Simulated Impact of the Tibetan Glacier Expansion on the Eurasian Climate and Glacial Surface Mass Balance during the Last Glacial Maximum

Glaciers over the Tibetan Plateau and surrounding regions during the Last Glacial Maximum (LGM) were much more extensive than during the preindustrial period (PI). The climate impact of such glacial expansion is studied here using the Community Atmosphere Model, version 4 (CAM4). To cover the range of uncertainty in glacier area during the LGM, the following three values are tested: 0.35 × 106, 0.53 × 106, and 0.70 × 106 km2. The added glacier is distributed approximately equally over the Pamir region and the Himalayas. If 0.70 × 106 km2 is used, the annual mean surface temperature of the glaciated regions would be cooled by ~3.5°C. The annual mean precipitation would be reduced by 0.2 mm day−1 (10%) and 2.5 mm day−1 (24%) over the Pamir region and Himalayas, respectively. The surface mass balance (SMB) of the glaciers changes by 0.55 m yr−1 (280%) and −0.32 m yr−1 (−20%) over the two regions, respectively. The changes in SMB remain large (0.29 and −0.13 m yr−1), even if the area of the Tibetan glacier were 0.35 × 106 km2. Therefore, based on the results of this particular model, the expansion of glaciers can either enhance or slow the glacial growth. Moreover, the expansion of glaciers over the Himalayas reduces summer precipitation in central and northern China by ~0.5 mm day−1 and increases summer precipitation in southern Asia by ~0.6 mm day−1. The expansion of glaciers over the Pamir region has a negligible influence on the precipitation in these monsoonal regions, which is likely due to its large distance from the main monsoonal regions.