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In the Arctic, observed decadal mean surface air temperatures (SATs) were 0.70°C–0.95°C lower around 1970 than those around 1940. The 35‐multimodel ensemble mean of historical simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibited Arctic surface cooling trend in 1940–1970, which could be attributed to external forcings. Multimodel ensemble means of CMIP6 Detection and Attribution Model Intercomparison Project historical simulations exhibited Arctic surface cooling of −0.22°C (±0.24°C) in 1970 versus 1940 and showed that anthropogenic aerosol forcings contributed to a cooling of −0.65°C (±0.37°C), which was partially offset by a warming of 0.44°C (±0.22°C) due to well‐mixed greenhouse gases. In addition to the anthropogenic aerosol forcings, multidecadal internal variability with a magnitude of 0.47°C was the component primarily contributing to the observed Arctic cooling. We identified a spatial pattern of pan‐Arctic multidecadal cooling due to the internal variability that resembles the 1940–1970 cooling pattern. Plain Language Summary: Instrumental records show Arctic surface cooling during the mid‐20th century (1940–1970) followed by ongoing rapid warming since 1970. Long‐term global warming has been extensively researched and has been primarily ascribed to anthropogenic greenhouse gas forcing. However, the factors contributing to the mid‐20th century Arctic surface cooling remain poorly constrained. In this work, multimodel analyses using state‐of‐the‐art climate models suggest that external factors may have contributed to the high‐latitude surface cooling observed in 1940–1970. Further analysis shows that both increased anthropogenic aerosols and multidecadal internal variability provide major contributions to the 1940–1970 Arctic surface cooling. By analyzing surface cooling via unforced long‐term climate simulations, we identified a spatial pattern of pan‐Arctic multidecadal cooling, similar to the observed cooling pattern in the Arctic during 1940–1970. Key Points: Most Coupled Model Intercomparison Project Phase 6/Detection and Attribution Model Intercomparison Project models represent the observed multidecadal surface cooling trend during the mid‐20th century (1940–1970) in the ArcticAnthropogenic aerosol forcing and multidecadal internal variability are the major components contributing to the 1940–1970 Arctic coolingWe identify a spatial pattern of pan‐Arctic multidecadal cooling due to internal variability that resembles the 1940–1970 cooling pattern [ABSTRACT FROM AUTHOR]

To investigate the pure long-term influence of single mega volcanic eruption (SMVE) of universal significance on Arctic temperature changes in summer and winter, the Samalas eruption in Indonesia which is the largest eruption over the past millennium is selected as an ideal eruption for simulation study based on Community Earth System Model. The significant Arctic cooling lasts for 16 years after the Samalas eruption. The obvious Arctic cooling shifts from summer to winter, and this seasonal change of cooling after the SMVE only exists in the high-latitude Arctic region. The cooling range in Arctic summer is larger than that in winter during the first 2 years, due to the strong weakening effect of volcanic aerosol on summer incident solar radiation and the snow-ice positive feedback caused by the rapid expansion of summer sea ice, while the winter sea ice in the same period doesn’t increase obviously. Starting from the third year, the Arctic winter cooling is more intense and lasting than summer cooling. The direct weakening effect of aerosol on solar radiation, which is the main heat source in Arctic summer, is greatly weakened during this period, making summer cooling difficult to sustain. However, as the main heat source in Arctic winter, the sea surface upward longwave radiation, sensible heat, and latent heat transport still maintain a large decrease. Furthermore, sea ice expansion and albedo increase result in the decrease in solar radiation and heat absorbed and stored by the ocean in summer. And the isolation effect of sea ice expansion on air-sea heat transfer in winter during this period makes the heat transfer from the ocean to the atmosphere correspondingly reduce in winter, thus intensifying the Arctic winter cooling. Additionally, the Arctic Oscillation (AO) changes from the negative phase to the positive phase in summer after the SMVE (such as Samalas), while it is reversed in winter. This phase change of AO is also one of the reasons for the seasonal changes in Arctic cooling.

Arctic Amplification is robustly seen in climate model simulations of future warming and in the paleoclimate record. Here, we focus on the past century of observations. We show that Arctic Amplification is only a recent phenomenon, and that for much of this period the Arctic cooled while the global‐mean temperature rose. To investigate why this occurred, we analyze large ensembles of comprehensive climate model simulations under different forcing scenarios. Our results suggest that the global warming from greenhouse gases was largely offset in the Arctic by regional cooling due to aerosols, with internal climate variability also contributing to Arctic cooling and global warming trends during this period. This suggests that the disruption of Arctic Amplification was due to a combination of factors unique to the 20th century, and that enhanced Arctic warming should be expected to be a consistent feature of climate change over the coming century. Plain Language Summary: Arctic Amplification is the phenomenon by which the Arctic warms at a faster rate than the global average. Evidence for the occurrence of Arctic Amplification is widely found in climate model simulations as well as in paleo proxy reconstructions of past climate changes. In this study, we investigate the extent to which Arctic Amplification has occurred in observations from the past century. We show that Arctic Amplification is only a recent phenomenon, and that for much of the 20th century, the Arctic cooled while the global‐mean temperature rose. We investigate why this happened using a range of climate model simulations, and we find that there were two main causes for these opposing trends. The first is that regional cooling from aerosols counteracted the warming from greenhouse gases in the Arctic. However, this cannot fully explain the observed trends. The second is that natural fluctuations of the climate system manifested in a pattern of Arctic cooling under global warming. This suggests that the disruption of Arctic Amplification was due to a combination of factors unique to the 20th century, implying that enhanced Arctic warming should be expected to be a consistent feature of climate change over the coming century. Key Points: For much of the past century the Arctic cooled while the globe warmed, with Arctic Amplification of warming only emerging more recentlyWithout increases in both aerosols and greenhouse gas emissions, Arctic Amplification would have occurred throughout the past centuryInternal variability also played an important role in setting the observed Arctic cooling and global warming trends [ABSTRACT FROM AUTHOR]

During the spring of 2021, rapid surface cooling in the Arctic area expanded to most of the East Asian region, featuring surface-temperature dipole patterns of the colder west (Mongolia and northern-central China) and the warmer east (eastern-northeastern China, the Yellow Sea, and Korea). Despite the decreasing trend of dusty days within Korea, a notable rise in the occurrence of transboundary mineral dust-induced dusty days was observed in contributing to an increase in PM 10 levels in the spring of 2021. This study investigated the PM 10 source apportionment of anthropogenic dust, mineral dust, and biomass burning in the East Asian region and its transboundary impact on Korea, within the context of the surface-temperature dipole pattern observed in April of 2021. Source apportionment of PM 10 was determined through a comparative analysis between baseline and sensitivity experiments conducted by means of a WRF-Chem simulation. In these sensitivity simulations, emissions from each source were systematically excluded to assess their individual contributions. PM 10 Base refers to baseline simulations, PM 10 Anthro to anthropogenic emissions, PM 10 Dust to mineral dust, and PM 10 Biomass to biomass burning. The colder west pattern was linked to increased synoptic-scale cyclonic activity, marked by higher positive potential vorticity, causing a sudden surge in severe dust storms over Mongolia and northern China. PM 10 Base levels were most elevated in the higher terrain of Mongolia, comprising predominantly PM 10 Dust (95%). However, the dominance of atmospheric-warming-induced anticyclones, represented by enhanced negative potential vorticity, prevailed over the lower terrain in the warmer east regions, obstructing the transboundary dispersion of PM 10 Base to Korea. Nevertheless, Korea experienced a transboundary contribution of PM 10 Dust , reaching 35%. In addition, the source apportionments indicated a PM 10 Anthro ratio of 55% in eastern China and a PM 10 Biomass ratio of 35% in northeastern China, contributing 25% and 5% respectively to Korea. During April 14–30, 2021, the dipole pattern evolved further to the significantly colder west (Mongolia and China) and the moderately warmer east (the Yellow Sea and Korea). The transboundary contributions of PM 10 Anthro , PM 10 Dust , and PM 10 Biomass were intensified as a composite mixture within Korea, an outcome attributed to the intermittent cyclones and subsequent anticyclones. • Dusty days fell in Korea, but mineral dust surged, raising PM 10 in spring 2021. • Arctic spring cooling led to an East Asian cold-west, warm-east dipole pattern. • The colder west amplified cyclones, sparking dust storms in Mongolia and China. • Warming-induced anticyclones obstructed the transboundary dispersion of mineral dust. • Dust from eastern-northern China impacted Korea's PM 10 in a warm anticyclone. [ABSTRACT FROM AUTHOR]