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Summer precipitation anomalies over eastern China are characterized spatially by meridionally banded structures fluctuating on interannual and interdecadal timescales, leading to regional droughts and floods. In addition to long-term trends, how these patterns may change under global warming has important implications for agricultural planning and water resources over this densely populated area. Using the latest Hadley Centre climate model, HadGEM3-GC2, this paper investigates the potential response of summer precipitation patterns over this region, by comparing the leading modes between a 4×CO2 simulation and the model’s pre-industrial control simulation. Empirical Orthogonal Function (EOF) analyses show that the first two leading modes account for about 20% of summer rainfall variability. EOF1 is a monopole mode associated with the developing phase of ENSO events and EOF2 is a dipole mode associated with the decaying phase of ENSO. Under 4×CO2 forcing, the dipole mode with a south-north orientation becomes dominant because of a strengthened influence from excessive warming of the Indian Ocean. On interdecadal time scales, the first EOF looks very different from the control simulation, showing a dipole mode of east-west contrast with enhanced influence from high latitudes. [ABSTRACT FROM AUTHOR]

Summer monsoon rainfall supplies over 55% of annual precipitation to global monsoon regions. As shown by more than 70% of models, including 30 models from CMIP5 and 30 models from CMIP6 under high-emission scenarios, North American (NAM) monsoon rainfall decreases in a warmer climate, in sharp contrast to the robust increase in Asian- African monsoon rainfall. A hierarchy of model experiments is analyzed to understand the mechanism for the reduced NAM monsoon rainfall in this study. Modeling evidence shows that the reduction of NAM monsoon rainfall is related to both direct radiative forcing of increased CO2 concentration and SST warming, manifested as fast and slow responses to abrupt CO2 quadrupling in coupled GCMs. A cyclone anomaly forms over the Eurasian-African continental area due to enhanced land-sea thermal contrast under increased CO2 concentration, and this leads to a subsidence anomaly on its western flank, suppressing the NAM monsoon rainfall. The SST warming acts to further reduce the rainfall over the NAM monsoon region, and the El Niño-like SST warming pattern with enhanced SST warming over the equatorial Pacific plays a key role in suppressing NAM rainfall, whereas relative cooling over the subtropical North Atlantic has no contribution. A positive feedback between monsoon precipitation and atmospheric circulation helps to amplify the responses of monsoon rainfall. [ABSTRACT FROM AUTHOR]

Mechanisms that cause changes in Madden–Julian oscillation (MJO) precipitation amplitude under global warming are examined in models from phase 5 of the Coupled Model Intercomparison Project. Under global warming in representative concentration pathway 8.5, MJO precipitation intensifies in most models relative to current climate while MJO wind circulations increase at a slower rate or weaken. Changes in MJO precipitation intensity are partially controlled by changes in moisture profiles and static stability. The vertical moisture gradient increases in the lower half of the troposphere in response to the surface warming, while the vertical static stability gradient increases due to preferential warming in the upper troposphere. A nondimensional quantity called α has been defined that gives the efficiency of vertical advective moistening associated with diabatic processes in the free troposphere, and has been hypothesized by previous studies to regulate MJO amplitude. The term α is proportional to the vertical moisture gradient and inversely proportional to static stability. Under global warming, the increased vertical moisture gradient makes α larger in models, despite increased static stability. Although α increases in all models, MJO precipitation amplitude decreases in some models, contrary to expectations. It is demonstrated that in these models more top-heavy MJO diabatic heating with warming overwhelms the effect of increased α to make vertical moisture advection less efficient. [ABSTRACT FROM AUTHOR]

Understanding local SST control on precipitation during monsoon is important for deducing climate change due to global warming, particularly for warm oceans. Studies of the relationship of the precipitation over tropical oceans with local sea surface temperature (SST), on the monthly scale, have shown that the propensity for precipitation is high for SST above a threshold of 27.5 ∘ C/28 ∘ C. However, for warm oceans with SST above the threshold such as the Bay of Bengal and South China Sea, for each SST, there is a large variation of precipitation and the SST–precipitation relationship is weak. On daily scale mean precipitation increases slightly with SST when precipitation lags SST by a few days, but the relationship between them is rather weak. But, when SST is above the threshold, for daily, pentad, 10-day and monthly time scales, and with or without time lag, the curve depicting the variation of mean precipitation with SST explains only a small fraction of precipitation variance and hence cannot be considered to be representative of the SST–precipitation relationship, or used to deduce the impact of SST on precipitation. On the other hand, the local control on precipitation is predominantly atmospheric dynamics with the relationship of variation of precipitation to low-level convergence on all timescales, being strong. This suggests that for warm oceans, the limiting resource for precipitation/convection is not SST but dynamics. [ABSTRACT FROM AUTHOR]

The impact of global warming–induced intertropical convergence zone (ITCZ) narrowing onto the higher-latitude circulation is examined in the GFDL Atmospheric Model, version 2.1 (AM2.1), run over zonally symmetric aquaplanet boundary conditions. A striking reconfiguration of the deep tropical precipitation from double-peaked, off-equatorial ascent to a single peak at the equator occurs under a globally uniform +4 K sea surface temperature (SST) perturbation. This response is found to be highly sensitive to the SST profile used to force the model. By making small (≤1 K) perturbations to the surface temperature in the deep tropics, varying control simulation precipitation patterns with both single and double ITCZs are generated. Across the climatologies, narrower regions of ascent correspond to more equatorward Hadley cell edges and eddy-driven jets. Under the global warming perturbation, the experiments in which there is narrowing of the ITCZ show significantly less expansion of the Hadley cell and somewhat less poleward shift of the eddy-driven jet than those without ITCZ narrowing. With a narrower ITCZ, the ascending air has larger zonal momentum, causing more westerly upper-tropospheric subtropical wind. In turn, this implies 1) the subtropical jet will become baroclinically unstable at a lower latitude and 2) the critical (zero wind) line will shift equatorward, allowing midlatitude eddies to propagate farther equatorward. Both of these mechanisms modify the Hadley cell edge position, and the latter affects the jet position. [ABSTRACT FROM AUTHOR]

Regional precipitation responses to land warming are separated from other aspects of CO2 forcing using idealized atmosphere‐only climate model experiments. Land warming is crucial in determining the regional responses to direct CO2 forcing and the plant physiological effect and partially mitigates the response to sea surface temperature (SST) warming. The plant physiological effect causes large reductions in transpiration over forest regions but also produces significant land warming which increases moisture convergence in tropical forest regions, opposing transpiration‐related reductions in precipitation. The balance between these two large terms differs by region and explains why some regions actually experience increased precipitation in response to reduced transpiration. Regional circulation changes driven by increased CO2 atmospheric radiative heating appear to be mainly related to land‐sea differences in water cycle adjustments rather than spatial variations in radiative heating. This drives increased rainfall in several monsoon regions, particularly over West Africa. SST warming generally leads to reduced precipitation over land and increases over the oceans, while the associated land warming enhances moisture convergence and precipitation over land. However, the combination of SST and land warming effects is highly nonlinear in the tropics, which is likely to be because of strong coupling between precipitation change and land warming. Plain Language Summary: Land is warming faster than the oceans in response to climate change. A new set of climate model experiments have been used to determine how this enhanced land warming could affect wind and rainfall patterns. In general, land warming drives winds that blow from ocean on to land, similar to a very large‐scale sea breeze. On its own, this would tend to increase rainfall over land. The expected overall rainfall change varies across different regions and depends on the balance between the effect of land warming and other aspects of climate change such as warming of the atmosphere and oceans and changes to water loss from plants. In several monsoon regions, the impact of direct heating of the atmosphere from increased carbon dioxide plays a very important role in rainfall change. In tropical forest regions, reduction in transpiration from plants in response to increased carbon dioxide has a large effect on the whole regional water cycle. Key Points: A new set of AGCM experiments are used to isolate the effect of land warming from other aspects of CO2 forcing and warmingLand warming is crucial in determining the precipitation pattern responses to direct CO2 forcing and plant physiological forcingThe combination of SST and land warming is strongly nonlinear in the tropics, though less so in the extratropics [ABSTRACT FROM AUTHOR]

The Mediterranean region is a climate hot spot, sensitive not only to global warming but also to water availability. In this work we document major temperature and precipitation changes in the Iberian Peninsula and margin during the last 2000 years and propose an interplay of the North Atlantic internal variability with the three atmospheric circulation modes (ACMs), (North Atlantic Oscillation (NAO), east atlantic (EA) and Scandinavia (SCAND)) to explain the detected climate variability. We present reconstructions of sea surface temperature (SST derived from alkenones) and on-land precipitation (estimated from higher plant n-alkanes and pollen data) in sedimentary sequences recovered along the Iberian Margin between the south of Portugal (Algarve) and the northwest of Spain (Galiza) (36 to 42° N). A clear long-term cooling trend, from 0 CE to the beginning of the 20th century, emerges in all SST records and is considered to be a reflection of the decrease in the Northern Hemisphere summer insolation that began after the Holocene optimum. Multi-decadal/centennial SST variability follows other records from Spain, Europe and the Northern Hemisphere. Warm SSTs throughout the first 1300 years encompass the Roman period (RP), the Dark Ages (DA) and the Medieval Climate Anomaly (MCA). A cooling initiated at 1300 CE leads to 4 centuries of colder SSTs contemporary with the Little Ice Age (LIA), while a climate warming at 1800 CE marks the beginning of the modern/Industrial Era. Novel results include two distinct phases in the MCA: an early period (900-1100 years) characterized by intense precipitation/ flooding and warm winters but a cooler spring-fall season attributed to the interplay of internal oceanic variability with a positive phase in the three modes of atmospheric circulation (NAO, EA and SCAND). The late MCA is marked by cooler and relatively drier winters and a warmer spring-fall season consistent with a shift to a negative mode of the SCAND. The Industrial Era reveals a clear difference between the NW Iberia and the Algarve records. While off NW Iberia variability is low, the Algarve shows large-amplitude decadal variability with an inverse relationship between SST and river input. Such conditions suggest a shift in the EA mode, from negative between 1900 and 1970 CE to positive after 1970, while NAO and SCAND remain in a positive phase. The particularly noticeable rise in SST at the Algarve site by the mid-20th century (±1970), provides evidence for a regional response to the ongoing climate warming. The reported findings have implications for decadal-scale predictions of future climate change in the Iberian Peninsula. [ABSTRACT FROM AUTHOR]

Global warming accelerates water cycle with features of regional difference. However, little is known about the physical mechanism behind the phenomenon. To reveal the links between water cycle and climatic environment, we analyzed the changes of water cycle elements and their relationships with climatic and environmental factors. We found that when global warming was significant during the period of 1986-2003, the precipitation in Tarim mountains as well as Xinjiang increased rapidly except for Tarim plains, which indicated that there existed a signal of acceleration for water cycle in Xinjiang. The speed of water cycle is mainly affected by altitude, latitude, longitude, slope direction, and the most fundamental element is temperature. Moreover, according to Clausius-Kela Bai Lung relation, we found that the climate change induced the increase of temperature and accelerated the local water cycle only for the wet places. Our results provide a possible physical mechanisms of water cycle and thus well link the climate change to water circulation. [ABSTRACT FROM AUTHOR]

Extreme climate events in China, including its 10 main river basins, were projected under global warming of 1.5 °C–4 °C using the latest version of a regional climate model (RegCM4) for dynamical downscaling, driven by the outputs of four global climate models. Firstly, evaluation indicated that the simulations satisfactorily reproduced the spatial distribution of temperature extremes and, although with lower performance, the spatial distributions of precipitation extremes were generally captured. Additionally, a better description was achieved over areas with complex terrains by using RegCM4. Next, the model was used to make projections under global warming of 1.5 °C–4 °C. Warm extremes were projected to increase, while cold events were projected to decrease, particularly in northern and western China. In addition, the number of wet days was projected to increase in the northern part of China, and to decrease in the southern part. The maximum consecutive five‐day precipitation and the precipitation intensity were projected to increase significantly throughout China, while the consecutive number of dry days was projected to significantly decrease in northern and western China. The changes of atmospheric moisture content and atmospheric circulation lead to the increase of extreme precipitation. Specifically, the increases in the indices of wetness were closely correlated with the summer precipitation, wind, moisture flux convergence, and surface specific humidity, while the consecutive number of dry days was related to the change in summer moisture flux convergence and precipitation in dry seasons. Notably, the magnitude of the changes in extremes events was projected to increase as the warming target increases. Key Points: A better description was achieved over areas with complex terrains by using RegCM4Model uncertainty in a high‐resolution ensemble of extremes was quantifiedThe magnitude of changes was projected to enhance as the global warming target increases [ABSTRACT FROM AUTHOR]

The mid‐Piacenzian (~3.3–3.0 Ma), which was characterized by high pCO2 (~400 ppm) and global surface air temperatures that were 1.84–3.60 °C above pre‐Industrial levels, provides clues to the likely changes in atmospheric dynamics in a future climate affected by anthropogenic warming, although its suitability as an analogue of the future climate has yet to be assessed. This study investigates the extent to which the dynamics of the East Asian summer monsoon during the mid‐Piacenzian can aid our understanding of East Asian summer monsoon behavior in the Extended Concentration Pathway version 4.5 scenario, using water vapor and moist static energy equations. The temperature‐dependent large‐scale moisture transport explains the similar pattern of precipitation increase in the two climates, whereas regional patterns of vertical motion differ significantly. Two of the main terms of the moist static energy equation control the changes in regional dynamics relative to the pre‐Industrial period. These terms relate to zonal advection of stationary eddy dry enthalpy by the mean zonal wind and meridional stationary eddy velocity over East Asia. Topographic differences between the two cases have a negligible effect on regional precipitation. Plain Language Summary: The mid‐Piacenzian (~3.3–3.0 Ma, mid‐Pliocene warm period) is the most recent warm period in Earth's history, characterized by high pCO2 levels (~400 ppm) and global warming (increase of 1.84–3.60 °C above pre‐Industrial levels). Thus, it is of interest to compare this period with atmospheric dynamics responses to anthropogenic warming in a future climate, especially in terms of the monsoon. This study investigates the extent to which the dynamics of the East Asian summer monsoon during the mid‐Piacenzian aid our understanding of the future behavior of the monsoon according to the Extended Concentration Pathway version 4.5 scenario. The analyses are based on water vapor and moist static energy equations. It is shown that increases in large‐scale moisture transport under thermal control in the two warm climates enhance East Asian summer monsoon precipitation. Regional differences in East Asian summer monsoon precipitation arise from different contributions of dynamic processes, primarily zonal warm advection by zonal wind and meridional stationary eddy velocity. Topographic differences between the two cases have a negligible effect on regional precipitation. Key Points: A comparison of summer monsoon dynamics over East Asia for the mid‐Piacenzian and the ECP4.5 scenario reveals both large‐scale similarities and regional differencesLarge‐scale similarity in moisture transport under thermal control and regional differences in vertical motion regulated by moist static energyNegligible effect of slight topographic difference on regional precipitation [ABSTRACT FROM AUTHOR]