Modeling the evolution of the world ocean ice cover in the 20th and 21st centuries

The current state of the simulation of sea ice cover as a component of new-generation global climate models is considered. Results from the model ensemble simulation of the observed world ocean ice cover, including its evolution in the 20th century, are analyzed, and projection of possible changes in the 21st century for three scenarios of anthropogenic forcing of the climate system are described. Unresolved problems and priorities for sea ice modeling are discussed.     

Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs

Outputs from simulations performed with current atmosphere-ocean general circulation models for the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4) are used to investigate the evolution of sea ice over the 20th and 21st centuries. We first use the results from the “Climate of the 20th Century Experiment” to assess the ability of these models to reproduce the observed sea ice cover changes over the periods 1981–2000 and 1951–2000. The projected sea ice changes over the 21st century in response to the IPCC Special Report on Emission Scenarios A1B are then examined. Overall, there is a large uncertainty in simulating the present-day sea ice coverage and thickness and in predicting sea ice changes in both hemispheres. Over the period 1981–2000, we find that the multimodel average sea ice extent agrees reasonably well with observations in both hemipsheres despite the wide differences between the models. The largest uncertainties appear in the Southern Hemisphere. The climate change projections over the 21st century reveal that the annual mean sea ice extent decreases at similar rates in both hemispheres, and that the reduction in annual mean sea ice volume is about twice that of sea ice extent reduction in the Northern Hemisphere, in agreement with earlier studies. We show that the amplitude of the seasonal cycle of sea ice extent increases in both hemispheres in a warming climate, with a larger magnitude in the Northern Hemisphere. Furthermore, it appears that the seasonal cycle of ice extent is more affected than the one of ice volume. By the end of the 21st century, half of the model population displays an ice-free Arctic Ocean in late summer.     

Changes in climatic characteristics of Northern Hemisphere extratropical land in the 21st century: Assessments with the IAP RAS climate model

Assessments of future changes in the climate of Northern Hemisphere extratropical land regions have been made with the IAP RAS climate model (CM) of intermediate complexity (which includes a detailed scheme of thermo- and hydrophysical soil processes) under prescribed greenhouse and sulfate anthropogenic forcing from observational data for the 19th and 20th centuries and from the SRES B1, A1B, and A2 scenarios for the 21st century. The annual mean warming of the extratropical land surface has been found to reach 2–5 K (3–10 K) by the middle (end) of the 21st century relative to 1961–1990, depending on the anthropogenic forcing scenario, with larger values in North America than in Europe. Winter warming is greater than summer warming. This is expressed in a decrease of 1–4 K (or more) in the amplitude of the annual harmonic of soil-surface temperature in the middle and high latitudes of Eurasia and North America. The total area extent of perennially frozen ground S _p in the IAP RAS CM changes only slightly until the late 20th century, reaching about 21 million km², and then decreases to 11–12 million km² in 2036–2065 and 4–8 million km² in 2071–2100. In the late 21st century, near-surface permafrost is expected to remain only in Tibet and in central and eastern Siberia. In these regions, depths of seasonal thaw exceed 1 m (2 m) under the SRES B1 (A1B or A2) scenario. The total land area with seasonal thaw or cooling is expected to decrease from the current value of 54–55 million km² to 38–42 in the late 21st century. The area of Northern Hemisphere snow cover in February is also reduced from the current value of 45–49 million km² to 31–37 million km². For the basins of major rivers in the extratropical latitudes of the Northern Hemisphere, runoff is expected to increase in central and eastern Siberia. In European Russia and in southern Europe, runoff is projected to decrease. In western Siberia (the Ob watershed), runoff would increase under the SRES A1B and A2 scenarios until the 2050s–2070s, then it would decrease to values close to present-day ones; under the anthropogenic forcing scenario SRES B1, the increase in runoff will continue up to the late 21st century. Total runoff from Eurasian rivers into the Arctic Ocean in the IAP RAS CM in the 21st century will increase by 8–9% depending on the scenario. Runoff from the North American rivers into the Arctic Ocean has not changed much throughout numerical experiments with the IAP RAS CM.     

Variations of temperature and hydrologic regimes of the region of Ladoga Lake catchment basin in the 20th and 21st centuries according to data of modern climate models

In the region of the Ladoga Lake catchment basin, we perform data analysis on a set of different modern climate models with different Intergovernmental Panel on Climate Change (IPCC) scenarios in the 20th and 21st centuries; this set includes global models such as ECHAM4/OPYC3 (Max Planck Institute for Meteorology, Germany), HadCM3 (Hadley Centre Coupled Model, England), and RCAO (Rossby Centre Regional Atmosphere-Ocean) models. Two variants of the boundary conditions for these climate models (Rossby Center of Swedish Meteorological and Hydrological Institute, SMHI) are used. We present the results of a diagnosis of the model-predicted near-surface temperature (T), precipitation (P), evaporation (E), and water budget (P-E) in the Ladoga Lake catchment based on their comparison with empirical data in twentieth century. We obtain scenario estimates of the variations of temperature and hydrologic regimes of Ladoga Lake catchment when IPCC IS92a, A2, and B2 scenarios are fulfilled, describing the prognostic growth of anthropogenic emissions of greenhouse gases and aerosol to the atmosphere, and discuss the recommendations for their use.     

Climate and carbon cycle variations in the 20th and 21st centuries in a model of intermediate complexity

The climate model of intermediate complexity developed at the Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM), has been supplemented by a zero-dimensional carbon cycle model. With the carbon dioxide emissions prescribed for the second half of the 19th century and for the 20th century, the model satisfactorily reproduces characteristics of the carbon cycle over this period. However, with continued anthropogenic CO₂ emissions (SRES scenarios A1B, A2, B1, and B2), the climate-carbon cycle feedback in the model leads to an additional atmospheric CO₂ increase (in comparison with the case where the influence of climate changes on the carbon exchange between the atmosphere and the underlying surface is disregarded). This additional increase is varied in the range 67–90 ppmv depending on the scenario and is mainly due to the dynamics of soil carbon storage. The climate-carbon cycle feedback parameter varies nonmonotonically with time. Positions of its extremes separate characteristic periods of the change in the intensity of anthropogenic emissions and of climate variations. By the end of the 21st century, depending on the emission scenario, the carbon dioxide concentration is expected to increase to 615–875 ppmv and the global temperature will rise by 2.4–3.4 K relative to the preindustrial value. In the 20th–21st centuries, a general growth of the buildup of carbon dioxide in the atmosphere and ocean and its reduction in terrestrial ecosystems can be expected. In general, by the end of the 21st century, the more aggressive emission scenarios are characterized by a smaller climate-carbon cycle feedback parameter, a lower sensitivity of climate to a single increase in the atmospheric concentration of carbon dioxide, a larger fraction of anthropogenic emissions stored in the atmosphere and the ocean, and a smaller fraction of emissions in terrestrial ecosystems.     

北极海冰与北半球大气环流及气温的相关性分析

利用NASA的北极海冰密集度资料(分辨率1.0°×0.25°,时间1979.10-2002.8)对冬季(12-2月)鄂霍次克海到白令海(42°-66°N、131°-158°W)的海冰场进行EOF分解,得到特征向量的空间分布及时间系数.利用NCEP再分析月资料(分辨率2.5°×2.5°,时间1979-2002年),采用合成分析的方法,分别对该区域海冰分布第一特征向量时间系数超过+0.5和低于-0.5年份做冬季500hPa高度、l000hPa高度、1000hPa气温的合成距平场.分析结果表明该区域的海冰分布与北半球中高纬度的大气环流和气温有显著的关系,同一模态下的海冰分布反位相时对应的大气状况也有明显的相反趋势.     

Regional structure of surface-air temperature fluctuations in northern Eurasia in the latter half of the 20th and early 21st centuries

The first empirical orthogonal functions (EOF1s) of surface-air temperature fluctuations for Russia and its neighboring states within the period 1950–2005 are analyzed. The spatial distribution of the EOF1, the first principal components (PC1s) of the observed air temperature (averaged over the summer, July, December–March, and individual winter months), and their time variations (including trend parameters, some spectral characteristics, and the quantitative indices of relation to circulation indices (on the basis of multiple step-by-step regression)) are considered. Significant seasonal differences have been revealed: the winter air-temperature fluctuations are characterized by a higher (when compared to summer) spatial coherence, especially in the latitudinal direction. The EOF1 of the winter air temperature (averaged over December–March) describes its fluctuations for almost all of Russia; in this case, no less than 70% of the PC1 variability is due to variations in several circulation indices; the main contribution (60%) is made by both the North Atlantic Oscillation (NAO) and Scandinavian (SCAND) indices. On the whole, over the periods 1951–2005 and 1971–2005, the NAO contribution exceeds the SCAND contribution to the winter temperature variability; the NAO is associated with a more rapid increase in air temperature in 1968–1997 and with the 1971–2005 trend. In 1951–1970 the main contribution to air temperature fluctuations was made by SCAND; the SCAND contribution exceeds the NAO contribution in the periods 1951–2005 and 1971–2005. The 1971–2005 and 1968–1997 temperature trends are completely described by variations in the NAO (70%) and SCAND (30%) indices for January and February.     

Variability of the Southern Hemisphere Subtropical Jet Stream in the Second Half of the 20th Century and Early 21st Century

Latitudinal position and wind speed of the Southern Hemisphere subtropical jet stream have been investigated on the basis of ERA-Interim, JRA-55, and NCEP–NCAR reanalysis data for 1948–2013. The analysis covers different time intervals in summer and winter seasons, as well as different spatial domains. It has been shown that the variability of the southern jet stream parameters in both winter and summer seasons is predominantly characterized by wind-speed weakening on the jet-stream axis and its poleward shift. The winter seasons of 2000–2013 identified a shift in the jet-stream axis toward the equator in the Atlantic (60°–0° W) and African (0°–60° E) sectors; the wind-speed increase in the Atlantic sector was statistically significant. The wind speed on the jet-stream axis in both winter and summer is closely related to the temperature difference in the upper tropospheric layer of 200–400 hPa between the latitudinal zones of 0°–30° S and 30°–60° S. A significant negative correlation (r = ?0.78) between wind speed and temperature difference has been revealed for the winter season in the upper tropospheric layer between the latitudinal zones of 30°–60° S and 60°–90° S, which can be explained by the Southern Annular Mode variability in this season. No such relationship has been found for the summer season.     

Arctic sea ice concentration and thickness data assimilation in the FIO-ESM climate forecast system

To improve the Arctic sea ice forecast skill of the First Institute of Oceanography-Earth System Model (FIO-ESM) climate forecast system, satellite-derived sea ice concentration and sea ice thickness from the Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) are assimilated into this system, using the method of localized error subspace transform ensemble Kalman ?lter (LESTKF). Five-year (2014–2018) Arctic sea ice assimilation experiments and a 2-month near-real-time forecast in August 2018 were conducted to study the roles of ice data assimilation. Assimilation experiment results show that ice concentration assimilation can help to get better modeled ice concentration and ice extent. All the biases of ice concentration, ice cover, ice volume, and ice thickness can be reduced dramatically through ice concentration and thickness assimilation. The near-real-time forecast results indicate that ice data assimilation can improve the forecast skill significantly in the FIO-ESM climate forecast system. The forecasted Arctic integrated ice edge error is reduced by around 1/3 by sea ice data assimilation. Compared with the six near-real-time Arctic sea ice forecast results from the subseasonal-to-seasonal (S2S) Prediction Project, FIO-ESM climate forecast system with LESTKF ice data assimilation has relatively high Arctic sea ice forecast skill in 2018 summer sea ice forecast. Since sea ice thickness in the PIOMAS is updated in time, it is a good choice for data assimilation to improve sea ice prediction skills in the near-real-time Arctic sea ice seasonal prediction.     

Simulation of climate changes in the 20th–22nd centuries with a coupled atmosphere-ocean general circulation model

The results of numerical experiments with a coupled atmosphere-ocean general circulation model on the reproduction of climate changes during the 20th century and on the simulation of possible climate changes during the 21st–22nd centuries according to three IPCC scenarios of variations in the concentrations of greenhouse and other gases, as well as the results of the experiments with the doubled and quadruple concentrations of CO₂, are considered. An increase in the near-surface air temperature during the 20th century and the features of the observed climate changes, such as warming in 1940–1950 and its slowing down in 1960–1970, are adequately reproduced in the model. According to the model, the air-temperature increase during the 22nd century (as compared to the end of the 20th century) varies from 2 K for the most moderate scenario to 5 K for the warmest scenario. This estimate is somewhat lower than the expected warming averaged over the data of all models presented in the third IPCC report. According to model data, in the 22nd century, under all scenarios, at the end of summer, a complete or almost complete sea-ice melting will occur in the Arctic. According to the model, by the year 2200, the sea level will vary by 20 to 45 cm as compared to the level at the end of the 20th century.     

Influence of radiation and circulation factors on climate change in Western Siberia at the end of the 20th century and beginning of the 21st century

An analysis of the air-temperature and atmospheric-pressure fields in Western Siberia is performed based on observations in 1976–2014; a comparison of temperature and pressure variability in two temporal intervals, 1976–2005 and 1985–2014, is carried out. The estimation of contributions from such climate-forming factors as radiation and circulation is performed for the same intervals. It is revealed that an increase in the annual mean ground–air temperature in the investigated region of Western Siberia was still taking place in the period of 1985–2014; however, the warming process was less active than in the 1976–2005 period. Winter months play the largest role in decreasing the temperature growth rate; during these months, the warming process was replaced by a cooling one in the second time interval. It is shown that the circulation factors, that is, the mechanisms described by indices of global circulation, played the dominant role in the period from 1985 to 2014.     

Changes in Dogger Bank macrofauna communities in the 20th century caused by fishing and climate

The macrofauna communities on the Dogger Bank (North Sea) from the 1920s, the 1950s and the 1980s to the 2000s were compared and identified five communities with similar spatial distribution throughout the 20th century. The abundance of dominant species in the five communities varied with time. Most obvious in the 1950s was the loss of the extensive Spisula and Mactra patches, which covered most of the shallow parts of the Bank in the 1920s. Since the 1980s, they have been found only as juveniles. The biological regime shift in the late 1980s caused an increase in macrofauna abundance, species numbers, diversity and southern species in most of the communities. The climate regime shift in 2001 had opposite effects in which the abundance, species numbers, diversity and southern species decreased in most of the communities. The increase in interface-feeding species and the decrease in sand-licking amphipods in the 2000s especially in the shallow Bank Community give evidence for climate driven changes in water masses, currents, storms, turbidity and food availability via planktonic or benthic primary production. Both fishing impact and climate change are hypothesised as explaining the changes in the Dogger Bank macrofauna communities.     

Severity of sea ice in the Southern Baltic Sea, Gulf of Finland and Gulf of Bothnia up 21st century

The study focused on the evaluation of probable changes in the severity of sea ice conditions occurring in 3 selected areas of the Baltic Sea: the Gulf of Bothnia, Gulf of Finland and the Southern Baltic Sea up to the year 2100. The areas have been chosen due to the high intensity of marine traffic (the Gulfs??of Bothnia and of Finland) and due to differences in sea ice conditions; winters in the Gulf of Bothnia were characterized as the most severe, whereas in the Southern Baltic were classified as the mildest ones. Consequently, three scenarios were taken into account in the study: A2 (slow rate of global economic development, market scenario), A1B (regional scenario, rapid economic development, with ecological priorities), B1 (sustainable, median economic development with strong ecological priorities), all three constructed on the basis of Special Report on Emissions Scenarios (SRES models of greenhouse gas emission). The probable changes of sea ice conditions expressed as severity index S were calculated from these models. The main results of the investigation are as follows, the variety of sea ice conditions occurring in specific regions of the Baltic will remain stable (i.e. the most severe winter conditions will still occur in Gulf of Bothnia, while the mildest in the Southern Baltic Sea). The most significant changes are likely to occur in the Southern Baltic, where some winters without ice cover in the Vistula Lagoon may happen. Nonetheless, some extremely severe winters will occur and also within specific seasons more winters with a lower number of days with ice will occur.     

21世纪格陵兰冰川融化速率对海平面变化的影响

本文利用大洋环流模式POP研究RCP4.5情景下21世纪格陵兰冰川不同的融化速率对全球及区域海平面变化的影响。结果显示:当格陵兰冰川的融化速率以每年1%增加时,全球大部分海域的动力和比容海平面变化基本不变,主要是由于格陵兰冰川在低速融化时并不会导致大西洋经向翻转流减弱。当格陵兰冰川的融化速率以每年3%和每年7%增加时,动力海平面在北大西洋副极地、大西洋热带、南大西洋副热带和北冰洋海域呈现出显著的上升趋势,这是因为格陵兰冰川快速融化导致大量的淡水输入附近海域,造成该上层海洋层化加强和深对流减弱,导致大西洋经向翻转流显著减弱;与此同时,热比容海平面在北冰洋、格陵兰岛南部海域和大西洋副热带海域显著下降,而在热带大西洋和湾流海域明显上升;此时盐比容海平面的变化与热比容海平面是反相的,这是由于大量的低温低盐水的输入,造成北大西洋副极地海域变冷变淡、大西洋经向翻转流和热盐环流显著减弱,引起了太平洋向北冰洋的热通量和淡水通量减少,导致了北冰洋海水变冷变淡,同时热带大西洋滞留了更多的高温高盐水,随着湾流被带到北大西洋,北大西洋副极地海域低温低盐的海水,被风生环流输运到副热带海域。     

海冰对北极海冰边缘区大洋光学观测的影响评估

Diffuse attenuation coefficient(DAC) of sea water is an important parameter in ocean thermodynamics and biology, reflecting the absorption capability of sea water in different layers. In the Arctic Ocean, however, sea ice affects the radiance/irradiance measurements of upper ocean, which results in obvious errors in the DAC calculation. To better understand the impacts of sea ice on the ocean optics observations, a series of in situ experiments were carried out in the summer of 2009 in the southern Beaufort Sea. Observational results show that the profiles of spectral diffuse attenuation coefficients of seawater near ice cover within upper surface of 50 m were not contaminated by the sea ice with a solar zenith angle of 55°, relative azimuth angle of 110°≤φ≤115° and horizontal distance between the sensors and ice edge of greater than 25 m. Based on geometric optics theory, the impact of ice cover could be avoided by adjusting the relative solar azimuth angle in a particular distance between the instrument and ice. Under an overcast sky, ice cover being 25 m away from sensors did not affect the profiles of spectral DACs within the upper 50 m either. Moreover, reliable spectral DACs of seawater could be obtained with sensors completely covered by sea ice.     

CMIP5气候模式模拟的北极海冰特征及其季节变化

This paper is focused on the seasonality change of Arctic sea ice extent(SIE) from 1979 to 2100 using newly available simulations from the Coupled Model Intercomparison Project Phase 5(CMIP5).A new approach to compare the simulation metric of Arctic SIE between observation and 31 CMIP5 models was established.The approach is based on four factors including the climatological average,linear trend of SIE,span of melting season and annual range of SIE.It is more objective and can be popularized to other comparison of models.Six good models(GFDL-CM3,CESM1-BGC,MPI-ESM-LR,ACCESS-1.0,Had GEM2-CC,and Had GEM2-AO in turn) are found which meet the criterion closely based on above approach.Based on ensemble mean of the six models,we found that the Arctic sea ice will continue declining in each season and firstly drop below 1 million km~2(defined as the ice-free state) in September 2065 under RCP4.5 scenario and in September 2053 under RCP8.5 scenario.We also study the seasonal cycle of the Arctic SIE and find out the duration of Arctic summer(melting season) will increase by about 100 days under RCP4.5 scenario and about 200 days under RCP8.5 scenario relative to current circumstance by the end of the 21 st century.Asymmetry of the Arctic SIE seasonal cycle with later freezing in fall and early melting in spring,would be more apparent in the future when the Arctic climate approaches to "tipping point",or when the ice-free Arctic Ocean appears.Annual range of SIE(seasonal melting ice extent) will increase almost linearly in the near future 30–40 years before the Arctic appears ice-free ocean,indicating the more ice melting in summer,the more ice freezing in winter,which may cause more extreme weather events in both winter and summer in the future years.     

Arctic climate changes and possible conditions of Arctic navigation in the 21st century

Assessments of current and expected climatic changes in the Arctic Basin are obtained, including ice-cover characteristics influencing the duration of the navigation season on the Northern Sea Route (NSR) along Eurasia and the Northwest Passage (NWP) along North America. The ability of modern climate models to simulate the average duration of the navigation season and its changes over recent decades is estimated. The duration of the navigation season for the NSR and NWP in the 21st century is estimated using an ensemble of climate models. The assessments differ significantly for the NSR and NWP. Unlike the NSR, the NWP reveals no large changes in the navigation season in the first 30 years of the 21st century. From the multimodel simulations, the expected duration of the navigation period by the late 21st century will be approximately 3 to 6 months for the NSR and 2 to 4 months for the NWP under the moderate anthropogenic SRES-A1B scenario.     

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April.     

辽东湾JZ20—2海域海冰参数的概率分布

基于辽东湾JZ2 0 2海域 1996 2 0 0 0年 4个冬季的海冰定点观测资料和海冰数值模拟结果 ,对该海域的平整冰厚、冰速、冰向和压缩强度等海冰参数进行了概率分析 ,确定了各自的分布参数 ,并对冰速和冰向进行了联合概率分析。结果表明 :冰厚和冰速分别服从对数正态分布和瑞利分布 ,海冰压缩强度服从正态分布。计算结果可用于JZ2 0 2海域海洋结构可靠性设计和疲劳累积损伤分析的海冰参数 ,也可作为其邻近海域的参考资料