Expected change of hydrologic cycle in Northern Eurasia due to disappearance of multiyear sea ice in the Arctic Ocean

The effects are considered that global warming and rapid sea ice decline in the Arctic (up to the formation of ice-free conditions in the Arctic Ocean in summer) made on the hydrological regime of Northern Eurasia. Ensemble computations of climate are provided and changes in the atmospheric water cycle and in water balance in large catchment areas after the loss of multiyear sea ice in the Arctic are estimated. Considerable changes in the hydrological regime are demonstrated on the example of the large catchments of the Siberian rivers; the changes are especially manifested in the period of intense snow melting, i.e., in spring and in early summer. It is revealed that the increase in the frequency of spring floods is expected in the river catchments adjoining the Arctic Ocean. It is demonstrated that the Arctic Ocean ice reduction does not exert as significant influence on variations in the water cycle in Northern Eurasia as the global warming does.     

A case study of a modelled episode of low Arctic sea ice

Simulations of the Arctic sea ice cover over the last 32 years generated by the HadGEM1 coupled climate model are able to capture the observed long term decline in mean September ice extent. HadGEM1 is also capable of producing an episode of low September ice extent of similar magnitude to the anomalously low extent observed in 2007. Using a heat budget analysis, together with diagnostics partitioning the changes in ice and snow mass into thermodynamic and dynamic components, we analyse the factors driving the long term decline in the ice mass and extent as well as those causing the modelled low ice event. The long term decline in the mass of ice and snow in HadGEM1 is largely due to extra melting during the summer, partly at the top surface of the ice, and partly via extra heating from the ocean as it warms due to the ice retreat. The episode of low summer ice extent is largely driven by the synoptic conditions over the summer moving the ice across and out of the Arctic basin, and also due to pre-conditioning of the snow and ice which is thinner than usual in the Eastern Arctic at the start of the melt season. This case study demonstrates that although HadGEM1 does not capture the persistent dipole pressure anomaly observed during the summer of 2007, it represents broadly similar mechanisms of generating a low ice extent.     

A sensitivity experiment for the removal of Arctic sea ice with the French spectral general circulation model

Sea ice has a major influence on climate in high latitudes. In this paper we analyzed the impact of removal of Arctic sea-ice cover on the climate simulated by a T42 20-level version of the French spectral model Emeraude. The control experiment was the second winter of an annual cycle simulation of the present climate. In the perturbed simulation the Arctic sea-ice cover was replaced by open ocean maintained at the freezing temperature of sea water. The zonal mean patterns of the model response were found to be in good agreement with earlier simulations of Fletcher et al. and Warshaw and Rapp. The atmospheric warming, caused by the increase of upward fluxes of sensible and latent heat and of longwave radiation from the ice-free ocean surface, is largely limited to the high latitudes poleward of 70° N and the lower half of the troposphere and leads to a surface pressure decrease and a precipitation increase over this area. We also analyze the geographical distribution of the response and the mechanisms that can explain the simulated cooling over Eurasia in relation to the energy budget at the surface. Finally, we discuss the reduction of cloud cover over the ice-free Arctic, which was an unexpected result of our simulation, and conclude that further studies are necessary to resolve the question of cumulus convection and cloud process parameterization in high latitudes.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

On the Response of the Greenland Ice Sheet to Greenhouse Climate Change

Numerical computations are performed with the three-dimensional polythermal ice-sheet model SICOPOLIS in order to investigate the possible impact of a greenhouse-gas-induced climate change on the Greenland ice sheet. The assumed increase of the mean annual air temperature above the ice covers a range from T = 1°C to 12°C, and several parameterizations for the snowfall and the surface melting are considered. The simulated shrinking of the ice sheet is a smooth function of the temperature rise, indications for the existence of critical thresholds of the climate input are not found. Within 1000 model years, the ice-volume decrease is limited to 10% of the present volume for T 3°C, whereas the most extreme scenario, T = 12°C, leads to an almost entire disintegration, which corresponds to a sea-level equivalent of 7 m. The different snowfall and melting parameterizations yield an uncertainty range of up to 20% of the present ice volume after 1000 model years.     

Inherent sea ice predictability in the rapidly changing Arctic environment of the Community Climate System Model, version 3

Seasonal predictions of Arctic sea ice have typically been based on statistical regression models or on results from ensemble ice model forecasts driven by historical atmospheric forcing. However, in the rapidly changing Arctic environment, the predictability characteristics of summer ice cover could undergo important transformations. Here global coupled climate model simulations are used to assess the inherent predictability of Arctic sea ice conditions on seasonal to interannual timescales within the Community Climate System Model, version 3. The role of preconditioning of the ice cover versus intrinsic variations in determining sea ice conditions is examined using ensemble experiments initialized in January with identical ice?Cocean?Cterrestrial conditions. Assessing the divergence among the ensemble members reveals that sea ice area exhibits potential predictability during the first summer and for winter conditions after a year. The ice area exhibits little potential predictability during the spring transition season. Comparing experiments initialized with different mean ice conditions indicates that ice area in a thicker sea ice regime generally exhibits higher potential predictability for a longer period of time. In a thinner sea ice regime, winter ice conditions provide little ice area predictive capability after approximately 1?year. In all regimes, ice thickness has high potential predictability for at least 2?years.     

The effect of snow on Antarctic sea ice simulations in a coupled atmosphere-sea ice model

 The effect of a snow cover on sea ice accretion and ablation is estimated based on the ‘zero-layer’ version sea ice model of Semtner, and is examined using a coupled atmosphere-sea ice model including feedbacks and ice dynamics effects. When snow is disregarded in the coupled model the averaged Antarctic sea ice becomes thicker. When only half of the snowfall predicted by the atmospheric model is allowed to land on the ice surface sea ice gets thicker in most of the Weddell and Ross Seas but thinner in East Antarctic in winter, with the average slightly thicker. When twice as much snowfall as predicted by the atmospheric model is assumed to land on the ice surface sea ice also gets much thicker due to the large increase of snow-ice formation. These results indicate the importance of the correct simulation of the snow cover over sea ice and snow-ice formation in the Antarctic. Our results also illustrate the complex feedback effects of the snow cover in global climate models. In this study we have also tested the use of a mean value of 0.16 Wm^-1 K^-1 instead of 0.31 for the thermal conductivity of snow in the coupled model, based on the most recent observations in the eastern Antarctic and Bellingshausen and Amundsen Seas, and have found that the sea ice distribution changes greatly, with the ice becoming much thinner by about 0.2 m in the Antarctic and about 0.4 m in the Arctic on average. This implies that the magnitude of the thermal conductivity of snow is of considerable importance for the simulation of the sea ice distribution. An appropriate value of the thermal conductivity of snow is as crucial as the depth of the snow layer and the snowfall rate in a sea ice model. The coupled climate models require accurate values of the effective thermal conductivity of snow from observations for validating the simulated sea ice distribution under the present climate conditions. Received: 20 November 1997/Accepted: 27 July 1998     

Is climate change affecting wolf populations in the high arctic?

Gobal climate change may affect wolves in Canadas High Arctic (80° N) acting through three trophic levels (vegetation, herbivores, and wolves). A wolf pack dependent on muskoxen and arctic hares in the Eureka area of Ellesmere Island denned and produced pups most years from at least 1986 through 1997. However, when summer snow covered vegetation in 1997 and 2000 for the first time since records were kept, halving the herbivore nutrition-replenishment period, muskox and hare numbers dropped drastically, and the area stopped supporting denning wolves through 2003. The unusual weather triggering these events was consistent with global-climate-change phenomena.     

The Impact of Sediment-Laden Snow and Sea Ice in the Arctic on Climate

Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant.     

Ice-free glacial northern Asia due to dust deposition on snow

During the Last Glacial Maximum (LGM, 21 kyr BP), no large ice sheets were present in northern Asia, while northern Europe and North America (except Alaska) were heavily glaciated. We use a general circulation model with high regional resolution and a new parameterization of snow albedo to show that the ice-free conditions in northern Asia during the LGM are favoured by strong glacial dust deposition on the seasonal snow cover. Our climate model simulations indicate that mineral dust deposition on the snow surface leads to low snow albedo during the melt season. This, in turn, caused enhanced snow melt and therefore favoured snow-free peak summer conditions over almost the entire Asian continent during the LGM, whereas perennial snow cover is simulated over a large part of eastern Siberia when glacial dust deposition is not taken into account.     

Quantifying Arctic contributions to climate predictability in a regional coupled ocean-ice-atmosphere model

The relative importance of regional processes inside the Arctic climate system and the large scale atmospheric circulation for Arctic interannual climate variability has been estimated with the help of a regional Arctic coupled ocean-ice-atmosphere model. The study focuses on sea ice and surface climate during the 1980s and 1990s. Simulations agree reasonably well with observations. Correlations between the winter North Atlantic Oscillation index and the summer Arctic sea ice thickness and summer sea ice extent are found. Spread of sea ice extent within an ensemble of model runs can be associated with a surface pressure gradient between the Nordic Seas and the Kara Sea. Trends in the sea ice thickness field are widely significant and can formally be attributed to large scale forcing outside the Arctic model domain. Concerning predictability, results indicate that the variability generated by the external forcing is more important in most regions than the internally generated variability. However, both are in the same order of magnitude. Local areas such as the Northern Greenland coast together with Fram Straits and parts of the Greenland Sea show a strong importance of internally generated variability, which is associated with wind direction variability due to interaction with atmospheric dynamics on the Greenland ice sheet. High predictability of sea ice extent is supported by north-easterly winds from the Arctic Ocean to Scandinavia.     

CICE海冰模式中反照率相关参数对北极海冰模拟的影响

国家气候中心气候系统模式BCC_CSM2.0最新耦合了美国Los Alamos国家实验室发展的海冰模式CICE5.0,为试验模式中与反照率相关参数的敏感性及其对模拟结果的影响,提高模式对北极海冰的模拟能力,选取海冰模式中3个主要参数进行了敏感性试验。利用以BCC_CSM2.0耦合框架为基础建立的海冰-海洋耦合模式,选取CORE资料为大气强迫场开展试验,试验的3个参数分别为冰/雪表面反射率、雪粒半径和雪粒半径参考温度。结果表明,参数取值的不同对北极海冰的模拟有显著的影响,优化后的取值组合极大提高了模式的模拟能力,主要表现在:（1）改善了对北极冬季海冰厚度的模拟,海冰厚度增大,与观测资料更为吻合;（2）显著提高了对北极夏季海冰密集度的模拟能力,从而模拟的北极海冰范围年际循环与观测更为一致。参数取值的优化改进了模式对海冰反照率的模拟,进而影响了冰面短波辐射的吸收和海冰表层的融化,最终提高了模式对海冰密集度和厚度的模拟效果。      

Linking the northern hemisphere sea-ice reduction trend and the quasi-decadal arctic sea-ice oscillation

The nature of the reduction trend and quasi-decadal oscillation in Northern Hemisphere sea-ice extent is investigated. The trend and oscillation that seem to be two separate phenomena have been found in data. This study examines a hypothesis that the Arctic sea-ice reduction trend in the last three decades amplified the quasi-decadal Arctic sea-ice oscillation (ASIO) due to a positive ice/ocean-albedo feedback, based on data analysis and a conceptual model proposed by Ikeda et al. The theoretical, conceptual model predicts that the quasi-decadal oscillation is amplified by the thinning sea-ice, leading to the ASIO, which is driven by the strong positive feedback between the atmosphere and ice-ocean systems. Such oscillation is predicted to be out-of-phase between the Arctic Basin and the Nordic Seas with a phase difference of 3/4, with the Nordic Seas leading the Arctic. The wavelet analysis of the sea ice data reveals that the quasi-decadal ASIO occurred actively since the 1970s following the trend starting in the 1960s (i.e., as sea-ice became thinner and thinner), as the atmosphere experienced quasi-decadal oscillations during the last century. The wavelet analysis also confirms the prediction of such out-of-phase feature between these two basins, which varied from 0.62 in 1960 to 0.25 in 1995. Furthermore, a coupled ice-ocean general circulation model (GCM) was used to simulate two scenarios, one without the greenhouse gas warming and the other having realistic atmospheric forcing along with the warming that leads to sea-ice reduction trend. The quasi-decadal ASIO is excited in the latter case compared to the no-warming case. The wavelet analyses of the simulated ice volume were also conducted to derive decadal ASIO and similar phase relationship between the Arctic Ocean and the Nordic Seas. An independent data source was used to confirm such decadal oscillation in the upper layer (or freshwater) thickness, which is consistent with the model simulation. A modified feedback loop for the sea-ice trend and ASIO was proposed based on the previous one by Mysak and Venegas and the ice/albedo and cloud/albedo feedabcks, which are responsible for the sea ice reduction trend.     

Declining summer snowfall in the Arctic: causes, impacts and feedbacks

Recent changes in the Arctic hydrological cycle are explored using in situ observations and an improved atmospheric reanalysis data set, ERA-Interim. We document a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. The snowfall decline is diagnosed as being almost entirely caused by changes in precipitation form (snow turning to rain) with very little influence of decreases in total precipitation. The proportion of precipitation falling as snow has decreased as a result of lower-atmospheric warming. Statistically, over 99% of the summer snowfall decline is linked to Arctic warming over the past two decades. Based on the reanalysis snowfall data over the ice-covered Arctic Ocean, we derive an estimate for the amount of snow-covered ice. It is estimated that the area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. We perform a series of sensitivity experiments in which inter-annual changes in snow-covered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall.     

2013年汛期气候预测的先兆信号及其应用

本文系统回顾了2013年汛期气候预测的主要先兆信号。其信号特征是：2013年前期赤道中东太平洋呈正常略偏冷的状态、冬季北极海冰异常偏少、青藏高原积雪偏少,这些特征对后期东亚夏季风有明显影响。通过对前期先兆信号的分析,国家气候中心比较准确地预测了东亚夏季风偏强、我国夏季主要多雨带偏北的特征,以及南海夏季风爆发偏早、长江中下游入梅偏晚且雨量少雨期短、华北雨季提前雨量偏多的季节内过程演变趋势。最后对汛期气候预测存在的不足进行了分析和讨论。     

Arctic climate change in 21st century CMIP5 simulations with EC-Earth

The Arctic climate change is analyzed in an ensemble of future projection simulations performed with the global coupled climate model EC-Earth2.3. EC-Earth simulates the twentieth century Arctic climate relatively well but the Arctic is about 2 K too cold and the sea ice thickness and extent are overestimated. In the twenty-first century, the results show a continuation and strengthening of the Arctic trends observed over the recent decades, which leads to a dramatically changed Arctic climate, especially in the high emission scenario RCP8.5. The annually averaged Arctic mean near-surface temperature increases by 12 K in RCP8.5, with largest warming in the Barents Sea region. The warming is most pronounced in winter and autumn and in the lower atmosphere. The Arctic winter temperature inversion is reduced in all scenarios and disappears in RCP8.5. The Arctic becomes ice free in September in all RCP8.5 simulations after a rapid reduction event without recovery around year 2060. Taking into account the overestimation of ice in the twentieth century, our model results indicate a likely ice-free Arctic in September around 2040. Sea ice reductions are most pronounced in the Barents Sea in all RCPs, which lead to the most dramatic changes in this region. Here, surface heat fluxes are strongly enhanced and the cloudiness is substantially decreased. The meridional heat flux into the Arctic is reduced in the atmosphere but increases in the ocean. This oceanic increase is dominated by an enhanced heat flux into the Barents Sea, which strongly contributes to the large sea ice reduction and surface-air warming in this region. Increased precipitation and river runoff lead to more freshwater input into the Arctic Ocean. However, most of the additional freshwater is stored in the Arctic Ocean while the total Arctic freshwater export only slightly increases.     

Arctic haze: Perturbation to the radiation field

Summary A model of the polluted arctic troposphere is constructed to estimate the magnitude and seasonal variation of the climate forcing function of arctic haze. Using a pill-box bathtub model for the Arctic and envisioning it to be filled with pollution from industrial sources in Eurasia, we estimate that maximum climate perturbation from arctic contamination occurs in the spring months. The major perturbation to the radiation budget is a lowering of the albedo (heating) of the earth-atmosphere system around the vernal equinox and is due to a trace amount (about 5% by mass) of black carbon associated with the removal-resistant submicron mode of aerosols. The black carbon over the reflecting polar ice/snow introduces a heating of about 1.5 degree per day into the haze layer.With 8 Figures     

北极海冰融化影响东亚冬季天气和气候的研究进展以及学术争论焦点问题

北极历来是影响东亚冬季天气、气候的关键区域之一。北极表面增暖要比全球平均快2~3倍,即所谓北极的放大效应。随着全球增暖的持续以及北极海冰的持续融化,北极的生态环境正在发生显著的变化,进而可能对北半球中、低纬度的天气、气候产生影响。本文概述了有关北极海冰融化影响冬季东亚天气、气候的主要研究进展,特别是自2000年以来,北极海冰异常偏少影响东亚冬季气候变率以及极端严寒事件的可能途径、存在的科学问题,以及学术界的争论焦点。秋、冬季节是北极海冰快速形成时期,此时北极海冰对大气环流的影响要强于大气对海冰的影响。近二十年来的研究结果表明,北极海冰异常偏少,不仅影响北冰洋局地的气温和降水变化,而且通过复杂的相互作用和反馈过程,对北半球中、低纬度的天气、气候产生影响。北极海冰通过以下两个可能机制来影响东亚冬季的天气、气候:（1）北极海冰的负反馈机制;（2）由海冰异常偏少引起的平流层-对流层相互作用机制。秋、冬季节北极海冰持续异常偏少,特别是,巴伦支海-喀拉海海冰异常偏少,既可以加强冬季西伯利亚高压（东亚冬季风偏强）,也可以导致冬季风偏弱。导致海冰影响不确定性的部分原因是:（1）夏季北极大气环流状态影响北极海冰异常偏少对冬季大气环流的反馈效果;（2）冬季大气环流对北极海冰异常偏少响应的位置、强度不同造成的。秋、冬季节北极海冰持续异常偏少,在适宜的条件下（例如,前期夏季北极大气环流的热力和动力条件,有利于加强北极海冰偏少对冬季大气的反馈作用）,可以激发出有利于冬季亚洲大陆极端严寒过程的大气环流异常。目前学术界争论焦点主要集中在以下两个方面:（1）关于北极增暖、北极海冰融化对中纬度区域影响的争论;（2）关于1980年代后期以来,冬季欧亚大陆表面气温呈现降温趋势的原因。目前,有关北极海冰融化影响冬季欧亚大陆次季节变化以及极端天气、气候事件的过程和机制,我们认知非常有限,亟需开展深入细致的研究。     

Albedo of coastal landfast sea ice in Prydz Bay,Antarctica: Observations and parameterization

The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica(off Zhongshan Station)during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters(e.g., snow thickness, ice thickness, surface temperature, and air temperature) were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.     

Changes in Arctic clouds during intervals of rapid sea ice loss

We investigate the behavior of clouds during rapid sea ice loss events (RILEs) in the Arctic, as simulated by multiple ensemble projections of the 21st century in the Community Climate System Model (CCSM3). Trends in cloud properties and sea ice coverage during RILEs are compared with their secular trends between 2000 and 2049 during summer, autumn, and winter. The results suggest that clouds promote abrupt Arctic climate change during RILEs through increased (decreased) cloudiness in autumn (summer) relative to the changes over the first half of the 21st century. The trends in cloud characteristics (cloud amount, water content, and radiative forcing) during RILEs are most strongly and consistently an amplifying effect during autumn, the season in which RILEs account for the majority of the secular trends. The total cloud trends in every season are primarily due to low clouds, which show a more robust response than middle and high clouds across RILEs. Lead-lag correlations of monthly sea ice concentration and cloud cover during autumn reveal that the relationship between less ice and more clouds is enhanced during RILEs, but there is no evidence that either variable is leading the other. Given that Arctic cloud projections in CCSM3 are similar to those from other state-of-the-art GCMs and that observations show increased autumn cloudiness associated with the extreme 2007 and 2008 sea ice minima, this study suggests that the rapidly declining Arctic sea ice will be accentuated by changes in polar clouds.     

Centennial-scale climate change from decadally-paced explosive volcanism: a coupled sea ice-ocean mechanism

Northern Hemisphere summer cooling through the Holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes. However, centennial-scale climate departures, such as the Little Ice Age, must be caused by other forcings, most likely explosive volcanism and changes in solar irradiance. Stratospheric volcanic aerosols have the stronger forcing, but their short residence time likely precludes a lasting climate impact from a single eruption. Decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea-surface temperatures that exceeds that of any single eruption. Here we use a global climate model to evaluate the potential long-term climate impacts from four decadally paced large tropical eruptions. Direct forcing results in a rapid expansion of Arctic Ocean sea ice that persists throughout the eruption period. The expanded sea ice increases the flux of sea ice exported to the northern North Atlantic long enough that it reduces the convective warming of surface waters in the subpolar North Atlantic. In two of our four simulations the cooler surface waters being advected into the Arctic Ocean reduced the rate of basal sea-ice melt in the Atlantic sector of the Arctic Ocean, allowing sea ice to remain in an expanded state for?>?100 model years after volcanic aerosols were removed from the stratosphere. In these simulations the coupled sea ice-ocean mechanism maintains the strong positive feedbacks of an expanded Arctic Ocean sea ice cover, allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated, potentially resulting in a centennial-scale or longer change of state in Arctic climate. The fact that the sea ice-ocean mechanism was not established in two of our four simulations suggests that a long-term sea ice response to volcanic forcing is sensitive to the stability of the seawater column, wind, and ocean currents in the North Atlantic during the eruptions.