Permian phytogeographic patterns and climate data/model comparisons

The most recent global icehouse-hothouse climate transition in earth history began during the Permian. Warmer polar conditions, relative to today, then persisted through the Mesozoic and into the Cenozoic. We focus here on two Permian stages, the Sakmarian (285-280 Ma) and the Wordian (267-264 Ma; also known as the Kazanian), integrating floral with lithological data to determine their climates globally. These stages postdate the Permo-Carboniferous glaciation but retain a moderately steep equator-to-pole gradient, judging by the level of floral and faunal differentiation. Floral data provide a particularly useful means of interpreting terrestrial paleoclimates, often revealing information about climate gradations between dry and wet end-member lithological indicators such as evaporites and coals. We applied multivariate statistical analyses to the Permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation. We then classified Sakmarian and Wordian terrestrial environments in a series of regional biomes (climate zones) by integrating information on leaf morphologies and phytogeography with patterns of eolian sand, evaporite, and coal distributions. The data-derived biomes are compared here with modeled biomes resulting from new Sakmarian and Wordian climate model simulations for a range of CO2 levels (one, four, and eight times the present levels), presented in our companion article. We provide a detailed grid cell comparison of the biome data and model results by geographic region, introducing a more rigorous approach to global paleoclimate studies. The simulations with four times the present CO2 levels (4 x CO2) match the observations better than the simulations with 1 x CO2, and, at least in some areas, the simulations with 8 x CO2 match slightly better than those for 4 x CO2. Overall, the 4 x CO2 and 8 x CO2 biome simulations match the data reasonably well in the equatorial and midlatitudes as well as the northern high latitudes. However, even these highest CO2 levels fail to produce the temperate climates in high southern latitudes indicated by the data. The lack of sufficient ocean heat transport into polar latitudes may be one of the factors responsible for this cold bias of the climate model. Another factor could be the treatment of land surface processes and the lack of an interactive vegetation module. We discuss strengths and limitations of the data and model approaches and indicate future research directions.