Gfdlgcm Gfdl Gcm Ncarccm Gcm Nasagiss

UGAMP GCM 1979

July CLIMAP SSTs prescribed

July CLIMAP SSTs prescribed

Annual 70m mixed layer ocean

July CLIMAP SSTs prescribed

July CLIMAP SSTs prescribed January

Annual CLIMAP SSTs prescribed

Annual CLIMAP SSTs prescribed r330

L200

r330

L200

0 ka BP

FIGURE 12.17 Principal changes in external forcing and internal climate system boundary conditions, from 18 ka B.P to the present. Insolation anomalies are shown for the northern hemisphere, for summer (JJA) and winter (DJF) as a percentage difference from present. Global mean annual sea-surface temperatures (SSTs) are as calculated by CLIMAP (1981) for open ocean areas and sea-ice regions. Ice is the percent of 18 ka ice volume, according to Denton and Hughes (1981). Glacial age aerosols are depicted on an arbitrary scale.The arrows along the bottom indicate GCM simulations for each time period, using the changes in forcing and boundary conditions shown (Kutzbach and Street-Perrott, 1985).

0 ka BP

FIGURE 12.17 Principal changes in external forcing and internal climate system boundary conditions, from 18 ka B.P to the present. Insolation anomalies are shown for the northern hemisphere, for summer (JJA) and winter (DJF) as a percentage difference from present. Global mean annual sea-surface temperatures (SSTs) are as calculated by CLIMAP (1981) for open ocean areas and sea-ice regions. Ice is the percent of 18 ka ice volume, according to Denton and Hughes (1981). Glacial age aerosols are depicted on an arbitrary scale.The arrows along the bottom indicate GCM simulations for each time period, using the changes in forcing and boundary conditions shown (Kutzbach and Street-Perrott, 1985).

180 150 120 90 60 30 0 30

Longitude

FIGURE 12.18 Schematic diagram illustrating the circulation pattern for 18 ka B.P. in January, based on a GCM experiment with thick Laurentide and European ice sheets (shaded).The main jet stream is split around the ice sheets; the dashed lines along the southern jet stream show the zone of increased precipitation. Surface wind systems are shown by open arrows.This result is from the NCAR GCM; not all GCMs show this bifurcation of upper air winds In LGM simulations (Kutzbach and Wright, 1985).

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