The physics of climate
The physics of climate
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DOI：
10.1002/j.1477-8696.1998.tb03978.x
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发表时间：
1998-04
期刊：
影响因子：
1.9
通讯作者：
W. J. Burroughs
中科院分区：
文献类型：
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作者：
W. J. Burroughs
夹在公众对厄尔尼比奥日益高涨的兴趣和京都气候变化国际谈判之间，很难想象还有什么会议能比皇家气象学会和皇家学会物理研究所在1997年10月29-30日举行的会议更具时代性。题为《气候物理学》的报告以气候研究领域的许多领军人物为特色，他们以令人震惊的坦率讨论了这些问题。理解由自然原因和人类活动引起的观测到的气候变化的关键是制作计算机模型，准确地模拟全球气候；没有其他方法。挑战是确定哪些物理过程很重要，并阐明它们是如何相互作用的，这样模型就可以探索系统任何部分的变化如何影响气候的其他部分。这需要准确地表示大气、海洋和陆地表面，以及它们彼此之间的联系方式。政府间气候变化专门委员会(气候变化专门委员会)第一工作组联合主席约翰·霍顿爵士在开幕词中指出了最困难的领域。首先，与大气中温室气体的积累有关的各种反馈过程，包括水蒸气的垂直分布和相关的云量变化，我们并不完全了解。此外，还需要更多地了解海洋的动态及其与大气的联系。最后，在没有人类活动的情况下估计气候的自然可变性是一个根本问题，这不仅需要包括准周期性的大范围波动(例如厄尔尼诺-南方生物振荡和北大西洋振荡)，而且还需要包括过去大约10000年没有发生过的剧烈变化是否可能由当前的事件触发。麻省理工学院的爱德华·赫姆兹随后介绍了他对混沌和可预测性的看法。其中包括一系列关于预测天气和气候发展的基本限制的富有启发性的观察，并利用了他作为混沌理论奠基人之一的无与伦比的经验。他讨论了观测缺乏准确性的问题和气候系统物理表示的错误之间的区别，前者始终是预测的基本限制，后者可以通过改进知识加以纠正。他的结论是，虽然天气不能在一到两周前预测，但可能有一种叫做‘气候’的东西是可以预测的；不幸的是，还不清楚全球天气系统的哪些组成部分(如果有的话)属于这一类。科罗拉多州立大学S教授考虑了一个根本问题，即我们是否可以通过采用热力学方法来研究气候系统，从而摆脱目前对日益复杂的大气环流模型(CGM)的依赖。他提出了一个变分原理，就像熵最小化准则的理论一样，它寻求定义一种与其适宜度的细节无关的状态。虽然这种方法似乎提供了一种不同的气候视角，但对我来说，这种方法如何能够迅速扩展为应对约翰·霍顿爵士概述的挑战的另一种方式并不明显。华盛顿大学的Dennzi Humann清楚地描述了云和水蒸气对气候辐射平衡所起的中心作用。一个简单的模型说明了这一点，该模型有一个海洋表面温度较高的水池，它产生了高耸的对流和邻近的一个具有低层流的冷水池。这对热带地区的环流过程提供了有趣的描述，并表明，虽然深对流对辐射平衡影响很小，但边界层云量的变化可以对气候变化起到明显的控制作用。这种低云产生了一种负反馈机制，它减少了由于CO增加一倍而导致的变暖，FIOM2.8到1.2℃。华盛顿大学的鲍勃·查尔森也探索了准确模拟云层的问题。除了很难定义云的自然性质外，人类活动的影响也有很大的不确定性，WBCH不仅会产生颗粒，还会改变自然形成的云的性质。净效应可能会使云层范围更广、持续时间更长、能够反射更多的阳光，导致气候有所降温，特别是在世界上人口较多的地区。关于我们对海洋的了解这一更广泛的问题，被Cad Wumch带入了尖锐的焦点，他在一篇关于近年来我们对海洋的看法如何变化的激动人心的分析中写道。历史上的观点是一个缓慢移动的系统，它在稳定气候方面扮演着一个巨大的飞轮的角色，可以使用粗略的分辨率和稳定的解决方案在较长的时间内对其进行建模。世界海洋环流实验等大规模海洋学研究和海洋卫星(如ERS-1、ERS-2和Topefloseidon)的观测显示，现在的情况更加复杂，各种尺度、所有时间尺度和所有深度都有湍流运动。这
Sandwiched between the rising tide of public interest in El Nbio and the international negotiations on climate change at Kyoto, it is difficult to imagine a more topical conference than that held by the Royal Meteorological Society and the Institute of Physics at the Royal Society on 29-30 October 1997. Entitled “The Physics of Climate”, it featured many of the leading figures in the world of climatic studies, who cofionted the issues with refieshing candour. The key to understanding observed climatic change due to both natural causes and human activities is to produce computer models, which accurately simulate the global climate; there is no other way forward. The challenge is to establish which physical processes matter and to formulate how they interact, so that models can explore how changes in any part of the system can affect the rest of the climate. This requires accurate representation of the atmosphere, the oceans, and land surfaces, and how they are linked to one another. In the opening address, Sir John Houghton, coChairman of Working Group I of the Intergovernmental Panel on Climate Change (PCC), identified the most difficult areas. First, there are the various feedback processes associated with the build-up of greenhouse gases in the atmosphere, including the vertical distribution of water vapour and associated alterations in cloudiness, which we do not fully understand. Then there is the need to know more about the dynamics of the oceans and their links with the atmosphere. Finally, there is the fundamental question of estimating the natural variability of climate in the absence of human activities, which need to cover not only quasi-cyclic large-scale fluctuations (e.g. the El Nbio-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)), but also whether past sudden dramatic changes, which have not occurred for some 10000 years or so, could be triggered by current events. Edward h m z , Massachusetts Institute of Technology (m), then presented his thinking on chaos and predictability. Thls included a series of illuminating observations on the fundamental limits to predicting weather and climate developments, and drew on his unrivalled experience as one of the founding fathers of chaos theory. He discussed the difference between the problems of the lack of accuracy of observations, which was something that would always be a fundamental limit to predictions, and errors in the physical representation of the climate system, which could be corrected with improving knowledge. He concluded that while the weather cannot be forecast more than a week or two ahead there might be something called ‘climate’ which was predictable; unfortunately it was not evident which, if any, of the components of the global weather system fell into th is category. G r m e S t e p h , Colorado State University, considered the underlying question of whether we could get away from the current reliance on general circulation models (CGMS), with their ever-mounting complexity, by adopting a thermodynamic approach to the climate system. He proposed a variational principle which, like the theory of the criterion of the minimisation of entropy, seeks to define a state which is independent of the details of its degrees of fitedom. While this approach appeared to provide a different perspective on the climate, it was not evident to me how th is could be expanded rapidly into an alternative way of grappling with the challenges outlined by Sir John Houghton. Dennzi Humann, University of Washington, presented a clear description of the central r6le played by clouds and water vapour on the radiative balance of the climate. This was illustrated by a simple model with a pool of high ocean surface temperature, which generated towering convection and an adjacent cool pool with low-level stratus. This provided an intriguing representation of circulation processes in the tropics and showed that, while deep convection had little effect on the radiative balance, changes in the amount of boundary-layer clouds could exert a sigdicant control on climate change. This low cloud produced a negative feedback mechanism which reduced the warming due to a doubling of CO, fiom 2.8 to 1.2degC. The problem of accurately modelling clouds was also explored by Bob Charlson, University of Washington. Apart fiom the great difficulty of defining the clouds’ natural properties, there are major uncertainties about the impact of human activities, wbch will not only produce particulates but also alter the properties of naturally occurring clouds. The net effect is likely to make clouds more extensive, longer lasting, and able to reflect more sunlight, leading to some cooling of the climate especially in the more populous regions of the world. The wider question of what we know about the oceans was brought into sharp focus by Cad Wumch, my in a stimulating analysis of how our view of the oceans has changed in recent years. The historical view was of a slowly moving system, which acted as a giant flywheel in steadying the climate, and which could be modelled over lengthy periods using coarse resolution and steady-state solutions. Large-scale oceanographic studies, such as the World Ocean Circulation Experiment, and the observations of oceanographic satellites (e.g. ERS-1, ERS-2 and Topefloseidon) now show a more complicated situation with turbulent motions taking place on every scale, on all time-scales, and at all depths. This