Early Paleocene vegetation and climate in Jiayin, NE China

The pollen and spores of the Wuyun Formation (Danian, Early Paleocene) from Jiayin County, Heilongjiang Province, Northeast China, are studied in this paper. The Danian vegetation at Wuyun was composed of mixed temperate and subtropical broad-leaved forest, with an admixture of conifers. The climatic parameters, obtained by the Coexistence Approach based on the palynological and megafossil data, are Mean Annual Temperature of 14.8–16.8°C, Mean Annual Precipitation of 815.8–1,571.8 mm. Combining other climatic parameters in the Tertiary, we obtained the latitudinal temperature gradients: 0.24 in Paleocene, 0.1 in Eocene, 0.45 in Miocene and 0.55 in Pliocene, in the area of East Asia. All these values and modern latitudinal gradient of 0.7 suggest a climatic transition from Paleocene to today: the temperature at higher latitudes first increased then decreased gradually during last 65 Ma, while it changed slightly in lower latitudes.     

Modeling impacts of vegetation in western China on the summer climate of northwestern China

Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.     

MM5对中全新世时期中国地区气候的模拟研究

MM5模式结果与地质记录的对比表明,这个模式系统可以较好地模拟中全新世时气候的变化,特别是模式模拟的降水变化与地质记录吻合得较好.区域模式的结果比全球模式结果有所改进.模式结果显示:与现代相比,中全新世时,中国地区的气温升高,夏季升温超过冬季.同时,中国的内蒙古东部地区、东北地区和华北地区降水显著增加;而中国的华东、华中、华南和西南地区降水减少.中国东部30°N以北地区夏季风增强;中国东部的冬季风减弱.从一系列敏感试验结果,可以发现:在中全新世时,中国地区的气温、风场和降水的变化主要受大尺度环流背景场变化的影响,其对降水变化的影响超过50%.其次受地表状况和植被变化的影响,植被的变化主要影响中国东部地区,使得在冬季和夏季中国地区均升温;而且,对华北部分地区降水变化的影响最大超过25%.地球轨道的变化使得中全新世时太阳辐射的季节变化较大,造成中全新世时中国地区在冬季降温,在夏季升温;同时,对东北和华北地区的降水有重要影响,其影响与植被变化的影响相当.中全新世时,大气中CO2的体积混合比为280×10-6,CO2的变化使得中伞新世时气温降低,但量级较小.影响中全新世时中国地区气候变化的因子,按影响程度由大到小的排序为:大尺度环流背景场、植被变化、地球轨道参数变化和CO2浓度变化.     

Chemical composition and source apportionment of rainwater at Guiyang, SW China

This study systematically analyzed the concentrations of cations and anions and determined the pH in the rainwater at Guiyang from Oct. 2008 to Sep. 2009. The pH in the rainwater varied between 3.35 and 9.99 with a volume-weighted mean value of 4.23. The volume-weighted mean concentrations of anions followed the order SO₄ ^2->Cl^->F^->NO₃ ^-, whereas the volume-weighted mean concentrations of cations followed the order Ca²⁺>NH₄ ⁺>Na⁺>Mg²⁺>K⁺. This finding indicates that SO₄ ^2- was the main anion and that Ca²⁺ and NH₄ ⁺ were the main cations. Significant correlations between each pair of ions (SO₄ ^2-, NO₃ ^-, NH₄ ⁺, Ca²⁺, and Mg²⁺) were observed, suggesting that CaSO₄, Ca(NO₃)₂, MgSO₄, Mg(NO₃)₂, NH₄NO₃, (NH₄)₂SO₄, and/or NH₄HSO₄ exist in the atmosphere at Guiyang. The soil-derived species (such as Ca²⁺) played an important role in the neutralization of the acidity in rainwater. The SO₄ ^2- and NO₃ ^- in the rainwater were mainly from anthropogenic sources, and their contributions accounted for 98.1 % and 94.7 %, respectively. NH₄ ⁺ was also most likely derived from anthropogenic sources, such as domestic and commercial sewage, and played an important role in the neutralization of the rainwater at Guiyang.     

Holocene climate evolution of the Ugii Nuur basin,Mongolia

In order to evaluate the Holocene palaeoenvironmental evolution of the Ugii Nuur basin, central Mongolia, investigations on chemical and mineralogical properties of lacustrine sediments were carried out on a 630 cm sediment core from lake Ugii Nuur. The interpretation of the record is based on a principal component analysis （PCA） of the elemental composition of the samples. The results show that lacustrine deposition started at 10.6 kyr BP. Low lake level conditions were identified during the Early Holocene （10.6-7.9 kyr BP）. The Mid Holocene （7.9-4.2 kyr BP） was characterized by generally higher lake levels and thus higher moisture supply, but it experienced strong climatic fluctuations. Arid conditions prevailed from 4.2-2.8 kyr BP and were followed by a stable, more humid phase until today.     

A review on vegetation models and applicability to climate simulations at regional scale

The lack of accurate representations of biospheric components and their biophysical and biogeochemical processes is a great source of uncertainty in current climate models. The interactions between terrestrial ecosystems and the climate include exchanges not only of energy, water and momentum, but also of carbon and nitrogen. Reliable simulations of these interactions are crucial for predicting the potential impacts of future climate change and anthropogenic intervention on terrestrial ecosystems. In this paper, two biogeographical (Neilson’s rule-based model and BIOME), two biogeochemical (BIOME-BGC and PnET-BGC), and three dynamic global vegetation models (Hybrid, LPJ, and MC1) were reviewed and compared in terms of their biophysical and physiological processes. The advantages and limitations of the models were also addressed. Lastly, the applications of the dynamic global vegetation models to regional climate simulations have been discussed.     

中国西天山季节性积雪热力特征分析

利用中国天山积雪雪崩站干、湿雪雪层内每隔5min一次的10层雪温数据,探讨了一次降雪过程后干、湿雪的雪层温度特征,对比分析了干、湿雪的雪面能量平衡方程中各分量的差异。结果表明:(1)整个冬半年积雪各层温度基本<0℃,雪温日变化振幅由雪面向下逐渐减小,积雪深层温度的波峰(谷)值稍滞后于积雪浅层温度极值1～2天。(2)湿雪冷中心的出现时间早于干雪,暖中心的出现时间晚于干雪,太阳辐射对湿雪的穿透深度大于干雪。(3)雪层温度振幅变化与能量吸收随雪深都呈指数衰减分布。积雪密度越大,吸收系数越小,穿透深度越大。(4)干雪雪面的感热通量和潜热通量几乎都为负值,积雪积累。湿雪雪面的潜热通量与感热通量方向相反,互相抵消,所以净辐射是导致湿雪消融的主要因素。     

Effects of a melted greenland ice sheet on climate, vegetation, and the cryosphere

This paper investigates the possible implications for the earth-system of a melting of the Greenland ice-sheet. Such a melting is a possible result of increased high latitude temperatures due to increasing anthropogenic greenhouse gas emissions. Using an atmosphere-ocean general circulation model (AOGCM), we investigate the effects of the removal of the ice sheet on atmospheric temperatures, circulation, and precipitation. We find that locally over Greenland, there is a warming associated directly with the altitude change in winter, and the altitude and albedo change in summer. Outside of Greenland, the largest signal is a cooling over the Barents sea in winter. We attribute this cooling to a decrease in poleward heat transport in the region due to changes to the time mean circulation and eddies, and interaction with sea-ice. The simulated climate is used to force a vegetation model and an ice-sheet model. We find that the Greenland climate in the absence of an ice sheet supports the growth of trees in southern Greenland, and grass in central Greenland. We find that the ice sheet is likely to regrow following a melting of the Greenland ice sheet, the subsequent rebound of its bedrock, and a return to present day atmospheric CO₂ concentrations. This regrowth is due to the high altitude bedrock in eastern Greenland which allows the growth of glaciers which develop into an ice sheet.     

Impact of vegetation feedback on the mid-Pliocene warm climate

Studying the vegetation feedback during warm periods of the past can lead to better understanding of those in the future.In this study,we conducted several simulations to analyze vegetation feedback during the mid-Pliocene warm period.The results indicate that the main features of vegetation change in the mid-Pliocene were a northward shift of needleleaf tree,an expansion of broadleaf tree and shrub,and a northward expansion of grass,as compared to the pre-industrial period.The global annual mean warming ratio caused by vegetation feedback was 12.1％,and this warming ratio was much larger in northern middle and high latitudes.The warming caused by vegetation change was directly related to the surface albedo change and was further amplified by snow/sea ice-albedo feedback.     

Hydrologic-energy balance constraints on the Holocene lake-level history of lake Titicaca, South America

A basin-scale hydrologic-energy balance model that integrates modern climatological, hydrological, and hypsographic observations was developed for the modern Lake Titicaca watershed (northern Altiplano, South America) and operated under variable conditions to understand controls on post-glacial changes in lake level. The model simulates changes in five environmental variables (air temperature, cloud fraction, precipitation, relative humidity, and land surface albedo). Relatively small changes in three meteorological variables (mean annual precipitation, temperature, and/or cloud fraction) explain the large mid-Holocene lake-level decrease (85 m) inferred from seismic reflection profiling and supported by sediment-based paleoproxies from lake sediments. Climatic controls that shape the present-day Altiplano and the sediment-based record of Holocene lake-level change are combined to interpret model-derived lake-level simulations in terms of changes in the mean state of ENSO and its impact on moisture transport to the Altiplano.     

Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation model

The response of the climate at high northern latitudes to slowly changing external forcings was studied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO₂ and CH₄ content were prescribed. The experiment reveals an early optimum (9–8 kyr BP) in most regions, followed by a 1–3°C decrease in mean annual temperatures, a reduction in summer precipitation and an expansion of sea-ice cover. These results are in general agreement with proxy data. Over the continents, the timing of the largest temperature response in summer coincides with the maximum insolation difference, while over the oceans, the maximum response is delayed by a few months due to the thermal inertia of the oceans, placing the strongest cooling in the winter half year. Sea ice is involved in two positive feedbacks (ice-albedo and sea-ice insulation) that lead regionally to an amplification of the thermal response in our model (7°C cooling in Canadian Arctic). In some areas, the tundra-taiga feedback results in intensified cooling during summer, most notably in northern North America. The simulated sea-ice expansion leads in the Nordic Seas to less deep convection and local weakening of the overturning circulation, producing a maximum winter temperature reduction of 7°C. The enhanced interaction between sea ice and deep convection is accompanied by increasing interannual variability, including two marked decadal-scale cooling events. Deep convection intensifies in the Labrador Sea, keeping the overall strength of the thermohaline circulation stable throughout the experiment.     

中国东北植被动态变化及其与气候因子的关系

基于GIMMS/NDVI数据,采用小波分析方法,在年内、年际尺度上研究了1982—2006年我国东北区域地表植被的动态变化,并分析了温度、降水等气候因子对植被动态变化的影响。结果表明:东北区域地表植被动态变化特征显著,总体上珋INDV(描述归一化植被指数(normalized difference vegetation index,NDVI)年际尺度平均状况)沿东北—西南方向递减,其中林地珋INDV及ΔINDV(描述NDVI年内变化)最大,分别为0.41和0.70,草地最小;草地区域珋INDV平均增加6.21%,耕地珋INDV有小幅增加,林地有所减小。温度、降水是影响地表植被动态变化的重要因素,总体上与温度的相关系数大于与降水的相关系数,年内尺度的相关系数大于年际尺度的相关系数;在年际尺度上,NDVI与温度的相关系数以耕地最大,平均为0.60,耕地和林地区域NDVI与降水的相关性不显著;在年内尺度上,NDVI与温度、降水的相关系数以林地最大,分别为0.90和0.75;滞后相关分析表明,在年际尺度上,温度对地表植被的影响随着滞后时间的延长以近似线性的趋势降低;在年内尺度上,温度、降水的影响随着滞后时间的延长而加速减小,温度和降水对林地的影响均较快;降水的影响较温度的持续时间更短。     

中国西部植被覆盖变化对北方夏季气候影响的数值模拟

植被覆盖的变化是气候变化的成因之一,植被改变对气候的反馈可能会加强或者减缓气候的变化.文中利用CCM3全球气候模式以及20世纪70年代和90年代中国西部的植被覆盖资料进行数值模拟试验,研究了这两个时期植被变化对北方夏季区域气候的影响.模拟结果表明:植被增加的地方,地面吸收的辐射通量增加;植被减少的地方,地面吸收的辐射通量减少.地面辐射平衡的变化造成局地大气热量异常,并引起周边大气热量的调整,从而导致东亚地区夏季大气环流异常.相对于70年代的植被状况,用90年代植被模拟的北方地区对流层上层为异常气旋性环流,而中、低层为异常反气旋环流,东北亚到中国东部盛行异常北风,同时西太平洋副热带高压强度偏弱、位置偏南.这种异常环流特征说明模拟的90年代中国东部夏季风明显减弱,异常的环流形势造成华北和东北地区夏季水汽输送减少,水汽辐合减弱,年降水量减少了40 mm,呈现减少的特征,这是和观测事实是比较吻合的.降水和环流的异常还造成华北和东北夏季平均地面气温降低了0.4-0.8℃.因此近30年来中国西部植被变化可能是东亚夏季风年代际变化以及北方夏季降水减少的一个重要因素.     

气候变化对阴山北麓木本植物物候期的影响

本文基于内蒙古农牧业气象观测站1994—2015年旱柳、榆树和小叶杨三种木本植物物候观测资料及同期气候数据,采用线性倾向估计、Pearson相关系数等方法,探讨了气候变化对阴山北麓木本植物物候的影响。结果表明：近22 a,阴山北麓旱柳、榆树和小叶杨的花芽开放期和落叶末期均表现为提前趋势,且落叶末期提前幅度较大,平均每10 a分别提前2.9 d、3.6 d、4.6 d。生长季缩短,平均生长季长度为182 d。气温是影响旱柳、榆树、小叶杨春季花芽开放期的关键气象因子,春季气温每升高1℃,花芽开放期提前4.1 d;而落叶末期对降水量较为敏感,水分条件是阴山北麓木本植物落叶末期的主要限制因子。     

A method for climate and vegetation reconstruction through the inversion of a dynamic vegetation model

Climate reconstructions from data sensitive to past climates provide estimates of what these climates were like. Comparing these reconstructions with simulations from climate models allows to validate the models used for future climate prediction. It has been shown that for fossil pollen data, gaining estimates by inverting a vegetation model allows inclusion of past changes in carbon dioxide values. As a new generation of dynamic vegetation model is available we have developed an inversion method for one model, LPJ-GUESS. When this novel method is used with high-resolution sediment it allows us to bypass the classic assumptions of (1) climate and pollen independence between samples and (2) equilibrium between the vegetation, represented as pollen, and climate. Our dynamic inversion method is based on a statistical model to describe the links among climate, simulated vegetation and pollen samples. The inversion is realised thanks to a particle filter algorithm. We perform a validation on 30 modern European sites and then apply the method to the sediment core of Meerfelder Maar (Germany), which covers the Holocene at a temporal resolution of approximately one sample per 30 years. We demonstrate that reconstructed temperatures are constrained. The reconstructed precipitation is less well constrained, due to the dimension considered (one precipitation by season), and the low sensitivity of LPJ-GUESS to precipitation changes.     

Statistical and dynamical assessment of vegetation feedbacks on climate over the boreal forest

Vegetation feedbacks over Asiatic Russia are assessed through a combined statistical and dynamical approach in a fully coupled atmosphere–ocean–land model, FOAM-LPJ. The dynamical assessment is comprised of initial value ensemble experiments in which the forest cover fraction is initially reduced over Asiatic Russia, replaced by grass cover, and then the climatic response is determined. The statistical feedback approach, adopted from previous studies of ocean–atmosphere interactions, is applied to compute the feedback of forest cover on subsequent temperature and precipitation in the control simulation. Both methodologies indicate a year-round positive feedback on temperature and precipitation, strongest in spring and moderately substantial in summer. Reduced boreal forest cover enhances the surface albedo, leading to an extended snow season, lower air temperatures, increased atmospheric stability, and enhanced low cloud cover. Changes in the hydrological cycle include diminished transpiration and moisture recycling, supporting a reduction in precipitation. The close agreement in sign and magnitude between the statistical and dynamical feedback assessments testifies to the reliability of the statistical approach. An additional statistical analysis of monthly vegetation feedbacks over Asiatic Russia reveals a robust positive feedback on air temperature of similar quantitative strength in two coupled models, FOAM-LPJ and CAM3–CLM3, and the observational record. CCR Contribution # 931.     

Modeling and analysis of the potential impacts on regional climate due to vegetation degradation over arid and semi-arid regions of China

The regional climate effects of vegetation change in arid and semi-arid regions of China, which has experienced serious grassland degradation, are investigated in this study using the Weather Research and Forecasting (WRF) regional climate model. Two long-term simulation experiments (from January 1, 1980 to March 1, 2010), one with the land cover derived from the original United States Geological Survey’s (USGS) data (denoted as CTL) and the other (denoted as SEN) with a modification of the former one by vegetation degradation in arid and semi-arid regions of China, are undertaken to investigate the influence of land cover change on regional climate over arid and semi-arid regions of China. The possible mechanisms of how land cover change affects the regional climate in arid and semi-arid regions of China are also examined. The simulation results indicate that when compared with the observation datasets, the WRF model simulates the spatial pattern of observed temperature and precipitation quite well. After vegetation degradation over the arid and semi-arid regions of China, the net radiation and evaporation are reduced mainly within the degraded areas in summer, consistent with the reduction in precipitation and the increase in 2-m air temperature (T2 m).     

Arctic climate change with a 2 ∘C global warming: Timing, climate patterns and vegetation change

The signatories to United Nations Framework Convention on Climate Change are charged with stabilizing the concentrations of greenhouse gases in the atmosphere at a level that prevents dangerous interference with the climate system. A number of nations, organizations and scientists have suggested that global mean temperature should not rise over 2 ^°C above preindustrial levels. However, even a relatively moderate target of 2 ^°C has serious implications for the Arctic, where temperatures are predicted to increase at least 1.5 to 2 times as fast as global temperatures. High latitude vegetation plays a significant role in the lives of humans and animals, and in the global energy balance and carbon budget. These ecosystems are expected to be among the most strongly impacted by climate change over the next century. To investigate the potential impact of stabilization of global temperature at 2 ^°C, we performed a study using data from six Global Climate Models (GCMs) forced by four greenhouse gas emissions scenarios, the BIOME4 biogeochemistry-biogeography model, and remote sensing data. GCM data were used to predict the timing and patterns of Arctic climate change under a global mean warming of 2 ^°C. A unified circumpolar classification recognizing five types of tundra and six forest biomes was used to develop a map of observed Arctic vegetation. BIOME4 was used to simulate the vegetation distributions over the Arctic at the present and for a range of 2 ^°C global warming scenarios. The GCMs simulations indicate that the earth will have warmed by 2 ^°C relative to preindustrial temperatures by between 2026 and 2060, by which stage the area-mean annual temperature over the Arctic (60–90^°N) will have increased by between 3.2 and 6.6 ^°C. Forest extent is predicted by BIOME4 to increase in the Arctic on the order of 3 × 10⁶ km² or 55% with a corresponding 42% reduction in tundra area. Tundra types generally also shift north with the largest reductions in the prostrate dwarf-shrub tundra, where nearly 60% of habitat is lost. Modeled shifts in the potential northern limit of trees reach up to 400 km from the present tree line, which may be limited by dispersion rates. Simulated physiological effects of the CO₂ increase (to ca. 475 ppm) at high latitudes were small compared with the effects of the change in climate. The increase in forest area of the Arctic could sequester 600 Pg of additional carbon, though this effect is unlikely to be realized over next century.     

中国古诗词中的云雾雨雪

从云雾降水物理学的角度学习和分析了一些中国古诗词。内容有:1）分析和统计了唐诗300首和毛泽东诗词中用到云雾雨雪等字的百分比,其分别占总首数的45%和66%;2）列举和分析了描述自然过程、大气过程有云雨雪等字的诗(词)句;3）从现代科学观出发,分析了在一些古诗词中有关云、雨、霜、露等的理解,并作了一些评述;4）对古诗词中直接描述云、雾、雨、雪的内容进行了评论。