Sustained glacier melt in the Himalayas has gradually spawned more than 5,000 glacier lakes that are dammed by potentially unstable moraines. When such dams break, glacier lake outburst floods ...(GLOFs) can cause catastrophic societal and geomorphic impacts. We present a robust probabilistic estimate of average GLOFs return periods in the Himalayan region, drawing on 5.4 billion simulations. We find that the 100-y outburst flood has an average volume of 33.5+3.7/−3.7 × 10⁶ m³ (posterior mean and 95% highest density interval HDI) with a peak discharge of 15,600+2,000/−1,800 m³·s−1. Our estimated GLOF hazard is tied to the rate of historic lake outbursts and the number of present lakes, which both are highest in the Eastern Himalayas. There, the estimated 100-y GLOF discharge (∼14,500 m³·s−1) is more than 3 times that of the adjacent Nyainqentanglha Mountains, and at least an order of magnitude higher than in the Hindu Kush, Karakoram, and Western Himalayas. The GLOF hazard may increase in these regions that currently have large glaciers, but few lakes, if future projected ice loss generates more unstable moraine-dammed lakes than we recognize today. Flood peaks from GLOFs mostly attenuate within Himalayan headwaters, but can rival monsoon-fed discharges in major rivers hundreds to thousands of kilometers downstream. Projections of future hazard from meteorological floods need to account for the extreme runoffs during lake outbursts, given the increasing trends in population, infrastructure, and hydropower projects in Himalayan headwaters.
With the enactment of Air Pollution Action Plan in 2013, the air quality improved in most Chinese cities, except that surface ozone (O3) increased markedly. Some recent studies have examined this ...issue and presented controversial opinions, but only focus on summertime ozone increase. This study extends a comprehensive analysis of the influencing factors on China's ozone changes from 2013 to 2017 out of the summer season, combining satellite data, ground measurements and model analyses. The annual trends of air pollutants, e.g., increase in 95th percentile O3 concentration (+1.4–8.7 μg m−3 yr−1), and decreases in fine particulate matter (PM2.5; −4.0~−7.5 μg m−3 yr−1) and sulfur dioxide (−2.6~−9.7 μg m−3 yr−1) are uncovered by satellite and observational data. Model results show that the attributions of surface O3 changes from 2013 to 2017 vary spatially and seasonally, and most regions are more affected by emission changes (−9.5–47.0 μg m−3) rather than meteorological changes (−8.1–21.3 μg m−3). In specific regions and seasons, e.g., south/southwestern and eastern China south of 35°N in May and July, the surface O3 responses to climate variability could have an equal or even greater importance than emission changes. In these major pollution control regions, e.g. northern and mid-eastern China, the precursor emissions control (11–35%) contributes in the same degree as the changes in aerosol effects (35–38%) to surface ozone enhancement in the warm seasons. More scientific emission controls and climate adaptation strategies are required to attain the synergetic control of atmospheric particulate matter and ozone in China.
Display omitted
•Air pollution trends are uncovered by satellite data and observations.•The attributions of surface O3 changes are more affected by emission changes.•O3 response to atmospheric warming is dominant south of 30°N in warm season.•NOx and VOCs control contributed equally as aerosol effect in NCP and East China.
A number of feedbacks regulate the response of Arctic sea ice to local atmospheric warming. Using a realistic coupled ocean‐sea ice model and its adjoint, we isolate a mechanism by which significant ...ice growth at the end of the melt season may occur as a lagged response to Arctic atmospheric warming. A series of perturbation simulations informed by adjoint model‐derived sensitivity patterns reveal the enhanced ice growth to be accompanied by a reduction of snow thickness on the ice pack. Detailed analysis of ocean‐ice‐snow heat budgets confirms the essential role of the reduced snow thickness for persistence and delayed overshoot of ice growth. The underlying mechanism is a snow‐melt‐conductivity feedback, wherein atmosphere‐driven snow melt leads to a larger conductive ocean heat loss through the overlying ice layer. Our results highlight the need for accurate observations of snow thickness to constrain climate models and to initialize sea ice forecasts.
Plain Language Summary
In this study we explore the relationship between Arctic sea ice growth and near‐surface air temperature in a modeling framework. By mapping the time‐ and space‐evolving sensitivity of the Arctic ice volume to changes in air temperature, we show that warming at the end of the melting season can lead to thicker ice at the end of the following winter. Warmer air temperatures can melt snow and remove the insulation it provides, exposing the ice surface to subfreezing air temperatures. We show that removal of this insulating snow layer is essential for enhancing sea ice growth later on, by allowing more heat to be conducted up and out of the underlying ocean, supporting seawater freezing. Our results highlight the importance of measuring snow thickness for accurately forecasting Arctic sea ice.
Key Points
Arctic sea ice sensitivity to atmospheric warming is computed using a numerical adjoint, revealing warming can lead to lagged sea ice growth
Snow melt—in response to early warming—is the key preconditioner, enabling large conductive ocean heat loss to support lagged ice growth
A pronounced excursion in the carbon-isotope composition of biospheric carbon and coeval seawater warming during the early Toarcian (∼183 Ma) has been linked to the large-scale transfer of ...12C-enriched carbon to the oceans and atmosphere. A European bias in the distribution of available data means that the precise pattern, tempo and global expression of this carbon cycle perturbation, and the associated environmental responses, remain uncertain. Here, we present a new cm-scale terrestrial-dominated carbon-isotope record through an expanded lower Toarcian section from Japan that displays a negative excursion pattern similar to marine and terrestrial carbon-isotope records documented from Europe. These new data suggest that 12C-enriched carbon was added to the biosphere in at least one rapid, millennial-scale pulse. Sedimentological analysis indicates a close association between the carbon-isotope excursion and high-energy sediment transport and enhanced fluvial discharge. Together, these data support the hypothesis that a sudden strengthening of the global hydrological cycle occurred in direct and immediate response to rapid carbon release and atmospheric warming.
•New high-resolution C-isotope stratigraphy from NW Panthalassa section through T-OAE.•Rapid (i.e. millennial-scale) carbon release suggested by C-isotope data.•Sudden strengthening of hydrological cycling in response to rapid C release.
Since the early 1990s, the Greenland ice sheet (GrIS) has been losing mass at an accelerating rate, primarily due to enhanced meltwater runoff following atmospheric warming. Here, we show that a ...pronounced latitudinal contrast exists in the GrIS response to recent warming. The ablation area in north Greenland expanded by 46%, almost twice as much as in the south (+25%), significantly increasing the relative contribution of the north to total GrIS mass loss. This latitudinal contrast originates from a different response to the recent change in large-scale Arctic summertime atmospheric circulation, promoting southwesterly advection of warm air toward the GrIS. In the southwest, persistent high atmospheric pressure reduced cloudiness, increasing runoff through enhanced absorption of solar radiation; in contrast, increased early-summer cloudiness in north Greenland enhanced atmospheric warming through decreased longwave heat loss. This triggered a rapid snowline retreat, causing early bare ice exposure, amplifying northern runoff.
This study analyzed the PM10 aerosol enhancement caused by East Asian atmospheric warming during transboundary transport in March of 2021. It was found to be cooled near the north polar area and to ...have shifted the polar vortices northward over the East Asian region in the mid-troposphere. The Siberian high was weakened and the East Asian region was characterized by a positive air temperature anomaly and negative zonal wind speeds. The increasing rate of air temperature anomalies at 2 m was higher in the high latitude areas over 40°N in Mongolia and northeastern China, causing a decrease in zonal wind speeds at 10 m over eastern China and Korea. The anomalous variations of the MODIS-induced aerosol optical depth (AOD) were found to be positive with the highest value of +0.93 in the area ranging from northeastern China to Korea, despite the recent decreasing trends. The positive anomalous region of the MODIS-induced AOD was correlated with positive air temperatures and negative zonal wind speeds, causing enhanced formations of secondary aerosols in the atmosphere. As cold northerly winds were suppressed in the East Asian region, anomalous high pressures (anticyclonic anomalies) developed frequently in eastern China and moved to Korea. The Weather Research and Forecasting model to which meteorological and climate data were applied coupled with Chemistry (WRF-Chem) simulations on increases in the PM10 enhancement ratio, indicating enhanced formation amounts, during transboundary transport for the period of March 13–15, 2021. An air mass near the high terrain surface over eastern China under the backward side of an anticyclone warmed and moved toward the relatively low terrain of the Yellow Sea and Korea in keeping with the height. Air temperature inversion developed in the anomalous warmer center in the mid-troposphere, reaching the surface of the Yellow Sea and Korea. High PM10 concentrations were constrained near the shallow inversion layer. Furthermore, the PM10 enhancement ratio showed a positive level over the Yellow Sea with nearly zero anthropogenic emissions on the surface, gradually increasing at a rate of approximately 60% in Korea. The hourly contribution by the warming-induced PM10 enhancement (PM10 CbWIE) was calculated and found to be at the highest level of 70% in Seoul, Korea. Among PM10 secondary inorganic aerosols, nitrate formations were enhanced during transboundary transport in the warming-induced anticyclone with reactions rich in ammonium. While the sulfate enhancement ratio reached a positive level over the Yellow Sea, the gradual decrease during transboundary transport may be reflected by the decreased emissions of sulfur dioxide in eastern China.
•PM10 aerosol enhancement caused by atmospheric warming during transboundary transport.•Anomalous variations of the aerosol optical depth from northeastern China to Korea.•Meteorological and climate data-applied WRF-Chem simulations in the East Asian region.•Enhanced formations of PM10 secondary aerosols in the warming-induced anticyclone.
Under anticipated future warming, the Greenland ice sheet (GrIS) will pass a threshold when meltwater runoff exceeds the accumulation of snow, resulting in a negative surface mass balance (SMB < 0) ...and sustained mass loss. Here, we dynamically and statistically downscale the outputs of an Earth system model to 1 km resolution to infer that a Greenland near‐surface atmospheric warming of 4.5 ± 0.3°C—relative to preindustrial—is required for GrIS SMB to become persistently negative. Climate models from CMIP5 and CMIP6 translate this regional temperature change to a global warming threshold of 2.7 ± 0.2°C. Under a high‐end warming scenario, this threshold may be reached around 2055, while for a strong mitigation scenario it will likely not be passed. Depending on the emissions scenario taken, our method estimates 6–13 cm sea level rise from GrIS SMB by the year 2100.
Plain Language Summary
Under continued climate warming, the Greenland ice sheet will pass a threshold if summertime meltwater runoff outweighs winter snowfall, resulting in sustained surface mass loss. Here, we project climate model data onto a 1 km resolution grid to show that the ice sheet will likely pass this threshold for a 4.5°C Greenland atmospheric warming relative to preindustrial (1850–1899), equivalent to a 2.7°C global warming. Using additional model projections under high, middle and low emission scenarios, we find that the surface mass loss threshold could be passed in the mid‐21st century under high‐end warming scenarios, but likely not for strong mitigation (low emissions) ones. The same method can be used to estimate sea level rise from Greenland surface mass loss, which yields 6–13 cm in the year 2100, dependent on future emissions.
Key Points
Greenland surface mass balance is projected at 1 km using dynamical and statistical downscaling
The surface mass balance becomes negative for a regional warming of 4.5 ± 0.3°C, compared to preindustrial, and 2.7 ± 0.2°C globally
For a fully grounded Greenland ice sheet, this warming would represent the threshold for sustained mass loss
Qingbingtan Glacier No. 72 in Mt. Tomor region is a cirque-valley glacier with complex topography and debris-covered areas. In-situ measurements from 2008 to 2013 revealed that both ice temperature ...and velocity are obviously higher than in other glaciers in this region. Comparison of digitized earlier topographic maps with recent satellite images indicates that the glacier had been retreating and thinning during the past decades. Between 1964 and 2008, its terminus retreat and area reduction was 41.16±0.6ma−1 and 0.034±0.030×10−3km2a−1, respectively, and thickness decreased at an average rate of 0.22±0.14ma−1 in the ablation area. The strongest ablation and terminus retreat occurred at the end of the last century and the beginning of this century rather than in most recent years, seeming to be related to increase in the debris coverage and thickness. The debris-covered area was 0.87km2, of which 0.66km2 is thicker than the critical thickness of 4cm, and thus the debris cover on this glacier has an alleviating ablation effect overall. Based on a comprehensive analysis of climate change, glacier response delay, glacial topographic features and debris cover influence, the glacier is likely to continue to retreat in the upcoming decades, yet with a gradually decreasing speed.
•A cirque-valley glacier with complex topography and debris-covered areas has been recently investigated in the Tomor region.•It is shown that the glacier is somewhat analogous to temperate one on movement and temperature regimes.•The strongest ablation occurred at the end of the last century and the beginning of this century.•Since inhibition of debris cover to melting, terminus retreat is to slow down, although it would keep shrinking in future.
The 2023 Antarctic sea ice extent (SIE) maximum on 7 September was the lowest annual maximum in the satellite era (16.98 × 106 km2), with the largest contributions to the anomaly coming from the Ross ...(37.7%, −0.57 × 106 km2) and Weddell (32.9%, −0.49 × 106 km2) Seas. The SIE was low due to anomalously warm (>0.3°C) upper‐ocean temperatures combined with anomalously strong northerly winds impeding the ice advance during the fall and winter. Northerly winds of >12 ms−1 in the Weddell Sea occurred because of negative pressure anomalies over the Antarctic Peninsula, while those in the Ross Sea were associated with extreme blocking episodes off the Ross Ice Shelf. The Ross Sea experienced an unprecedented SIE decrease of −1.08 × 103 km2 d−1 from 1 June till the annual maximum. The passage of quasi‐stationary and explosive polar cyclones contributed to periods of southward ice‐edge shift in both sectors.
Plain Language Summary
Sea ice provides a vital habitat for life in the Southern Ocean, and plays an important role in the ocean circulation, the dynamics of the Earth's climate, the biogeochemical cycle, and the regional ecosystem. Climatologically, Antarctic sea ice expands northwards from the continent each autumn and winter. However, in 2023 an unprecedented slow ice expansion occurred in the Southern Ocean ahead of the annual maximum on 7 September of 16.98 × 106 km2, which was 1.46 × 106 km2 below the long‐term average. In fact, the area covered by ice remained at a record low level every day from 21 April 2023 until 11 November 2023. Our findings suggest that an impact of upper‐ocean warming and changes in winds, combined with heat and moisture fluxes, extreme winds and high ocean waves associated with polar cyclones (storms), contributed to these record low ice conditions. In particular, cyclones caused episodes of exceptional slow ice expansion or even retreat, leading to negative ice anomalies. For instance, the ice‐edge in the Weddell Sea was moved southwards quickly in a few days (up to 256 km southward) with an ice area loss of ∼2.3 × 105 km2, equivalent to the size of United Kingdom.
Key Points
The 2023 Antarctic sea ice extent maximum on 7 September (16.98 × 106 km2) was the lowest annual maximum in the satellite era
Anomalous upper‐ocean warming and strong northerly winds contributed to impeding the ice expansion in the Ross and Weddell Seas
Quasi‐stationary and explosive polar cyclones contributed to periods of southward ice‐edge shift in both sectors
Alpine glacier retreat has increased markedly since the late 1980s and is commonly linked to the effects of rising temperature on the surface melt. Less considered are processes associated with ...glacier snout‐marginal surface collapse. A survey of 22 retreating Swiss glaciers suggests that collapse events have increased in frequency since the early 2000s, driven by ice thinning and reductions in glacier‐longitudinal ice flux. Detailed measurement of a collapse event at one glacier showed 0.02 m/day vertical surface deformation above a meandering main subglacial channel. However, with low rates of longitudinal flux (<1.3 m/year), this was insufficient to close the channel in the snout marginal zone. We hypothesize that an open channel maintains contact between subglacial ice and the atmosphere, allowing greater incursion of warm air up‐glacier, thus enhancing melt from below. The associated meandering of subglacial channels at glacier snouts leads to surface collapse and removal of ice via fluvial processes.
Plain Language Summary
Mountain glaciers have been melting and retreating more rapidly since the onset of accelerated atmospheric warming in the late 1980s. Our study examines 22 Swiss glaciers in order to understand why, for some glaciers, the ice surface close to the glacier margin breaks down and forms collapse features, and for others, it does not. We find that the combination of thin ice having a low surface slope results in locally reduced ice flow, which causes subglacial channels to close more slowly and eventually leads to channel roof collapse. A detailed study based on ground‐penetrating radar and drone surveys at one of the glaciers showed that the subglacial channel there is very wide and shallow, and that its strongly sinuous shape may have contributed to a recent ice‐surface collapse. Ice blocks from the melting and collapsing channel were flushed out by the proglacial stream. We observe that such collapse features have become more frequent as air temperatures increase. Visibly, they may contribute to more rapid glacier recession.
Key Points
A survey of 22 Alpine glaciers shows increased margin collapse frequency linked to rapid climate warming since the 1980s
Collapse appears to be associated with glacier thinning, stagnation of snout margins and reduced rates of subglacial channel closure
Intensive study of a collapse event confirms that up‐glacier extension of an unpressurized subglacial channel drives the collapse process
PDF
