Global patterns of increasing interannual variability of surface air temperature throughout the Holocene

We examine the interannual variability of surface air temperature throughout the Holocene and the associated mechanisms by using our new set of Holocene transient simulations spanning from 11.5 ka before present to the preindustrial period. The interannual variability of annual, winter, and summer temperature increases with a linear trend of 0.005, 0.007, and 0.005 °C/ka globally since 11.5 ka, respectively. The temperature variability evolution can be explained by the orbital forcing in most regions, with an additional impact from the retreat of ice sheets over North America and Europe but overall little effect from the change of atmospheric greenhouse gas concentrations. In response to the insolation change from the early to late Holocene primarily due to the precession, variations in energy balance components contribute to the enhanced temperature variability by a global mean of 8−10%. Specifically, surface net heat flux and radiation flux at the top of atmosphere generally play dominant roles, while atmospheric energy convergence minus storage partially offsets it at the global scale. Regionally, cloud effects and sea surface temperature variability are important in low latitudes, while sea ice changes are main factors in mid- to high-latitude oceans. Due to the seasonal contrast in insolation, various responses of global surface mean temperature and its meridional gradient, sea ice fraction, total cloud, and surface soil moisture result in the seasonal difference of temperature variability change, particularly in the Arctic Ocean and northern continents. The simulated temperature variability change throughout the Holocene is qualitatively consistent with most of the available proxy data, although uncertainties still exist from both sides.