Ice-albedo Feedback Research Articles

An Optimal Atmospheric Circulation Mode in the Arctic Favoring Strong Summertime Sea Ice Melting and Ice–Albedo Feedback

Abstract The rapid decline of summer Arctic sea ice over the past few decades has been driven by a combination of increasing greenhouse gases and internal variability of the climate system. However, uncertainties remain regarding spatial and temporal characteristics of the optimal internal atmospheric mode that most favors summer sea ice melting on low-frequency time scales. To pinpoint this mode, we conduct a suite of simulations in which atmospheric circulation is constrained by nudging tropospheric Arctic (60°–90°N) winds within the Community Earth System Model, version 1 (CESM1), to those from reanalysis. Each reanalysis year is repeated for over 10 model years using fixed greenhouse gas concentrations and the same initial conditions. Composites show the strongest September sea ice losses are closely preceded by a common June–August (JJA) barotropic anticyclonic circulation in the Arctic favoring shortwave absorption at the surface. Successive years of strong wind-driven melting also enhance declines in Arctic sea ice through enhancement of the ice–albedo feedback, reaching a quasi-equilibrium response after repeated wind forcing for over 5–6 years, as the effectiveness of the wind-driven ice–albedo feedback becomes saturated. Strong melting favored by a similar wind pattern as observations is detected in a long preindustrial simulation and 400-yr paleoclimate reanalysis, suggesting that a summer barotropic anticyclonic wind pattern represents the optimal internal atmospheric mode maximizing sea ice melting in both the model and natural world over a range of time scales. Considering strong contributions of this mode to changes in Arctic climate, a better understanding of its origin and maintenance is vital to improving future projections of Arctic sea ice.

Emerging unprecedented lake ice loss in climate change projections

Seasonal ice in lakes plays an important role for local communities and lake ecosystems. Here we use Large Ensemble simulations conducted with the Community Earth System Model version 2, which includes a lake simulator, to quantify the response of lake ice to greenhouse warming and to determine emergence patterns of anthropogenic lake ice loss. Our model simulations show that the average duration of ice coverage and maximum ice thickness are projected to decrease over the next 80 years by 38 days and 0.23 m, respectively. In the Canadian Arctic, lake ice loss is accelerated by the cold-season polar amplification. Lake ice on the Tibetan Plateau decreases rapidly due to a combination of strong insolation forcing and ice-albedo feedbacks. Comparing the anthropogenic signal with natural variability represented by the Large Ensemble, we find that lake ecosystems in these regions may be exposed to no-analogue ice coverage within the next 4-5 decades.

New insight into the influence of the Greenland high on summer Arctic sea ice

The Greenland high (GL-high) coincides with a local center of action of the summer North Atlantic Oscillation and is known to have significant influence on Greenland ice sheet melting and summer Arctic sea ice. However, the mechanism behind the influence on regional Arctic sea ice is not yet clear. In this study, using reanalysis datasets and satellite observations, the influence of the GL-high in early summer on Arctic sea ice variability, and the mechanism behind it, are investigated. In response to an intensified GL-high, sea ice over the Beaufort Sea shows significant decline in both concentration and thickness from June through September. This decline in sea ice is primarily due to thermodynamic and mechanical redistribution processes. Firstly, the intensified GL-high increases subsidence over the Canadian Basin, leading to an increase in surface air temperature by adiabatic heating, and a substantial decrease in cloud cover and thus increased downward shortwave radiation. Secondly, the intensified GL-high increases easterly wind frequency and wind speed over the Beaufort Sea, pushing sea ice over the Canadian Basin away from the coastlines. Both processes contribute to an increase in open water areas, amplifying ice–albedo feedback and leading to sea ice decline. The mechanism identified here differs from previous studies that focused on northward moisture and heat transport and the associated increase in downward longwave radiation over the Arctic. The impact of the GL-high on the regional sea ice (also Arctic sea ice extent) can persist from June into fall, providing an important source for seasonal prediction of Arctic sea ice. The GL-high has an upward trend and reached a record high in 2012 that coincided with a record minimum summer Arctic sea ice extent, and has strong implications for summer Arctic sea ice changes.

Deciphering the Role of Aerosol‐Induced Snow Albedo Feedback on Dust Emission Over the Tibetan Plateau

AbstractThe aerosol‐induced snow albedo effect (SAE) and its feedback on the dust emission over the Tibetan Plateau are investigated using the regional climate model (RegCM4.6) coupled with the SNow, ICe, and Aerosol Radiative model. The deposition of absorbing aerosols (black carbon and dust) decreases the albedo of snow over the Himalayan‐Tibetan region, which results in significant surface warming of 1–4 K. This aerosol‐induced surface warming and accelerated snow melting decreased fractional snow cover by 8% and number of snow cover days by 20 days over the region. Compared to the control simulation, this early and more exposure of nonvegetated land resulted in the increase of the dust emission flux by 60% over central Tibet and therefore the columnar dust loading by 10%–40%. This effect alone results in a surface cooling of −4 Wm−2 and also increases the occurrence of dust events by 10%–20%. Therefore, the snow darkening effect due to the deposition of black carbon and dust increases the local emission of dust aerosols, which further increases the aerosol‐induced snow melting and thus perturbs the air quality and radiation balance over the high mountains of Asia.

Snow Albedo Feedbacks Enhance Snow Impurity‐Induced Radiative Forcing in the Sierra Nevada

This study employs a fully coupled meteorology‐chemistry‐snow model to investigate the impacts of light‐absorbing particles (LAPs) on snow darkening in the Sierra Nevada. After comprehensive evaluation with spatially and temporally complete satellite retrievals, the model shows that LAPs in snow reduce snow albedo by 0.013 (0–0.045) in the Sierra Nevada during the ablation season (April‐July), producing a midday mean radiative forcing of 4.5 W m−2 which increases to 15–22 W m−2 in July. LAPs in snow accelerate snow aging processes and reduce snow cover fraction, which doubles the albedo change and radiative forcing caused by LAPs. The impurity‐induced snow darkening effects decrease snow water equivalent and snow depth by 20 and 70 mm in June in the Sierra Nevada bighorn sheep habitat. The earlier snowmelt reduces root‐zone soil water content by 20%, deteriorating the forage productivity and playing a negative role in the survival of bighorn sheep.

Greenland Ice Sheet Rainfall, Heat and Albedo Feedback Impacts From the Mid‐August 2021 Atmospheric River

AbstractRainfall at the Greenland ice sheet Summit 14 August 2021, was delivered by an atmospheric river (AR). Extreme surface ablation expanded the all‐Greenland bare ice area to near‐record‐high with snowline climbing up to 788 ± 90 m. Ice sheet wet snow extent reached 46%, a record high for the 15–31 August AMSR data since 2003. Heat‐driven firn deflation averaged 0.14 ± 0.05 m at four accumulation area automatic weather stations (AWSs). Energy budget calculations from AWS data indicate that surface heating from rainfall is much smaller than from either the sensible, latent, net‐longwave or solar energy fluxes. Sensitivity tests show that without the heat‐driven snow‐darkening, melt at 1,840 m would have totaled 28% less. Similarly, at 1,270 m elevation, without the bare ice exposure, melting would have been 51% less. Proglacial river discharge was the highest on record since 2006 for late August and confirms the melt‐sustaining effect of the albedo feedback.

Contribution of the Tibetan Plateau Winter Snow Cover to Seasonal Prediction of the East Asian Summer Monsoon

ABSTRACT How to improve the prediction skill of the East Asian summer monsoon (EASM) is a challenging but essential issue. This study examines the impact of the winter Tibetan Plateau (TP) snow cover (TPSC) on the subsequent EASM during the past two decades. Based on the high-resolution MODIS/Terra snow cover data, a new snow cover critical area (76°−83°E, 28°−35°N) is identified in the southwestern TP for the EASM seasonal prediction. Results show that the increase of the TPSC within this critical area during prior winter significantly increases summer precipitation over the Yangtze River Basin (YRB). The TPSC anomaly induces anomalous cooling in the overlying atmospheric column, leading to an anomalous cyclonic circulation in the upper troposphere. Such anomalous cyclonic circulation may further contribute to the local snow cover increase, and through such a snow-albedo feedback process, the excessive TPSC anomaly is strengthened and persists through the following summer. Coexisting with the positive anomalous TPSC, the South Asian High, the western Pacific Subtropical High, and the Subtropical Westerly Jet shift southward. A deep cyclonic circulation is induced in northeastern China by the excessive TPSC anomaly, which is reproduced in the linear baroclinic model simulation. Northerly flow is crucial for accumulating water vapour and favours more rainfall over the YRB. A physical empirical prediction model is established to quantify the TPSC contribution to the seasonal prediction of the EASM. Empirical hindcast output shows the prediction skill of the EASM is significantly improved with the additional predictor of the winter TPSC. In particular, the TPSC has greatly improved the prediction of the extreme EASM in 2020. The above results indicate that the prior winter TPSC anomaly in this critical area can provide another predictability source for the EASM, besides El Niño-Southern Oscillation and the North Atlantic Oscillation.

Spring snow-albedo feedback from satellite observation, reanalysis and model simulations over the Northern Hemisphere

Spring snow-albedo feedback from satellite observation, reanalysis and model simulations over the Northern Hemisphere

Spatiotemporal evolution of melt ponds on Arctic sea ice

Melt ponds on sea ice play an important role in the Arctic climate system. Their presence alters the partitioning of solar radiation: decreasing reflection, increasing absorption and transmission to the ice and ocean, and enhancing melt. The spatiotemporal properties of melt ponds thus modify ice albedo feedbacks and the mass balance of Arctic sea ice. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition presented a valuable opportunity to investigate the seasonal evolution of melt ponds through a rich array of atmosphere-ice-ocean measurements across spatial and temporal scales. In this study, we characterize the seasonal behavior and variability in the snow, surface scattering layer, and melt ponds from spring melt to autumn freeze-up using in situ surveys and auxiliary observations. We compare the results to satellite retrievals and output from two models: the Community Earth System Model (CESM2) and the Marginal Ice Zone Modeling and Assimilation System (MIZMAS). During the melt season, the maximum pond coverage and depth were 21% and 22 ± 13 cm, respectively, with distribution and depth corresponding to surface roughness and ice thickness. Compared to observations, both models overestimate melt pond coverage in summer, with maximum values of approximately 41% (MIZMAS) and 51% (CESM2). This overestimation has important implications for accurately simulating albedo feedbacks. During the observed freeze-up, weather events, including rain on snow, caused high-frequency variability in snow depth, while pond coverage and depth remained relatively constant until continuous freezing ensued. Both models accurately simulate the abrupt cessation of melt ponds during freeze-up, but the dates of freeze-up differ. MIZMAS accurately simulates the observed date of freeze-up, while CESM2 simulates freeze-up one-to-two weeks earlier. This work demonstrates areas that warrant future observation-model synthesis for improving the representation of sea-ice processes and properties, which can aid accurate simulations of albedo feedbacks in a warming climate.

The Mesoscale Response to Global Warming over the Pacific Northwest Evaluated Using a Regional Climate Model Ensemble

AbstractThis paper describes the downscaling of an ensemble of 12 general circulation models (GCMs) using the Weather Research and Forecasting (WRF) Model at 12-km grid spacing over the period 1970–2099, examining the mesoscale impacts of global warming as well as the uncertainties in its mesoscale expression. The RCP8.5 emissions scenario was used to drive both global and regional climate models. The regional climate modeling system reduced bias and improved realism for a historical period, in contrast to substantial errors for the GCM simulations driven by lack of resolution. The regional climate ensemble indicated several mesoscale responses to global warming that were not apparent in the global model simulations, such as enhanced continental interior warming during both winter and summer as well as increasing winter precipitation trends over the windward slopes of regional terrain, with declining trends to the lee of major barriers. During summer there is general drying, except to the east of the Cascades. The 1 April snowpack declines are large over the lower-to-middle slopes of regional terrain, with small snowpack increases over the lower elevations of the interior. Snow-albedo feedbacks are very different between GCM and RCM projections, with the GCMs producing large, unphysical areas of snowpack loss and enhanced warming. Daily average winds change little under global warming, but maximum easterly winds decline modestly, driven by a preferential sea level pressure decline over the continental interior. Although temperatures warm continuously over the domain after approximately 2010, with slight acceleration over time, occurrences of temperature extremes increase rapidly during the second half of the twenty-first century.Significance StatementThis paper provides a unique high-resolution view of projected climate change over the Pacific Northwest and does so using an ensemble of regional climate models, affording a look at the uncertainties in local impacts of global warming. The paper examines regional meteorological processes influenced by global warming and provides guidance for adaptation and preparation.

Enhanced Arctic warming amplification revealed in a low-emission scenario

The Arctic region has warmed faster than the global mean in past decades. Future climate change projections also suggest this Arctic warming amplification will continue. Here, using 50-member historical and future scenario simulations by a single climate model, we find that Arctic warming amplification is stronger in a low-emission scenario, compared to a high-emission scenario, after the mid-2040s. This is because in the low-emission scenario, sea ice continues to exist beyond 2040 and the ice-albedo feedback therefore maintains Arctic warming, unlike other latitudes. By contrast, in the high-emission scenario summer sea ice melts away by about 2050. Multi-model analyses show that the strength of Arctic amplification in the low-emission scenario is highly correlated with the amount of sea-ice reduction, whereas this relationship weakens in the high-emission scenario. Our results indicate that climate change mitigation may have a side effect because Arctic warming persists even if the global warming is stabilized.

Bidecadal Temperature Anomalies Over the Tibetan Plateau and Arctic in Response to the 1450s Volcanic Eruptions

AbstractVolcanic eruptions have been the most dominant natural forcing of climate change over the past millennium, affecting temperature change at multiple timescales. However, how volcanic eruptions affect regional temperature variability on the decadal timescale remains unclear. We analyzed the bidecadal effects of volcanic eruptions in the mid‐fifteenth century on two representative regions (the Tibetan plateau [TP] and the Arctic) in the Northern Hemisphere by combining proxy reconstructions, model ensemble simulations, and model sensitive experiments. The results show that the TP experienced bidecadal cooling during the mid‐fifteenth century as a result of the long‐term heat uptake in the midlatitude ocean that reduced latent heat transfer to the atmosphere. A positive sea ice–albedo feedback led to a bidecadal summer temperature decrease in the Arctic comparable to that on the TP, whereas the Arctic winter experienced stronger bidecadal cooling caused by a reduced ocean–atmosphere energy exchange and atmospheric poleward energy transport. In addition, our results show that it took ∼20 years for the temperature in these two regions to return to the level that existed before the first eruption, and this was linked to the strengthening of the Atlantic Meridional Overturning Circulation and ocean heat transport.

Arctic sea ice sensitivity to lateral melting representation in a coupled climate model

Abstract. The melting of sea ice floes from the edges (lateral melting) results in open-water formation and subsequently increases absorption of solar shortwave energy. However, lateral melt plays a small role in the sea ice mass budget in both hemispheres in most climate models. This is likely influenced by the simple parameterization of lateral melting in sea ice models that are constrained by limited observations. Here we use a coupled climate model (CESM2.0) to assess the sensitivity of modeled sea ice state to the lateral melt parameterization in preindustrial and 2×CO2 runs. The runs explore the implications of how lateral melting is parameterized and structural changes in how it is applied. The results show that sea ice is sensitive both to the parameters determining the effective lateral melt rate and the nuances in how lateral melting is applied to the ice pack. Increasing the lateral melt rate is largely compensated for by decreases in the basal melt rate but still results in a significant decrease in sea ice concentration and thickness, particularly in the marginal ice zone. Our analysis suggests that this is tied to the increased efficiency of lateral melting at forming open water during the summer melt season, which drives the majority of the ice–albedo feedback. The more seasonal Southern Hemisphere ice cover undergoes larger relative reductions in sea ice concentration and thickness for the same relative increase in lateral melt rate, likely due to the hemispheric differences in the role of the sea-ice–upper-ocean coupling. Additionally, increasing the lateral melt rate under a 2×CO2 forcing, where sea ice is thinner, results in a smaller relative change in sea ice mean state but suggests that open-water-formation feedbacks are likely to steepen the decline to ice-free summer conditions. Overall, melt processes are more efficient at forming open water in thinner ice scenarios (as we are likely to see in the future), suggesting the importance of accurately representing thermodynamic evolution. Revisiting model parameterizations of lateral melting with observations will require finding new ways to represent salient physical processes.

Observations and Simulated Mechanisms of Elevation-Dependent Warming over the Tropical Andes

Abstract Many mountain regions around the world are exposed to enhanced warming when compared to their surroundings, threatening key environmental services provided by mountains. Here we investigate this effect, known as elevation-dependent warming (EDW), in the Andes of Ecuador, using observations and simulations with the Weather Research and Forecasting (WRF) Model. EDW is discernible in observations of mean and maximum temperature in the Andes of Ecuador, but large uncertainties remain due to considerable data gaps in both space and time. WRF simulations of present-day (1986–2005) and future climate (RCP4.5 and RCP8.5 for 2041–60) reveal a very distinct EDW signal, with different rates of warming on the eastern and western slopes. This EDW effect is the combined result of multiple feedback mechanisms that operate on different spatial scales. Enhanced upper-tropospheric warming projects onto surface temperature on both sides of the Andes. In addition, changes in the zonal mean midtropospheric circulation lead to enhanced subsidence and warming over the western slopes at high elevation. The increased subsidence also induces drying, reduces cloudiness, and results in enhanced net surface radiation receipts, further contributing to stronger warming. Finally, the highest elevations are also affected by the snow-albedo feedback, due to significant reductions in snow cover by the middle of the twenty-first century. While these feedbacks are more pronounced in the high-emission scenario RCP8.5, our results indicate that high elevations in Ecuador will continue to warm at enhanced rates in the twenty-first century, regardless of emission scenario. Significance Statement Mountains are often projected to experience stronger warming than their surrounding lowlands going forward, a phenomenon known as elevation-dependent warming (EDW), which can threaten high-altitude ecosystems and lead to accelerated glacier retreat. We investigate the mechanisms associated with EDW in the Andes of Ecuador using both observations and model simulations for the present and the future. A combination of factors amplify warming at mountain tops, including a stronger warming high in the atmosphere, reduced cloudiness, and a reduction of snow and ice at high elevations. The latter two factors also favor enhanced absorption of sunlight, which promotes warming. The degree to which this warming is enhanced at high elevations in the future depends on the greenhouse gas emission pathway.

Effects of Aerosol–Induced Snow Albedo Feedback on the Seasonal Snowmelt Over the Himalayan Region

AbstractAerosol‐induced snow darkening and its feedback on seasonal snow cover, snowmelt, and runoff were investigated using the Regional Climate Model (RegCM4.6) coupled with SNow, Ice, and Aerosol Radiation (SNICAR) and aerosol modules over the Himalayas during the melting season (March‐September). The snow albedo reduction due to the deposition of absorbing aerosols increases the 2 m air temperature (1.47°C) and thus decreases the snow cover (10.6%) over the Himalayas during spring. This aerosol‐induced excess warming accelerates the seasonal snowmelt (1.2 mm day−1), which reduces the number of snow‐covered periods by more than 20 days throughout the Himalayas. The accumulated total snowmelt also increased by 41.3% over the Himalayas during the melting season. The early snowmelt and increase in runoff due to aerosol forcing have significant implications on rivers originating from the western Himalayas (Indus Basin). The change in snowmelt distribution and doubling of snowmelt extremes due to aerosol‐induced snow darkening could also translate to an increase in flood risks across the Himalayan river basins. Therefore, the present study highlights the importance of aerosol‐induced snow albedo forcing and its feedback on snowmelt and runoff over the Himalayan region, which has further implications on water availability over the South Asian region.

Environmental inferno- Wildfire emitted aerosols

Wildfire-emitted aerosols could have a huge impact on global climate by disrupting the global radiation balance. The Community Earth Model Of the system with regulated daily smoke aerosol releases is used in this work to evaluate the effects of fire aerosols on global climate, with a focus on climate feedbacks. The total wildfire aerosol thermal influence (RE) is predicted for being 20.78 6 0.29 W m22, with shortwave RE (REaci; 20.70 6 0.20 W m22) accounting for the majority of the RE. The annual global warming shift DT is 20.64 6 0.16 K, with northern hemisphere experiencing the highest change. In the Arctic, where the shortwave REaci is strong, there is a decline. The build-up of Arctic Sea ice is associated to the cooling, which acts to amplify the Arctic cooling through positive ice-albedo feedback. The quick reaction (irrelevant to DT) tends to lower surface latent heat flow into the atmosphere in the tropics to counter compelling smoke black carbon absorbing, which decreases rainfall in tropical land regions (southern Africa and South America). Climate feedback processes (pertaining to DT) result in a significant reduction in surface latent heat flux over global ocean areas, which could account for the vast majority (;80%) of global precipitation reduction. Precipitate is formed in deep tropical latitudes (58N), but rises in the tropical ocean of the Southern Hemisphere, owing to a southern displacement of the inter - tropical convergence transitional zone and a lowering of the Hadley system in the Southern Hemisphere. Through intensifying cross-equator atmospheric heat transport, such changes could partially compensate for the interhemispheric temperature asymmetry induced by boreal forest fire aerosol indirect effects. This paper deals with wildfire aerosols' impact on forest biomass, the global energy budget, and climate, as well as ways to replenish them.

Automated mapping of the seasonal evolution of surface meltwater and its links to climate on the Amery Ice Shelf, Antarctica

Abstract. Surface meltwater is widespread around the Antarctic Ice Sheet margin and has the potential to influence ice shelf stability, ice flow and ice–albedo feedbacks. Our understanding of the seasonal and multi-year evolution of Antarctic surface meltwater is limited. Attempts to generate robust meltwater cover time series have largely been constrained by computational expense or limited ice surface visibility associated with mapping from optical satellite imagery. Here, we add a novel method for calculating visibility metrics to an existing meltwater detection method within Google Earth Engine. This enables us to quantify uncertainty induced by cloud cover and variable image data coverage, allowing time series of surface meltwater area to be automatically generated over large spatial and temporal scales. We demonstrate our method on the Amery Ice Shelf region of East Antarctica, analysing 4164 Landsat 7 and 8 optical images between 2005 and 2020. Results show high interannual variability in surface meltwater cover, with mapped cumulative lake area totals ranging from 384 to 3898 km2 per melt season. By incorporating image visibility assessments, however, we estimate that cumulative total lake areas are on average 42 % higher than minimum mapped values. We show that modelled melt predictions from a regional climate model provide a good indication of lake cover in the Amery region and that annual lake coverage is typically highest in years with a negative austral summer SAM index. Our results demonstrate that our method could be scaled up to generate a multi-year time series record of surface water extent from optical imagery at a continent-wide scale.

Impact of snow‐albedo feedback termination on terrestrial surface climate at midhigh latitudes: Sensitivity experiments with an atmospheric general circulation model

AbstractTo examine the effect of the snow‐albedo feedback (SAF) on the current surface climate across terrestrial regions at mid–high latitudes, we perform a series of idealized sensitivity experiments using an atmospheric general circulation model (AGCM), in which the snow albedo is assumed to be considerably smaller than that in the control experiment. When the snow albedo is reduced, the fall and spring surface air temperatures (SATs) in northern Eurasia are considerably higher than those in the control experiment. Particularly, the spring SAT at terrestrial high latitudes rises by more than 10°C, due to low snow albedo. Despite the small surface snow albedo during both fall and spring, the fall temperature difference between the two experiments is smaller than that during spring. The feedback with the hydrological effect, which accelerates snowmelt, is either nonexistent or weak during periods of seasonally low air temperatures. This result indicates that the hydrological effect significantly influences the SAF, and different magnitudes of the hydrological effect including cloud differences are a possible source of SAF uncertainty between models. The radiative albedo effect also impacts the evolution of the snow area in central Asia and eastern Europe through changes in lateral water vapour transport. Furthermore, the experiments indicate that the cooling effect of snow on land is necessary for the strength of the Siberian High and the pattern of Arctic Oscillation, suggesting that snow cover may also significantly extend the duration of Arctic Oscillation effects.

Climate sensitivity in the northern high latitudes using the Brazilian Earth System Model

An expressive number of scientific publications including the recent IPCC-AR6 report have warned about the effects of the ongoing and the projected climate change in the northern high latitudes as response to CO2 forcing. Here we investigate the response of the Arctic region to an increase in atmospheric CO2 concentration using the Brazilian Earth System Model (BESM-OA2.5) and other three state-of-the-art Global Climate Model from the CMIP5 project. We evaluated the Arctic climate sensitivity through the Polar amplification using two numerical experiments: (i) piControl numerical experiment and (ii) abrupt 4xCO2. Our results showed that the northern high latitudes are described as the most climatically sensitive areas of the world, with strongest warming occurring in winter (DJF) and autumn (SON). The Arctic climate sensitivity is linked to changes in sea ice extent and sea ice thickness. Considering this scenario, it is expected that the Arctic will become ice-free in summer time and covered only by first-year-sea ice in the remaining months. We suggest that the projected sea ice albedo feedback will reinforce the Arctic warming with lack of understanding effects beyond the Arctic region.

Warming amplification with both altitude and latitude in the Tibetan Plateau

AbstractMany studies have examined elevation‐dependent warming in mountain regions of the world, yet little attempt has been undertaken to examine the relationship of the observed warming with both altitude and latitude on a regional scale. Here, based on the mean temperature series (1961–2015) of 105 stations in the Tibetan Plateau, the signals of warming amplification with these two factors are quantified using four groups of methods. The results, highly consistent for the different methods, confirm that the warming for the Tibetan Plateau is not only elevation‐dependent, but also latitude‐dependent, and the magnitude of altitudinal amplification trend is two orders of magnitude larger than that of latitudinal amplification trend on the annual and seasonal scales over the period 1961–2015. The annual warming is amplified by 0.066°C 10 year−1·km−1 of altitude and 0.016 × 10−2°C 10 year−1·km−1 of latitude (or 0.018°C 10 year−1·degree−1 of latitude), with the highest altitudinal (latitudinal) amplification in winter (autumn), followed by autumn (winter) and the lowest in spring and summer. Meanwhile, the estimates of altitude and latitude components of the regional warming shows that the contribution of latitude to the regional warming is larger than that of altitude on the annual scale and for all seasons excepting summer, due primarily to the much larger range of latitude than the range of altitude covered by all the stations used. Moreover, analysis of the number of snow cover days demonstrates that the snow albedo feedback has played a significant role in enhancing the warming in the Tibetan Plateau during the recent sub‐period 1996–2015, due to the decrease of snow cover days in the spring, autumn and winter seasons. These results highlight an integrated picture of Tibetan Plateau warming amplification, and a clear snow albedo feedback effect on the regional amplification, allowing better investigation of impacts and mechanisms.