The role of GCM resolution in simulating glacial inception

• Published in: The Holocene
• Main Authors: Vavrus, Steve, Philippon-Berthier, Gwenaëlle, Kutzbach, John E., Ruddiman, William F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2011
• Subjects: Paleontology; Earth-Surface Processes; Ecology; Archeology; Global and Planetary Change; Baffin Island; Canada; Northern Rockies; Baffin; Ice Sheet
• Online Access: http://dx.doi.org/10.1177/0959683610394882; http://journals.sagepub.com/doi/pdf/10.1177/0959683610394882

We test the influence of model resolution on glacial inception using a coupled atmosphere–slab ocean version of NCAR’s CCSM3 GCM. Simulations employ a modern orbital configuration and greenhouse gas concentrations representing both recent (year 1990) and hypothetically lower values based on Ruddiman’s Early Anthropogenic Hypothesis (240 ppm CO 2 , 450 ppb CH 4 ). We ran the model at two different horizontal resolutions: relatively coarse (spectral T42, approximately 2.8°) and comparatively fine (T85, approximately 1.4°). Under contemporary greenhouse forcing, permanent boreal snow cover extent in the two model configurations is similar, but lowering greenhouse gas concentrations generates much more extensive glacial inception in the T85 experiment (150% increase) than at T42 resolution (80% increase). Furthermore, the spatial patterns of glacial inception differ considerably. Only the T85 version produces permanent snow cover over the Rocky Mountains and Baffin Island, consistent with geologic evidence for early glaciation in the northern Rockies and Laurentide ice sheet nucleation in northeastern Canada. Although enhanced sensitivity at higher resolution is largely attributable to the expected colder and wetter conditions over elevated topography, much of the response is also driven dynamically. Atmospheric pressure changes at the surface and aloft differ considerably between model resolutions. The T85 circulation anomalies favor a stronger onshore moisture flux and therefore more snowfall over the northern Rockies and Baffin Island. Although these experiments are driven by greenhouse forcing rather than orbital anomalies, our findings may apply to general mechanisms of glacial inception.