Mid-Holocene ocean and vegetation feedbacks over East Asia

Mid-Holocene ocean and vegetation feedbacks over East Asia were investigated by a set of numerical experiments performed with the latest version 4 of the Community Climate System Model (CCSM4). Most of the annual and seasonal surface air temperature and precipitation changes during the mid-Holocene relative to the pre-industrial period were found to result from a direct response of the atmosphere to insolation forcing, while dynamic ocean and vegetation could modulate regional climate over East Asia to a certain extent. Because of its thermal inertia, the dynamic ocean induced an additional warming (cooling) of 0.5 K in boreal winter, 0.0003 K in boreal summer, and 1.0 K in boreal autumn (0.6 K in boreal spring) averaged across China during the mid-Holocene, and hence counteracted (amplified) the direct response except in summer, collectively leading to a weak annual warming of 0.2 K at the national scale. The contribution of dynamic vegetation to mid-Holocene temperature change was small overall. It gave rise to an additional annual cooling of 0.2 K, 0.1 K in winter, 0.2 K in summer, and 0.4 K in autumn, but a warming of 0.1 K in spring regionally averaged over China. On the other hand, ocean feedback led to a small enhancement of precipitation by 0.04 mm day 1 in winter and 0.05 mm day 1 in autumn, but induced a reduction of precipitation by 0.14 mm day 1 for the annual mean, 0.29 mm day 1 in spring, and 0.34 mm day 1 in summer at the national scale, which tended to weaken East Asian summer monsoon rainfall. The influence of dynamic vegetation on precipitation was comparatively small, with a regionally averaged precipitation change of –0.002 mm day 1 on the annual scale, –0.03 mm day 1 in winter and spring, –0.01 mm day 1 in summer, and 0.06 mm day 1 in autumn over the country. Taken together, ocean feedback narrowed the model–data mismatch in annual and winter temperatures over China during the mid-Holocene, while dynamic vegetation feedback contributed little to temperature and precipitation changes over East Asia.