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The concept of climate sensitivity emerges for a quantitative measurement of the amount of warming in association with the increase of atmospheric CO2 concentration. Here we provide a perspective on the climate sensitivity and associated transient climate response using the latest literature, both of which have been highly concerned in recent decades.

The teleconnection between the Atlantic Multidecadal Oscillation (AMO) and eastern China summer precipitation (ECSP) for the modern period has been emphasized in the past few decades. We test its stability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) based on the composite results of the median of six models under the Paleoclimate Modeling Intercomparison Project Phase3 (PMIP3) framework. During the MCA, ECSP generally increases in positive AMO phases relative to negative phases, similar to the modern teleconnection, while during the LIA, the precipitation tends to reduce over eastern China, especially in the Yangtze River basin. Decomposing the precipitation change on the basis of a diagnostic moisture budget manifests that the different AMO-related precipitation changes stem from distinct effects of circulation-induced moisture convergence during the two periods. Compared with negative AMO phases, positive AMO phases during the MCA show an anomalous lower-level cyclone and upper-level anticyclone over eastern China that facilitate the upward motion anomaly and precipitation excess. During the LIA, a barotropic anticyclone centers in Northeast China and weakens the high-level westerlies over eastern China; this favors descending and upper-level divergence anomalies and leads to precipitation decreases. The distinct convergence changes are determined by differing propagation paths of the AMO-induced teleconnection wave train during the two periods.

We compare the ability of coupled global climate models from the phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively) in simulating the temperature and precipitation climatology and interannual variability over China for the period 1961\2-2005 and the climatological East Asian monsoon for the period 1979–2005. All 92 models are able to simulate the geographical distribution of the above variables reasonably well. Compared with earlier CMIP5 models, current CMIP6 models have nationally weaker cold biases, a similar nationwide overestimation of precipitation and a weaker underestimation of the southeast\3-northwest precipitation gradient, a comparable overestimation of the spatial variability of the interannual variability, and a similar underestimation of the strength of winter monsoon over northern Asia. Pairwise comparison indicates that models have improved from CMIP5 to CMIP6 for climatological temperature and precipitation and winter monsoon but display little improvement for the interannual temperature and precipitation variability and summer monsoon. The ability of models relates to their horizontal resolutions in certain aspects. Both the multi-model arithmetic mean and median display similar skills and outperform most of the individual models in all considered aspects.

Changes in extreme climate have caused widespread concern, and it is important to understand how climate extremes will link to global warming intensity at the regional scale. Based on the daily minimum and maximum temperature and precipitation outputs from 25 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models under the Representative Concentration Pathways 8.5 (RCP8.5) scenario, we project the linkage of future regional climate extremes to the global mean temperature increase above preindustrial levels. Results show that regionally averaged changes in absolute temperature extremes (the coldest night and the warmest day) scale linearly with global warming intensity. In contrast, changes in cold nights and cold days in all regions, warm nights in low latitudes, and warm days in Southeast Asia exhibit nonlinear relationships with the global mean temperature increase, which manifests rapid changes in early warming stages and weak changes in late warming stages. The percentile-based temperature extremes vary at large magnitudes as global warming intensifies in low latitudes, while large values are seen in middle and high latitudes for the coldest night and warmest day, respectively; large intermodel spread occurs in the strong scaling areas, except for cold days and cold nights. Regional mean changes in extreme precipitation show consistent linear trends with global warming, and different indices vary in magnitude with region. Extreme heavy precipitation events increase linearly with global warming in high latitudes with larger magnitudes. The intermodel spread is generally large in low latitudes and will increase with warming. The work presented here can provide effective support to decision makers for developing adaptation and mitigation measures.

The assumption of a stationary global signal linked to El Niño–Southern Oscillation (ENSO) events is often used in paleo-ENSO proxy data interpretation. This paper attempts to investigate whether the assumption is valid during the last glacial maximum (LGM) over the region 60°S–90°N, 60°E−60°W. Using four models within phase 3 of the Paleoclimate Modeling Intercomparison Project framework that well reproduce ENSO-induced variabilities, differences from the preindustrial period to LGM in the ENSO-related sea surface temperature pattern and its impacts are investigated. Compared to the preindustrial period, the ENSO impacts are revealed to weaken and shift eastward during the LGM. According to multimodel medians, ENSO impacts on precipitation and near-surface air temperature are attenuated over most regions of concern, with percentage changes in both parameters averaging −21% for the whole region; the ENSO-induced Pacific–North America (PNA) teleconnection pattern is weakened, manifested by the 41% diminished center over the North Pacific and the almost vanished activity centers over the continent. Spatially, there is a zonal contraction of 13° for the sea surface warming of ENSO, as well as eastward migration over 10° for the ENSO-induced positive precipitation anomaly center over the tropical Pacific and the PNA teleconnection pattern outside the tropics. The aforementioned changes are linked to the altered climatic background during the LGM, which features a 16° eastward shift for the Pacific Walker circulation rising branch and a weakened waveguide in the midlatitudes. The results suggest that the hypothesis of stationary ENSO impacts should be applied cautiously to the past.

The East Asian summer monsoon (EASM) intensified during the early to mid-Holocene relative to the present primarily due to orbital forcing. However, on the regional scale, changes in the monsoonal precipitation exhibit considerable spatial disparity, and the underlying mechanisms remain unresolved. In this study, the dynamic processes responsible for the difference of the EASM precipitation between the mid-Holocene and preindustrial period are systematically examined using the CMIP5 multimodel simulations. The moisture budget diagnostic identifies vertical motion as the key factor determining the cross-like precipitation pattern in East Asia. Relative to the preindustrial period, the mid-Holocene anomalous ascending motion corresponds well with the excessive precipitation over northern and southern China, and vice versa for west-central China, the Korean peninsula, Japan, and its marginal seas. In the framework of the moist static energy budget, the increased insolation and the attendant intensification of land–sea thermal contrast give rise to anomalous ascending motions, while descending motions are fundamentally forced by the decreased latitudinal insolation gradient. In particular, thermodynamic changes, namely, the reduced pole–equator temperature and humidity gradients, account for the downward motions over the northwestern Pacific. Dynamic changes, namely, the weakened westerlies, play a leading role in suppressing updrafts in west-central China. This study highlights that the orbital-scale monsoonal precipitation changes are not solely determined by local radiative forcing as repeatedly emphasized before. The latitudinal uneven distribution of insolation is crucial to explain the spatial inhomogeneity in the EASM precipitation changes during the Holocene.

Based on surface air temperature and precipitation observation data and NCEP/NCAR atmospheric reanalysis data, this study evaluates the prediction of East Asian summer climate during 1959–2016 undertaken by the CESM (Community Earth System Model) large-ensemble initialized decadal prediction (CESM-DPLE) project. The results demonstrate that CESM-DPLE can reasonably capture the basic features of the East Asian summer climate and associated main atmospheric circulation patterns. In general, the prediction skill is quite high for surface air temperature, but less so for precipitation, on the interannual timescale. CESM-DPLE reproduces the anomalies of mid- and high-latitude atmospheric circulation and the East Asian monsoon and climate reasonably well, all of which are attributed to the teleconnection wave train driven by the Atlantic Multidecadal Oscillation (AMO). A transition into the warm phase of the AMO after the late 1990s decreased the geopotential height and enhanced the strength of the monsoon in East Asia via the teleconnection wave train during summer, leading to excessive precipitation and warming over East Asia. Altogether, CESM-DPLE is capable of predicting the summer temperature in East Asia on the interannual timescale, as well as the interdecadal variations of East Asian summer climate associated with the transition of AMO phases in the late 1990s, albeit with certain inadequacies remaining. The CESM-DPLE project provides an important resource for investigating and predicting the East Asian climate on the interannual and decadal timescales.

The eastern China summer precipitation is related to the Pacific Decadal Oscillation (PDO) on interdecadal time scales in modern times, but it remains unclear whether such a relationship holds prior to the instrumental period. We examine this relationship during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). According to a composite analysis using simulations of the HadCM3 model, which is selected from nine available climate models, the PDO–eastern China summer precipitation relationship varies with climatic background. The modern relationship features deficient precipitation over North and South China and excessive precipitation in the Yangtze–Huai River Valley in positive PDO phases compared with negative phases. In contrast, there is more precipitation over South and North China but less in the Yangtze–Huai River Valley during the MCA and widespread below-normal summer precipitation over eastern China during the LIA. Such different PDO-related precipitation patterns between the MCA and LIA are closely linked to distinct changes in local atmospheric circulation. Compared with negative PDO phases, positive phases during the MCA show an anomalous Pacific–Japan/East Asia–Pacific pattern over East Asia and strengthened high-level westerlies centering on 120°E and 25–30°N, which lead to the triple pattern in the precipitation anomaly. During the LIA, a cyclonic anomaly occurs over the South China Sea–Philippine Sea in the lower and middle troposphere, and two upper-level low trough anomalies occur over East Asia, causing the anomalous precipitation deficit. The different PDO-related local circulations are found to be relevant to the thermodynamic effect of low-latitude sea surface temperature and summer precipitation over India, as well as the propagation of upstream wave trains.

Both wind strength and anthropogenic emissions have been assumed to be the dominant factors in determining the occurrence of hazy weather in China. However, few records are available with sufficient temporal length and resolution, which enable the two signals to be separated, and hence address the dynamics of haze days and the global impact of the anthropogenic emissions in China, particularly in the context of global warming. Here we present the first long-term (last 180 years) lake sediment records of changes in wind strength and atmospheric loading of anthropogenic emissions in China. Our results show that the atmospheric loading of anthropogenic emissions and haze formation are closely related to the changes in wind strength associated with temperature changes, which are likely forced by tropical sea surface temperature. Comparison of our results with Pb isotope records from Japan and with the record of Pb concentrations in Greenland ice core indicates that the anthropogenic pollutants emitted in China stagnate mainly over the source area and neighboring regions, which thus favors haze formation under a warming climate. However, they would be transported worldwide under conditions of strong winds and decreased temperature. Climatic warming, together with the periodic changes in temperature, has caused unprecedented heavy haze days in recent decades in China. The observed pattern of periodic temperature variations suggests that in the next 30 years, wind strength will increase and thus reduce the incidence of haze days. However, this reduction may be attenuated by continued climatic warming as anthropogenic greenhouse gases emissions continue.

The late Pliocene is a pre-Quaternary warming period compared to the preindustrial period. Here, based on the updated PRISM4 (Pliocene Research, Interpretation and Synoptic Mapping version 4) boundary conditions from the Pliocene Model Intercomparison Project phase 2 (PlioMIP2), seven experiments are conducted to simulate the global monsoon in the late Pliocene interglacial period and further investigate the impacts from changes in the individual boundary conditions by using the Community Earth System Model (CESM 1.0.4). The simulated late Pliocene interglacial climate is generally warmer and wetter than the preindustrial period climate, with an expanded monsoon domain, particularly in North Africa, Asia and Australia. The differences in topography, vegetation and lakes outside of Greenland and Antarctica account for the greatest contribution to monsoon changes. Moreover, orbital parameter variations further significantly affect monsoon domains and lead to significant fluctuations in monsoon precipitation and winds on the orbital scale, and the changed magnitude is even larger than that between the late Pliocene and preindustrial period when orbital forcing is not considered.

Most models in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) underestimate the surface air temperature over China in both winter and summer. Understanding the weather regime in association with the simulated temperature variability is of high interest to get insight into those biases. Based on the weather regime method, we investigated the contributions of large-scale dynamics and non-dynamical processes to temperature biases and inter-model spread. The weather regimes associated with the observational temperature patterns were obtained through a k-means clustering algorithm applied to daily 500 hPa geopotential height anomalies. Here we identified the clustering number of weather regimes using the classifiability and reproducibility indices which can provide the optimal clustering number to obtain objective clustering. Both indices suggested the weather regimes in East Asia can be classified as four clusters in winter (December–January–February) and three in summer (June–July–August). The results indicated that the first and second weather regimes were related to the cold temperature anomalies in China during winter, and the three weather regimes could not effectively classify the temperature patterns during summer. The ensemble mean of 23 CMIP5 models overestimated the occurrence frequencies of the second weather regime, which corresponds to a weaker high latitude westerly jet over East Asia during winter. The 500 hPa geopotential height anomalies and the inter-model spread over the Tibetan Plateau may be associated with the limited ability of the CMIP5 models in simulating the thermal effects of plateau in summer. We also found that the non-dynamical processes had major contribution to the ensemble-mean biases, and the large-scale dynamics played a minor role. The non-dynamical processes substantially affected the inter-model spread, especially over the Tibetan Plateau and the Sichuan Basin, during both winter and summer. The results suggested that improving the simulation of regional processes may help to improve model performance. The use of multi-model mean is recommended since it performs better than most of individual models.

The surface uplift of the Tibetan Plateau (TP) had important effects on the evolution of both the regional and global climate during the Cenozoic. Geological evidence indicated that the timing of the uplifts of the main and marginal TP was probably different. However, many previous modelling studies only investigated the effects of the uplift of the whole TP on climate under modern boundary conditions and it remained unclear what was the difference between the effects of the uplifts of the main and marginal TP on climate and how changed boundary conditions influenced these effects. We used numerical modelling to investigate these questions. Our modelling results indicated that the uplifts of the main and marginal TP had different effects on climate. In particular, under modern boundary conditions, the uplift of the main TP decreased annual precipitation throughout inland Asia and in South Asia, increased annual precipitation in East Asia, and markedly changed the summer and winter low-level winds in Asia. By contrast, the uplift of the marginal TP increased the annual precipitation in South Asia, strengthened the seasonality of winds and enlarged the monsoon domain in East Asia. Thus, although the main TP was the major part of the TP in spatial terms, its uplift did not have the dominant effects on climate in all aspects. Moreover, changes in the boundary conditions – for example, from modern to ~30 Ma – could further influence the effects of the uplifts of the whole TP and its sub-regions on climate, particularly for the precipitation in South Asia and monsoon domain in East Asia. These results highlighted the different effects of the uplifts of the main and marginal TP on climate and emphasized the importance of accompanied boundary conditions when investigating the effects of the uplifts of the whole TP and its sub-regions on climate.

The mid-Piacenzian (Pliocene) warm period (approximately 3.3–3.0 Ma) monsoon not only provides us with a useful insight into the future monsoon under a warming scenario with high atmospheric CO2 concentration but is also hypothesized to play a key role in climate feedback through impact on the carbon cycle on a geological timescale. The monsoon evolution over time is one key to test this hypothesis. In this sense, we examine the mid-Piacenzian global land monsoon area (GLMA), precipitation (GLMP), and GLMP intensity (GLMPI) using all available model data from the Pliocene Model Intercomparison Project phase 1 (PlioMIP1). Relative to the pre-industrial period, both the GLMA and GLMP increase in the mid-Piacenzian and by an average of 7.3% and 5.8%, respectively. On a large scale, the increased GLMP comes mainly from northern Africa, Asia, and northern Australia. Quantitatively, it is the variation of GLMA, not of GLMPI, that makes a major contribution to the GLMP change. Further analysis reveals that anomalous inland water vapor transportation due to the reduced large-scale meridional thermal contrast in the mid-to-upper troposphere, together with the variation of vertical moisture advection and evaporation, explains most of the global land monsoon changes. A model–data comparison shows that the simulated monsoon precipitation variations are roughly consistent with the reconstructions in northern Africa, Asia, northern Australia, Central America, and eastern South America. Moreover, the intensified mid-Piacenzian Asian monsoon, which is supported by both simulations and reconstructions, or an overall intensified global land monsoon is hypothesized to contribute to the lowering of atmospheric CO2 concentration and the subsequent onset of the sustained major Northern Hemisphere glaciation.

Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes (ELAs) in western China during the last glacial maximum (LGM) are investigated to deepen our understanding of the surface environment on the Tibetan Plateau. Relative to the preindustrial period, the summer surface air temperatures decrease by 4–8°C while the annual precipitation decreases by an average of 25% across the Tibetan Plateau during the LGM. Under the joint effects of reductions in summer temperature and annual precipitation, the LGM ELAs in western China are lowered by magnitudes that vary with regions. The ELAs in the southern margin and northwestern Tibetan Plateau decline by approximately 1100 m; the central hinterland, by 650–800 m; and the eastern part, by 550–800 m, with a downward trend from southwest to northeast. The reduction in ELAs is no more than 650 m in the Tian Shan Mountains within China and approximately 500–600 m in the Qilian Mountains and Altai Mountains. The high-resolution models to reproduce the low values of no more than 500 m in ELA reductions in the central Tibetan Plateau, which are consistent with the proxy records from glacier remains. The accumulation zones of the Tibetan Plateau glaciers are mainly located in the marginal mountains during the LGM and have areas 2–5 times larger than those of the modern glaciers but still do not reach the central part.

The 4.2 ka BP event has been widely investigated since it was suggested to be a possible cause for the collapse of ancient civilizations. With the growth of proxy records for decades, however, both its nature and its spatial pattern have become controversial. Here we examined multi-proxy data of the grain-size distribution, ostracode assemblage, pollen assemblage, and the pollen-reconstructed mean annual precipitation from a sediment core at Hulun Lake in northeastern Inner Mongolia spanning the period between 5000 and 3000 cal. yr BP to identify the nature and the associated mechanism of the 4.2 ka BP event occurring in the monsoonal region of eastern Asia. Higher sand fraction contents, littoral ostracode abundances, and Chenopodiaceae pollen percentages together with lower mean annual precipitation reveal a significant dry event at the interval of 4210–3840 cal. yr BP that could be a regional manifestation of the 4.2 ka BP event in the northern margin of the East Asian summer monsoon (EASM). We suggest that the drought would be caused by a decline in the intensity of the EASM on millennial-to-centennial scales that could be physically related to persistent cooling of surface waters in the western tropical Pacific and the North Atlantic. The cooling of western tropical Pacific surface waters could reduce moisture production over the source area of the EASM, while the cooling of North Atlantic surface waters could suppress northward migrations of the EASM rain belt, both leading to a weakened EASM and thus decreased rainfall in the northern margin of the EASM.

Motivated by studies of tropical expansion under modern global warming, the behavior of the tropical belt during the Last Glacial Maximum (LGM) relative to the preindustrial period has been investigated in this study, using simulations from phase 3 of the Paleoclimate Modelling Intercomparison Project (PMIP3) under the framework of phase 5 of the Coupled Model Intercomparison Project (CMIP5). The tropical belt width changes determined by multiple metrics present two opposite tendencies. One refers to the poleward migration of the tropical edge as measured by the steep tropopause gradient and the subtropical jet, and the other suggests that the LGM tropics become narrower as measured by the Hadley cell extent, the eddy-driven jet, and the latitude where precipitation minus evaporation equals zero. The magnitude of such changes widely differs across models and metrics. In absolute terms, the multimodel mean total width changes range from 0.6° to 1.7° among metrics, with contributions predominantly from the Northern Hemisphere. Furthermore, the two metrics that indicate tropical widening are located in the upper troposphere. Such widening is closely related to the vertical and meridional temperature gradient changes in the subtropical regions. The other metrics are located in the middle and lower troposphere, and their variations are directly or indirectly related to changes in the low-level baroclinicity. The diverse responses of metrics to the LGM boundary conditions suggest that the tropical belt width changes and their climatic impacts are distinguished by the different measurements. The selection of metrics should correspond to the specific tropical properties of concern.

This study investigates terrestrial moisture changes and associated mechanisms during the last glacial maximum (LGM; approximately 21,000 calendar years ago) using multi-model simulations from the Paleoclimate Modelling Intercomparison Project phase 3 (PMIP3). Considering that terrestrial moisture is not determined solely by precipitation, an aridity index (AI) is employed for measuring the terrestrial moisture by combining the effects of both precipitation and potential evapotranspiration (PET), where the latter represents atmospheric water demand and is greatly decreased mainly by the intense cooling during the LGM. Compared to the preindustrial period, the magnitude of global mean terrestrial moisture change is small, as the wetness brought by decreased PET counteracts the dryness induced by decreased precipitation. Regionally, the moisture changes depend on the different combinations of changes in precipitation and PET: (i) drying occurs where precipitation deceases and PET hardly changes, such as the northern tropical Americas and Southeast Asia; (ii) wetting is found in regions with precipitation increases and PET decreases (e.g., northwestern Africa and the central Andes), and their contributions are comparable; (iii) in particular, wetting can also occur in regions of decreased precipitation if a sufficient decrease in PET also occurs (i.e., southeastern North America and the northern and southern parts of eastern Asia), with the latter wetting effect reversing the former drying effect. The multi-model median field is consistent with available paleo-records in southern North America, the northern tropical Americas, the Andes, northwestern Africa, the southern Iberian Peninsula, southwestern Africa, the central part of eastern Asia, and Java but disagrees with proxies in Australia, central Brazil, southeastern Africa, the northern Iberian Peninsula, and the southern part of eastern Asia.

Using a set of numerical experiments from 39 CMIP5 climate models, we project the emergence time for 4◦C global warming with respect to pre-industrial levels and associated climate changes under the RCP8.5 greenhouse gas concentration scenario. Results show that, according to the 39 models, the median year in which 4◦C global warming will occur is 2084. Based on the median results of models that project a 4◦C global warming by 2100, land areas will generally exhibit stronger warming than the oceans annually and seasonally, and the strongest enhancement occurs in the Arctic, with the exception of the summer season. Change signals for temperature go outside its natural internal variabilities globally, and the signal-tonoise ratio averages 9.6 for the annual mean and ranges from 6.3 to 7.2 for the seasonal mean over the globe, with the greatest values appearing at low latitudes because of low noise. Decreased precipitation generally occurs in the subtropics, whilst increased precipitation mainly appears at high latitudes. The precipitation changes in most of the high latitudes are greater than the background variability, and the global mean signal-to-noise ratio is 0.5 and ranges from 0.2 to 0.4 for the annual and seasonal means, respectively. Attention should be paid to limiting global warming to 1.5◦C, in which case temperature and precipitation will experience a far more moderate change than the natural internal variability. Large inter-model disagreement appears at high latitudes for temperature changes and at mid and low latitudes for precipitation changes. Overall, the intermodel consistency is better for temperature than for precipitation.

The global cooling, regional tectonic uplift, and land-sea redistribution have long been considered as the main drivers of the long-term evolution of dry climates during the Cenozoic. However, their relative importance is still a matter of hot debate. The effect of mountain uplift on forming the global mid-latitude dry climates has been widely investigated by lines of geologic evidences and numerical experiments based on atmospheric general circulation models. These previous simulation results are directly derived from the mountain climatic effects, without considering the superimposed effects due to sea surface temperature changes caused by mountain uplift. In order to address this issue, the impact of global topography on the arid environment is investigated by three numerical experiments of different mountain uplift scenarios performed with a global coupled atmosphere–ocean model CESM. The CESM consists of atmosphere, land, ocean, and sea ice components that exchange state information and fluxes through a coupler. The low-resolution version of CESM with less computationally expensive is used for this study. In addition, an aridity index is further taken to measure the global dryland area driven by mountain uplift. The aridity index is defined as the ratio of annual precipitation to potential evapotranspiration. The latter represents the evaporative demand of the atmosphere, which is composed of four meteorological parameters including surface air temperature, relative humidity, wind speed, and available energy. The relative contribution of these five factors to the aridity index is further evaluated to identify the underlying potential mechanism in response to the mountain uplift. By using the three simulations with modern topography, without global topography, and without the Tibetan Plateau, it is accessible to examine how the global mountain uplift affects the factors controlling the aridity index. In the global no-topography experiment, the subtropical arid zones in all continents exhibit an overall symmetrically zonal distribution. As the global mountain uplifts, on the one hand, southeastern and central Asia, southeastern North America, and central South America vary from arid to wet areas, while inland Eurasia and the coast of East Africa degenerate from humid to arid areas. The Tibetan Plateau uplift mainly affects the limited areas of Eurasia and eastern Africa. On the other hand, the topography of Eurasia and Africa relieves the aridification of coastal and northern North Africa, but to a certain extent, exacerbates the arid environment in central North Africa and western North and South America. The Tibetan Plateau uplift aggravates the drought climate on its western side, including the Middle East and most parts of North and East Africa. As a whole, the global mountain uplift leads to an overall decrease in the subtropical arid areas, with the expanded arid areas being less than the increased wet areas. The quantitative analysis of aridity index indicates that, the global topography uplift affects the terrestrial drought climate primarily by changing precipitation, and then by modifying the potential evapotranspiration. Their contributions to the aridity index are qualitatively consistent in the spatial pattern but different in magnitude. Among the impact factors of the potential evapotranspiration, the uplift of the terrain affects the aridity mainly through changes in relative humidity and near-surface air temperature, and then near-surface wind speed. To some extent, these simulation results agree qualitatively with the evidence of reconstructed geological records and previous atmosphere-only model results, indicating that the present study has scientific and palaeoclimate significance and thus helps to deepen the understanding of the climatic effect of global topography.

Based on the zonal mass streamfunction, the mid-Holocene annual and seasonal changes in the tropical Pacific Walker circulation (PWC) are examined using numerical simulations from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity strengthened (with an average increase of 0.26 × 1014 kg2 m−2 s−1 or 5%), and both the western edge and center of the PWC cell shifted westward (by an average of 4° and 3°, respectively) in the majority of the 29 models used for analysis during the mid-Holocene. Those changes were closely related to an overall increase in the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial Pacific. Annual mean PWC changes come mainly from boreal warm seasons. In response to the mid-Holocene orbital forcing, Asian and North African monsoon rainfall was strengthened due to large-scale surface warming in the Northern Hemisphere in boreal warm seasons, which led to an intensified large-scale thermally direct east–west circulation, resulting in the enhancement and westward shift of the tropical PWC. The opposite occurred during the mid-Holocene boreal cold seasons. Taken together, the change in the monsoon rainfall over the key tropical regions of Asia and North Africa and associated large-scale east–west circulation, rather than the equatorial Pacific SST change pattern, played a key role in affecting the mid-Holocene PWC strength.

Based upon simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the vertical and regional characteristics of the northern westerlies during the Last Glacial Maximum (LGM) are investigated in this study. At the Northern Hemispheric scale, all nine available models simulate a poleward shift of the 200-hPa jet, and eight models simulate an equatorward shift of the 850-hPa jet compared to the preindustrial period; these shifts are of approximately 2°–3° latitude for the arithmetic multimodel mean. The upper-tropospheric cooling in the tropics, possibly due to reduced latent heat release, is expected to account for the poleward shift of the 200-hPa jet through the thermal wind relationship. Changes in the midlatitude baroclinic instability in response to the amplified polar cooling are associated with the jet stream in the lower troposphere through anomalous eddy activity. In particular, the types of predominant baroclinic eddies are regionally dependent. The behavior of the 850-hPa jet over the North Pacific is steered by transient eddies and characterized by a southward displacement during the LGM. By contrast, the remarkable enhancement of the North Atlantic jet stream throughout the troposphere is associated with the notably increased stationary eddy momentum convergence, presumably due to the presence of the Laurentide ice sheet over North America. In comparison with the proxy records, although there is no observational evidence explicitly indicating changes of the upper-level northern westerlies, the simulated LGM 850-hPa westerly wind field is indirectly concordant with the reconstructed moisture conditions over the Mediterranean region and southwestern North America.

Based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) daily dataset, we investigate changes of the terrestrial extreme climates given that the global mean temperature increases persistently under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Compared to preindustrial conditions, more statistically significant extreme temperatures, precipitations, and dry spells are expected in the 21st century. Cold extremes decrease and warm extremes increase in a warmer world, and cold extremes tend to be more sensitive to global warming than the warm ones. When the global mean temperature increases, cold nights, cold days, and warm nights all display nonlinear relationships with it, such as the weakening of the link projected after 3 °C global warming, while the other indices generally exhibit differently, with linear relationships. Additionally, the relative changes in the indices related to extreme precipitation show significantly consistent linear changes with the global warming magnitude. Compared with the precipitation extremes, changes in temperature extremes are more strongly related to the global mean temperature changes. For the projection of the extreme precipitation changes, models show higher uncertainty than that in extreme temperature changes, and the uncertainty for the precipitation extremes becomes more remarkable when the global warming exceeds 5 °C.

The causes of the change in amplitude of El Niño–Southern Oscillation (ENSO) during the mid-Holocene were investigated by diagnosing the model simulations that participated in the Paleoclimate Modelling Intercomparison Project phases 2 and 3. Consistent with paleoclimate records, 20 out of the 28 models reproduced weaker-than-preindustrial ENSO amplitude during the mid-Holocene. Two representative models were then selected to explore the underlying mechanisms of air–sea feedback processes. A mixed layer heat budget diagnosis indicated that the weakened ENSO amplitude was primarily attributed to the decrease in the Bjerknes thermocline feedback, while the meridional advective feedback also played a role. During the mid-Holocene, the thermocline response to a unit anomalous zonal wind stress forcing in the equatorial Pacific weakened in both models because of the increased ENSO meridional scale. A further investigation revealed that the greater ENSO meridional width was caused by the strengthening of the Pacific subtropical cell, which was attributed to the enhanced mean trade wind that resulted from the intensified Asian and African monsoon rainfall and associated large-scale east–west circulation in response to the mid-Holocene orbital forcing.

Surface uplifting from the northern East Asian mountains has had an important effect on the evolution of the East Asian climate since the Late Miocene; however, the uplifting climate effects from each of these mountains remain unclear. This paper compares the climate effects of surface uplifts from the northern Tibetan Plateau (TP), the Tianshan, and the Mongolian Plateau (MP) on the East Asian climate. Our model results indicate that each of these mountains has different climate effects along an uplifting sequence from south to north. Compared to the combined surface uplifts from the northern TP and the Tianshan, the last surface uplift from the MP made a greater contribution to the decreased annual precipitation over inland Asia north of ~45°N and strengthened summer middle tropospheric westerly wind on its north side; furthermore, it made a comparable contribution to the intensified winter low-level (850 hPa) northwesterlies in northern East Asia and intensified winter middle tropospheric westerly wind over the region from East Asia to the northwestern Pacific. However, different uplift scenarios influenced these uplifting climate effects. For example, if the MP rose without the northern TP and the Tianshan, the uplifting climate effects of the MP described above largely weakened. In comparison, the combined further surface uplifts of the northern TP and the Tianshan had a more marked regional climate effect, particularly for the winter monsoon wind, and summer and winter middle tropospheric westerly wind.

The investigation into the past behavior of the East Asian summer monsoon (EASM) and Australian summer monsoon (ASM) is potentially helpful for advancing our knowledge of projected future changes. Geological evidence supports an in-phase change of the two monsoon systems over the last millennium, but the dynamic mechanisms and timescale-dependence are not fully understood. Using model outputs from the Paleoclimate Modelling Intercomparison Project Phase III, we investigated EASM and ASM variations, their phase relationship during the last millennium, and their dynamic mechanisms. According to selected “best-performance” models capable of reproducing reconstructed Asian–Australian monsoon changes, EASM and ASM showed significant in-phase changes only on centennial timescales, with intensified EASM/ASM during the Medieval Climate Anomaly (MCA) and weakened monsoons during the Little Ice Age (LIA). Moreover, the synchronous variation was more robust during the LIA relative to the MCA. The strengthened (weakened) EASM during the MCA (LIA) is attributed to an enhanced (reduced) land–sea temperature contrast and a northward (southward) shift of the subtropical westerly jet stream during boreal summer. During the same period, the ASM was reinforced (suppressed) due to the enhanced (reduced) lower-level easterly from the western Pacific and southward (northward) shift of upper-level westerly during austral summer. Meanwhile, the stronger (weaker) EASM/ASM during the MCA (LIA) was associated with expansion (retreat) of the local Intertropical Convergence Zone and an enhanced (reduced) zonal temperature gradient over the equatorial Pacific. Our results imply that the synchronous change in the Asian–Australian monsoon may be caused by inherent solar variations, further strengthening previous findings.

In this study, we analyzed numerical experiments undertaken by 10 climate models participating in PMIP3 (Paleoclimate Modelling Intercomparison Project Phase 3) to examine the changes in interannual temperature variability and coefficient of variation (CV) of interannual precipitation in the warm period of the Medieval Climate Anomaly (MCA) and the cold period of the Little Ice Age (LIA). With respect to the past millennium period, the MCA temperature variability decreases by 2.0% on average over the globe, and most of the decreases occur in low latitudes. In the LIA, temperature variability increases by a global average of 0.6%, which occurs primarily in the high latitudes of Eurasia and the western Pacific. For the CV of interannual precipitation, regional-scale changes are more significant than changes at the global scale, with a pattern of increased (decreased) CV in the midlatitudes of Eurasia and the northwestern Pacific in the MCA (LIA). The CV change ranges from −7.0% to 4.3% (from −6.3% to 5.4%), with a global average of −0.5% (−0.07%) in the MCA (LIA). Also, the variability changes are considerably larger in December–January–February with respect to both temperature and precipitation.

Using daily mean, maximum, and minimum surface air temperature (abbreviated as Tmean, Tmax, and Tmin, respectively) data from CN05.2 and the Met Office Hadley Centre observation data-sets for 1961–2012, the trends in day-to-day variability of Tmean, Tmax, and Tmin (abbreviated as DVTTmean, DVTTmax, and DVTTmin, respectively) are examined. It is revealed that the annual trends of DVTTmean, DVTTmax, and DVTTmin are all negative in Northeast China (NEC), and more obvious in North China than in South China. Seasonal trends of DVTTmean are also negative in NEC, except in summer. For DVTTmax, trends are generally more obvious than DVTTmin in all seasons in NEC; moreover, trends in spring are obvious in both the north and the south, but trends in summer and winter are more obvious in the southern region than in the northern part. As far as DVTTmin is concerned, except in autumn, seasonal trends are more obvious in the north than in other regions of the country.

International audience; A century ago, the pioneering book published in 1924 Die Klimate der geologischen Vorzeit explained by plate motion the evolution of vegetation revealed in sedimentary records. Nevertheless, they did not invoke climate changes. In the second part of the 20th century, the intricate relationship between tectonics, long-term carbon cycle, and climate was depicted by Walker (1981). Since these major steps, climate modeling of the Earth system kept on improving and including more and more components and processes to enable the investigation of deep time periods using general circulation model that can account for atmosphere and ocean dynamics. Here we illustrate long but drastic climate changes clearly related with tectonics, through three different examples: (1) the crucial role of paleogeography (continental distribution) to explain the drawdown of atmospheric carbon dioxide and the huge glaciation associated that occurred during the Neoproterozoic period; (2) the shrinkage of large epicontinental Paratethys that covered a large part of Eastern Europe and Western Asia and its impact on both monsoonal systems (African and Asian) since 40 Ma; and (3) the large impact of mountain range uplifts since Eocene both in Asia (Tibetan Plateau and Himalaya) and in Africa (buildup of the rift), on atmosphere and ocean dynamics. These studies not only allow for testing the ability of Earth system models to capture long-term changes of Earth climate, but they also pinpoint the pivotal role tectonics played in shaping the long-term evolution of atmospheric CO 2 and monsoon patterns.

Identifying potential external forcings on dryland aridity at various timescales and clarifying underlying mechanisms can advance our knowledge of dryland climate behaviors. To address this issue, we examine the past 21 ka using a set of transient simulations driven by realistic climatic forcings, as well as multiple types of proxies. The simulations suggest the evolution of dryland aridity and dominant forcings vary over time and region. On average, global drylands feature two-phase aridification at the orbital scale: the first phase occurs before the Holocene and is dominated by ice sheet melting and rising greenhouse gas (GHG) concentrations, followed by the second phase driven by the summer insolation decrease over northern high latitudes after the early Holocene; different from the wetness during the orbital-scale glacial period, millennium-scale cold events forced by meltwater discharges correspond to desiccation, punctuating the long-term trend during the last deglaciation. In addition, the average aridity changes for drylands are larger than those for global landmasses under all forcings except GHG concentrations. Spatially, the dominant external forcings and aridity responses to the same forcing vary regionally, mainly related to the latitude and hemisphere. Further diagnosis indicates the manners to affect aridity, namely through altering precipitation or evaporative capacity, vary by forcing. The aforementioned evolution of the simulated aridity matches well with the proxies in most dryland zones. This study provides a scenario of time-varying responses of dryland aridity to external forcings over the last 21 ka and may shed light on the future changes.

This paper addresses the interannual variation of winter air temperature over Northeast China and its connection to preceding Eurasian snow cover. The results show that there is a significant negative correlation between October Eurasian snow cover and following-winter air temperature over Northeast China. The snow cover located in eastern Siberia and to the northeast of Lake Baikal plays an important role in the winter air temperature anomaly. More (less) eastern Siberia snow in October can cause an atmospheric circulation anomaly pattern in which the atmospheric pressure is higher (lower) than normal in the polar region and lower (higher) in the northern mid-high latitudes. Due to the persistence of the eastern Siberia snow from October to the following winter, the winter atmospheric anomaly is favorable (unfavorable) to the widespread movement of cold air masses from the polar region toward the northern mid-high latitudes and, hence, lower (higher) temperature over Northeast China. Simultaneously, when the October snow cover is more (less), the SST in the northwestern Pacific is continuously lower (higher) as a whole; then, the Aleutian low and the East Asia trough are reinforced (weakened), favoring the lower (higher) temperature over Northeast China.

Based on the daily mean temperature data of CN05.2 from 1961 to 2012, cold events (CEs) are first divided into two categories according to their duration: strong cold events (SCEs) and weak cold events (WCEs). Then, the characteristics of CEs, SCEs, and WCEs during springtime are investigated. The results indicate that in the pre-1990s epoch, ENSO and Arctic Oscillation events in the previous winter are closely related to SCEs in the following spring. The multidecadal variations of CEs, SCEs, and WCEs are obvious. The intensity trend for SCEs is significantly negative, but it seems less apparent for WCEs. Further analysis reveals that when both SCEs and WCEs occur, a typical East Asian trough in the 850- hPa wind field, whose northwesterly wind component invades Northeast China (NEC) and causes freezing days, can be found in every decade. For the SCEs, a cold vortex, with its center located over Okhotsk and northeasterly current affecting NEC, is found as an additional feature. For the WCEs, the cold vortex is located in Karafuto and its northwesterly airflow intrudes into NEC. As for the difference between SCEs and WCEs, the northwestern flow is weaker while the northeastern counterpart is stronger during the SCEs, in all decades. In the Takaya–Nakamura flux and divergence fields, for the SCEs, a divergence center exists over NEC; and over its downstream regions, a stronger divergence center appears, not like a wave train. However, the opposite is the case for the WCEs; moreover, the wave train appears clearly during the WCEs, which means that the wave energy can propagate and dissipate more easily during WCEs.

Using model results from the first phase of the Pliocene Model Intercomparison Project (PlioMIP) and four experiments with CAM4, the intensified African summer monsoon (ASM) in the mid-Piacenzian and corresponding mechanisms are analyzed. The results from PlioMIP show that the ASM intensified and summer precipitation increased in North Africa during the mid-Piacenzian, which can be explained by the increased net energy in the atmospheric column above North Africa. Further experiments with CAM4 indicated that the combined changes in the mid-Piacenzian of atmospheric CO2 concentration and SST, as well as the vegetation change, could have substantially increased the net energy in the atmospheric column over North Africa and further intensified the ASM. The experiments also demonstrated that topography change had a weak effect. Overall, the combined changes of atmospheric CO2 concentration and SST were the most important factor that brought about the intensified ASM in the mid-Piacenzian.

Using simulations performed by all available climate models participating in the latest Paleoclimate Modelling Intercomparison Project (PMIP) phase 3 (PMIP3), we revisited the climate over China and the East Asian monsoon during the last glacial maximum (LGM; 21,000 years ago). Similar to previous results obtained from the PMIP phases 1 and 2 (PMIP1/2) models, all nine models reproduced colder than the pre-industrial annual and seasonal temperatures over China during the LGM and underestimated the annual cooling as evidenced by proxy data. The LGM annual and seasonal precipitation and evaporation over China consistently decreased in the models, whereas the very small LGM change in net precipitation (precipitation minus evaporation) differed among models. The annual net precipitation change during the LGM was broadly consistent with reconstructed moisture conditions over most parts of China, especially over the western Tibetan Plateau where the PMIP1/2 models disagreed with the proxy data. Moreover, the LGM winter monsoon circulation weakened (strengthened) over the East Asian continent in four (one) of five models; the summer monsoon circulation generally weakened in two models, whereas it weakened north and strengthened south of about 30°N over East Asia in three models. The spatial patterns of the LGM change in East Asian winter and summer monsoons in the PMIP3 models differed somewhat from those in the PMIP1/2 simulations.

The distributions of frozen ground and active layer thickness (ALT) during the last glacial maximum (LGM) and pre-industrial periods in China were investigated using Coupled Model Intercomparison Project Phase 5 (CMIP5) model experiments. Compared to the pre-industrial period, the LGM climate was ~ 5 °C colder and featured significantly higher freezing indices on the Tibetan Plateau and in Northeast China. Frozen ground expanded widely in the LGM. The extents of permafrost and seasonally frozen ground in China were 4.11 × 106 km2 and 4.97 × 106 km2, respectively, which are 2.42 × 106 km2 larger and 1.45 × 106 km2 smaller, respectively, than the pre-industrial levels. Moreover, the colder climate and longer duration also resulted in LGM ALT values that were 1.3 m less than the pre-industrial values in the permafrost areas common to both periods. Altitudinal permafrost was present mainly on the Tibetan Plateau and adjacent mountains in West China between 28°N and 41°30′N and covered an area of ~ 2.63 × 106 km2. Latitudinal permafrost was present mainly in Northeast China and occupied an area of 1.48 × 106 km2. The southern limit of latitudinal permafrost was located ~ 10° of latitude farther south during the LGM than during the pre-industrial period. The LGM simulation results agree reasonably well with previous reconstructions, with the exception of an underestimation in the permafrost extent. Although relatively high-level disagreement exists between the models in terms of the exact locations of the southern limits, the ensemble average is still able to represent the large-scale spatial pattern of frozen ground remarkably well.

Towards a better insight into the timing and climate change associated with a 2 °C global warming above pre-industrial levels in the 21st century, here we perform an analysis of all pertinent experiments within the framework of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Considering equally all available CMIP5 models, the probability of crossing the 2 °C target before the year 2100 is 26, 86, and 100% for the Representative Concentration Pathways 2.6 (RCP2.6), 4.5 (RCP4.5), and 8.5 (RCP8.5) scenarios, respectively, with the median years of 2054 for RCP4.5 and 2042 for RCP8.5. A 2 °C global warming would not be felt equally round the globe: stronger warming occurs over land than over the ocean, and the strongest warming occurs in the Arctic. Almost all temperature changes are larger than natural internal variability. Global average signal-to-noise ratios (S/N) of annual and seasonal temperature changes are in the range 3.2–5.0, and the largest values occur at low latitudes due to the lower background variability. Precipitation tends to increase at high latitudes but decrease in the subtropics, while all changes are smaller than natural internal variability except in parts of the high northern latitudes. The S/N of annual (seasonal) precipitation changes averages only 0.2 (no more than 0.1) for the globe.

The modulation of the orbitally induced variation in the El Nino/Southern Oscillation (ENSO) by Tibetan Plateau (TP) topography was investigated with four fully coupled ocean–atmosphere model experiments under the modern boundary conditions. The modeled orbitally induced ENSO change was strongly affected by the presence of the TP. Specifically, in the experiments with orbital forcing at 6 ka in comparison to the counterpart experiments with modern orbital forcing, it was shown that the orbitally forced ENSO variability was slightly weakened by 3% in the presence of the TP but increased significantly by 13% in the simulation of the absence of the TP. This difference was primarily attributed to the anomalous zonal winds over the tropical central-to-eastern Pacific in response to the increased summertime incoming insolation, which was intrinsically related to the different changes in the Asian monsoon and tropical Pacific Walker circulation. Under the absence of modulation by the TP, the anomalous westerly winds dominated the equatorial Pacific and favored the development of a stronger El Nino event and, in turn, the further intensification of La Nina due to the stronger heat discharge during the recession of the stronger El Nino. In contrast, the simulation with the presence of the TP showed the enhanced easterly wind anomalies in the boreal summer over the tropical Pacific, which further reduced (increased) the magnitude of the El Nino (La Nina) event in the subsequent winter. These results suggest that the TP is a potentially crucial boundary condition for evaluating the changes in the ENSO dynamics on orbital scales during the Cenozoic.

Based on simulations with 15 climate models in the Pliocene Model Intercomparison Project (PlioMIP), the regional climate of East Asia (focusing on China) during the mid-Pliocene is investigated in this study. Compared to the pre-industrial, the multi-model ensemble mean (MMM) of all models shows the East Asian summer winds (EASWs) largely strengthen in monsoon China, and the East Asian winter winds (EAWWs) strengthen in south monsoon China but slightly weaken in north monsoon China in the mid-Pliocene. The MMM of all models also illustrates a warmer and wetter mid-Pliocene climate in China. The simulated weakened mid-Pliocene EAWWs in north monsoon China and intensified EASWs in monsoon China agree well with geological reconstructions. However, there is a large model–model discrepancy in simulating mid-Pliocene EAWW, which should be further addressed in the future work of PlioMIP.

Previous climate modeling studies suggest that the surface uplift of the Himalaya–Tibetan plateau (TP) is a crucial parameter for the onset and intensification of the East Asian monsoon during the Cenozoic. Most of these studies have only considered the Himalaya–TP in its present location between ∼26°N and ∼40°N despite numerous recent geophysical studies that reconstruct the Himalaya–TP 10° or more of latitude to the south during the early Paleogene. We have designed a series of climate simulations to explore the sensitivity of East Asian climate to the latitude of the Himalaya–TP. Our simulations suggest that the East Asian climate strongly depends on the latitude of the Himalaya–TP. Surface uplift of a proto-Himalaya–TP in the subtropics intensifies aridity throughout inland Asia north of ∼40°N and enhances precipitation over East Asia. In contrast, the rise of a proto-Himalaya–TP in the tropics only slightly intensifies aridity in inland Asia north of ∼40°N, and slightly increases precipitation in East Asia. Importantly, this climate sensitivity to the latitudinal position of the Himalaya–TP is non-linear, particularly for precipitation across East Asia. The simulated precipitation patterns across East Asia are significantly different between our scenarios in which a proto-plateau is situated between ∼11°N and ∼25°N and between ∼20°N and ∼33°N, but they are similar when the plateau translates northward from between ∼20°N and ∼33°N to its modern position. Our simulations, when interpreted in the context of climate proxy data from Central Asia, support geophysically-based paleogeographic reconstructions in which the southern margin of a modern-elevation proto-Himalaya–TP was located at ∼20°N or further north in the Eocene.

Based on observation and reanalysis data, 77 coupled global climate models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Third (TAR), Fourth (AR4), and Fifth (AR5) Assessment Reports are evaluated in terms of their ability to simulate the mean state and year-to-year variability of surface air temperature at 2 m and precipitation over China and the climatological East Asian monsoon for the late decades of the 20th century. Results show that GCMs reliably reproduce the geographical distribution of the variables considered. Compared with observations, however, most GCMs have topography-related cold biases (although these are smaller than those found in previous studies), excessive precipitation, an underestimated southeast–northwest precipitation gradient, an overestimated magnitude and spatial variability of the interannual variability of temperature and precipitation, and an inadequate strength of the East Asian monsoon circulation. Pairwise comparison reveals that GCMs continue to improve from the TAR via the AR4 to the AR5 for temperature, but have little change for precipitation and the East Asian monsoon. The ability of GCMs varies with season and is affected to certain degree by their horizontal resolutions. Both the arithmetic mean and the median of multiple GCMs are little affected by filtering GCMs in terms of their ability, and the multi-model mean outperforms most of individual GCMs in every respect.

The transient response of the climate system to anomalously large freshwater input to the high latitude seas is examined using the newly developed Bergen Climate Model. A 150-yr twin-experiment has been carried out, consisting of a control and a freshwater integration. In the freshwater integration, the freshwater input to the Arctic Ocean and the Nordic Seas is artificially increased by a factor of 3, or to levels comparable to those found during the last deglaciation. The obtained response shows a reduced maximum strength of the Atlantic Meridional Overturning Circulation (AMOC) over the first 50 yr of about 6 Sv (1 Sv =10 6 m 3 s −1 ), followed by a gradual recovery to a level comparable to the control integration at the end of the period. The weakened AMOC in the freshwater integration is caused by reduced deep-water formation rates in the North Atlantic subpolar gyre and in the Nordic Seas, and by a reduced southward flow of intermediate water masses through the Fram Strait. The recovery of the AMOC is caused by an increased basin-scale upwelling in the Atlantic Ocean of about 1 Sv, northward transport of saline waters originating from the western tropical North Atlantic, and a surface wind field maintaining the inflow of Atlantic Water to the Nordic Seas between the Faroes and Scotland. Associated with the build-up of more saline waters in the western tropical North Atlantic, a warming of ~0.6 °C over the uppermost 1000 m of the water column is obtained in this region. This finding is consistent with paleo records during the last deglaciation showing that the tropics warmed when the high latitudes cooled in periods with reduced AMOC. Furthermore, the results support the presence of a coupled North-Atlantic-Oscillation-like atmosphere–sea-ice–ocean response mode triggered by the anomalous freshwater input. Throughout most of the freshwater integration, the atmospheric circulation is characterized by anomalously low sea level pressure in the Nordic Seas and anomalously high sea level pressure over Spain. This forces the North Atlantic Drift to follow a more easterly path in the freshwater integration than in the control integration, giving an asymmetric sea surface temperature response in the northern North Atlantic, and thereby maintaining the properties of the AtlanticWater entering the Nordic Seas between the Faroes and Scotland throughout the freshwater integration.