Mountains are the water towers of the world, supplying a substantial part of both natural and anthropogenic water demands
. They are highly sensitive and prone to climate change
, yet their ...importance and vulnerability have not been quantified at the global scale. Here we present a global water tower index (WTI), which ranks all water towers in terms of their water-supplying role and the downstream dependence of ecosystems and society. For each water tower, we assess its vulnerability related to water stress, governance, hydropolitical tension and future climatic and socio-economic changes. We conclude that the most important (highest WTI) water towers are also among the most vulnerable, and that climatic and socio-economic changes will affect them profoundly. This could negatively impact 1.9 billion people living in (0.3 billion) or directly downstream of (1.6 billion) mountainous areas. Immediate action is required to safeguard the future of the world's most important and vulnerable water towers.
Mt. Everest, one of the most coveted climbing mountains on earth, also contains the highest altitude chemical contamination on land. For the first time, meltwater and snow samples from Mt. Everest's ...Khumbu Glacier were analyzed for “forever chemicals” per- and polyfluoroalkyl substances (PFAS). Our research team utilized solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify pollutants sampled from Everest Base Camp, Camp 1, Camp 2, and Everest Balcony. From the 14 PFAS compounds tested for, we found perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexanoic acid (PFHxA) in Mt. Everest snow and meltwater. The highest concentrations found were 26.14 ng/L and 10.34 ng/L PFOS at Base Camp and Camp 2, respectively. However, PFAS species were seen within 1–2 orders of magnitude in all sampling sites with detection, potentially suggesting a widespread presence on the mountain. Our samples are the highest altitude PFAS samples ever retrieved and indicate the need for further sampling both on Mt. Everest and in the below-glacier watershed.
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•For the first time, PFAS were found in snow and meltwater on Mt. Everest from below the Base Camp to the Balcony.•Samples from the Base Camp to the Summit are the first to characterize chemical deposition on the mountain.•Combined atmospheric and local direct deposition elevate concentrations above other alpine regions.•Human pollution impacts on Mt. Everest are both visible and chemical.
A Mt. Everest ice core spanning 1860–2000 AD and analyzed at high resolution for black carbon (BC) using a Single Particle Soot Photometer (SP2) demonstrates strong seasonality, with peak ...concentrations during the winter‐spring, and low concentrations during the summer monsoon season. BC concentrations from 1975–2000 relative to 1860–1975 have increased approximately threefold, indicating that BC from anthropogenic sources is being transported to high elevation regions of the Himalaya. The timing of the increase in BC is consistent with BC emission inventory data from South Asia and the Middle East, however since 1990 the ice core BC record does not indicate continually increasing BC concentrations. The Everest BC and dust records provide information about absorbing impurities that can contribute to glacier melt by reducing the albedo of snow and ice. There is no increasing trend in dust concentrations since 1860, and estimated surface radiative forcing due to BC in snow exceeds that of dust in snow. This suggests that a reduction in BC emissions may be an effective means to reduce the effect of absorbing impurities on snow albedo and melt, which affects Himalayan glaciers and the availability of water resources in major Asian rivers.
We compare paleoclimate proxy records from central Greenland and the Aegean Sea to offer new insights into the causes, timing, and mechanisms of Holocene atmosphere-ocean interactions. A direct ...atmospheric link is revealed between Aegean sea surface temperature (SST) and high-latitude climate. The major Holocene events in our proxies of Aegean SST and winter/spring intensity of the Siberian High (GISP2 K super(+) record) follow an ~2300 year spacing, recognised also in the Delta super(14)C record and in worldwide Holocene glacier advance phases, suggesting a solar modulation of climate. We argue that the primary atmospheric response involved decadal-centennial fluctuations in the meridional pressure gradient, driving Aegean SST events via changes in the strength, duration, and/or frequency of northerly polar/continental air outbreaks over the basin. The observed natural variability should be accounted for in predictions of future climate change, and our timeframe for the Aegean climate events in addition provides an independent chronostratigraphic argument to Middle Eastern archaeological studies.
The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000
yrs. It has been suggested that the LIA might be the most recent of the Dansgaard–Oeschger events, which are ...better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~
2
°C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods.
► During the Little Ice Age Antarctica experienced overall cooler conditions. ► Antarctica was in phase with the Northern Hemisphere Little Ice Age event. ► Hence, the sea saw mechanism cannot explain this latest rapid climate change event. ► The thermohaline circulation is unlikely to have been the main driver.
Two ice cores were retrieved from high elevations (~5800 m a.s.l.) at Mt. Nyainqêntanglha and Mt. Geladaindong in the southern and central Tibetan Plateau region. The combined tracer analysis of ...tritium (3H), 210Pb and mercury, along with other chemical records, provided multiple lines of evidence supporting that the two coring sites had not received net ice accumulation since at least the 1950s and 1980s, respectively. These results implied an annual ice loss rate of more than several hundred millimeter water equivalent over the past 30–60 years. Both mass balance modeling at the sites and in situ data from the nearby glaciers confirmed a continuously negative mass balance (or mass loss) in the region due to dramatic warming in recent decades. Along with a recent report on Naimona'nyi Glacier in the Himalayas, the findings suggest that the loss of accumulation area of glacier is a possibility from the southern to central Tibetan Plateau at high elevations, probably up to about 5800 m a.s.l. This mass loss raises concerns over the rapid rate of glacier ice loss and associated changes in surface glacier runoff, water availability, and sea levels.
Changing climate conditions affect dust emissions and the global dust cycle, which in turn affects climate and biogeochemistry. In this study we use observationally constrained model reconstructions ...of the global dust cycle since the Last Glacial Maximum, combined with different simplified assumptions of atmospheric and sea ice processing of dust‐borne iron, to provide estimates of soluble iron deposition to the oceans. For different climate conditions, we discuss uncertainties in model‐based estimates of atmospheric processing and dust deposition to key oceanic regions, highlighting the large degree of uncertainty of this important variable for ocean biogeochemistry and the global carbon cycle. We also show the role of sea ice acting as a time buffer and processing agent, which results in a delayed and pulse‐like soluble iron release into the ocean during the melting season, with monthly peaks up to ~17 Gg/month released into the Southern Oceans during the Last Glacial Maximum (LGM).
Key Points
Data‐constrained time‐slice CESM simulations estimate global dust variability since LGM
Budgets and uncertainties in dust and soluble iron deposition to key ocean regions for biogeochemical cycles
Elevated soluble iron inputs to the Atlantic sector of the Southern Ocean in the LGM
The demonstration that natural climate variability during the last glacial cycle shifted rapidly between remarkable extremes has dramatically revised the understanding of climate change. To further ...advance our understanding, research continues into the timings, geographic distribution, and nature of the millennial-scale climate extremes, and into the mechanisms for intra- and inter-hemispheric transmission of variability through the climate/ocean system. Complementing the traditional definition of the timings of millennial-scale climate variability from ice-core δ^sup 18^O records, we here further narrow down the temporal constraints by determining statistically significant anomalies in the major ion series of the GISP2 ice core. This exercise offers an objective definition of the timing of climatic anomalies in Northern Hemisphere palaeoclimate proxy records of the last 110,000 years that significantly improves the potential for inter-calibration of 'ice-core tuned' chronostratigraphies. We then present a process-oriented synthesis of proxy records from the Northern Hemisphere. This leads to a conclusion that the Dansgaard-Oeschger (D-O) style fluctuations in these records are (virtually) in phase, since all fall within a clear (atmospheric) pattern of concerted relative dominance shifts between polar/westerly dominated winter-type conditions and tropical/monsoon dominated summer-type conditions. Finally, we speculate on a monsoon-related mechanism that could help explain the anomalously long duration of D-O interstadials 12, 8, and 1, which coincided with cooling trends in Antarctic records.PUBLICATION ABSTRACT
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