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The out‐of‐phase mode of winter surface air temperature anomalies (SATAs) over northern Central Asia (NCA; 45°–65°N, 40°–100°E) between January and February is investigated in this study. This mode corresponds to warm (cold) SATAs in January (February) over NCA and is mainly modulated by the enhanced tropical convection anomalies over the Maritime Continent in previous late December, associated with MJO phase 4. These tropical convection anomalies can induce anomalous tropospheric Rossby‐wave sources over the North Pacific in late December. The eastward‐propagating Rossby‐wave train, triggered by these anomalous Rossby‐wave sources, can cause negative and positive tropospheric geopotential height anomalies over the Greenland–Scandinavia region and NCA in the following early–mid‐January, subsequently leading to warm SATAs over NCA in January. The negative geopotential height anomalies over the Greenland–Scandinavia region in early–mid‐January can trigger upward‐propagating wave activity fluxes (WAFs) into the stratosphere, resulting in negative stratospheric geopotential height anomalies in late January–early February. These stratospheric anomalies, by triggering downward‐propagating WAFs, can in turn lead to positive tropospheric geopotential height anomalies over the Greenland–Scandinavia region in early February. These anomalies over the Greenland–Scandinavia region can maintain themselves in the following mid‐ and late February by feedback of anomalous storm tracks, and cause negative geopotential height anomalies and subsequently cold SATAs over NCA in February by triggered southeastward‐propagating Rossby‐wave train. [ABSTRACT FROM AUTHOR]

Many studies have examined the influence of global climate change and regional human activities on the climate of arid Central Asia, but their separate contributions have rarely been reported due to lack of a comprehensive description of regional human activities, especially the irrigation process, in the model. In this study, we conducted two sets of 40‐year continuous simulations with and without human activities to distinguish the effects of regional human activities and global climate change on the surface air temperature (T2), humidity (Q2) and precipitation of a typical mountain‐oasis‐desert system in northern Tianshan by using a modified WRF‐Noah model with irrigation processes. The results indicated that the annual average T2, Q2 and convective precipitation during the past 40 years increased by 0.393°C, 0.063 g/kg and 0.014 mm/d, respectively, and the annual average large‐scale precipitation and total annual average precipitation decreased by approximately −0.017 and −0.003 mm/d, respectively. Regional human activities contributed 52.63% and 50.38% of the change in large‐scale precipitation and total precipitation, respectively, while global climate change accounted for more than 80% of the change in temperature and humidity. Among the human activities, irrigation had the largest impact on T2/Q2 over the local irrigation region and on precipitation in the upstream Tianshan mountainous area. However, for the whole region, the increase in the green vegetation fraction was the core factor that impacted the regional climate. Our results can deepen the understanding of the attribution and mechanism of climate change and provide water and heat change references for other mountain‐oasis‐desert systems in arid endorheic regions. Plain Language Summary: We counted the separate contributions of global climate change and regional human activities on the surface air temperature (T2), humidity (Q2) and precipitation of arid Central Asia by difference of two sets of 40‐year continuous simulations with and without human activities. The results indicated that regional human activities contributed 52.63% and 50.38% of the change in large‐scale precipitation and total precipitation, respectively, while global climate change accounted for more than 80% of the change in temperature and humidity. Among the human activities, irrigation had the largest impact on T2/Q2 over the local irrigation region and on precipitation in the upstream Tianshan mountainous area. But the vegetation greening was main reason for the changes of regional climate for the whole region. Our results can deepen the understanding of the attribution and mechanism of climate change and provide water and heat change references for other mountain‐oasis‐desert systems in arid endorheic regions. Key Points: The attribution and mechanism of regional climate change in a typical mountain‐oasis‐desert system of arid Central Asia were exploredGlobal climate change dominated regional temperature change while regional human activities dominated regional precipitation changeThe increase in the green vegetation fraction was the core factor that impacted regional climate [ABSTRACT FROM AUTHOR]

The recent summer surface air temperature (SAT) changes over densely populated Eurasia exhibit a non‐uniform pattern with amplified warming over Europe and East Asia (EA) but weak warming over Central Asia (CA), forming a wave train‐like structure. However, the key factors that determine this non‐uniform warming pattern remain unclear. By analyzing observations and model simulations, here, we show that more than half of the SAT multidecadal variations from 1950 to 2014 over Europe‐west Asia and EA may have resulted from external forcing, rather than from internal variability in the Atlantic as previously thought. In contrast, the recent SAT over CA is influenced mainly by internal variations in the Atlantic and Pacific oceans. Large ensemble model simulations suggest that the forced SAT multidecadal variations over Eurasia are mainly caused by changes in greenhouse gases and aerosols. Our findings provide strong evidence for major impacts of external forcing on multidecadal climate variations over Eurasia. Plain Language Summary: Previous studies have documented non‐uniform decadal warming rates in summer since the mid‐1990s over densely populated Eurasia, with amplified warming over Europe and East Asia (EA) but weak warming over Central Asia. This unique tripole warming pattern and its cause have attracted considerable attention. It may arise from internal variability (IV; e.g., Atlantic Multidecadal Oscillation [AMO]) and/or external forcing. Furthermore, it was found that the recent AMO resulted from both IV and decadal changes in aerosols. Thus, the relative contributions of IV and external forcing to the recent Eurasian warming pattern remain unclear. Here we show that the surface air temperature multidecadal variations since 1950 over Eurasia are caused by both IV and external forcing, with more than half of the variations over Europe‐west Asia and EA resulted from external forcing (i.e., greenhouse gases [GHGs] and aerosols), in contrast to the previous notion that the non‐uniform warming is mainly originated from the Atlantic Ocean. Looking ahead into the upcoming decades, aerosols will continue to decrease, whereas the AMO will likely be in its positive phase. These changes, together with continued increases in GHGs, will accelerate warming trends over Eurasia and further exacerbate summer heat waves. Key Points: More than half of the multidecadal surface air temperature (SAT) variations from 1950 to 2014 over Europe‐west Asia and East Asia resulted from external forcingThe forced SAT multidecadal variations over Eurasia are mainly caused by changes in greenhouse gases and aerosolsOur study helps reconcile human and natural drivers of the tripole pattern of multidecadal summer temperature variations over Eurasia [ABSTRACT FROM AUTHOR]

In this study, the climate changes over Arid Central Asia (ACA) during the mid‐Holocene (approximately 6,000 calendar years ago, MH) and the Last Glacial Maximum (approximately 21,000 calendar years ago, LGM) were investigated using multimodel simulations derived from the Paleoclimate Modelling Intercomparison Project Phase 3 (PMIP3). During the MH, the multimodel median (MMM) shows that in the core region of ACA, the regionally averaged annual surface air temperature (SAT) decreases by 0.13°C and annual precipitation decreases by 3.45%, compared with the preindustrial (PI) climate. The MMM of the SAT increases by 1.67/0.13°C in summer/autumn, whereas it decreases by 1.23/1.11°C in spring/winter. The amplitude of the seasonal cycles of the SAT increases over ACA due to different MH orbital parameters. For precipitation, the regionally averaged MMM decreases by 5.77%/5.69%/0.39%/5.24% in spring/summer/autumn/winter, respectively. Based on the analysis of the aridity index (AI), compared with the PI, a drier climate appears in southern Central Asia and western Xinjiang due to decreasing precipitation. During the LGM, the MMM shows that the regionally averaged SAT decreases by 5.04/4.36/4.70/5.12/5.88°C and precipitation decreases by 27.78%/28.16%/31.56%/27.74%/23.29% annually and in the spring, summer, autumn, and winter, respectively. Robust drying occurs throughout almost the whole core area. Decreasing precipitation plays a dominant role in shaping the drier conditions, whereas strong cooling plays a secondary but opposite role. In response to the LGM external forcings, over Central Asia and Xinjiang, the seasonal cycle of precipitation has a smaller amplitude compared with that under the PI climate. In the model‐data comparison, the simulated MH moisture changes over ACA are to some extent consistent with the reconstructions, further confirming that drier conditions occurred during that period than during the PI. [ABSTRACT FROM AUTHOR]