Warm Arctic-Cold Eurasia pattern helps predict spring wildfire burned area in West Siberia.

Extreme wildfires have devastating impacts on multiple fronts, and associated carbon greatly heats the earth's climate. Whether and how to predict wildfires becomes a critical question. In this study, we find that the preceding-winter "warm Arctic-cold Eurasia" (WACE) pattern significantly enlarges the spring burned area in West Siberia. The winter WACE and accompanying snow reduction result in dryness and vegetation exposure in West Siberia in spring, increasing fire risks. A multiple linear regression model is constructed that successfully predicts the spring burned area in West Siberia one season in advance (R-squared coefficient=0.64). The same predictors also well predict the corresponding fire carbon emissions. Independent predictions for spring burned area in 2019 and 2020 are very close to observations, with a mean absolute percentage error of only 3.0%. The findings of this study provide a possibility for guarding humans against extreme wildfires and predicting sharp rises in carbon emissions.

Traditional Meiyu-Baiu has been suspended by global warming.

More than 1000 years, the Meiyu-Baiu have shaped the uniqueness of natural resources, civilization and culture in the Yangtze River Basin of China and the main islands of Japan. In recent decades, frequent rainstorms and droughts have seemingly diminished the misty features of traditional Meiyu-Baiu rainfall. However, there is still no consensus on whether their traditional nature is suspended. In this study, we quantitatively demonstrate that the Meiyu-Baiu almost completely lost their traditional features during 1961-2023, ∼80% of which can be attributed to anthropogenic warming. Furthermore, in a warmer future, the traditional Meiyu-Baiu will be more unlikely to appear. This study underscores the urgency in adapting to climate shift because destructive extremes are measurably taking the place of mild and maternal rains.

Recent autumn sea ice loss in the eastern Arctic enhanced by summer Asian-Pacific Oscillation.

Recent rapid Arctic sea ice loss was documented as combined results from anthropogenic forcing and climate system internal variability. However, the role of internal variability is not well understood. Here, we propose that the Asian-Pacific Oscillation (APO), an intrinsic atmospheric mode featuring out-of-phase variations in upper-tropospheric temperatures between Asia and the North Pacific, is one driver for autumn sea ice variability in the eastern Arctic. The positive summer APO favors warming of the mid-latitude North Atlantic sea surface temperatures. This warming persists to autumn and in turn triggers strong anticyclonic anomalies over the Barents-Kara-Laptev Seas and weak lower-tropospheric cyclonic anomalies over the East Siberian Sea, enhancing moisture transport into the eastern Arctic. Such changes consequently increase lower-tropospheric humidity, downwelling longwave radiation, and surface air temperature in the eastern Arctic, thereby melting sea ice. Hence, a recent tendency of the summer APO towards the positive phase accelerates autumn sea ice loss in the eastern Arctic.

Subseasonal variability and the "Arctic warming-Eurasia cooling" trend.

The "Arctic warming-Eurasia cooling" trend has significantly affected the changes of weather patterns and climate extremes at lower latitudes and has attached huge attentions. However, this winter trend weakened from 2012 to 2021. In the same time period, subseasonal reversals between the warm Arctic-cold Eurasia (WACE) and cold Arctic-warm Eurasia (CAWE) patterns became more frequent and the subseasonal intensity of the WACE/CAWE pattern was still comparable with that from 1996 to 2011. This study highlighted the co-occurrence of this subseasonal variability and trend changes in the WACE/CAWE pattern based on long-term reanalysis datasets and Coupled Model Intercomparison Project Phase 6 simulations. The preceding sea surface temperature anomalies in the tropical Atlantic and Indian oceans had significant primary impacts on the WACE/CAWE pattern in early and late winter, respectively, which were confirmed by numerical experiments based on the Community Atmosphere Model and Atmospheric Model Intercomparison Project. Their coordination worked to effectively modulate the subseasonal phase reversal between the WACE and CAWE patterns just like what happened in the winters of 2020 and 2021. Findings of the present study imply that subseasonal changes need to be considered in the prediction of climate extremes at mid- to low latitudes.

Meteorological influences on co-occurrence of O3 and PM2.5 pollution and implication for emission reductions in Beijing-Tianjin-Hebei.

Co-occurrence of surface ozone (O3) and fine particulate matter (PM2.5) pollution (CP) was frequently observed in Beijing-Tianjin-Hebei (BTH). More than 50% of CP days occurred during April-May in BTH, and the CP days reached up to 11 in two months of 2018. The PM2.5 or O3 concentration associated with CP was lower than but close to that in O3 and PM2.5 pollution, indicating compound harms during CP days with double-high concentrations of PM2.5 and O3. CP days were significantly facilitated by joint effects of the Rossby wave train that consisted of two centers associated with the Scandinavia pattern and one center over North China as well as a hot, wet, and stagnant environmental condition in BTH. After 2018, the number of CP days decreased sharply while the meteorological conditions did not change significantly. Therefore, changes in meteorological conditions did not really contribute to the decline of CP days in 2019 and 2020. This implies that the reduction of PM2.5 emission has resulted in a reduction of CP days (about 11 days in 2019 and 2020). The differences in atmospheric conditions revealed here were helpful to forecast the types of air pollution on a daily to weekly time scale. The reduction in PM2.5 emission was the main driving factor behind the absence of CP days in 2020, but the control of surface O3 must be stricter and deeper. Electronic Supplementary Material: Supplementary material is available in the online version of this article at 10.1007/s11430-022-1070-y.

Synergetic roadmap of carbon neutrality and clean air for China.

It is well recognized that carbon dioxide and air pollutants share similar emission sources so that synergetic policies on climate change mitigation and air pollution control can lead to remarkable co-benefits on greenhouse gas reduction, air quality improvement, and improved health. In the context of carbon peak, carbon neutrality, and clean air policies, this perspective tracks and analyzes the process of the synergetic governance of air pollution and climate change in China by developing and monitoring 18 indicators. The 18 indicators cover the following five aspects: air pollution and associated weather-climate conditions, progress in structural transition, sources, inks, and mitigation pathway of atmospheric composition, health impacts and benefits of coordinated control, and synergetic governance system and practices. By tracking the progress in each indicator, this perspective presents the major accomplishment of coordinated control, identifies the emerging challenges toward the synergetic governance, and provides policy recommendations for designing a synergetic roadmap of Carbon Neutrality and Clean Air for China.

Why super sandstorm 2021 in North China?

Severe sandstorms reoccurred in the spring of 2021 after an absence for more than 10 years in North China. The dust source area, located in Mongolia, suffered destructive cooling and warming in early and late winter, which loosened the land. A lack of precipitation, excessive snow melt and strong evaporation resulted in dry soil and exiguous spring vegetation. A super-strong Mongolian cyclone developed on the bare and loose ground, and easily blew and transported large amounts of sand particles into North China. Furthermore, top-ranking anomalies (sea ice shift in the Barents and Kara Sea, and sea surface temperatures in the east Pacific and northwest Atlantic) were found to induce the aforementioned tremendous climate anomalies in the dust source area. Analyses, based on large-ensemble Coupled Model Intercomparison Project Phase 6, yield results identical to the reanalysis data. Thus, the climate variabilities at different latitudes and synoptic disturbances jointly facilitated the strongest spring sandstorm over the last decade.

Synergetic impacts of precursory climate drivers on interannual-decadal variations in haze pollution in North China: A review.

North China suffers from severe haze pollution and has received widespread attentions since the winter of 2012. In addition to human activities, climate variability also plays an important role, particularly in the interannual-decadal variations in the number of haze days in North China (HDNC). Many previous studies separately explored numerous preceding climate drivers, including Arctic sea ice, Eurasia snow and soil moisture, sea surface temperature in Pacific and Atlantic and forcing of Tibetan Plateau, but lacked assessment and analysis of the joint effects. In this study, we reviewed their impacts on HDNC and associated physical mechanisms. Beyond that, the synergetic effects were newly revealed by the observations and numerical experiments with fixed emissions. The preceding signals explained approximately 66% of the interannual-decadal variations in HDNC by exciting teleconnection patterns in winter and influencing the local dispersion conditions in North China. Furthermore, some future research directions were identified, such as the subseasonal variations in HDNC, subseasonal-seasonal prediction of haze by numerical climate models, and changing relationships between HDNC and climate conditions.

Long-term health impact of PM2.5 under whole-year COVID-19 lockdown in China.

The health impact of changes in particulate matter with an aerodynamic diameter <2.5 µm (PM2.5) pollution associated with the COVID-19 lockdown has aroused great interest, but the estimation of the long-term health effects is difficult because of the lack of an annual mean air pollutant concentration under a whole-year lockdown scenario. We employed a time series decomposition method to predict the monthly PM2.5 concentrations in urban cities under permanent lockdown in 2020. The premature mortality attributable to long-term exposure to ambient PM2.5 was quantified by the risk factor model from the latest epidemiological studies. Under a whole-year lockdown scenario, annual mean PM2.5 concentrations in cites ranged from 5.4 to 68.0 µg m-3, and the national mean concentration was reduced by 32.2% compared to the 2015-2019 mean. The Global Exposure Mortality Model estimated that 837.3 (95% CI: 699.8-968.4) thousand people in Chinese cities would die prematurely from illnesses attributable to long-term exposure to ambient PM2.5. Compared to 2015-2019 mean levels, 140.2 (95% CI: 122.2-156.0) thousand premature deaths (14.4% of the annual mean deaths from 2015 to 2019) attributable to long-term exposure to PM2.5 were avoided. Because PM2.5 concentrations were still high under the whole-year lockdown scenario, the health benefit is limited, indicating that continuous emission-cutting efforts are required to reduce the health risks of air pollution. Since a similar scenario may be achieved through promotion of electric vehicles and the innovation of industrial technology in the future, the estimated long-term health impact under the whole year lockdown scenario can establish an emission-air quality-health impact linkage and provide guidance for future emission control strategies from a health protection perspective.

Climate anomalies contributed to the rebound of PM2.5 in 2018 under intensified regional air pollution preventions.

Rigorous air pollution managements since 2013 resulted in decreasing trend in fine particulate matter (PM2.5) in China. Regional air pollution prevention measures were extra implemented in the "2 + 26" region since 2017. However, haze pollution dramatically rebounded in the winter of 2018. Both of the observed analyses and the numerical results (basing on a global 3-D chemical transport model) demonstrated that, although intensified prevention measures existed, atmospheric circulation and local meteorological conditions still significantly influenced the variation in haze pollution. The simulated PM2.5 concentrations (with fixed emissions) driven by meteorology in 2018 were 12-15% higher than those with atmospheric circulations in 2017 both under a low and a high emission level, close to the observed 10% PM2.5 rebound. In 2018, positive sea ice anomalies around Beaufort Sea and "triple pattern" anomalies of sea surface temperature in the North Pacific and North Atlantic enhanced the anomalous anticyclonic circulations over the air-polluted region, and thus resulted in minimum surface wind speed during 1979-2018 and 16.8% shallower boundary layer than those in 2017. In the stagnated air of winter 2018, the transported dispersion of pollutant particles was weakened, however more secondary aerosols were produced by enhanced chemical reactions, which jointly contributed to the PM2.5 rebound in 2018.

Future atmospheric circulations benefit ozone pollution control in Beijing-Tianjin-Hebei with global warming.

Surface ozone pollution has become increasingly serious in recent years. Ozone pollution will damage human health and reducing social productivity in China. Basing on an ozone weather index (OWI) that captured the effects of climate on the ground-level ozone, large ensemble simulations by the Community Earth System Model were introduced to project future impacts of atmospheric circulation on ozone pollution in Beijing-Tianjin-Hebei in late-21st century. In the future, atmospheric circulations will favour the control of ozone pollution in Beijing-Tianjin-Hebei region. The OWI decreased overall during the 21st century, which was nearly ignored by other studies on ozone projections. The OWI decrease was mainly due to the increase in regional precipitation and partly due to the changes of wind and the temperature difference between 200 hPa and lower-troposphere. The increased total precipitation in the 21st century, mainly due to the increase in convectional precipitation, weakened the production of surface ozone by its shading effect (related to more cloud cover) and wet deposition impact. During 2061-2100, the South Asia High will move southward, and the west Pacific subtropical high will shift eastward; thus, the convergence of water vapour will mainly occur in South China. Consequently, the large-scale precipitation will decrease over northern China. However, because of climate warming, the increase in specific humidity in Beijing-Tianjin-Hebei region (BTH) will enhance convectional precipitation, which will be more than 4 times the decrease in large-scale precipitation.