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This paper examines variations of the surface air temperature (SAT) over China and the globe in the twentieth century simulated by 19 coupled climate models driven by historical natural and anthropogenic forcings. Most models perform well in simulating both the global and the Northern Hemispheric mean SAT evolutions of the twentieth century. The inclusion of natural forcings improves the simulation, in particular for the first half of the century. The reproducibility of the SAT averaged over China is lower than that of the global and hemispheric averages, but it is still acceptable. The contribution of natural forcings to the SAT over China in the first half of the century is not as robust as that to the global and hemispheric averages. No model could successfully produce the reconstructed warming over China in the 1920s. The prescribed natural and anthropogenic forcings in the coupled climate models mainly produce the warming trends and the decadal- to interdecadal-scale SAT variations with poor performances at shorter time scales. The prominent warming trend in the last half of the century over China and its acceleration in recent decades are weakly simulated. There are discrepancies between the simulated and observed regional features of the SAT trend over China. Few models could produce the summertime cooling over the middle part of eastern China (27°–36°N), while two models acceptably produce the meridional gradients of the wintertime warming trends, with north China experiencing larger warming. Limitations of the current state-of-the-art coupled climate models in simulating spatial patterns of the twentieth-century SAT over China cast a shadow upon their capability toward projecting credible geographical distributions of future climate change through Intergovernmental Panel on Climate Change (IPCC) scenario simulations. [ABSTRACT FROM AUTHOR]

This study investigates the effects of global and regional sea surface temperature (SST) warming from the Industrial Revolution to the present on the stratosphere using a climate model, and estimates the relative contributions of SST warming in different regions. The observed global SST warming is found to cause colder and stronger stratospheric zonal circulations in the high latitudes of both hemispheres, and a colder lower stratosphere in the tropics and ozone depletion. This occurs because the warming in the tropical Atlantic and in the north Indian Ocean and North Pacific strongly cool the stratosphere in the southern and northern high latitudes, respectively. The cooling in the lower stratosphere at lower and midlatitudes is mainly caused by SST warming in the tropical Pacific and north Indian Ocean. The changes in stratospheric temperature are related to changes in circulation and ozone. In addition, we investigate the effects on the stratosphere of ideal 1-K uniform warming of SST in different oceans and compare these effects with those caused by the realistic SST warming. The observed global SST warming and 1-K uniform global SST warming have opposite effects on the high-latitude stratosphere in both hemispheres: 1-K uniform global SST warming results in warmer and weaker stratospheric zonal circulations and a corresponding increase in ozone. This is because the 1-K uniform increase in SST in the tropical Pacific causes extremely strong warming and weakening stratospheric zonal circulations. The contribution of a 1-K uniform increase of SST in the tropical Pacific to stratospheric temperature, circulation, and ozone anomalies overwhelms that of a 1-K uniform increase of SST in other regions. [ABSTRACT FROM AUTHOR]

Previous work showed that the poleward expansion of the annual-mean zonal-mean atmospheric circulation in response to global warming is strongly modulated by changes in clouds and their radiative heating of the surface and atmosphere. Here, a hierarchy and an ensemble of global climate models are used to study the circulation impact of changes in atmospheric cloud-radiative heating in the absence of changes in sea surface temperature (SST), which is referred to as the atmospheric pathway of the cloud-radiative impact. For the MPI-ESM model, the atmospheric pathway is responsible for about half of the total cloud-radiative impact, and in fact half of the total circulation response. Changes in atmospheric cloud-radiative heating are substantial in both the lower and upper troposphere. However, because SST is prescribed the atmospheric pathway is dominated by changes in upper-tropospheric cloud-radiative heating, which in large part results from the upward shift of high-level clouds. The poleward circulation expansion via the atmospheric pathway and changes in upper-tropospheric cloud-radiative heating are qualitatively robust across three global models, yet their magnitudes vary by a factor of 3. A substantial part of these magnitude differences are related to the upper-tropospheric radiative heating by high-level clouds in the present-day climate. A comparison with observations highlights the model deficits in representing the radiative heating by high-level clouds and indicates that reducing these deficits can contribute to improved predictions of regional climate change. [ABSTRACT FROM AUTHOR]

How the globally uniform component of sea surface temperature (SST) warming influences rainfall in the African Sahel remains insufficiently studied, despite mean SST warming being among the most robustly simulated and theoretically grounded features of anthropogenic climate change. A prior study using the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 atmospheric general circulation model (AGCM) demonstrated that uniform SST warming strengthens the prevailing northerly advection of dry Saharan air into the Sahel. The present study uses uniform SST warming simulations performed with 7 GFDL and 10 CMIP5 AGCMs to assess the robustness of this drying mechanism across models and uses observations to assess the physical credibility of the severe drying response in AM2.1. In all 17 AGCMs, mean SST warming enhances the free-tropospheric meridional moisture gradient spanning the Sahel and with it the Saharan dry-air advection. Energetically, this is partially balanced by anomalous subsidence, yielding decreased precipitation in 14 of the 17 models. Anomalous subsidence and precipitation are tightly linked across the GFDL models but not the CMIP5 models, precluding the use of this relationship as the start of a causal chain ending in an emergent observational constraint. For AM2.1, cloud–rainfall covariances generate radiative feedbacks on drying through the subsidence mechanism and through surface hydrology that are excessive compared to observations at the interannual time scale. These feedbacks also act in the equilibrium response to uniform warming, calling into question the Sahel's severe drying response to warming in all coupled models using AM2.1. [ABSTRACT FROM AUTHOR]

Future changes in tropical cyclone (TC) activity and structure are investigated using the outputs of a 14-km mesh climate simulation. A set of 30-yr simulations was performed under present-day and warmer climate conditions using a nonhydrostatic icosahedral atmospheric model with explicitly calculated convection. The model projected that the global frequency of TCs is reduced by 22.7%, the ratio of intense TCs is increased by 6.6%, and the precipitation rate within 100 km of the TC center increased by 11.8% under warmer climate conditions. These tendencies are consistent with previous studies using a hydrostatic global model with cumulus parameterization. The responses of vertical and horizontal structures to global warming are investigated for TCs with the same intensity categories. For TCs whose minimum sea level pressure (SLP) reaches less than 980 hPa, the model predicted that tangential wind increases in the outside region of the eyewall. Increases in the tangential wind are related to the elevation of the tropopause caused by global warming. The tropopause rise induces an upward extension of the eyewall, resulting in an increase in latent heating in the upper layers of the inclined eyewall. Thus, SLP is reduced underneath the warmed eyewall regions through hydrostatic adjustment. The altered distribution of SLP enhances tangential winds in the outward region of the eyewall cloud. Hence, this study shows that the horizontal scale of TCs defined by a radius of 12 m s−1 surface wind is projected to increase compared with the same intensity categories for SLP less than 980 hPa. [ABSTRACT FROM AUTHOR]