Ice Cores from the St. Elias Mountains, Yukon, Canada: Their Significance for Climate, Atmospheric Composition and Volcanism in the North Pacific Region

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 –02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (103 – 104 year) ice-core records of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this region. Comparison of these records has allowed for variations in climate and atmospheric composition to be linked with changes in the vertical structure and dynamics of the North Pacific atmosphere, providing a unique perspective on these changes over the Holocene. Owing to their privileged location, cores from the St. Elias Icefields also contain a remarkably detailed record of aerosols from various sources around or across the North Pacific. In this paper we review major scientific findings from the study of St. Elias Mountain ice cores, focusing on five main themes: (1) The record of stable water isotopes (δ18O, δD), which has unique characteristics that differ from those of Greenland, other Arctic ice cores, and even among sites in the St. Elias; (2) the snow accumulation history; (3) the record of pollen, biomass burning aerosol, and desert dust deposition; (4) the record of long-range air pollutant deposition (sulphate and lead); and (5) the record of paleo-volcanism. Our discussion draws on studies published since 2000, but based on older ice cores from the St. Elias Mountains obtained in 1980 and 1996

Desertification

IPCC SPECIAL REPORT ON CLIMATE CHANGE AND LAND (SRCCL) Chapter 3: Climate Change and Land: An IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystem

Global impacts of land degradation

Study commissioned by the Scientific, Technical and Advisory Panel (STAP) of the Global Environment Facility (GEF) to support the development of the new GEF focal area of Land Degradatio

Climate and Land Degradation

On the occasion of the Seventh session of the Conference of Parties, The World Meteorological Organization (WMO) has prepared this brochure which explains the role of different climatic factors in land degradation and WMO's contribution in addressing this important subject. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional, Informal education, General public

Late Holocene Climate and Environmental Reconstruction Derived from the Asian Ice Core Array (AICA)

Recent climate change has impacted natural and human systems across the Earth, emphasizing the need for greater understanding of both the existing and changing natural and anthropogenic forcing mechanisms and subsequent responses of the Earth’s climate system. High-resolution, multi-parameter ice core records retrieved and analyzed from two Asian Ice Core Array (AICA) sites, Geladaindong (central Tibetan Plateau) and Inilchek (central Tien Shan) were utilized to reconstruct atmospheric chemical concentrations and composition over the past ~100-500 years, improving the understanding of late Holocene climate and environmental variability in Asia. Both ice cores were analyzed for major and trace elements, major soluble ions, stable water isotopes and radionuclides. The 147 m Geladaindong record (1477-1982) provides a Ca proxy for atmospheric dust concentrations and westerly wind strength over the Tibetan Plateau. Corresponding declines in zonal wind velocities, and subsequent declines in dust transport, are likely the result of increasing temperatures lowering meridional pressure gradients (i.e. weakening the Siberian High) over large portions of northern Asia. Late twentieth century concentrations suggest the lowest atmospheric dust concentration and the weakest westerly wind strength in the past ~500 years. The 160 m Inilchek record (1908–1995) established the natural baseline and subsequent anthropogenic increases of Pb, Cd and Cu concentrations during the twentieth century. Element concentrations and enrichment factor trends suggest Soviet industrial and agricultural sources between the 1950s-1980s and dominant Chinese sources during the late 1980s-1990s. Increases in regional mining activities during the 1950s-1970s potentially resulted in enriched mineral dust compositions (e.g. Al, Ti, Mn), suggesting commonly assumed crustal reference species may be biased and potentially underestimate non-crustal contributions at Inilchek. A major soluble ion record from Inilchek revealed dominant dust proxy species (Ca2+) had the highest concentrations during the 1950s-1970s, with subsequent declining decadal trends to the 1990s, likely reflecting regional dust storm activity in central Asia post-1950, that has been associated with coupled atmospheric circulation variability and anthropogenic activities. Excess concentration trends of NO3-, K+, SO42- and Cl- suggest discernable anthropogenic inputs beginning in the 1950s-1970s and peaking until the mid-late 1980s, followed by declines, coinciding with Soviet industrial and agricultural emission records

Influence of Central Siberian snow‐albedo feedback on the spring East Asian dust cycle and connection with the preceding winter Arctic oscillation

The Asian dust cycle has significant effects on the climate and environment, while its spatiotemporal variability and change mechanisms are not yet completely understood. Reanalysis data from the Modern‐Era Retrospective Analysis for Research and Applications, version 2 (MERRA2), data set are used to explore the spatiotemporal distribution of the East Asian dust cycle and possible reasons for the interannual variations. Based on the empirical orthogonal function analysis, the dominant mode of dust emissions from the East Asian deserts in the dust season (spring) shows that the Gobi Desert contributes most of the interannual variance of dust emissions in East Asia. The patterns of the regional circulation, temperature, and radiation are analyzed by regressing these variables against the principal component time series of the first empirical orthogonal function mode. The results show that the enhanced dust emissions are associated with a cyclonic circulation anomaly and cooling in the lower and middle troposphere over Central Siberia. The cooling is attributed to local snow‐albedo and cloud‐albedo feedbacks. The surface cooling is conducive to maintain the snow cover, whereas the cooling in the middle troposphere is associated with the increase of the relative humidity and cloud cover. The increased snow and cloud cover reflect more shortwave radiation, tending to maintain or amplify the surface cooling. It is also found that the negative phase of the Arctic Oscillation in winter initiates the surface cooling in the next spring and results in positive snow‐albedo and cloud feedbacks in Central Siberia, eventually enhancing the East Asian dust cycle

Aerosol-cloud-precipitation interaction based on remote sensing and cloud-resolving modeling over the Central Himalayas

The Central Himalayan region experiences pronounced orographic precipitation related to the South Asian summer monsoon, typically occurring from June to September. Atmospheric aerosols can influence regional and global climate through aerosol-radiation (ARI) and aerosol-cloud interactions (ACI). The study of the aerosol-precipitation relationship over the Central Himalayan region during the summer monsoon season is important due to extreme pollution over the upwind Indo-Gangetic Plains, enhanced moisture supply through monsoonal flow, and steep terrain of the Himalayas modulating the orographic forcing. This dissertation aims to study the impact of atmospheric aerosols, from natural and anthropogenic sources, in modulating the monsoonal precipitation, cloud processes, and freezing isotherm over the central Himalayas. The long-term (2002 – 2017) satellite-retrieved and reanalysis datasets showed regardless of the meteorological forcing, compared to relatively cleaner days, polluted days with higher aerosol optical depth is characterized by the invigorated clouds and enhanced precipitation over the southern slopes and foothills of the Himalayas. The mean freezing isotherm increased by 136.2 meters in a polluted environment, which can be crucial and significantly impact the hydroclimate of the Himalayas. Due to the limitations of satellite-retrieved observational data, these results underlined the need for state-of-the-art Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in a cloud-resolving scale to better represent and study the impact of the aerosols from different sources through radiation and microphysics pathways over the complex terrain of the Central Himalayas. A cloud-resolving WRF-Chem simulation is performed to assess the impact of anthropogenic and remotely transported dust aerosols on the convective processes and elevation-dependent precipitation. Long-range transported dust aerosols significantly impacted cloud microphysical properties and enhanced the precipitation by 9.3% over the southern slopes of the Nepal Himalayas. The mid-elevation of the Central Himalayas, generally between 1000 and 3000 meters, acted as the region below and above which the diurnal variation and precipitation of various intensities (light, moderate, and heavy) responded differently for ARI, ACI, and the combined effect of aerosols. Due to the ARI effect of aerosols, the light precipitation is suppressed by 17% over the Central Himalayas. The ACI effect dominated and resulted in enhanced heavy precipitation by 12% below 2000 m ASL, which can potentially increase the risk for extreme events (floods and landslides). In contrast, above 2000 m ASL, the suppression of precipitation due to aerosols can be critical for the regional supply of water resources. The overview of the study suggests that the natural and anthropogenic aerosols significantly modulate the convective processes, monsoonal precipitation, and freezing isotherm over the Central Himalayan region, which could pose significant consequences to the changing Himalayan hydroclimate

Warming effect of dust aerosols modulated by overlapping clouds below

Due to the substantial warming effect of dust aerosols overlying clouds and its poor representation in climate models, it is imperative to accurately quantify the direct radiative forcing (DRF) of above-cloud dust aerosols. When absorbing aerosol layers are located above clouds, the warming effect of aerosols strongly depends on the cloud macro- and micro-physical properties underneath, such as cloud optical depth and cloud fraction at visible wavelength. A larger aerosol-cloud overlap is believed to cause a larger warming effect of absorbing aerosols, but the influence of overlapping cloud fraction and cloud optical depth remains to be explored. In this study, the impact of overlapping cloud properties on the shortwave all-sky DRF due to springtime above-cloud dust aerosols is quantified over northern Pacific Ocean based on 10-year satellite measurements. On average, the DRF is roughly 0.62 Wm^(−2). Furthermore, the warming effect of dust aerosols linearly increases with both overlapping cloud fraction and cloud optical depth. An increase of 1% in overlapping cloud fraction will amplify this warming effect by 1.11 Wm^(−2)τ^(−1). For the springtime northern Pacific Ocean, top-of-atmosphere cooling by dust aerosols turns into warming when overlapping cloud fraction is beyond 0.20. The variation of critical cloud optical depth beyond which dust aerosols switch from exerting a net cooling to a net warming effect depends on the concurrent overlapping cloud fraction. When the overlapping cloud coverage range increases from 0.2 to –0.4 to 0.6–0.8, the corresponding critical cloud optical depth reduces from 6.92 to 1.16. Our results demonstrate the importance of overlapping cloud properties for determining the springtime warming effect of dust aerosols

Satellite-Based Assessment of Possible Dust Aerosols Semi-Direct Effect on Cloud Water Path over East Asia

The semi-direct effects of dust aerosols are analyzed over eastern Asia using 2 years (June 2002 to June 2004) of data from the Clouds and the Earth s Radiant Energy System (CERES) scanning radiometer and MODerate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, and 18 years (1984 to 2001) of International Satellite Cloud Climatology Project (ISCCP) data. The results show that the water path of dust-contaminated clouds is considerably smaller than that of dust-free clouds. The mean ice water path (IWP) and liquid water path (LWP) of dusty clouds are less than their dust-free counterparts by 23.7% and 49.8%, respectively. The long-term statistical relationship derived from ISCCP also confirms that there is significant negative correlation between dust storm index and ISCCP cloud water path. These results suggest that dust aerosols warm clouds, increase the evaporation of cloud droplets and further reduce cloud water path, the so-called semi-direct effect. The semi-direct effect may play a role in cloud development over arid and semi-arid areas of East Asia and contribute to the reduction of precipitation

Melting of Major Glaciers in the Western Himalayas: Evidence of Climatic Changes from Long Term MSU Derived Tropospheric Temperature Trend (1979-2008)

Global warming or the increase of the surface and atmospheric temperatures of the Earth, is increasingly discernible in the polar, sub-polar and major land glacial areas. The Himalayan and Tibetan Plateau Glaciers, which are the largest glaciers outside of the Polar regions, are showing a large-scale decrease of snow cover and an extensive glacial retreat. These glaciers such as Siachen and Gangotri are a major water resource for Asia as they feed major rivers such as the Indus, Ganga and Brahmaputra. Due to scarcity of ground measuring stations, the long-term observations of atmospheric temperatures acquired from the Microwave Sounding Unit (MSU) since 1979–2008 is highly useful. The lower and middle tropospheric temperature trend based on 30 years of MSU data shows warming of the Northern Hemisphere’s midlatitude regions. The mean month-to-month warming (up to 0.048±0.026 K/year or 1.44 K over 30 years) of the mid troposphere (near surface over the high altitude Himalayas and Tibetan Plateau) is prominent and statistically significant at a 95% confidence interval. Though the mean annual warming trend over the Himalayas (0.016±0.005 K/year), and Tibetan Plateau (0.008±0.006 K/year) is positive, the month to month warming trend is higher (by 2–3 times, positive and significant) only over a period of six months (December to May). The factors responsible for the reversal of this trend from June to November are discussed here. The inequality in the magnitude of the warming trends of the troposphere between the western and eastern Himalayas and the IG (Indo-Gangetic) plains is attributed to the differences in increased aerosol loading (due to dust storms) over these regions. The monthly mean lowertropospheric MSU-derived temperature trend over the IG plains (dust sink region; up to 0.032±0.027 K/year) and dust source regions (Sahara desert, Middle East, Arabian region, Afghanistan-Iran-Pakistan and Thar Desert regions; up to 0.068±0.033 K/year) also shows a similar pattern of month-to-month oscillation and six months of enhanced and a statistically significant warming trend. The enhanced warming trend during the winter and pre-monsoon months (December–May) may accelerate glacial melt. The unequal distribution of the warming trend over the year is discussed in this study and is partially attributed to a number of controlling factors such as sunlight duration, CO2 trends over the region (2003–2008), water vapor and aerosol distribution