Lc. Sloan et al., Effect of sea surface temperature configuration on model simulations of "equable" climate in the Early Eocene, PALAEOGEO P, 167(3-4), 2001, pp. 321-335
A major challenge in paleoclimate modeling studies is reproducing the "equa
ble" climate conditions recorded by proxy climate data. This challenge has
long been a focus in studies of Eocene paleoclimate. Climate models consist
ently overestimate mean annual temperature range (MATR) relative to proxy d
ata interpretations and produce minimum temperatures that are far lower tha
n proxy estimates. We hypothesize that the lack of accurate sea surface tem
peratures (SSTs) and a complete annual cycle definition is responsible for
some of these model-data discrepancies in Eocene comparisons. To test this
hypothesis, we developed two Eocene annual cycle SST data sets as boundary
conditions for model experiments and ran full annual cycle and abbreviated
cycle (perpetual) cases. When a perpetual case is replaced by a full annual
cycle of SST values, the January 0 degreesC isotherm (freezeline) over Nor
th America shifts poleward by similar to5 degrees latitude and MATR is redu
ced by similar to5 degreesC. A change from one annual SST cycle to another,
equally plausible, annual SST cycle results in a further latitudinal migra
tion (similar to5 degrees) of the freezeline and another similar to5 degree
sC change in continental interior MATR. Overall, the global mean annual and
cold month mean temperatures show little sensitivity to the forcing, while
MATR shows larger sensitivity in some continental regions. Our results sug
gest that the annual cycle of SSTs and the actual SST values incorporated i
nto experiments are major sources of the model-data continental temperature
discrepancies reported in past paleoclimate modeling studies. We also find
that the relatively coarse spatial resolution of the topography incorporat
ed into paleoclimate models is an additional source of the discrepancy. (C)
2001 Elsevier Science B.V. All rights reserved.