The Earth's Climate System: An Overview 地球气候系统导论

The Earth's Climate System: An Overview

地球气候系统导论

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Opening Remarks

开篇语

When you glance out your window on any given day, you might observe blue skies and sunshine, or perhaps grey clouds and rain. These immediate atmospheric conditions constitute what we call weather—the short-term state of the atmosphere at a particular time and place. Weather encompasses the daily fluctuations in temperature, humidity, precipitation, wind, cloud cover, and visibility that we experience and observe directly. It is the weather that determines whether you need an umbrella, whether you should wear a coat, or whether it is a good day for a picnic. Weather is inherently variable, often changing from hour to hour and from day to day, and sometimes from one moment to the next in the form of sudden thunderstorms or unexpected temperature drops.

当你某一天望向窗外时，你可能会看到蔚蓝的天空和明媚的阳光，也可能是灰色的云层和雨水。这些即时的的大气状态就是我们所说的天气（weather）——特定时间和地点大气的短期状态。天气涵盖了温度、湿度、降水、风、云量和能见度等我们直接体验和观察到的日常波动。正是天气决定了你是否需要带伞，是否应该穿外套，或者今天是否适合野餐。天气具有固有的可变性，经常逐小时甚至逐天地变化，有时还会以突如其来的雷暴或意外的气温骤降等形式在某一刻发生变化。

However, when we speak of climate, we are referring to something fundamentally different and far more comprehensive. Climate represents the long-term statistical summary of weather conditions over a extended period, typically defined as at least 30 years by the World Meteorological Organization (WMO). This statistical perspective means that climate is not characterized by individual weather events but rather by the patterns, averages, extremes, and variability of weather over time. When we describe a region as having a "Mediterranean climate," we are communicating that this area typically experiences hot, dry summers and mild, wet winters—a pattern that persists year after year and defines the general living conditions, agricultural practices, and even cultural traditions of the region.

然而，当我们谈论气候（climate）时，我们指的是根本上不同且更为全面的概念。气候代表的是在较长时间段内天气状况的长期统计摘要，世界气象组织（WMO）通常将其定义为至少30年。这种统计视角意味着气候不是以个别天气事件为特征，而是以随时间推移的天气模式、平均值、极端情况和变率为特征。当我们描述一个地区具有"地中海气候"时，我们传达的是该地区通常经历炎热干燥的夏季和温和湿润的冬季——这种模式年复一年地持续存在，定义了该地区的一般生活条件、农业实践甚至文化传统。

The distinction between weather and climate is not merely semantic; it has profound implications for how we understand, predict, and respond to environmental conditions. Weather forecasting allows us to predict atmospheric conditions days or perhaps a week or two in advance with reasonable accuracy. Climate prediction, on the other hand, deals with changes in the statistical properties of the climate system over decades or centuries. The famous aphorism often attributed to climate scientist Judith Graham captures this distinction: "Weather is your mood; climate is your personality." Just as a person's personality represents their enduring characteristics despite daily mood fluctuations, climate represents the persistent patterns of Earth's atmospheric system despite the constant bustle of daily weather variations.

天气与气候之间的区别不仅仅是语义上的；它对我们如何理解、预测和应对环境条件具有深远的影响。天气预报使我们能够以合理的准确性预测数天甚至一两周内的大气状况。另一方面，气候预测涉及的是数十年或数个世纪内气候系统统计特性的变化。这句常被归因于气候科学家朱迪思·格雷厄姆的著名格言捕捉到了这种区别的精髓："天气是你的情绪，气候是你的人格。"正如一个人的性格代表了他们尽管有日常情绪波动但仍保持的持久特征一样，气候代表了地球大气系统尽管日常天气变化不断，但仍保持的持续模式。

This conceptual distinction forms the foundation upon which the entire study of climate science rests. Throughout this book, we will explore the mechanisms that drive Earth's climate, the evidence that reveals its history and current state, and the implications of its projected future changes. In this opening chapter, we lay the groundwork by introducing the major components of Earth's climate system, explaining how these components interact through various feedback mechanisms, and demonstrating through the lens of paleoclimatology that our planet's climate has never been static.

这一概念性区别构成了整个气候科学研究的基础。在本书中，我们将探索驱动地球气候的机制，揭示其历史和当前状态的证据，并探讨其预测未来变化的影响。在这开篇章节中，我们通过介绍地球气候系统的主要组成部分、解释这些组成部分如何通过各种反馈机制相互作用，并以古气候学的视角证明我们的星球气候从未是静止的，来奠定基础。

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The Five Spheres of Earth's Climate System

地球气候系统的五大圈层

Earth's climate is not produced by the atmosphere alone. Rather, it emerges from the complex interactions among five major components, or "spheres," that together constitute the climate system. These five spheres—the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere—each play distinct yet interconnected roles in regulating Earth's energy balance, driving atmospheric circulation, and determining the distribution of heat and moisture across the planet. Understanding the climate system requires appreciating both the individual characteristics of each sphere and the ways in which they influence one another through physical, chemical, and biological processes.

地球的气候并非仅由大气产生。相反，它产生于五个主要组成部分或"圈层"之间的复杂相互作用，这些圈层共同构成了气候系统（climate system）。这五个圈层——大气圈、水圈、冰雪圈、岩石圈和生物圈——各自在调节地球能量平衡、推动大气环流以及决定热量和水分在地球上的分布方面发挥着独特却又相互关联的作用。理解气候系统需要既欣赏每个圈层的个别特征，也理解它们通过物理、化学和生物过程相互影响的方式。

The Atmosphere: Earth's Protective Envelope

大气圈：地球的保护性外壳

The atmosphere (大气圈) is perhaps the most immediately recognizable component of the climate system, as it is the thin layer of gases that surrounds Earth and within which all terrestrial life exists. Composed primarily of nitrogen (approximately 78%) and oxygen (approximately 21%), the atmosphere also contains trace amounts of argon, carbon dioxide, water vapor, and various other gases. This gaseous envelope extends from Earth's surface to altitudes of hundreds of kilometers, though the vast majority of its mass—approximately 99%—is concentrated within the first 30 kilometers, a region known as the troposphere.

大气圈（atmosphere）也许是气候系统中最容易被识别的组成部分，因为它是我们周围包围着地球并承载所有陆地生命生存的那层薄薄的气体。地球大气主要由氮气（约78%）和氧气（约21%）组成，还包含微量的氩气、二氧化碳、水蒸气和各种其他气体。这层气体外壳从地球表面延伸至数百公里的高度，但其质量的绝大部分——约99%——集中在前30公里内，这一区域被称为对流层。

The atmosphere serves multiple critical functions in the climate system. First and foremost, it acts as a selective filter for solar radiation, allowing visible light to pass through relatively unimpeded while absorbing or scattering ultraviolet radiation and infrared thermal radiation. This selective transmission creates the natural greenhouse effect (自然温室效应), a process essential for maintaining Earth's surface temperature at a level suitable for life as we know it. Without the greenhouse effect, Earth's average surface temperature would be approximately -18°C (0°F) instead of the actual average of about 15°C (59°F). The greenhouse effect operates when certain atmospheric gases—known as greenhouse gases—absorb and re-emit infrared radiation, thereby trapping heat near Earth's surface.

大气在气候系统中发挥着多个关键功能。首先也是最重要的是，它充当太阳辐射的选择性过滤器，允许可见光相对不受阻碍地通过，同时吸收或散射紫外线和红外热辐射。这种选择性传输产生了自然温室效应（natural greenhouse effect），这一过程对于将地球表面温度维持在适合我们所知的生命存在的水平至关重要。如果没有温室效应，地球的平均表面温度将约为-18°C（0°F），而不是实际的约15°C（59°F）。温室效应发生在某些被称为温室气体的气体吸收并重新发射红外辐射时，从而将热量捕获在地球表面附近。

The atmosphere also serves as a medium for heat redistribution through atmospheric circulation. Differential heating of Earth's surface by the Sun drives convection currents that move warm air upward and laterally, while cooler, denser air sinks and flows toward the equator. These circulation patterns create the prevailing winds, storm systems, and weather patterns that characterize different regions. Additionally, the atmosphere transports water vapor evaporated from oceans and land surfaces, releasing it as precipitation when the vapor condenses into clouds. This atmospheric water transport, or hydrological cycle, is fundamental to the distribution of freshwater resources across the planet.

大气还充当通过大气环流重新分配热量的介质。太阳对地球表面的差异加热驱动了对流气流，使暖空气向上和侧向移动，而更冷、密度更大的空气下沉并流向赤道。这些环流模式产生了不同地区特有的盛行风、风暴系统和天气模式。此外，大气运输从海洋和陆地表面蒸发的水蒸气，当蒸汽凝结成云时将其释放为降水。这种大气水传输或水循环（hydrological cycle）是地球上淡水资源分布的基础。

The atmosphere's composition is not fixed; it has evolved dramatically over Earth's 4.5-billion-year history, and it continues to change in response to natural processes and human activities. Variations in atmospheric composition, particularly concentrations of greenhouse gases like carbon diox