Causes of climate change over the past 1000 years

Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic (pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models' value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the approximately 1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.     

Natural variability of Greenland climate, vegetation, and ice volume during the past million years

The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest developed some 400,000 years ago during the "warm" interval of marine isotope stage 11, providing a time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.     

Orbital and millennial Antarctic climate variability over the past 800,000 years

A high-resolution deuterium profile is now available along the entire European Project for Ice Coring in Antarctica Dome C ice core, extending this climate record back to marine isotope stage 20.2, approximately 800,000 years ago. Experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation. We assessed the general correspondence between Dansgaard-Oeschger events and their smoothed Antarctic counterparts for this Dome C record, which reveals the presence of such features with similar amplitudes during previous glacial periods. We suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records.     

The history of South American tropical precipitation for the past 25,000 years

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.     

Flood basalt volcanism during the past 250 million years

A chronology of the initiation dates of major continental flood basalt volcanism is established from published potassium-argon (K-Ar) and argon-argon (Ar-Ar) ages of basaltic rocks and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales. Estimated errors of the initation dates of the volcanic episodes determined from the distributions of the radiometric ages are, approximately, plus or minus 4 percent. There were 11 distinct episodes during the past 250 million years. Sometimes appearing in pairs, the episodes have occurred quasi-periodically with a mean cycle time of 32 +/- 1 (estimated, error of the mean) million years. The initiation dates of the episodes are close to the estimated dates of mass extinctions of marine organisms. Showers of impacting comets may be the cause.     

南平市近58年冬季气候变化及特征分析

利用南平市3个代表站1951-2009年气象资料,统计分析冬季降水和气温变化特征。结果显示,58年来南平市冬季平均气温呈上升趋势,平均最低气温上升明显,降水呈波动性,近10年呈相对少雨年。通过相关分析,用逐步回归方程建立冬季气温趋势预报。     

近62年来汉中市极端降水变化研究

【目的】对汉中市极端降水事件的变化趋势进行研究,为汉中地区防洪减灾和水资源调控决策提供参考依据。【方法】利用1951-2012年的汉中市逐日降水资料,采用百分位阈值划分极端降水事件,并通过滑动平均、Mann-Kendall检验、趋势分析等方法,对汉中市极端降水事件的变化趋势进行研究。【结果】近62年来,汉中市年极端降水量、年极端降水日数及年极端降水强度以年代际尺度波动变化,但总体略呈下降趋势,且年极端降水量的下降速率为-0.5mm/年。但在1987年之后,各项极端降水指标均呈明显增加趋势,年极端降水量和年极端降水日数呈显著的线性增加趋势,年极端降水量增加速率达7.52mm/年。2006-2008年,汉中市年最大日降水量、年极端降水量、年极端降水强度呈显著增多增强趋势。【结论】进入21世纪后,汉中市极端降水事件引发的自然灾害呈增加趋势,应加强调控及防治能力,预防洪涝灾害的发生。     

近10年中国土地评价研究进展

以土地评价为研究对象,通过查阅和分析近10年来中外学者发表的相关学术论文,介绍了土地评价的方法以及与GIS的综合应用,探讨了农用地评价、土地资源、适宜性和可持续性评价以及应用等方面的发展状况.     

晋江市近50年气候及农业灾害性天气变化特征分析

用福建省晋江市1961-2010年的气象资料,分析其气候变化及农业灾害性天气的特征和规律,并使用2011-2016年资料数据进行对比分析,结果表明:近半个多世纪以来,晋江市的气温和降水量呈上升趋势,日照时数呈下降趋势,气温变化存在明显的突变现象,气候变暖的最大贡献为冬季;21世纪以来降水量偏多的时段主要出现在夏季、秋季;1991年以来,春季低温阴雨、秋季寒露风天气发生概率明显减小,强度减弱,而暴雨和大暴雨天气发生次数、强度明显增加,降水相对集中,严重旱灾发生概率呈明显增加趋势。     

广西大豆育种四十年进展与展望

[目的]总结分析改革开放四十年以来广西大豆育种进展,并结合广西大豆生产需求和自身优势,对今后广西大豆育种提出相关建议,为广西大豆产业发展提供理论依据.[方法]根据公开发表文献资料及育种单位提供的内部材料,从遗传育种研发体系、新品种选育及推广、优异种质鉴评与育种亲本创制、育种方法与技术创新等方面,对改革开放开始—"八五"(S6.5-8.5)、"九五"—"十五"(S9.5-10.5)、"十一五"(S11.5)和"十二五"至今(S12.5-)4个时期的广西大豆育种进展进行总结分析,并提出今后广西大豆育种研究方向和侧重点.[结果]广西大豆育种项目、经费及其来源均迅速增加,其中项目由S6.5-8.5时期的2个增加至S12.5-的23个,经费由S6.5-8.5时期的5万元增加至S12.5-时期的1260万元,S11.5时期起建成5个大豆育种平台.至今,正式通过审定命名的大豆品种共39个,其中春大豆28个,夏大豆11个;通过国家农作物品种审定委员会和广西农作物品种审定委员会双审定品种3个,国家农作物品种审定委员会审定品种5个,广西农作物品种审定委员会审定品种31个;S6.5-8.5、S9.5-10.5、S11.5和S12.5-时期分别有4、10、12和13个品种通过审定;37个通过有性杂交选育而成,2个通过系统选育而成;高蛋白品种15个,高油品种2个,双高品种4个,菜用品种1个、高异黄酮品种2个、高抗镉金属品种2个.39个大豆品种共追溯到40个祖先亲本,平均每个育成品种有1.03个,高于全国平均水平(0.52个),且祖先亲本中,有11个是广西本地种质,占27.5%;有22个是我国其他省(区)种质,占55.0%;有7个是国外种质,占17.5%.春大豆育种骨干亲本9个,夏大豆育种骨干亲本6个.优良大豆新品种的育成及大面积推广,获省部级科技进步奖7项.广西大豆高产育种主要利用育成品种(祖先亲本含丰产性好的种质材料)或丰产性好的国外引种作为直接亲本.广西大豆种质资源丰富,至今收集保存有6000余份,但利用率低(地方种质资源利用率不足2%,野生大豆种质利用率为0).[建议]加大科研投入,丰富育种手段,加快大豆种质资源的挖掘、创新及利用,尤其是野生大豆种质资源的驯化和利用;在保持广西大豆高蛋白优势的同时,加强选育高产、优质、抗逆、耐荫、适宜机械化的绿色大豆新品种,尤其是夏大豆品种;加快特色专用型大豆新品种选育.     

Variations in terrigenous input into the deep equatorial atlantic during the past 24,000 years

Estimates of terrigenous fluxes at three different water depths at two sites in the equatorial Atlantic by normalization against excess (230)Th flux indicate that the flux of terrigenous material to the seafloor was significantly higher during the last glacial period than it is today. Fluxes started to decrease during deglaciation and reached minimal values in the middle of the Holocene. From 15,000 to 5,000 years ago, there was a substantial increase in flux with increasing water depth below 2,800 meters; this increase may reflect resuspension and lateral transport of slope and rise sediment, possibly because of intensification of deepwater circulation during that period.     

近50年夏季气候变化及对嘉定农业生产的影响

应用上海嘉定站夏季平均气温、最高气温、最低气温资料,对当地近50年夏季气温变化进行了统计分析,发现近50年气温上升明显,降水变化趋势不明显,并针对这一现象提出调整种植季节、调整农业产业结构等建议。     

过去300年东北地区林地和草地覆盖变化

东北地区是我国森林、草场资源最为丰富的地区之一。近300年来,耕地扩张、森林砍伐、草地退化等所导致的显著土地覆盖变化会通过对陆-气之间碳通量和地表反照率的改变,进而对气候系统产生影响。该文采用历史文献分析、原始潜在植被恢复等方法,结合驱动力分析,重建了过去300年东北地区林地和草地自然覆盖变化状况。可提供空间分辨率至县、时间分辨率约为100年的东北地区林地和草地覆盖数据,为气候模拟、碳排放估计等相关研究提供真实的历史数据;得到对过去300年,东北地区林地和草地覆盖变化特征的认识:过去300年,东北地区林地、草地所占比例分别减少了约15％、10％;18—19世纪,东北的天然植被覆盖几乎处于原始状态,林地、草地减少的地区主要集中在辽东、辽西等农垦区;1900—1950年为林地、草地减少最为迅速的时期,辽东、辽西的天然植被几乎均被破坏殆尽,鸭绿江流域、长白山地区森林减少十分显著,草地界线已明显向西退缩;20世纪后半期,林地覆盖在空间上呈扩张趋势,局部地区仍在减少,而草地覆盖在空间上则一直呈缩小趋势。      

Surface and deep ocean interactions during the cold climate event 8200 years ago

Evidence from a North Atlantic deep-sea sediment core reveals that the largest climatic perturbation in our present interglacial, the 8200-year event, is marked by two distinct cooling events in the subpolar North Atlantic at 8490 and 8290 years ago. An associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the Atlantic meridional overturning circulation. The existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying Laurentide Ice Sheet margin.     

Role of seasonality in the evolution of climate during the last 100 million years

A simple climate model has been used to calculate the effect of past changes in the land-sea distribution on the seasonal cycle of temperatures during the last 100 million years. Modeled summer temperatures decreased over Greenland by more than 10 degrees C and over Antarctica by 5 degrees to 8 degrees C. For the last 80 million years, this thermal response is comparable in magnitude to estimated atmospheric carbon dioxide effects. Analysis of paleontological data provides some support for the proposed hypothesis that large changes due to seasonality may have sometimes resulted in an ice-free state due to high summer temperature rather than year-round warmth. Such "cool" non-glacials may have prevailed for as much as one-third of the last 100 million years.     

安徽省近33年农业气象灾害年景评估

利用安徽省1978-2010年农作物播种面积、受灾类型及其受灾面积资料,分析农业气象灾害时空分布特征;采用灰色关联度及农业气象综合灾损模型,开展农业气象灾害年景评估.结果表明:安徽省气象灾害造成的农作物受灾面积年际波动大;农业气象灾害空间分布特点为淮北地区最重,江淮之间南部和沿江地区次之,大别山区、皖南山区以及部分城市周边相对较轻.各类气象灾害对农业受灾的影响大小依次为:暴雨洪涝＞旱灾＞风雹灾＞低温雨雪冰冻灾,其中暴雨洪涝和旱灾影响大,受灾程度重;安徽省农业气象灾害较轻年景出现频率为55％,其中灾害最轻年份为1981年,而较重年景占12％.灾害最重的年份为1991年.上述年景评估结果与安徽省农业受灾历史记录较吻合.     

转型时期俄罗斯利益集团政治参与研究:二十年来的回顾、进展与述评

俄罗斯转型时期利益集团政治参与研究,是一个跨学科的选题。具有重要的理论意义和现实意义。主要涉及三个领域:一是俄罗斯社会转型研究,二是利益集团政治研究,三是俄罗斯转型时期的利益集团政治参与研究。本文对于近二十年来的国内外的相关研究做一回顾,指出了存在的问题:研究成果较少;宏观研究多;缺乏系统性;研究广度、深度有待进一步加强;研究方法单一。并指出进一步深入研究的七大路径。     

广东省近60年极端气温的时空演变研究

极端气温反映了气候变化的趋势, 对极端气温的时空特征进行深入分析能更准确地预报各种极端天气事件的发生.根据广东省1961-2019年的36个台站逐日最高气温和最低气温资料,利用RClimDex模型、结合Mann-Kendall 非参数检验方法及空间插值、Pearson相关性分析等方法探究了广东省近60年间极端气温的时空演变特征. 结果表明,广东省在近60年间,极端气温指数的年际倾向率呈现上升趋势,在近10年以来极端气温变化趋势的上升幅度更为明显,表明广东省近60年间极端气温呈显著变暖趋势. 极端高温指数中极高值（Max Tmax, TXx）和日最低气温的极低值(Min Tmax, TNn)发生突变的时间分别在90年代末期和80年代初期,且TNn、日最低气温的极高值(Max Tmin, TNx)率先开始呈上升趋势. 空间分布上,TXx表现为离海岸线的距离越远,温度越高,日最高气温的极低值(Min Tmax, TXn)、TNn刚好与之相反,TNx则表现为纬度越高温度越低,呈现出海陆地带性和纬度地带性特征. 广东省不同区域极端气温极值指数变化趋势与整个广东省情况大体一致,但珠三角地区的极端气温极值指数上升趋势更快. 极端气温指数与自然、社会经济因素均存在相关性,其中纬度和人口数量对其影响更大.     

Comment on "Reconstructing past climate from noisy data"

von Storch et al. (Reports, 22 October 2004, p. 679) criticized the ability of the "hockey stick" climate field reconstruction method to yield realistic estimates of past variation in Northern Hemisphere temperature. However, their conclusion was based on incorrect implementation of the reconstruction procedure. Calibration was performed using detrended data, thus artificially removing a large fraction of the physical response to radiative forcing.