A simple model that tracks global land area and its average latitude to specify CO2 levels and consequent surface temperatures has been used to infer paleotem-peratures of 20 Phanerozoic global paleogeographic reconstructions. The model is based on the premise that global CO2 levels and temperature are directly proportional to the average latitude of the world landmass and inversely proportional to total land area. In all 20 cases, inferred CO2 and paleotemperature values are plausible and generally compatible with previous estimates. However, raw model output must be refined to take into account changes in rates of other climate modifiers such as orogeny, organic carbon burial, and precipitation that can be inferred from additional evidence.
Results show a warm (19°C) ice-free Cambrian world of small land area (75% emergent) at mid-latitudes (35°). Rapid equatorward migration of world landmass to 25° latitude then led to a cool (13°C) ice-capped late Ordovician world that was 70% emergent. Equally rapid migration back to higher latitudes (39°) by the Silurian coupled with decreased emergence (64%) produced the warmest temperatures of the Phanerozoic (22°). Return of the landmass to mid-latitudes (32°) coupled with reemergence (71%) by early Devonian reestablished cooler (18°) temperatures. As Pangea coalesced from early Devonian to late Carboniferous, percent emergence continually increased to virtually 100% as average latitude continually increased to 38°, resulting in an ice-capped world of 16°C. High organic carbon burial rates and orogeny at that time would suggest that our temperature estimates are slightly too high for this interval. By early Triassic, our results indicate continual ice-enhanced emergence at virtually 100% and equatorward migration of land to 33° latitude, yielding a global temperature of 16°C. Other lines of evidence (absence of ice, low organic carbon burial, weak orogeny, aridity) suggest a slightly warmer world, or at least one with a lower pole-equator thermal gradient. From Triassic to mid Cretaceous, average latitude again increased to 38° and emergence decreased to 75%, producing a warming of global temperature to 20°C. Cretaceous to Recent results indicate that average latitude of the landmass decreases to 30° as India and Australia move equatorward and that there is an increase to as much as 100% emergence during maximum late Cenozoic ice-sheet growth. Corresponding global temperatures decline to as low as 13°C.