Response of the Greenland and Antarctic Ice Sheets to Multi-Millennial Greenhouse Warming in the Earth System Model of Intermediate Complexity LOVECLIM

Calculations were performed with the Earth system model of intermediate complexity LOVECLIM to study the response of the Greenland and Antarctic ice sheets to sustained multi-millennial greenhouse warming. Use was made of fully dynamic 3D thermomechanical ice-sheet models bidirectionally coupled to an atmosphere and an ocean model. Two 3,000-year experiments were evaluated following forcing scenarios with atmospheric CO₂ concentration increased to two and four times the pre-industrial value, and held constant thereafter. In the high concentration scenario the model shows a sustained mean annual warming of up to 10°C in both polar regions. This leads to an almost complete disintegration of the Greenland ice sheet after 3,000 years, almost entirely caused by increased surface melting. Significant volume loss of the Antarctic ice sheet takes many centuries to initiate due to the thermal inertia of the Southern Ocean but is equivalent to more than 4 m of global sea-level rise by the end of simulation period. By that time, surface conditions along the East Antarctic ice sheet margin take on characteristics of the present-day Greenland ice sheet. West Antarctic ice shelves have thinned considerably from subshelf melting and grounding lines have retreated over distances of several 100 km, especially for the Ross ice shelf. In the low concentration scenario, corresponding to a local warming of 3?C4°C, polar ice-sheet melting proceeds at a much lower rate. For the first 1,200 years, the Antarctic ice sheet is even slightly larger than today on account of increased accumulation rates but contributes positively to sea-level rise after that. The Greenland ice sheet loses mass at a rate equivalent to 35 cm of global sea level rise during the first 1,000 years increasing to 150 cm during the last 1,000 years. For both scenarios, ice loss from the Antarctic ice sheet is still accelerating after 3,000 years despite a constant greenhouse gas forcing after the first 70?C140 years of the simulation.     

The Use of Equivalent Temperature to Analyse Climate Variability

Equivalent temperature based in the NCEP/NCAR reanalysis database has been used as a simultaneous measure of temperature and humidity. Its variations during the 1958-1998 added to the effect of the inclusion of satellite data during the late seventies have been analyzed. An increase of the globally averaged equivalent temperature has been detected, the trend has been considerably greater during the first half of the study period and significant differences can be found between continental and oceanic areas. The relation of the trend with four of the main modes of climate variability has been assessed. The North Atlantic Oscillation and the Artic Oscillations are closely related to the equivalent temperature over the North Atlantic basin, extending toward Northern Asia in the second case. El Niño/Southern Oscillation and the Antarctic Oscillation seem to have a more global effect.     

利用ICESat数据解算南极冰盖冰雪质量变化

南极冰盖冰雪质量变化反映了全球气候变化,并且直接影响着全球海平面变化.ICESat测高卫星的主要任务之一就是要确定南北两极冰盖的质量变化情况并评估其对全球海平面变化的影响.本文利用2003年10月至2008年12月的ICESat测高数据,针对南极DEM分辨率有限的特殊性,通过求解坡度改正值,解决重复轨道地面脚点不重合的问题,计算了南极大陆(86°S以北区域,后文所述南极冰盖均不包括86°S以南区域)在这5年里的冰雪质量变化情况,得到东南极冰盖的质量变化为-18±20Gt/a,西南极-26±6Gt/a,南极冰盖的冰雪质量变化为-44±21Gt/a,对全球海平面上升的影响约为0.12mm·a~(-1).解算结果表明,南极冰盖质量亏损主要集中在西南极阿蒙森海岸附近冰川以及东南极波因塞特角区域.     

Global aridification in the second half of the 20th century and its relationship to large-scale climate background

The variation in surface wetness index (SWI), which was derived from global gridded monthly precipi- tation and monthly mean surface air temperature datasets of Climatic Research Unit (CRU), from 1951― 2002 over global land was analyzed in this paper. The characteristics of the SWI variation in global continents, such as North America, South America, Eurasia, Africa, and Australia, were compared. In addition, the correlation between the SWI variation of each continent (or across the globe) and the large-scale background closely related to SST variations, which affects climate change, was analyzed. The results indicate that the SWI variation shows distinct regional characteristics in the second half of the 20th century under global warming. A drying trend in the last 52 years occurred in Africa, Eurasia, Australia and South America, most obviously in Africa and Eurasia. North America shows a wetting trend after 1976. A 30-year period of dry-wet oscillation is found in South America and Australia; the latest is in a drying period in two regions. The results also revealed that global warming has changed the dry-wet pattern of the global land. South America and Australia have a drying trend despite in- creases in precipitation. This indicates that increases in surface air temperature cannot be ignored in aridification studies. Global dry-wet variation is closely related to large-scale SST variations: the drying trend in Africa and Eurasia and the wetting trend in North America are correlated with Pacific Decadal Oscillation (PDO); the interdecadal oscillation of SWI in South America and Australia is consistent with the interdecadal variation in Southern Oscillation Index (SOI).     

Experimental observation on the characteristics of the near-surface turbulence over the Antarctic ice sheets during the polar day period

Based on the ultrasonic anemometer/thermometer data in the East Antarctic coastal area ice sheets ob-tained first by Chinese scientists, turbulent intensity, kinetic energy and sensible heat of turbulence, surface roughness height drag coefficient and normalized variation were calculated and analysed using the eddy-correlation method. The results show that the values of roughness height and drag coefficient are 4.3 X 10 m and 1.8x 10 -³, respectively. These turbulent parameters have apparent diurnal variations. Project supported by the National Natural Science Foundation of China (Grant No. 49675252).     

Preconditioning and ozone hole filling in the Antarctic Spring

The temporal variations in mean zonal wind, horizontal temperature gradient at 30 mb and Total Ozone in Antarctic Spring (1 Sept.–30 Nov.) for nine seasons (1979–1987) were examined. The ozone hole filling commenced when the zonal flow decelerated to 50–58 m.sec^–1 at 30 mb. Our calculation of Rossby critical wave number with vertical shear suited for Antarctic Spring indicated that flow is preconditioned for vertical propagation of Rossby critical wave number two at this range of zonal flow. This preconditioning can be attributed to the diabatic heating in the Antarctic Spring since no sudden minor warmings/coolings have occurred during the period.     

全球变暖背景下东亚气候变化的最新情景预测

在最新的SRES A2和B2温室气体排放情景下,利用国际上7个气候模式针对未来全球变暖的数值模拟结果,本文着重分析了东亚区域气候21世纪的变化趋势. 研究揭示：中国大陆年均表面气温升高过程与全球同步,但增幅在东北、西部和华中地区较大,且表现出明显的年际变化;全球年均表面气温增幅纬向上大体呈带状分布,两极地区最为明显,并在北极地区达到最大;此外,21世纪后半段北半球高纬度地区的年平均强升温幅度主要来自于冬季增温. 在21世纪前50年,温室气体含量的增加除在一定程度上会增加青藏高原大部分夏季降水量外,不会对中国大陆其余地区的年、季节平均降水量产生较大影响;但持续的温室气体含量增加将最终导致大陆降水量几乎是全域性的增加.     

Anatomy of a eustatic event during the Turonian (Late Cretaceous) hot greenhouse climate

Sequence stratigraphic studies consider relative change in sea level (as regulated by eustasy, local tectonics and sediment supply) as the main builder of the stratigraphic record. Eustasy has generally been considered as a consequence of the growth and decay of continental ice sheets that would explain large, rapid changes in sea level, even during periods of relative global climatic warmth. However, such a mechanism has become increasingly difficult to envision during times of extreme global warmth such as the Turonian, when the equator-to-pole temperature gradient was very low and the presence of polar ice seems improbable. This paper investigates the timing and extent of sea level falls during the late Cenomanian through Turonian, especially the largest of those events, sequence boundary KTu4, which occurred during the middle to late Turonian peak of the Cretaceous hot greenhouse climate. We conclude that the amplitude of the widespread third-order sea level fall in the middle Turonian that is centered at ~91.8 Ma varies at different locations depending on the influence of dynamic topography on local tectonics and regional climatic conditions. Ice volume variations seem unlikely as a mechanism for controlling sea level at this time. However, this causal factor cannot be ruled out completely since Antarctic highlands (if they existed in the Late Cretaceous) could sequester enough water as ice to cause eustatic falls. To ascertain this requires detailed tomographic imaging of Antarctica, followed by geodynamic modeling, to determine whether high plateaus could have existed to accumulate ephemeral ice sheets. Other mechanisms for sea level change, such as transference between ground water (a small amplitude shorter time scale effect) and the ocean and entrainment and release of water from the mantle to the oceanic reservoir (a potentially large amplitude and longer time scale process), are intriguing and need to be explored further to prove their efficacy at third-order time scales.     

Climate variation since the Last Interglaciation recorded in the Guliya ice core

The climatic and environmental variations since the Last Interglaciation are reconstructed based on the study of the upper 268 m of the 309-m-long Guliya ice core. Five stages can be distinguished since the Last Interglaciation from the δ¹⁸O record in the Guliya ice core: Stage 1 (Deglaciation), Stage2 (the Last Glacial Maximum), Stage 3 (interstadial), Stage 4 (interstadial in the early glacial maximum) and Stage 5 (the Last Interglaciation). Stage 5 can be divided further into 5 substages; a, b, c, d, e. The δ¹⁸O record in the Guliya ice core indicates clearly the close correlation between the temperature variation on the Tibetan Plateau and the solar activities. The study indicates that the solar activity is a main forcing to the climatic variation on the Tibetan Plateau. Through a comparison of the ice core record in Guliya with that in the Greenland and the Antarctic, it can be found that the variation of large temperature variation events in different parts of the world is generally the same, but the variation amplitude of temperature is different. Project supported by thc Climbing Program of the State Eighth Five-Year Plan and the National Natural Science Foundation of China.     

Dissolved inorganic carbon in the ocean and climate

Changes in the climate conditions in the recent decade arouse the heightened interest to the problem of the greenhouse effect and consequently to studying the dynamics of CO₂ concentration in the ocean-atmosphere system. The modern changes in CO₂ concentration and temperature can result both from the anthropogenic influence and from the rhythms of natural processes. The results of modelling carbon equilibrium in the World Ocean water for the Quaternary suggest that the modern climate change is a part of natural climate variations having taken place for at least more than 400 thousand years.     

Microseism Variations in Response to Antarctic Seasonal Changes in Sea Ice Extent

The temporal and spatial distributions of Antarctic sea ice play important roles in both the generation mechanisms and the signal characteristics of microseisms. This link paves the way for seismological investigations of Antarctic sea ice. Here we present an overview of the current state of seismological research about microseisms on Antarctic sea ice. We first briefly review satellite remote-sensing observations of Antarctic sea ice over the past 50 years. We then systematically expound upon the generation mechanisms and source distribution of microseisms in relation to seismic noise investigations of sea ice, and the characteristics of Antarctic microseisms and relationship with sea ice variations are further analyzed. We also analyze the continuous data recorded at seismic station BEAR in West Antarctica from 2011 to 2018 and compare the microseism observations with the corresponding satellite remote-sensing observations of Antarctic sea ice. Our results show that:(1) the microseisms from the coastal regions of West Antarctica exhibit clear seasonal variations, SFM with maximum intensities every April-May and minimum intensities around every October-November; while DFM intensities peak every February-March, and reach the minimum around every October. Comparatively, the strong seasonal periodicity of Antarctic sea ice in better agreement with the observed DFM; and (2) microseism decay is not synchronous with sea ice expansion since the microseism intensity is also linked to the source location, source intensity (e.g., ocean storms, ocean wave field), and other factors. Finally, we discuss the effect of Southern Annular Mode on Antarctic sea ice and microseisms, as well as the current limitations and potential of employing seismological investigations to elucidate Antarctic sea ice variations and climate change.     

On the hourly contribution of global cloud-to-ground lightning activity to the atmospheric electric field in the Antarctic during December 1992

ELF magnetic field measurements from 10 to 135 Hz at Arrival Heights, Antarctica, are used as a proxy measure of global cloud-to-ground lightning activity. Simultaneous hourly recordings of the atmospheric electric field on the surface of the Earth at South Pole during December 1992 make possible a detailed comparison between global cloud-to-ground lightning activity and the atmospheric electric field. Although the mean diurnal variation of the ELF magnetic field and the atmospheric electric field exhibit a remarkable similarity in shape and phase, the hourly departures from their mean diurnal variations are poorly correlated. We quantify the variability of the atmospheric electric field which can be explained by global cloud-to-ground lightning activity through linear regression analysis. To estimate an accuracy of this method, it is applied to simultaneous measurements of the ELF magnetic field at Søndrestrømfjord, Greenland, for comparison. The resulting hourly contribution of global cloud-to-ground lightning activity to the atmospheric electric field in the Antarctic during December 1992 is ∼40±10%, and the contribution of global cloud-to-ground lightning activity to hourly departures from the mean diurnal variation of the atmospheric electric field is ∼25±10%.     

On the effect of emissions from aircraft engines on the state of the atmosphere

Emissions from aircraft engines include carbon dioxide, water vapour, nitrogen oxides, sulphur components and various other gases and particles. Such emissions from high-flying global civil subsonic air traffic may cause anthropogenic climate changes by an increase of ozone and cloudiness in the upper troposphere, and by an enhanced greenhouse effect. The absolute emissions by air traffic are small (a few percent of the total) compared to surface emissions. However, the greenhouse effect of emitted water and of nitrogen oxides at cruise altitude is potentially large compared to that of the same emissions near the earth’s surface because of relatively large residence times at flight altitudes, low background concentrations, low temperature, and large radiative efficiency. Model computations indicate that emission of nitrogen oxides has doubled the background concentration in the upper troposphere between 40○N and 60○N. Models also indicate that this causes an increase of ozone by about 5-20%. Regionally, the observed annual mean change in cloudiness is 0.4%. It is estimated that the resultant greenhouse effect of changes in ozone and thin cirrus cloud cover causes a climatic surface temperature change of 0.01-0.1 K. These temperature changes are small compared to the natural variability. Recent research indicates that the emissions at cruise altitude may increase the amount of stratospheric aerosols and polar stratospheric clouds and thereby have an impact on the atmospheric environment. Air traffic is increasing about 5-6% per year, fuel consumption by about 3%, hence the effects of the related emissions are expected to grow. This paper surveys the state of knowledge and describes several results from recent and ongoing research.     

Global pattern of trends in the upper atmosphere and ionosphere: Recent progress

The global pattern of long-term trends and changes in the upper atmosphere and ionosphere has been presented by Laštovička et al. [2006a. Global change in the upper atmosphere. Science 314 (5803), 1253–1254]. Trends in the mesospheric temperature, electron concentration in the lower ionosphere, electron concentration and height of its maximum in the E-region, electron concentration in the F1-region maximum, thermospheric neutral density and F-region ion temperature qualitatively agree with consequences of the enhanced greenhouse effect and form a consistent pattern of global change in the upper atmosphere. Three groups of parameters were identified as not-fitting this global pattern, the F2-region ionosphere, mesospheric water vapour, and the mesosphere/upper thermosphere dynamics. The paper reports progress in development of the global pattern of trends with emphasis to these three open problems. There are several other factors contributing to long-term trends, namely the stratospheric ozone depletion, mesospheric water vapour concentration changes, long-term changes of geomagnetic activity and of the Earth's magnetic field.     

The effect of seafloor topography in the Southern Ocean on tabular iceberg drifting and grounding

Antarctic tabular icebergs are important active components in the ice sheet-ice shelf-ocean system. Seafloor topography is the key factor that affects the drifting and grounding of icebergs, but it has not been fully investigated. This study analyzes the impact of seafloor topography on the drifting and grounding of Antarctic tabular icebergs using Bedmap-2 datasets and iceberg route tracking data from Brigham Young University. The results highlight the following points. (1) The quantitative distributions of iceberg grounding events and the tracking points of grounded icebergs are mainly affected by iceberg draft and reach their peak values in sea water with depths between 200 m and 300 m. The peak tracking point number and linear velocity of free-drifting icebergs are found in the Antarctic Slope Front (water depth of approximately 500 m). (2) The area of possible grounding regions of small-scale icebergs calved from ice shelf fronts accounts for 28% of the sea area at water depths less than 2000 m outside the Antarctic coastline periphery (3.62 million km²). Their spatial distribution is mainly around East Antarctica and the Antarctic Peninsula. The area of possible grounding regions of large tabular icebergs with long axes larger than 18.5 km (in water depths of less than 800 m) accounts for 74% of the sea area. (3) The iceberg drifting velocity is positively correlated with ocean depth in areas where the depth is less than 2000 m (R=0.85, P<0.01). This result confirms the effect of water depth variations induced by seafloor topography fluctuations on iceberg drifting velocity.     

Relation between the atmospheric characteristics in the antarctic regions and the space weather factors

Considerable variations in the cloud cover level and air temperature, related to the variations in GCRs and IMF, have been revealed based on an analysis of the meteorological and aerological data obtained at Vostok station from 1974 to 1994. It has been found out that the cloud cover at Vostok decreased, on average, by 35% a day after powerful Forbush decreases in GCRs following a considerable increase in the southward IMF component. In the years of solar activity minimum, when the variations in SCRs and GCRs are insignificant, the cloudiness and surface temperature increase on a day of B _z minimum and decrease on a day of maximum as compared to the average level. On days of B _z minimum, the air temperature rises at altitudes of h = 3.5–7 km, remains almost unchanged at an altitude of h = 8 km, and slightly decreases at higher altitudes. An increase in cloudiness at altitudes below 8 km causes warming, probably due to the greenhouse effect, because the temperature of the Earth’s surface decreases.     

Temporal Variability of Lower Stratosphere Temperature

Inter-monthly to inter-decadal global variability of lower stratosphere temperature (LST) is studied in order to improve current knowledge on its variability and trends, as well as natural and anthropogenic influences upon it. Principal Component Analysis (PCA) with S-mode Varimax rotated PCA were used. The first seven components, which explain 70% of variance make it possible to determine homogeneous LST behaviour zones with little overlap between areas, and practically no unclassified areas. Composite time series, referred to as reference series, in the core of the subregions defined by each of the PCs, were calculated in order to obtain the temporal patterns. The equatorial-tropical zone and the subtropical area display warmings caused by the eruptions of El Chichon and Mt. Pinatubo volcanoes as well as the strong influence of the Quasi-Biennial Oscillation (QBO) which leads to equatorial warming (cooling) in the west (east) phase and cooling (warming) in subtropical latitudes. Only low latitudes show some kind of global teleconnection between hemispheres. Significant correlation with several ocean/atmosphere index time-series like ENSO, Antarctic and Arctic Oscillations (AAO, AO), Arctic Circumpolar Vortex was detected over latitudinally separate regions. Antarctic and Arctic ozone hole values were contrasted with warming and cooling features registered in mid and high latitudes in both hemispheres. The LST reference series exhibit a negative trend, commonly attributed to the increase in greenhouse gases that lead to a warming of the troposphere and a cooling of the stratosphere, in all sub regions. The highest cooling rate of − 0.65 °C/ decade is detected in the Gobi desert, and the lowest values of −0.1 °C/ decade over the NE of Canada and Greenland which indicates the great longitudinal variability that the LST trends may present. The difference with other authors is mainly due to the fact that results are based either on latitudinal averages or radiosonde data.     

Regional and global effects of southern ocean constraints in a global model

Global ocean circulation models do not usually take high-latitude processes into account in an adequate form due to a limited model domain or insufficient resolution. Without the processes in key areas contributing to the lower part of the global thermohaline circulation, the characteristics and flow of deep and bottom waters often remain unrealistic in these models. In this study, various sections of the Bremerhaven Regional Ice Ocean Simulation model results are combined with a global inverse model by using temperature, salinity, and velocity constraints for the Hamburg Large Scale Geostrophic ocean general circulation model. The differences between the global model with and without additional constraints from the regional model demonstrate that the Weddell Sea circulation exerts a significant influence on the course of the Antarctic Circumpolar Current with consequences for Southern Ocean water mass characteristics and the spreading of deep and bottom waters in the South Atlantic. The influence of the Ross Sea is found to be less important in terms of global influences. However, regional changes in the Pacific sector of the Southern Ocean are found to be of Ross Sea origin. The additional constraints change the hydrographic conditions of the global model in the vicinity of the Antarctic Circumpolar Current in such a way that transport values, e.g., in Drake Passage no longer need to be prescribed to obtain observed transports. These changes not only improve the path and transport of the Antarctic Circumpolar Current but affect the meso- and large-scale circulation. With a higher (lower) mean Drake Passage transport, the mean Weddell Gyre transport is lower (higher). Furthermore, an increase (decrease) in the Antarctic Circumpolar Current leads to a decrease (increase) of the circum-Australian flow, i.e., a decrease (increase) of the Indonesian Throughflow.     

区域气候模式RegCM3对华北地区未来气候变化的数值模拟

采用高水平分辨率区域气候模式进行区域未来气候变化预估,对理解全球增暖对区域气候的潜在影响和科学评估区域气候变化有很好的参考价值.这里对国家气候中心使用25 km高水平分辨率区域气候模式RegCM3单向嵌套全球模式MIROC3.2_hires在观测温室气体(1951—2000)和IPCC A1B温室气体排放情景下(2001—2100)进行的共计150年长时间模拟结果,进行华北地区未来气温、降水和极端气候事件变化的分析.模式检验结果表明:模式对当代(1981—2000)气温以及和气温有关的极端气候事件(霜冻日数、生长季长度)的空间分布和数值模拟较好;对降水及和降水有关的极端气候事件(强降水日期、降水强度、五日最大降水量)能够模拟出它们各自的主要空间分布特征,但在模拟数值上存在偏大、偏强的误差.和全球模式驱动场相比,区域模式模拟的气温、降水和极端气候事件有明显的改进.2010—2100年华北地区随时间区域平均气温升高幅度逐渐增大,随之霜冻日数逐渐减少,生长季长度逐渐增多;同时随温室效应的不断加剧,未来降水呈增加的趋势,强降水日期和五日最大降水量逐渐增多、降水强度逐渐增大.从空间分布看,21世纪末期(2081—2100)气温、降水以及有关的极端气候事件变化比21世纪中期(2041—2060)更加明显.