Permian phytogeographic patterns and climate data/model comparisons

The most recent global "icehouse-hothouse" climate transition in earth hist ory began during the Permian. Warmer polar conditions, relative to today, t hen 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-Carbonif erous glaciation but retain a moderately steep equator-to-pole gradient, ju dging by the level of floral and faunal differentiation. Floral data provid e a particularly useful means of interpreting terrestrial paleoclimates, of ten 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 inte rpretation. We then classified Sakmarian and Wordian terrestrial environmen ts in a series of regional biomes ("climate zones") by integrating informat ion on leaf morphologies and phytogeography with patterns of eolian sand, e vaporite, 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 pres ent 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 si mulations with four times the present CO2 levels (4 x CO2) match the observ ations better than the simulations with 1 x CO2, and, at least in some area s, the simulations with 8 x CO2 match slightly better than those for 4 x CO 2. Overall, the 4 x CO2 and 8 x CO2 biome simulations match the data reason ably well in the equatorial and midlatitudes as well as the northern high l atitudes. However, even these highest CO2 levels fail to produce the temper ate climates in high southern latitudes indicated by the data. The lack of sufficient ocean heat transport into polar latitudes may be one of the fact ors responsible for this cold bias of the climate model. Another factor cou ld be the treatment of land surface processes and the lack of an interactiv e vegetation module. We discuss strengths and limitations of the data and m odel approaches and indicate future research directions.