Simulating the East Asian summer monsoon (EASM) rain belt has been proven challenging for climate models. In this study, the impacts of high resolution to the simulation of spatial distributions and rainfall intensity of the EASM rain belt are revealed based on Atmospheric Model Intercomparison Project (AMIP) simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) models. A set of sensitivity experiments is further performed to eliminate the potential influences of differences among CMIP5 models. The results show that the high-resolution models improve the intensity and the spatial pattern of the EASM rainfall compared to the low-resolution models, further valid in the sensitivity experiments. The diagnosis of moist static energy (MSE) balance and moisture budgets is further performed to understand the mechanisms underlying the enhancements. Both analyses indicate that the improved EASM rainfall benefits from the intensified meridional convergence along the EASM rain belt simulated by the high-resolution models. In addition, such convergence is mainly contributed by intensified stationary meridional eddy northerly flows over the central northern areas of China and southerly flows over the south of Japan due to increased model resolution, which is robust in the sensitivity experiments. Further analysis indicates that the stationary meridional eddy flow changes in high-resolution simulations are related to the barotropic Rossby wave downstream of the Tibetan Plateau resulting from increased resolution.

The mid-Pliocene warm period (~ 3.3–3.0 Ma) is often considered as the last sustained warm period with close enough geographic configurations compared to the present one associated with atmospheric CO₂ concentration (405 ± 50 ppm) higher than the modern level. For this reason, this period is often considered as a potential analogue for the future climate warming, with the important advantage that for mid-Pliocene many marine and continental data are available. To investigate this issue, we selected the RCP4.5 scenario, one of the current available future projections, to compare the pattern of tropical atmospheric response with the past warm mid-Pliocene climate.

We use three Atmosphere-Ocean General Circulation Model (AOGCM) simulations (RCP4.5 scenario, mid-Pliocene and present-day simulation) carried out with the IPSL-CM5A model and investigate atmospheric tropical dynamics through Hadley and Walker cell responses to warmer conditions, considering that the analysis can provide some assessment of how these circulations will change in the future. Our results show that there is a damping of the Hadley cell intensity in the northern tropics and an increase in both subtropics. Moreover, northern and southern Hadley cells expand poleward. The response of the Hadley cells is stronger for the RCP4.5 scenario than for the mid-Pliocene, but in very good agreement with the fact that the atmospheric CO₂ concentration is higher in the future scenario than in the mid-Pliocene (543 versus 405 ppm). Concerning the response of the Walker cell, we show that despite very large similarities, there are also some differences. Common features to both scenarios are: weakening of the ascending branch, leading to a suppression of the precipitation over the western tropical Pacific. The response of the Walker cell is stronger in the RCP4.5 scenario than in the mid-Pliocene but also depicts some major differences, as an eastward shift of its rising branch in the future scenario compared to the mid-Pliocene.

In this paper, we explain the dynamics of the Hadley and Walker cells, and show that despite a minor discrepancy, the mid-Pliocene is certainly an interesting analogue for future climate changes in tropical areas

The origin of the temperature divergence between Holocene proxy reconstructions and model simulations remains controversial, but it possibly results from potential biases in the seasonality of reconstructions or in the climate sensitivity of models. Here we present an extensive dataset of Holocene seasonal temperatures reconstructed using 1310 pollen records covering the Northern Hemisphere landmass. Our results indicate that both summer and winter temperatures warmed from the early to mid-Holocene (~11–7 ka BP) and then cooled thereafter, but with significant spatial variability. Strong early Holocene warming trend occurred mainly in Europe, eastern North America and northern Asia, which can be generally captured by model simulations and is likely associated with the retreat of continental ice sheets. The subsequent cooling trend is pervasively recorded except for northern Asia and southeastern North America, which may reflect the cross-seasonal impact of the decreasing summer insolation through climatic feedbacks, but the cooling in winter season is not well reproduced by climate models. Our results challenge the proposal that seasonal biases in proxies are the main origin of model–data discrepancies and highlight the critical impact of insolation and associated feedbacks on temperature changes, which warrant closer attention in future climate modelling.