第二届人地系统模型与模拟国际研讨会

正近百年来以全球变暖为首要特征的气候变化已成为国际社会和科学界广泛认同的事实。气候变暖与全球水循环、陆地生态系统、冰雪圈相互作用,对全球及区域尺度的生态环境产生了深远影响,成为制约人类社会可持续发展的重要因素。近几十年来,气候变化受到学界广泛关注,有关气候变化机理与预测、气候变化影响及气候变化的适应等一系列科     

全球气候变暖 海水变冷变淡

澳大利亚海洋学家研究发现,近20年来由于全球气候变暖,海洋温度和海水含盐量均出现下降趋势。 据最近一期法国《科学与生活》杂志报道,澳大利亚海洋学家在对1930至1980间的海洋资料数据与近年来在太平洋和印度洋的测试数据进行对比发现不同层面的海水温度均开始变凉,此外,在距海面500米到1000米深处,海水含盐量也明显下降。 科学家解释说,气温升高使南北极冰雪融化,融化的冰雪进入大洋,导致海水中含盐量降低和温度下降。     

冰川研究：数据聚焦分析

冰川／冰盖分布面积占全球陆地面积的10％，占全球淡水资源的75％。冰川／冰盖是最敏感、最直接、最易于辩识、长纪录、高分辨的气候变化信息指示器和储存体，是气候系统的重要组成部分。冰芯可以揭示以往地球的气温、降水量的变化、温室气体含量、火山喷发、沙漠演化、大气环流状况、太阳活动、生物地球化学循环等过程和事件信息。冰雪现代过程信息是冰川资源变化信息的重要组成部分，是揭示和认识过去气候环境变化不可或缺的基础数据。近100年来，全球变暖趋势明显，冰川融化相应加快，对全球海平面变化造成巨大影响。     

气候变暖谁之过

20世纪以来的全球变暖已是不可否认的事实：过去100年来全球平均表面温度升高了约0．74℃,近25年来升温出现加速。全球变暖的证据还来自于观测到的海洋和冰冻圈的明显变化,包括热带海洋的升温、海平面上升,海冰和雪盖面积减退以及普遍的冰川退缩等。科学数据表明,人类活动是导致全球变暖的主要因素。     

面向未来的车用碳中性、可再生合成燃料

自19世纪奥托发明汽油机、狄塞尔发明柴油机以来,化石燃料作为汽车的能源为人类社会和经济的发展做出了巨大贡献,但如今世界正面临由化石燃料带来的气候变化等挑战.美国国家海洋和大气管理局观测显示,2019年5月大气层中的CO2浓度达到了415.26 mg/L,这是人类有史以来的最高值,CO2浓度的增加对环境造成了一系列显著的负面影响,导致全球变暖,进而引起两极冰川融化、海平面上升、海洋风暴增多、土地干旱、沙漠化面积增大等.     

全球气候变暖对海洋生态系统的影响

2009年年底在丹麦首都哥本哈根召开的世界气候大会再次引起了世人对全球气候变化的强烈关注。对于大多数人而言,虽然他们对全球变暖引起的环境变化有着切身的感受,但是,海洋生态系统与他们的生活似乎相距遥远，他们对海洋里面发生的事情可能是一无所知。不幸的是，海洋生态系统面临的危机绝不亚于陆地生态系统。     

关注因气候变暖引发的环境问题

近百年来,由于工业的发展导致大气中CO2等温室气体浓度的增高,造成“温室效应”,并引起地球变暖,极地冰雪融化,全球海平面上升。有些学者通过模拟研究,认为如果CO2排放量增加一倍,全球平均温度将会增加2-4℃。如果按照现在CO2的排放速度,50年后全球温度将升高1．5-4．5℃,海平面将上升20-140厘米。     

走访变暖的五大洲——马克·林纳斯三年气候考察之旅

南太平洋小岛图瓦卢即将被海洋吞没,中国北部内蒙古草原开始沙漠化,秘鲁人的生命之源安第斯山上的冰雪开始融化……英国人马克·林纳斯用三年的时间,走遍五大洲,在已经受到气候变暖影响的地区向世人发出警报。     

雾霾或可提升海洋吸收温室气体能力

<正>"雾霾严重危害人类健康和陆地生态系统,但也并非一无是处。"山东大学环境研究院教授李卫军和英国伯明翰大学研究员时宗波接受科技日报记者采访时表示,雾霾颗粒物有可能增加海洋吸收二氧化碳的能力,从而部分延缓全球变暖。相关研究成果发表在近期出版的《科学·进展》杂志上。     

人类共同的使命——应对全球气候变化，加强荒漠化防治

全球气候变化已成为目前国内外政界、学界及社会群众广泛关注的焦点问题。这次全球气候变化的突出表现是，全球表面平均温度自上世纪以来已升高0．6℃，特别是近40年，由于近地球8公里内大气层温度增高，冰川出现大范围融化，极端恶劣天气频率增加，引起干旱、水资源紧张、森林衰退、草地退化、耕地沙化等灾害。不仅对自然生态系统产生巨大影响，而且对社会、经济、文化乃至人类可持续发展和生存造成威胁。     

Dual modes of the carbon cycle since the Last Glacial Maximum

The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling. During the last four transitions from glacial to interglacial conditions, over which such abrupt warmings occur, ice records indicate that the CO2 concentration of the atmosphere increased by roughly 80 to 100 parts per million by volume. But the causes of the atmospheric CO2 concentration increases are unclear. Here we present the stable-carbon-isotope composition (delta 13 CO2) of CO2 extracted from air trapped in ice at Taylor Dome, Antarctica, from the Last Glacial Maximum to the onset of Holocene times. The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years, one when climate was changing relatively slowly and another when warming was rapid, each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans. delta 13 CO2 increased between 16.5 and 9 thousand years ago by slightly more than would be estimated to be caused by the physical effects of a 5 degrees C rise in global average sea surface temperature driving a CO2 efflux from the ocean, but our data do not allow specific causes to be constrained.     

Vertical structure of recent Arctic warming

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades-a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades may have played a role. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.     

海冰的数值模拟

在前人工工作基础上建立了海冰的数值模型，建立了动量方程的迭代差分格式及连续方程的分裂差分格式。数值试验表明所建模型及差分格式的可行性，所得结果较好地反映了冰的形成及演变过程。     

Mass and volume contributions to twentieth-century global sea level rise

The rate of twentieth-century global sea level rise and its causes are the subjects of intense controversy. Most direct estimates from tide gauges give 1.5-2.0 mm yr(-1), whereas indirect estimates based on the two processes responsible for global sea level rise, namely mass and volume change, fall far below this range. Estimates of the volume increase due to ocean warming give a rate of about 0.5 mm yr(-1) (ref. 8) and the rate due to mass increase, primarily from the melting of continental ice, is thought to be even smaller. Therefore, either the tide gauge estimates are too high, as has been suggested recently, or one (or both) of the mass and volume estimates is too low. Here we present an analysis of sea level measurements at tide gauges combined with observations of temperature and salinity in the Pacific and Atlantic oceans close to the gauges. We find that gauge-determined rates of sea level rise, which encompass both mass and volume changes, are two to three times higher than the rates due to volume change derived from temperature and salinity data. Our analysis supports earlier studies that put the twentieth-century rate in the 1.5-2.0 mm yr(-1) range, but more importantly it suggests that mass increase plays a larger role than ocean warming in twentieth-century global sea level rise.     

北冰洋海平面变化的观测和研究现状

回顾北冰洋海平面观测和研究现状,总结了北冰洋海平面变化特征和变化机制。北冰洋海平面季节变化受海冰生消、蒸发降水和陆地径流季节变化的影响,由比容变化主导;年际到年代际海平面变化受北极涛动影响显著,可用风场异常导致的淡水分布来解释。盐比容变化是深水洋盆海平面变化的主导因素,由之引起的质量变化控制陆架海域和北冰洋平均的海平面变化。近期波弗特环流区域海平面上升极快,与波弗特高压持续增强及淡水积聚有关。气候变暖会导致北冰洋海平面持续上升。海冰快速减退和格陵兰岛冰川融化对北冰洋海平面变化的影响有待深入研究。数据的短缺和观测的不确定性目前仍然制约北冰洋海平面变化的研究工作,高分辨率数值模拟有望成为未来研究的重要工具。     

Antarctic ice-sheet loss driven by basal melting of ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales.     

Reconstructed changes in Arctic sea ice over the past 1,450 years

Arctic sea ice extent is now more than two million square kilometres less than it was in the late twentieth century, with important consequences for the climate, the ocean and traditional lifestyles in the Arctic. Although observations show a more or less continuous decline for the past four or five decades, there are few long-term records with which to assess natural sea ice variability. Until now, the question of whether or not current trends are potentially anomalous has therefore remained unanswerable. Here we use a network of high-resolution terrestrial proxies from the circum-Arctic region to reconstruct past extents of summer sea ice, and show that-although extensive uncertainties remain, especially before the sixteenth century-both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years. Enhanced advection of warm Atlantic water to the Arctic seems to be the main factor driving the decline of sea ice extent on multidecadal timescales, and may result from nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation. These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically forced warming.     

North Pacific seasonality and the glaciation of North America 2.7 million years ago

In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch's orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago late-summer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.     

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

The Palaeocene/Eocene thermal maximum, approximately 55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from 18 degrees C to over 23 degrees C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10 degrees C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms--perhaps polar stratospheric clouds or hurricane-induced ocean mixing--to amplify early Palaeogene polar temperatures.     

Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets, but their impact on the Greenland ice sheet in a warming climate remains uncertain. Although some studies suggest that greater melting produces greater ice-sheet acceleration, others have identified a long-term decrease in Greenland's flow despite increased melting. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4?centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62?±?16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone. Instead, it mirrors that of mountain glaciers, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet's response to climate warming.