共查询到20条相似文献，搜索用时 31 毫秒
1.
Tyler Volk 《Climatic change》2003,58(1-2):13-19
Lenton and Wilkinson (2003), in response to me (Volk, 2002), have offered a number of important ideas for a Gaia theory of `regulatory feedbacks'between life and the global environment. After what are generally positive comments on a selection of their concepts, I focus my reply on one specific point of disagreement. Contrary to the claim of Lenton and Wilkinson, nitrogen fixation is merely another example of how a by-product affects the shared environment among organisms. For Gaia theory to properly incorporate evolution by natural selection, we must distinguish between life's products and by-products. Because organisms evolve in environments altered by these by-products, I continue to support the idea that feedback loops in the biosphere contain segments based solely upon by-products of organisms' metabolisms. 相似文献
2.
The Gaia Hypothesis: Fact, Theory, and Wishful Thinking 总被引：4，自引：0，他引：4
James W. Kirchner 《Climatic change》2002,52(4):391-408
Organisms can greatly affect their environments, and the feedback coupling between organisms and their environments can shape the evolution of both. Beyond these generally accepted facts, the Gaia hypothesis advances three central propositions: (1) that biologically mediated feedbacks contribute to environmental homeostasis, (2) that they make the environment more suitable for life, and (3) that such feedbacks should arise by Darwinian natural selection. These three propositions do not fare well under close scrutiny. (1) Biologically mediated feedbacks are not intrinsically homeostatic. Many of the biological mechanisms that affect global climate are destabilizing, and it is likely that the net effect of biological feedbacks will be to amplify, not dampen, global warming. (2) Nor do biologically mediated feedbacks necessarily enhance the environment, although it will often appear as if this were the case, simply because natural selection will favor organisms that do well in their environments – which means doing wellunder the conditions that they and their co-occurring species have created. (3) Finally, Gaian feedbacks can evolve by natural selection, but so can anti-Gaian feedbacks. Daisyworld models evolve Gaian feedback because they assume that any trait that improves the environment will also give a reproductive advantage to its carriers (over other organisms that share the same environment). In the real world, by contrast, natural selection favors any trait that gives its carriers a reproductive advantage over its non-carriers, whether it improves or degrades the environment (and thereby benefits or hinders its carriers and non-carriers alike). Thus Gaian and anti-Gaian feedbacks are both likely to evolve. 相似文献
3.
《Global Environmental Change》2003,13(2):137-144
Human society affects environmental change but is also vulnerable to these changes. This relation has generated a number of theories that either focus on how we affect the environment or how the environment affects us. Few theories explicitly focus on the interaction. This paper will establish the range of data required to give an assessment of how likely an ecosystem is to change (which we label environmental sensitivity) and the ability of communities to adapt (social resilience). These findings allow us to generate a new method for assessing the reflexive relation between society and the environment. 相似文献
4.
The Effect of the Screen on the Mass, Momentum, and Energy Exchange Rates of a Uniform Crop Situated in an Extensive Screenhouse 总被引：2，自引：2，他引：0
The area of crops cultivated in extensive screenhouses is rapidly growing, especially in semi-arid and arid regions. Water
vapour, carbon dioxide, and sensible heat released or taken up by crops within such protected environments can substantially
alter the immediate micro-environment, which in turn, affects these fluxes. This amplified interaction between plants and
their microclimate challenges simple assessments on how partially covering the crop by a screen modifies plant water uptake
and photosynthesis. Via a newly proposed higher-order closure model, the effects of a screen on the mean flow field, turbulent
stresses, radiative and energy fluxes, as well as scalar sources, sinks, fluxes, and mean scalar concentration within screenhouses
are explored. As a starting point, an extensive screenhouse is assumed thereby reducing the sensitivity of the model results
to the precise geometric configuration of the screenhouse. The model findings for the screenhouse are presented and referenced
against their open field counterpart. The radiation modulation and changes to turbulent transport due to the presence of the
screen are investigated. In general, the presence of a screen results in a warmer and more humid environment inside the screenhouse,
promoting reductions in both canopy photosynthesis and transpiration. However, the overall effect of the screen is to enhance
water-use efficiency thereby resulting in water savings for the same amount of gross primary production. 相似文献
5.
Summary Numerical simulations of thunderstorms using initial conditions from an Oklahoma storm event on 26 April 1984 have been carried out using the Klemp-Wilhelmson cloud model. Two thermodynamic and two horizontal wind profiles are mixed to create four initial storm environments. The two initial thermodynamic profiles are designated as moderately and highly unstable. Both hodographs have considerable vertical wind shear, with the extremely unstable profile having substantially stronger storm-relative curvature shear in the lowest few kilometers, as measured by the helicity of the environment. Storms are initialized with two different temperature-perturbation warm bubbles. A variety of storms, qualitatively covering the range observed on this day, are simulated. With a strongly sheared, moderate instability environment, the two different temperature-perturbation simulations differ qualitatively, unlike the other pairs of simulations.Of particular interest is the simulation carried out with the weaker temperature-perturbation. It displays many of the characteristics of observed low-precipitation (LP) supercell storms. Without artificially suppressing rainfall, this storm produces very little precipitation over the first 6000 s of its lifetime. During this time, there is no strong downdraft at the lowest model level and vorticity at that level is much less than the values aloft. We hypothesize that LP storms can be generated by smaller initial impulses than classic supercells in environments typically associated with a supercell storm, as speculated by Bluestein and Parks (1983), since they are more susceptible to turbulent entrainment in highly sheared environments.With 15 Figures 相似文献
6.
Geoffrey Heal 《Climatic change》2009,96(3):275-297
What have we learned from the outpouring of literature as a result of the Stern Review of the Economics of Climate Change? A lot. We have explored the model space and the parameter space much more thoroughly. The Stern Review has catalyzed a fundamental rethinking of the economic case for action on climate change. We are in a position to give some conditions that are sufficient to provide a case for strong action on climate change, but we need more work before we have a fully satisfactory account of the relevant economics. In particular, we need to understand better how climate change affects natural capital—the natural environment and the ecosystems comprising it—and how this in turn affects human welfare. 相似文献
7.
随着城市化的迅猛发展,气象台站观测环境受到不同程度影响,有些台站甚至已经处于城市中心,影响了台站观测资料的代表性和准确性。本文利用2007年黄淮海渭河区199个气象台站20 km环境调查资料以及2005—2007年气温观测资料,对比分析了居民区台站和农田区台站气温观测值的差异。结果表明:居民区台站气温平均高于农田区台站0.662℃;台站周围建筑物对最低气温观测影响最大,对最高气温观测影响最小;不同季节的影响程度从大到小依次为冬季、春季、秋季、夏季;观测场周围建筑物对不同时刻气温观测的影响程度从大到小依次为02:00,20:00,08:00,14:00;随着下垫面比例的增大,两类台站的气温差不断加大。 相似文献
8.
Happiness is greater in natural environments 总被引：2，自引：0，他引：2
Links between wellbeing and environmental factors are of growing interest in psychology, health, conservation, economics, and more widely. There is limited evidence that green or natural environments are positive for physical and mental health and wellbeing. We present a new and unique primary research study exploring the relationship between momentary subjective wellbeing (SWB) and individuals’ immediate environment within the UK. We developed and applied an innovative data collection tool: a smartphone app that signals participants at random moments, presenting a brief questionnaire while using satellite positioning (GPS) to determine geographical coordinates. We used this to collect over one million responses from more than 20,000 participants. Associating GPS response locations with objective spatial data, we estimate a model relating land cover to SWB using only the within-individual variation, while controlling for weather, daylight, activity, companionship, location type, time, day, and any response trend. On average, study participants are significantly and substantially happier outdoors in all green or natural habitat types than they are in urban environments. These findings are robust to a number of alternative models and model specifications. This study provides a new line of evidence on links between nature and wellbeing, strengthening existing evidence of a positive relationship between SWB and exposure to green or natural environments in daily life. Our results have informed the UK National Ecosystem Assessment (NEA), and the novel geo-located experience sampling methodology we describe has great potential to provide new insights in a range of areas of interest to policymakers. 相似文献
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10.
力觉临场感遥操作机器人系统是一个典型的人-机-环交互系统.环境是遥操作机器人系统最终的环节,也是操作者感知和作用的对象,环境的动力学特性对整个遥操作机器人系统的控制性能会产生直接的影响.通过分析环境在力觉临场感遥操作机器人系统中的动力学特性,建立了环境在碰撞接触、线性平稳接触和非线性平稳接触3类情况下的动力学模型,并给出了模型的等效阻抗形式,为力觉临场感遥操作机器人系统的分析提供了基础. 相似文献
11.
干、湿环境下中尺度对流系统发生的环流背景和地面特征分析 总被引：10，自引：2，他引：8
对2007～2010 年暖季(6～9 月)发生在江淮和黄淮流域46 个对流天气过程的环流背景和地面特征进行了统计研究。根据整层可降水量小于或大于等于50 mm 将这些个例发生的环境分成干环境(10 个个例)和湿环境(36 个个例)。干环境下发生强对流的天气形势可以分为槽后型和副高边缘型,湿环境下的天气形势可分为槽前型、副高边缘型和槽后型,湿环境下有明显的暖湿区配合。湿环境下槽前型发生的概率最高,地面系统较为复杂,有静止锋、倒槽、冷锋和暖锋,而干环境下在本研究的个例中无槽前型发生。干、湿环境下副高边缘型的对流,从地面到500 hPa 都发生在副高后部的“S”流型的拐弯处,但部分湿环境个例低层有切变线。干环境下槽后型的发生概率较高,而湿环境下发生概率则相对较少。由这些研究表明,干、湿环境下强对流系统的触发和维持机制存在明显的差异。 相似文献
12.
This work deals with the analysis of an isolated tornadic supercell thunderstorm that took place on the plain of Friuli Venezia Giulia (Italy) causing several damage. The analysis is performed using different kind of data, looking in the available information for possible signatures that could be helpful in the forecasting and nowcasting procedures. The analysis reveals that rather than a single cause for the tornadic storm development, there is an “interaction” of several effects. In particular, a favorable environment seems to be produced by the interplay between synoptic and mesoscale environments with a fundamental role played by orography. Radar data, in particular Doppler measurements, are fundamental to the recognition and interpretation of the events but in this particular case they could give little useful information for the forecasting and nowcasting procedures. The most robust signals of an environment prone to the onset of severe deep moist convection come from the thermal gradients at the ground and by the vertical profile analysis. The reason why the event took place in that specific place and not in others is still unknown. 相似文献
13.
D. W. Sanders 《Climatic change》1986,9(1-2):187-194
Under natural conditions, balanced ecological systems develop in which the soil is protected by a cover of different plants. When man modifies the environment, in his attempts to produce more food, fiber and fuel, the ecological system is changed.This often results in the soil being exposed to the processes of accelerated water erosion. In this way, millions of hectares of land, particularly in the semi arid areas are now eroding.This paper stresses that the most important principle in controlling water erosion is to develop a new balanced system which is not only productive but which is also stable.Water erosion control schemes should therefore be based on the selection and introduction of correct land use.Examples are given of the types of measures that may be needed for cultivated, grazing and forestry lands.In some cases, a change in land use may also have to be supported by the construction of physical conservation measures. Some common examples of such measures are briefly described. 相似文献
14.
Yu-Kun QIAN Chang-Xia LIANG Zhuojian YUAN Shiqiu PENG Junjie WU Sihua WANG 《大气科学进展》2016,33(5):614-631
Based on 25-year(1987–2011) tropical cyclone(TC) best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence(EFC) exceeding 10 m s~(-1)d~(-1). Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach~120 m s~(-1)d~(-1) during the extratropical-cyclone(EC) stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear(VWS). Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs(not in the EC stage), it was found that environments with a moderate EFC value generally below ~25 m s~(-1)d~(-1) are more favorable for a TC's intensification than those with extremely large EFC. 相似文献
15.
气候变化对环境与健康的影响日益受到关注。分析了气候变化对大气环境、水环境和土壤环境的胁迫效应,阐述了气候变化对生态系统和人体健康的影响,并概述了气候变化对不同介质环境以及对生态系统与人体健康影响研究的进展。这一工作可以为今后气象与环境领域开展进一步研究提供基本框架。 相似文献
16.
In the Balearic Islands, located in the Western Mediterranean, 27 tornadoes and 54 waterspouts have been recorded during the period 1989–1999. A climatology focusing, which focuses on path length, F-scale velocity, season and time of occurrence, is presented. September and October appear to be the months with the highest frequency of appearance. The environment in which thunderstorm producing tornadoes and waterspouts developed has been analysed. Main thermodynamic stability indices reveal that no specific conditions are required for the tornado and waterspout genesis. It is also found that these events form in air masses colder than that indicated by the climatology of the region. Analyses of helicity and CAPE demonstrate that, in most of the cases, the environments were not favourable for mesocyclone formation and supercell development. 相似文献
17.
环境场对近海热带气旋突然增强与突然减弱影响的对比分析 总被引：16，自引：1，他引：15
采用动态合成分析法对近海突然加强(RITC)和突然减弱(RWTC)两类热带气旋(TC)的环境场进行对比分析。研究表明:(1)两类TC形势场差异较明显,且影响RITC的南亚高压比影响RWTC的南亚高压强。(2)突变前后RITC有充足水汽供应配合较强辐合及上升运动,TC不断获得水汽凝结释放的潜热,使得损耗的能量得到补充和加强,高层辐散突变后减弱,使得TC能量得以保存和聚集,暖心结构被不断增加的潜热能所加强,有利于TC强度的爆发。(3)RWTC突变前后中低层上升运动减弱,中低层辐合变化不大,且由于水汽供应不足,TC获得的凝结潜热不足以补充TC自身的能量损耗,并且高层的上升运动及辐散突变后均加强,这些均有利于TC中心高层暖心热量不断减少,从而促使TC强度快速减弱。 相似文献
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19.
A sensitivity of squall-line intensity to environmental static stability under various shear and moisture conditions 总被引：2，自引：0，他引：2
Squall lines develop in various climate regions having diverse environmental profiles of wind shear, moisture, and temperature. In order to explore the sensitivity of squall lines to these environmental profiles, we have performed an extensive set of numerical simulations under various shear and moisture conditions in midlatitude-continental and tropical–oceanic temperature environments. From the results of the sensitivity simulations and the analyses of the environmental parameters, it is found that the static stability in a convectively unstable layer is of primary importance in determining the strength of squall lines. Under temperature environments having the same static stability, convective available potential energy (CAPE) and precipitable water content (PWC) well describe the squall-line intensity. Vertical shear also plays an important role in determining the squall-line structure as well as the intensity through the interaction with surface cold pool. The combination of the static stability in a convectively unstable layer, CAPE, and PWC should be examined in diagnosing the intensity of squall lines that develop with an optimal shear for their environment. 相似文献
20.
Summary Surface residue is an integral part of many cropping systems, and there are opportunities to optimise its value as mulch by improving our understanding of how it affects the near surface soil physical environment. In this study we use field measurements and a coupled soil heat and water flow model to demonstrate the effects of partial surface mulch on the near surface soil physical environment. The model is based on general physical laws and allows analysis of general system behaviour in response to changes in both inputs and systems variables. The field measurements were obtained on both a clay and a sand soil from experiments carried out in the semi-arid tropics. The treatments included a bare soil surface and 0 (completely mulched), 5 cm and 15 cm bare row zones. Both measurements and simulations showed that partial surface mulch cover can have dramatic effects on the soil physical environment near the soil surface, with the development of very strong horizontal gradients across bare soil—mulched soil boundaries. They also show that bare row zones are able to act as either a source or sink for heat and water, and that the resultant soil environmental conditions will exert strong control of soil biological activity. Although model simulations did not always match exactly with the specific measurements, they did capture the major trends given by the field data. While this suggests a certain robustness about the way the processes are modeled, there are several areas in which the model needs improvement and these are highlighted in the paper.Journal Paper No. J16277 of the Iowa Agricultural Home Economics Experiment Station, Ames, IA.With 9 Figures 相似文献