GLACIAL-INTERGLACIAL CLIMATE CHANGE DURING THE LATE PALEOZOIC: A CLIMATE MODELING PERSPECTIVE

Late Pleistocene climate change was dominated by glacial-interglacial climate fluctuations that were largely driven by the Northern Hemisphere ice-sheet response to changes in Earth's orbit. The extent to which Late Paleozoic ice age climate was susceptible to orbital changes is not known.

To investigate this issue, we have conducted a series of global climate simulations of the Late Paleozoic using GENESIS version 2.3, a coupled atmosphere-biome-ice sheet model. These experiments predict climate, vegetation, and continental ice-sheet responses to changes in Earth's orbit and atmospheric pCO₂. At low levels of pCO₂, 140-280 ppm, climate and vegetation sensitivity to changes in Earth's orbit is very large due to glacial-interglacial variations in the size and distribution of Gondwana ice sheets. For example, when summer solar insolation is at a minimum in the Southern Hemisphere and Gondwana ice sheets are most extensive, the mean position of the Intertropical Convergence Zone is in the Northern Hemisphere and low-latitude biomes consist largely of temperate forest. When summer solar insolation is at a maximum in the Southern Hemisphere, the mean position of the Intertropical Convergence Zone lays in the Southern Hemisphere and low-latitude biomes are mainly desert. In these experiments, glacioeustatic changes are as great as 245 m. At high levels of pCO₂, 2240 ppm or greater, the climate sensitivity to orbital changes is substantially reduced due to the absence of continental ice on Gondwana. These experiments suggest that, like the Pleistocene, the Late Paleozoic ice age climate was likely dominated by orbitally-driven glacial-interglacial variations that had a substantial impact on many aspects of global climate.