四川人地关系日趋紧张的原因及对策

本文分四个阶段分析了四川人地关系的变化情况及人地关系的现状；以量化的方式重点分析了四川人地关系变化的原因；简要分析了人地关系的变化给农业生产所带来的影响；针对人地关系变化的主要原因,提出了缓解人地矛盾的对策。本文的重点是对四川人地关系变化原因,尤其是近期人地关系变化原因的分析,其目的是让人们认识近期四川人地关系变化的主要原因,以对症下药,采取有效的措施,缓解四川的人地矛盾。     

泸沽湖沉积物α纤维素的提取及其稳定碳同位素研究初探

湖泊沉积是环境气候变化的敏感指示器 ,在沉积过程中有机大分子α纤维素不易发生降解 ,其碳链上的C、H、O原子也不会与外界发生交换 ,故沉积物α纤维素的碳同位素能真实地反映原始环境信息。湖泊沉积物中的α纤维素含量少 ,笔者经过反复条件试验 ,得出了从湖泊沉积物提取α纤维素的简便可行的方法。泸沽湖是云贵高原上一半封闭湖泊 ,湖区人为活动干扰较微弱 ,该湖对环境变化敏感。笔者提取了泸沽湖沉积物柱的α纤维素 ,并研究了其碳同位素 ,结果表明 ,α纤维素碳同位素灵敏、精确地反映了该湖一百年来的环境信息 :泸沽湖沉积物有机质以内生为主 ;气候变化趋势为冷—暖—冷—暖。     

The Dynamics of Rural Vulnerability to Global Change: The Case of southern Africa

Research on the agricultural impacts of global change frequently emphasizesthe physical and socioeconomic impacts of climate change, yet globalchanges associated with the internationalization of economic activity mayalso have significant impacts on food systems. Together, climate change andglobalization are exposing farmers to new and unfamiliar conditions.Although some farmers may be in a position to take advantage of thesechanges, many more are facing increased vulnerability, particularly in thedeveloping world. This paper considers the dynamics of agriculturalvulnerability to global change through the example of southern Africa. Wedemonstrate that the combination of global and national economic changesis altering the context under which southern African farmers cope withclimate variability and adapt to long-term change. We find that farmers whoformerly had difficulty adapting to climatic variability may become lessvulnerable to drought-related food shortages as the result of tradeliberalization. At the same time, however, removal of national credit andsubsidies may constrain or limit adaptation strategies of other farmers,leaving them more vulnerable to climate variability and change.     

安西极旱荒漠国家级自然保护区鸟类资源的消长变化

1988-1989年安西极旱荒漠自然保护区进行了首次全面的综合考察,为了解1988年以来保护区鸟类资源的变化及其原因,2002-2004年又4次调查了该地区鸟类的种类及数量。15年来安西自然保护区的鸟类资源变化明显。鸟类种类新增加31种(其中甘肃新记录3种),但同时减少了36种。国家重点保护鸟类由原来的18种下降到16种。与1988-1989年相比,2002-2004年春季和夏季鸟类数量下降,秋季数量增加;各个季节的优势种的种类和数量都发生明显变化。影响安西自然保护区鸟类资源变化的主要原因是鸟类迁徙和人类活动。     

Impact of Climate Change on Possible Scenarios for Egyptian Agriculture in the Future

If no timely measures are taken to adapt Egyptian agriculture to possible climate warming, the effects may be negative and serious. Egypt appears to be particularly vulnerable to climate change because of its dependence on the Nile River as the primary water source, its large traditional agricultural base, and its long coastline, already undergoing both intensifying development and erosion. A simulation study characterized potential yield and water use efficiency decreases on two reference crops in the main agricultural regions with possible future climatic variation, even when the beneficial effects of increased CO₂ were taken into account. On-farm adaptation techniques which imply no additional cost to the agricultural system, did not compensate for the yield losses with the warmer climate or improve the crop water-use efficiency. Economic adjustments such as the improvement of the overall water-use efficiency of the agricultural system, soil drainage and conservation, land management, and crop alternatives are essential. If appropriate measures are taken, negative effects of climate change in agricultural production and other major resource sectors (water and land) may be lessened. This revised version was published online in August 2006 with corrections to the Cover Date.     

减少农业甲烷排放的技术选择

文章总结了温室气体甲烷的最新研究进展,包括:甲烷对全球变暖的贡献,甲烷的排放机理以及优先研究的领域;估算了我国农业甲烷排放的贡献:中国约占世界人工源甲烷排放量的10.48％,其中农业排放占一半以上;根据实验结果,提出了筛选低排放水稻品种、水分管理、施肥管理、改进饲料、使用添加剂和生长调节剂、改进遗传、促进繁育等减少稻田和反刍家畜甲烷排放的若干技术选择。     

论政府抓农业的重点所在

针对当前地方政府偏重于高利润农业项目，导致“三高”农业重点旁移的现象，阐述政府抓农业重点的必要住，指出其重点在于：（１）抓调查研究，抓政策；（２）抓农业教育与农业科研；（３）抓既带战略性而农民又力所不及和缺乏积极性的项目；（４）抓农技推广机构和队伍．而高利润的农业项目可由市场来调节．并从发展“三高’农业的需要以及当前出现的农民单施化肥的短期行为、人均耕地面积下降、地力下降、丢荒弃耕的情况等方面阐述政府重点抓培肥地力的重要性．     

Self-organized digging activity in ant colonies

Many ant species adjust the volume of their underground nest to the colony size. We studied whether the regulation of the volume of excavated sand could result from an interplay between recruitment processes and ant density. Experiments were performed with different group sizes of workers in the ant Messor sancta. When presented with a thin homogeneous sand disk, these groups excavated networks of galleries in less than 3 days. The excavation dynamics were logistic shaped, which suggests the existence of a double feedback system: a positive one resulting in an initial exponential growth phase, and a negative one leading the dynamics to a saturation phase. The total volume of excavated sand was almost proportional to the number of workers. We then developed a model in which we incorporated the quantitative behavioral rules of the workers digging activity. A positive feedback was introduced in the form of a recruitment process mediated by pheromones. The model predicts that the excavation dynamics should be logistic shaped and the excavation should almost stop despite the absence of any explicit negative feedback. Moreover, the model was able to reproduce the positive linear relationship between nest volume and colony size.Communicated by K. Ross     

Neural network modelling for the analysis of forcings/temperatures relationships at different scales in the climate system

A fully non-linear analysis of forcing influences on temperatures is performed in the climate system by means of neural network modelling. Two case studies are investigated, in order to establish the main factors that drove the temperature behaviour at both global and regional scales in the last 140 years. In particular, our neural network model shows the ability to catch non-linear relationships among these variables and to reconstruct temperature records with a high degree of accuracy. In this framework, we clearly show the need of including anthropogenic inputs for explaining the temperature behaviour at global scale and recognise the role of El Niño southern oscillation for catching the inter-annual variability of temperature data. Furthermore, we analyse the relative influence of global forcing and a regional circulation pattern in determining the winter temperatures in Central England, showing that the North Atlantic oscillation represents the driven element in this case study. Our modelling activity and results can be very useful for simple assessments of relationships in the complex climate system and for identifying the fundamental elements leading to a successful downscaling of atmosphere–ocean general circulation models.     

Governing the termination problem in solar radiation management

ABSTRACT

Technologies for Solar Radiation Management (SRM) could limit global warming by manipulating the Earth’s radiation balance. A major objection to SRM is the termination problem: the catastrophic consequences that are likely to result from its sudden discontinuation. The termination problem limits the reversibility of policy choices and poses the risk of inadvertent or enforced program collapse. It is often considered a major impediment to the governability of SRM. In a first attempt to systematically engage with the question of institutional design for resolving the termination problem, the scenarios in which the termination problem arises as well as their respective drivers are identified. Scenarios and drivers are then used to derive institutional solutions in the form of excludable benefits, scientific oversight and phase-out mechanisms. While other objections to SRM may remain valid, it is concluded that the termination problem raises fewer challenges for international governance than is usually assumed.