Aspects of the Glacial-deglacial Climate of Western North America

Abstract:

We have completed a series of global climate simulations from the LGM (21 ka) to present at 3‑ky increments with GENMOM, a coupled A/OGCM with a nominal horizontal resolution of 3.75°. Each time segment was forced by appropriate boundary conditions (insolation, GHGs, ice sheets, sea level,) and run out for 1100 years to ensure minimal drift in the temperature of the deep ocean. GENMOM produces LGM and mid-Holocene (6 ka) climates consistent with paleoenvironmental data and the PMIP2 and CMIP5/PMIP3 simulations. The climate sensitivity is attributed to the interplay of various boundary conditions changes throughout the deglaciation as the ice sheets melt, the seasonality of insolation increases and GHG concentrations rise. Given the dominance of the Laurentide Ice Sheet and insolation-driven continental heating during the deglaciation and MH, these controls are particularly evident in the hydroclimate of NA. We use our simulations alone and combined with the PMIP simulations to explore aspects of the evolution of the glacial‑Holocene hydroclimate of Western North America related to changes in storm tracks and the strength of the monsoon circulation. We find variable agreement and disagreement among the models, particularly in the Southwest monsoon regions. We also find that, while the LGM moisture climatologies of the models may be locally consistent with paleoenvironmental data, the precipitation and temperature fields from the models produce substantial variability in simulations of the LIS as modeled by the CISM-GLIMMER ice sheet model, suggesting deficiencies in modeled regional and hemispheric circulation, moisture transport, or the surface energy balance over the ice.