📚 4.7.4 Human Impact on the Carbon Cycle | 人类对碳循环的影响
Carbon is the fundamental building block of life, and its continuous movement through the atmosphere, oceans, soil and living organisms is known as the carbon cycle. In this article, we will explore the key reservoirs and processes that keep carbon circulating, and then examine how human activities – particularly the burning of fossil fuels and deforestation – are disrupting this delicate balance, leading to an enhanced greenhouse effect and global climate change.
碳是生命的基本构成元素，它在大气、海洋、土壤和生物之间持续循环的过程被称为碳循环。本文将探讨维持碳循环的关键碳库与过程，并分析人类活动——尤其是化石燃料的燃烧与森林砍伐——如何打破这一微妙的平衡，从而导致温室效应增强和全球气候变化。
1. Overview of the Carbon Cycle | 碳循环概述
The carbon cycle describes the pathways through which carbon atoms are recycled in nature. The main carbon reservoirs include the atmosphere (as carbon dioxide and methane), the oceans (dissolved carbonates), terrestrial biomass (plants and animals), soils (organic matter) and the lithosphere (fossil fuels and sedimentary rocks). Carbon moves between these stores through processes such as photosynthesis, respiration, decomposition, combustion and sedimentation.
碳循环描述了碳原子在自然界中循环的途径。主要的碳库包括大气（以二氧化碳和甲烷形式存在）、海洋（溶解的碳酸盐）、陆地生物量（动植物）、土壤（有机质）以及岩石圈（化石燃料和沉积岩）。碳通过光合作用、呼吸作用、分解作用、燃烧和沉积等过程在这些储存库之间流动。
2. Photosynthesis and Respiration | 光合作用与呼吸作用
otosynthesis can be summarised as: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Opposing this, respiration – carried out by all living organisms – e two processes maintain a natural short-term balance of carbon dioxide in the atmosphere.
光合作用从大气中吸收二氧化碳并将其转化为葡萄糖，植物利用葡萄糖构建生物量。光合作用的化学方程式可总结为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。与之相反，所有生物进行的呼吸作用在分解有机化合物释放能量时，将二氧化碳释放回大气。呼吸可表示为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量。这两种过程共同维持着大气中二氧化碳的短期自然平衡。
3. Carbon Stores and Sinks | 碳库与碳汇
Carbon sinks are reservoirs that absorb more carbon than they release. The oceans are the largest active carbon sink, dissolving atmospheric CO₂ and storing it as dissolved carbonates and bicarbonates. Forests, particularly tropical rainforests, act as significant terrestrial carbon sinks because trees lock up large amounts of carbon in their wood and leaves. Soil also stores carbon in the form of humus and other organic matter. Over geological timescales, dead organisms can be compressed into fossil fuels or carbonate rocks, removing carbon from the active cycle for millions of years.
碳汇是指吸收的碳多于释放的碳的储存库。海洋是最大的活跃碳汇，它能溶解大气中的二氧化碳，并以溶解的碳酸盐和碳酸氢盐形式储存。森林，特别是热带雨林，是重要的陆地碳汇，因为树木将大量碳固定在木材和树叶中。土壤也以腐殖质和其他有机质的形式储存碳。在地质时间尺度上，死亡生物可被压缩形成化石燃料或碳酸盐岩，使碳脱离活跃循环数百万年。
4. Fossil Fuels and Geological Carbon | 化石燃料与地质碳
Fossil fuels – coal, oil and natural gas – are formed from the remains of ancient plants and animals that were buried under layers of sediment and subjected to high pressure and temperature over millions of years. This process trapped carbon that had once been part of the biosphere in the lithosphere. Before the industrial era, this carbon remained effectively locked away, keeping atmospheric CO₂ concentrations relatively stable at around 280 parts per million (ppm).
化石燃料——煤、石油和天然气——由远古动植物遗骸被埋藏在沉积物层之下，经过数百万年高压高温作用而形成。这一过程将曾经属于生物圈的碳困在了岩石圈中。在工业化时代之前，这些碳一直被封存，使大气二氧化碳浓度相对稳定地保持在约 280 ppm。
5. Combustion of Fossil Fuels | 化石燃料的燃烧
f methane: CH₄ + 2O₂ → CO₂ + 2H₂O + energy. This process transfers carbon that had been locked in the lithosphere for millions of years back into the atmosphere in a matter of decades, sharply increasing the atmospheric concentration of CO₂, which now exceeds 420 ppm.
人类的工业化大量开采并燃烧化石燃料，极大地改变了碳循环。燃烧是一种放热反应，碳氢化合物与氧气反应，释放出二氧化碳、水蒸气和能量。一个简单的例子是甲烷的燃烧：CH₄ + 2O₂ → CO₂ + 2H₂O + 能量。这一过程将岩石圈中封存了数百万年的碳在短短几十年内转移回大气层，导致大气二氧化碳浓度急剧上升，目前已超过 420 ppm。
6. Deforestation and Land-Use Change | 森林砍伐与土地利用变化
Deforestation, especially the large-scale clearing of tropical rainforests, reduces the size of a vital carbon sink. When trees are felled and burned, the carbon stored in their biomass is rapidly released as CO₂. Additionally, the loss of forest cover means less photosynthesis is available to remove CO₂ from the atmosphere. Converting forested land to agriculture or urban areas also exposes soil carbon to oxidation, further contributing to atmospheric carbon levels.
森林砍伐，特别是大规模清除热带雨林，减少了一个重要的碳汇面积。当树木被砍伐并焚烧时，其生物量中储存的碳会迅速以二氧化碳形式释放。此外，森林覆盖的丧失意味着通过光合作用从大气中吸收二氧化碳的量减少。将林地转为农业用地或城市区域还会使土壤中的碳暴露并氧化，进一步增加大气碳含量。
7. Rising Atmospheric Carbon Dioxide | 大气二氧化碳浓度上升
The combined effects of fossil fuel combustion and deforestation have led to an unprecedented rise in atmospheric CO₂ levels. Measurements from observatories such as Mauna Loa show a clear upward trend. This increase is overwhelmingly driven by human activities, as confirmed by isotopic analysis that distinguishes between carbon from fossil fuels and carbon from natural sources. The higher CO₂ concentration disrupts the natural carbon cycle, overwhelming the capacity of oceans and forests to act as effective carbon sinks.
化石燃料燃烧和森林砍伐共同导致大气二氧化碳浓度以前所未有的速度上升。来自莫纳罗亚等观测站的测量数据清晰地显示了上升趋势。同位素分析可以区分化石燃料来源的碳和天然来源的碳，证实这种增加主要是由人类活动驱动的。更高的二氧化碳浓度打乱了自然碳循环，使海洋和森林作为有效碳汇的能力不堪重负。
8. Enhanced Greenhouse Effect | 增强的温室效应
The Earth’s greenhouse effect is a natural phenomenon where certain gases trap heat in the atmosphere, maintaining an average surface temperature suitable for life. However, adding excessive CO₂ – along with other greenhouse gases like methane and nitrous oxide – enhances this effect. More infrared radiation is absorbed and re-emitted back towards the Earth, causing the planet’s average temperature to rise. This is often referred to as global warming, and it is the primary driver of current climate change.
地球的温室效应是一种自然现象，某些气体将热量困在大气中，使地表平均温度维持在适合生命生存的范围。然而，过量排放的二氧化碳以及其他温室气体如甲烷和一氧化二氮增强了这一效应。更多的红外辐射被吸收并重新辐射回地面，导致地球平均温度升高。这通常被称为全球变暖，也是当前气候变化的主要驱动因素。
9. Consequences of Disrupting the Carbon Cycle | 碳循环破坏的后果
Disruption of the carbon cycle has far-reaching environmental consequences. These include rising sea levels due to thermal expansion and melting ice caps, more frequent and intense extreme weather events, ocean acidification as excess CO₂ dissolves in seawater, shifts in ecosystems and loss of biodiversity, and threats to food and water security. Coral bleaching, for example, is directly linked to warmer and more acidic oceans, both of which are caused by increased atmospheric CO₂.
碳循环的破坏会带来深远的环境后果。这些后果包括：由于热膨胀和冰盖融化导致的海平面上升，更频繁和强烈的极端天气事件，过量二氧化碳溶于海水造成的海洋酸化，生态系统的迁移与生物多样性的丧失，以及对粮食和水资源安全的威胁。例如，珊瑚白化就与海水变暖和海洋酸化直接相关，而这两者都是由大气二氧化碳增加引起的。
10. Reducing the Human Carbon Footprint | 减少人类碳足迹
Mitigating the human impact on the carbon cycle requires a combination of strategies at individual, national and global levels. Key approaches include transitioning from fossil fuels to renewable energy sources such as solar, wind and hydropower, improving energy efficiency, reforestation and afforestation projects to restore carbon sinks, developing carbon capture and storage technologies, and promoting sustainable agricultural practices that protect soil carbon. International agreements like the Paris Agreement aim to limit global temperature rise by cutting greenhouse gas emissions.
减轻人类对碳循环的影响需要在个人、国家和全球层面采取多种策略。关键措施包括：从化石燃料转向太阳能、风能和水力等可再生能源，提高能源效率，开展植树造林和再造林项目以恢复碳汇，开发碳捕集与封存技术，以及推广保护土壤碳的可持续农业实践。《巴黎协定》等国际协议旨在通过减少温室气体排放来限制全球气温上升。
11. Key Definitions for IGCSE Revision | IGCSE 复习关键定义
- Carbon cycle: the continuous process by which carbon is exchanged between the atmosphere, organisms, oceans and the Earth’s crust. / 碳循环：碳在大气、生物、海洋和地壳之间不断交换的连续过程。
- Carbon sink: a reservoir that absorbs more carbon than it releases, e.g. oceans and forests. / 碳汇：吸收的碳多于释放的碳的储存库，如海洋和森林。
- Greenhouse effect: the trapping of heat in the Earth’s atmosphere by greenhouse gases. / 温室效应：温室气体将热量困在地球大气层中的现象。
- Enhanced greenhouse effect: the increase in the natural greenhouse effect due to human activities adding more greenhouse gases. / 增强的温室效应：由于人类活动增加更多温室气体导致自然温室效应加剧。
- Deforestation: the large-scale removal of trees, reducing carbon uptake and often releasing stored carbon. / 森林砍伐：大规模砍伐树木，减少碳吸收并常常释放储存的碳。
12. Summary and Exam Tips | 总结与考试技巧
In IGCSE Science, you should be able to describe the main processes of the carbon cycle and explain how human activities such as burning fossil fuels and deforestation increase atmospheric carbon dioxide. You are expected to link this to the enhanced greenhouse effect and some consequences of global warming. When answering exam questions, use specific examples – for instance, quote that CO₂ levels have risen from approximately 280 ppm before the industrial revolution to over 420 ppm today, and name consequences such as sea-level rise and ocean acidification. Remember that carbon sinks are natural buffers, but their capacity is limited.
在IGCSE科学中，你应能描述碳循环的主要过程，并解释燃烧化石燃料和森林砍伐等人类活动如何增加大气二氧化碳。你需要将这些与增强的温室效应和全球变暖的一些后果联系起来。在回答考试问题时，请使用具体例子——例如，说明二氧化碳浓度已从工业革命前约 280 ppm 上升到如今的 420 ppm 以上，并列举海平面上升和海洋酸化等后果。请记住，碳汇是天然的缓冲系统，但其容量是有限的。
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
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