Search

Concurrent heat extremes (CHEs) are becoming increasingly common in the mid‐high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase‐locking behavior in Wave‐4 pattern, particularly after mid‐1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave‐4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (∼30%), Northeast Asia (∼25%), and northwestern coast of North America (∼15%), while reducing the likelihood in central North America and northern Central Asia. During 1979–2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid‐high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave‐4 pattern. Plain Language Summary: Researchers have found that concurrent heat extremes are becoming more common in the Northern Hemisphere. This study discovered that a specific weather pattern, called as Wave‐4, became more prominent after the mid‐1990s and is linked to these heat extremes. This pattern increases the probability of heatwave occurrences in Eastern Europe, Northeast Asia, and northwestern coast of North America while decreasing them in central North America and northern Central Asia. Between 1979 and 2022, the identified Wave‐4 pattern contributed to more than two‐thirds of the increase in heat extremes in the northern hemisphere, affecting around 333.5 million people. It is also determined that unusual radiation levels over the Eastern European Plain and West Siberian Plain are significant factors contributing to the Wave‐4 pattern. This information helps us better understand the causes and characteristics of heat extremes in different parts of the world. Key Points: The Phase‐locked Rossby wave‐4 pattern dominates the concurrent heat extremes across the Northern HemisphereThe identified pattern exposed approximately 333.5 million people to heat extremesRadiation anomalies over the Eastern European Plain and West Siberian Plain play pivotal roles as forcing sources of the pattern [ABSTRACT FROM AUTHOR]

In recent decades, water scarcity is a significant constraint for socioeconomic development and threatens livelihood in an agriculture-based developing country like Pakistan. The water crisis in the country is projected to exacerbate in the coming years, especially in the southern parts. This dire situation calls for an investigation of major droughts, associated water scarcity, and changes in teleconnection patterns over Southern Pakistan. Moderate to low Southeastern monsoon (SEM) precipitation triggered the extreme drought episode (2017--2020) over Southern Pakistan and intensified the water scarcity. This study explored the severity of the respective drought event, underlying mechanisms, and changes in water scarcity over Southern Pakistan. To investigate the future changes (1980--2050) in water scarcity, coupling models (global hydrological models (GHMs)-global climate models (GCMs)) have been used to achieve the interannual performance of water availability and total water consumption. Besides, future scenarios used in this study are the combinations of SSPs and RCPs, including middle-of-the-road (SSP1-RCP4.5) and fossil-fueled development (SSP2-RCP8.5). The findings indicated a precipitation deficit of 45% during the 4-year (2017--2020), depicting the worst events in the past 50 years. South Pakistan observed the worst SEM droughts over the last 50 years, as 2000--2005 was the worst drought (precipitation deficit of 75%), followed by 2017--2020 with a 49% of precipitation deficit. Water scarcity was exacerbated by the extreme dry spells that developed over most of southern Pakistan between 2017 and 2020 as a result of moderate-to- exceptionally low SEM precipitation. Furthermore, this drought episode was accompanied by the cool phase in the Pacific and equatorial Indian Oceans. The future changes in water scarcity over the southern regions of Pakistan present a sharp increase under the SSP2-RCP8.5 scenario and are anticipated to be intensified in already stressed regions. This research is essential for environmentalists, and water resources managers, and provided crucial information to identify the hot spot areas in the target region so that water scarcity problems could be reduced in the future. [ABSTRACT FROM AUTHOR]

Using non-accidental mortality records from 195 sites and 11 model simulations from the Coupled Model Intercomparison Project phase 6, we assessed future avoidable heat-related deaths associated with emission mitigation after accounting for population changes in China. Without human-induced climate change in the 21st century, China's heat-related mortality would drop by 48–72% (95% confidence interval (CI): 40–76%), especially at high latitudes and altitudes (up to 80%). Nationally, 15,576–87,612 (95% CI: 6605–106,736) heat-related deaths per year would potentially be avoided by reducing emissions. For most of China, temperature changes dominate the variation in heat-related deaths, while in Central and South China, population changes will have a greater influence. These not only reinforce the necessity of mitigating emissions but also suggest that adjusting population structure and spatial distribution could be applied in some areas to minimize warming impacts on public health. Notably, given that abatement will hardly bring immediate success within the next twenty years, more healthcare infrastructures are urgently needed to manage potential growing heat risks. Particularly in Northwest and South China, where future heat-related deaths would still be 110–140% of current levels (1995–2014) even without anthropogenic warming. We also found that without historical human-induced emissions, China's low level of technology (medical and economic) might increase current heat-related mortality by 57%, even though warming could be mitigated. Consequently, we believe that mitigating climate change risks also requires consideration of the economic/medical losses from lowering emissions. [ABSTRACT FROM AUTHOR]

Previous studies indicated that, on synoptic scale, the severe haze in eastern China (EC) is affected by the atmospheric circulation variations. However, it is still unclear what are the dominant atmospheric circulation patterns influencing the severe winter haze conditions in EC and what are the differences between them. To systematically determine the dominant synoptic atmospheric circulation patterns of severe haze in different regions of EC, we use the Hierarchical Clustering Algorithm to classify the local geopotential height anomalies at 500-hPa over the stations with severe haze and obtained three dominant synoptic atmospheric circulation types based on observed PM2.5 concentration and NCEP/NCAR reanalysis. Circulation Type1 is accompanied by significant north wind component anomalies over northern China and causes severe haze pollution over the Yangtze River valley. Although the local meteorological conditions are not conducive to haze formation and accumulation, the severe haze in Yangtze River valley is related to the pollution transportation caused by the north wind anomalies. During the haze days with circulation Type2, the joint affection of East Atlantic-West Russia teleconnection pattern and winter East Asia subtropical jet stimulate and maintain the anticyclonic anomalies over northeast Asia, which provides meteorological conditions conducive to the occurrence of severe haze over the whole EC. The circulation Type3 mainly caused severe haze events in northeast China through the establishment of blocking high over the Okhotsk Sea. The results provide a basis for establishing haze prediction and management policies applicable to different regions in EC. [ABSTRACT FROM AUTHOR]

This study discusses the interannual variation of spring precipitation in Northeast China (NECSP) from 1980 to 2016 and its relationship with Arctic sea ice based on observation data and numerical experiments. The observed results reveal that the leading mode of NECSP mainly exhibits a homogenous pattern with a significant interannual variation. The NECSP has a significant negative correlation with the preceding winter Barents Sea ice concentration (BSIC) at the interannual scale. In the preceding winter, the decreased BSIC resulted in positive geopotential height anomalies over the polar region, which could weaken the polar vortex and westerly winds, forming a cyclonic anomaly indirectly over West Siberia. The circulation anomalies resulted in a zonal dipole pattern of preceding winter snow water equivalent (SWE) anomalies in the mid‐high latitudes of Eurasia with less SWE over Eastern Europe and more SWE over West Siberia. The SWE anomalies in winter could persist to the subsequent spring and facilitate more precipitation over Northeast China (NEC) by local thermal processes affecting circulation anomalies over Eurasia. On the other hand, the negative preceding winter BSIC anomalies can persist to spring, increasing the NECSP by strengthening the cyclonic anomalies over NEC. In this study, the response of the atmosphere to the thermal effect of SWE is further verified by using the linear baroclinic model (LBM). The response of NECSP to BSIC loss is tested by using the Community Atmosphere Model version 5.3 (CAM5.3). [ABSTRACT FROM AUTHOR]

Following the December 2015 Paris Agreement, there is an international effort to limit global warming at 1.5 and 2.0°C relative to the pre‐industrial level. However, there is inadequate research quantifying the difference in extreme temperature between the two target levels, especially in Africa. This study used historical and future low‐warming projections of NCAR‐CESM to assess the differences in extreme temperature events under 1.5 and 2.0°C future scenarios relative to the recent climate taken from 1976 to 2005 over Africa. The results show that compared with the present day, the magnitude of the highest temperature (TXx) will increase by approximately 1.6/2.2°C in 1.5/2.0°C warming worlds, with more substantial warming in Sahara and Southern Africa. The lowest temperature (TNn) will increase by ∼1.9/2.5°C in 1.5/2.0°C future climates, where SAH and SAF will experience a higher intensity of warming followed by Eastern Africa and Western Africa regions. The frequency of hot days (TX90p) is projected to increase with global warming across the continent, with a high increase in SAF and SAH. The frequency of cold days (TN10p) is expected to decrease with global warming in many parts of Africa except in WAF. In most regions, there were no apparent changes revealed in the Warm Spell Duration Indicator relative to the recent climate across the continent except SAH in 1.5 and 2.0°C warming levels, while a decrease in Cold Spell Duration Indicator will be in SAH. Assessment of the avoided impacts in 1.5 relative to 2.0°C indicates that limiting global warming at 1.5 rather than 2.0°C could reduce the intensity, frequency and duration of extreme temperatures from 3 to 81%. However, the magnitude of avoided impacts differs among indices and sub‐regions. Hence, it is paramount for the African continent to limit global warming at 1.5 instead of 2.0°C. [ABSTRACT FROM AUTHOR]

Previous studies using observed data suggested a decreasing trend in the frequency of cold surge (CS) over East Asia (EA) under global warming. However, the future change of CSs in different paths is relatively understudied. In this study, after evaluating the classification of CSs paths and the trend of CSs in different paths in historical simulation, the changes of CS paths in EA in future warming scenario have been investigated using the latest 21 models from the phase six of the Coupled Model Intercomparison Project (CMIP6) under the shared socioeconomic pathways (SSP245) scenario. First of all, the observed paths of winter CS in EA from 1979 to 2013 are tracked by the Flexible Particle (FLEXPART) model using ERA‐Interim daily reanalysis datasets, and the CS paths are divided into the northwestern path, northern path, and western path by hierarchical clustering algorithm. Random forest algorithm is introduced to match the future CSs according to the observed classification results. The projected results indicate that the frequency of total CSs will decrease significantly in the 21st century with a trend of −0.47 times/10a. Compared with the late 20th century, the total CSs, the CSs in the northwestern path and the western path decrease by 49, 61, and 60%, respectively, in the late 21st century, while the CSs in northern path do not show a significant trend. The substantial decrease of the northwestern path CSs and the western path CSs make the proportion of northern path CSs in total CSs rise from 19.5% in the late 20th century to 37.3% in the late 21st century. It means the strong CSs are still frequent in the future, probably due to the stability of the northern path CSs. [ABSTRACT FROM AUTHOR]