#2 The Earth, the Greenhouse Effect, and the Carbon Cycle

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• Topic: The Earth, the Greenhouse Effect, and the Carbon Cycle (NST1070). Framework: Earth is composed of interacting systems/spheres that govern climate, life, and energy balance.

Key idea: Study focus on how land, water, air, and living systems interact to regulate climate, with emphasis on the greenhouse effect and the carbon cycle as central processes linking these spheres.

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• Outline of the course object:
  • Earth Systems and Interactions
  • The Greenhouse Effect
  • The Carbon Cycle

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• The Earth is studied as a system of interacting components (spheres):
  • Geosphere (land/rocks)
  • Hydrosphere (water)
  • Atmosphere (air)
  • Biosphere (living things)

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• The four major Earth systems (spheres):
  • Land
  • Water
  • Air/Gases (Atmosphere)
  • Living things (Biosphere)

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• Land = Geosphere: The lithosphere/geosphere is the rocky outer shell of the planet, consisting of the crust and the brittle upper mantle. It is the most rigid outer layer of Earth and forms the solid part of the planet.
  • Source: Hanif et al. 2020, Lithosphere/Geosphere in Environmental Chemistry. DOI: https://doi.org/10.1002/9781119651055.ch6

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• How the world’s land is used: Global land area by use and land cover (Our World in Data visualizations).
• Key notes from the visualization:
  • Land categories are not distributed by region in the map; they represent total areas covered by each use type.
  • Land uses as a percentage of global land area are shown in square brackets.
  • Definitions used in the data:
  • Cropland: land used for crop production minus land used for producing animal feed.
  • Livestock area: combined grazing land and cropland used for animal feed.
  • Barren land: land cover with less than one-third vegetation or cover.
  • Summary categories with approximate shares (as shown):
  • Livestock [27%] (associated with meat and dairy production; grazing & feed crops)
  • Glaciers [10%] (Permanent snow & ice)
  • Deserts/deserts, salt flats, rocks (Barren land) [19%]
  • Built-up area [1%] (Villages, towns, cities and infrastructure)
  • Forests [26%]
  • Shrub/woody vegetation [8%]
  • Freshwater [1%]
  • Others reflect water bodies; Lakes, rivers, etc.
  • The data are based on FAO and World Bank statistics; map projection: equal-area Eckert IV.
  • Data visualization available at OurWorldinData.org.

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• Water = Hydrosphere: The hydrosphere is the total amount of water on a planet, including surface water, groundwater, and water in the air. Water can exist as liquid, vapor, or ice.
• On Earth, liquid water exists on the surface in oceans, lakes, and rivers.

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• Earth’s water distribution (summary from slide):
  • Oceans: 97%
  • Freshwater: 3%
  • Groundwater: 70%
  • 29% easily accessible freshwater
  • Soil moisture: 38%
  • Lakes: 52%
  • Water supply (sum of accessible freshwater) in some visual aggregations
  • Water vapor: 1%
  • Rivers: 1%
  • Water in living things: 1%
• Note: The slide layout is a bit jumbled; the intent is to show the vast majority of Earth’s water is in oceans, with freshwater comprising a small minority, distributed among groundwater, surface water (lakes/rivers), soil moisture, etc. Copyright and visualization details are provided in the slide.

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• Air = Atmosphere: The atmosphere is a layer of gas and suspended solids extending from the Earth’s surface upward to thousands of miles, thinning with altitude and bound by Earth’s gravity.
• Source: Hanif et al. 2020, Lithosphere/Geosphere in Environmental Chemistry. DOI: https://doi.org/10.1002/9781119651055.ch6

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• Major atmospheric composition (dry air):
  • Oxygen: ext{O}_2 ext{ ~20.9%}
  • Nitrogen: ext{N}_2 ext{ ~78.1%}
  • Argon, Carbon Dioxide, Helium, Hydrogen, Krypton, Neon, Xenon, Neon, Krypton, Neon, etc. (trace gases)
  • Included trace gases and components: Argon (0.93%), Carbon dioxide (CO₂), Methane (CH₄), Nitrous oxide (N₂O), Ozone, Sulfur dioxide, Water vapor, Xenon, etc.
• Illustrative note: These are the major constituents of the atmosphere; CO₂ is a well-known trace gas with climate relevance.

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• World Oxygen Production (by source):
  • Land plants: 20.0%
  • Large marine algae: 30.0%
  • Phytoplankton: 50.0%
• This distribution shows biological sources of atmospheric O₂ via photosynthesis across terrestrial, coastal/marine, and open-ocean ecosystems.

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• Living Things = Biosphere: The biosphere includes all life on Earth, including the living organisms and the remains of organisms that have died and not yet decomposed.
• Source: Hanif et al. 2020, as above.

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• The Earth’s four interlinked spheres in a simplified schematic:
  • Lithosphere (Geosphere) [Land]
  • Atmosphere (Air)
  • Hydrosphere (Water)
  • Biosphere (Living things)

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• Biotic vs Abiotic:
  • Biotic: living or once-living components (plants, animals, bacteria).
  • Abiotic: non-living components (water, soil, atmosphere).
• Interactions among these components are critical for ecosystem function.

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• Biotic and Abiotic components (illustrative examples):
  • Biotic: Fungi, Plants, Animals, Protists, Bacteria
  • Abiotic: Soil, Water, Humidity, Temperature, Air, etc.
• This page emphasizes the interaction of living organisms with abiotic factors in the environment.

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• Systems Interactions – Air, Water, and Land:
  • Atmosphere (air): composition of gases surrounding Earth (abiotic).
  • Geosphere (land): five layers of Earth’s crust (abiotic).
  • Hydrosphere (water): all solid and liquid water on Earth (abiotic).
  • Biosphere (life): living organisms and their interactions with the other three systems (biotic).

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• Changes across Earth systems:
  • Changes in solar inputs affect climate forcing.
  • Changes in the atmosphere include composition and circulation patterns.
  • Hydrological Cycle changes influence precipitation, evaporation, etc.
  • Other system interactions include aerosols, clouds, ozone, land-use change, ocean circulation, cryosphere changes (snow, sea ice, ice sheets, glaciers), and land-surface processes (orography, vegetation, ecosystems).
  • There are feedbacks among: Atmosphere–Biosphere, Atmosphere–Ice, Land–Biosphere–Atmosphere, and Land–Hydrosphere–Atmosphere interactions.
• The diagram (NOAA-based) shows coupled processes such as precipitation, evaporation, sea ice coupling, and cryosphere interactions with hydrosphere and land.

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• The Greenhouse Effect (intro slide): The greenhouse effect is the natural warming of Earth that results when gases in the atmosphere trap heat from the sun that would otherwise escape into space.

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• The Greenhouse Effect (definition): The natural warming of the Earth due to greenhouse gases that trap heat in the lower atmosphere and surface, reducing the loss of infrared radiation to space.

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• Greenhouse effect specifics:
  • Energy from the sun warms Earth; some energy escapes back into space.
  • Greenhouse gases that trap heat include CO₂, CH₄, N₂O, and water vapor.
  • Troposphere is the atmospheric layer where this trapping occurs.
  • Without the atmosphere, Earth would be about 0°F; with the atmosphere, Earth is about 60°F warmer.
  • Source: World Meteorological Organization (WMO) Greenhouse Gas Bulletin (2016); Climate context from Climate Central summarizing the WMO bulletin.

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• The greenhouse gas mechanism (three-step):
  1) Atmosphere transmits shortwave radiation (SWR) from the Sun to Earth.
  2) Earth absorbs SWR and re-emits longwave radiation (LWR) back toward space; some is absorbed by greenhouse gases, warming the surface.
  3) Greenhouse gases trap part of the re-emitted longwave radiation, keeping heat in the lower atmosphere and surface.
• Key greenhouse gases include Water Vapor, CO₂, CH₄, and N₂O.

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• Incoming Shortwave Radiation (SWR) and outputs:
  • Natural fluctuations in solar output affect SWR.
  • SWR reflected by the atmosphere and surface, interacting with aerosols, clouds, ozone, and chemical reactions.
  • Outgoing Longwave Radiation (OLR) is the energy emitted to space by Earth.
  • Processes like SWR absorption by aerosols/clouds, and by greenhouse gases, modify the balance between SWR and LWR.
  • Latent and sensible heat fluxes also contribute to the surface-to-atmosphere energy exchange.
• The figure (IPCC AR5 Fig1-1 style) shows the complexity of surface albedo, ocean color, wave height, cloud feedbacks, vegetation changes, and carbon cycle feedbacks in the climate system.

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• Conclusion from the greenhouse mechanism: This process helps explain why we understand global warming as a consequence of climate change.

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• Difference between terms:
  • Climate Change: A long-term change in average weather patterns across local, regional, and global scales.
  • Global Warming: The long-term heating of Earth’s surface since the pre-industrial period (roughly 1850–1900) due to human activities that increase heat-trapping greenhouse gases.

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• Side-by-side definitions:
  • Global Warming: Gradual increase in the surface temperature of Earth.
  • Climate Change: Long-term change of weather patterns (including global warming and its side effects).
• What causes them? CO₂ and other greenhouse gases; human factors or natural changes in Earth.
• Example: The rise in global mean surface temperature by about 1.5°C and 2.0°C scenarios; changes in plant phenology (bloom times) as a consequence.

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• Historical context: Earth started warming after roughly 100,000 years of an ice age, known as a glacial termination.
• Human influence began to become significant around the 1830s, with early human activities affecting climate.

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• FAQ3.1: Impact of 1.5°C and 2.0°C global warming:
  • Temperature rise is not uniform globally.
  • Higher increases in some regions for hot days and cold nights than others.
  • +1.5°C: Change in average temperature of hottest days.
  • +2.0°C: Change in average temperature of hottest days.
  • +1.5°C: Change in average temperature of coldest nights.
  • +2.0°C: Change in average temperature of coldest nights.
• The page shows a temperature range map with projected changes under different warming scenarios.

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• Projections under higher vs lower emission scenarios:
  • Higher Emissions Scenario (mid-century ~2040–2059; end-of-century ~2080–2099): Temperature changes reaching approximately +12°F (~+7°C) in some scenarios, with spatial variation.
  • Lower Emissions Scenario: Temperature changes roughly lower in mid- and end-century, though still significant.
  • The figure shows a gradient of temperature changes from 0 to >10°C, illustrating regional differences.

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• Question: How does human activity increase greenhouse gases, and how does it reduce them? (Caption in the slide shows a prompt, likely for discussion or a quiz item.)

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• 5-minute break (break in the lecture).

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• The Carbon Cycle: Introduction slide.

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• Carbon basics:
  • Key component of all known life on Earth.
  • Carbon is found in complex molecules bonded with other elements (especially oxygen, hydrogen, phosphorus, nitrogen).
  • Carbon is abundant, lightweight, and small, making it easy for enzymes to manipulate carbon-containing compounds.

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• Coal: a combustible sedimentary rock rich in carbon; formed from compressed plant remains; classified as organic matter; therefore it is an organic sedimentary rock.

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• Formation factors and energy considerations:
  • Formation rate depends on heat/pressure.
  • More pressure → solid coal; More heat → natural gas; Some heat + some pressure → liquid oil.
  • Source material at the time of death matters: swamp gives coal, ocean gives oil and natural gas.

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• Carbon forms: Inorganic carbon (non-living, not bound up in living organic matter):
  • Examples: CO₂, CO, CaCO₃ (carbonates).
  • Organic carbon (living or once-living material): humans, animals, plants, microorganisms, etc.; carbon bonded with other elements.

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• Examples of organic vs inorganic compounds:
  • Organic: DNA, Methane (CH₄), Benzene, etc.
  • Inorganic: Salt (NaCl), Carbon dioxide (CO₂), Diamond (carbon allotrope, but often considered inorganic in many contexts), etc.

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• Processes moving carbon between inorganic and organic forms:
  • Photosynthesis moves inorganic carbon to organic form (CO₂ + H₂O → organic sugars).
  • Respiration, decomposition, and combustion move carbon from organic back to inorganic form (organic → CO₂, CO, etc.).

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• Photosynthesis (intake):
  • Inputs: Sunlight, Carbon Dioxide (CO₂), Water (H₂O).
  • Outputs: Glucose (C₆H₁₂O₆) and Oxygen (O₂).
  • Process details: Light-dependent reactions capture energy; chlorophyll absorbs light; water is split to release O₂; Calvin cycle (light-independent) builds glucose.

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• Leaf structure (illustrative): cross-section showing cells and organelles involved in photosynthesis (chloroplasts, chlorophyll in chloroplasts), and the role of light in driving the reactions.
• Key processes depicted: Light-dependent reactions producing ATP and NADPH; light-independent (Calvin cycle) fixing CO₂ into organic molecules (glucose).

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• Respiration: Involves producing ATP from glucose using oxygen; outputs CO₂, water, and heat.
• General respiration equation (glucose catabolic process) and energy yield (ATP) are depicted.

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• Cellular respiration diagram: shows Glycolysis, Krebs cycle, Electron Transport Chain, and the main outputs: ATP, CO₂, H₂O, and heat.

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• Relationship between photosynthesis and cellular respiration (opposing but complementary):
  • Photosynthesis occurs in plant cells (chloroplasts) producing glucose and O₂.
  • Cellular respiration occurs in mitochondria of plants and animals, consuming glucose and O₂ to produce ATP, CO₂, and H₂O.

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• Decomposition: Breakdown of dead organic matter by decomposers and scavengers; producers of CO₂ through microbial respiration as they convert organic carbon to inorganic forms.
• Similar chemical equation to cellular respiration, but carbon source differs (dead organic matter instead of living glucose).
• Key idea: Decomposition is a major pathway returning carbon to the atmosphere and soils.

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• Decomposition process and the development of soil organic matter:
  • Dead plant material forms detritus; decomposers break it down; minerals are released; humus is formed; nutrients are mobilized to roots.

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• Main drivers of decomposition:
  • Temperature
  • Water availability
  • Organic matter quality
  • Decomposer community
• Concept: DOM stands for Dead Organic Matter; DOM respiration releases CO₂ to the atmosphere.
• Interaction cycle: Photosynthesis fixes carbon; decomposition returns carbon to soil and atmosphere; autotrophs and heterotrophs cycle carbon through ecosystems.

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• Energy flow in biology concept:
  • Autotrophs: Producers who produce their own food (through photosynthesis or chemosynthesis).
  • Heterotrophs: Consumers who rely on other organisms for food.

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• Carbon cycle trophic roles:
  • Primary producers perform photosynthesis (autotrophs).
  • All living things respire (including trees, phytoplankton).
  • Primary/secondary/tertiary consumers cannot perform photosynthesis; they are heterotrophs and require energy stored in organic matter.
• The basic photosynthesis and respiration equations (simplified):
  • Photosynthesis: 6CO2 + 6H2O
    ightarrow C6H{12}O6 + 6O2
  • Respiration: C6H{12}O6 + 6O2
    ightarrow 6CO2 + 6H2O + ATP

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• Biogeochemistry cycles – Sources:
  • SOURCE = a pool that releases more of a molecule than it accepts (through emissions or runoff).
  • Examples of carbon sources: burning fossil fuels, forest fires, animal respiration, plant degradation.
  • Sources are worldwide; some larger than others.
  • Plastics increasingly act as a carbon source in some contexts.

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• Fossil fuels image and categories (Oil, Natural Gas, Coal) illustrating the major fossil carbon sources used for energy.

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• Fossil fuel consumption data (Our World in Data, 2024):
  • Global fossil fuel consumption around 140,000 TWh (terawatt-hours) of primary energy; values shown across several tiers (e.g., 140k, 120k, 100k, etc.) to illustrate scale.
  • Fossil fuel consumption per capita (2024) shown for different regions/countries (e.g., USA, Australia, Europe, Germany, China, UK, South Africa) with per-capita values given in kWh per person (e.g., 20,390 kWh to 61,277 kWh).
  • Explanatory notes provided about units:
  • 1 TWh = 1,000,000,000 kWh; a Watt-hour is energy delivered by one watt for one hour; 1 Wh = 3600 J. Primary energy accounts for energy before transformation losses (e.g., coal before burning).
  • Data source: Our World in Data; Energy Institute - Statistical Review of World Energy (2025); Smil (2017).

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• Biogeochemistry Cycles – Sink (storage/sequestration):
  • A SINK is a pool that accepts more molecule than it releases (storage/reservoir).
  • Examples: Plants, the ocean, soil, fungi can act as carbon sinks.

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• Reference to scientific source: Pan et al. 2024. The enduring world forest carbon sink. Nature, 631(8021), 563-569.

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• Carbon pathways and interactions:
  • Burning, CO₂ emissions from wood and fossil fuels, plant respiration, and animal respiration contribute to atmospheric CO₂ levels.
  • Fixation and consumption by plants and animals, soil and decomposition cycles link carbon to water and microbe processes.
  • Sequestration processes in soils, dissolved CO₂ in water, and regeneration through photosynthesis close the cycle.
  • Diagrammatic representation includes atmospheric CO₂, oceans, forests, and artificial techniques as components of carbon management.

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• Baltic Sea carbon sink example:
  • Healthy Baltic Sea acts as a carbon sink with carbon burial and nutrient cycling.
  • Degraded Baltic Sea can become a carbon source, releasing CO₂ and CH₄.

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• Carbon pathways in the environment: Oceans, Forests, and Artificial Techniques (as potential sinks/sources and management options).

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• Systems integration recap:
  • Lithosphere (Land) • Atmosphere (Air) • BIOSPHERE • Hydrosphere (Water)

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• Questions? (Review prompts for understanding the material and testing comprehension.)

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• Reminders:
  • HW #1 due September 3rd 11:59 PM
  • Readings due September 3rd before class
  • The Imperative for Climate Action to Protect Health

Notes on structure and connections

• The Earth is presented as a system of four interacting spheres: Geosphere (land), Hydrosphere (water), Atmosphere (air), and Biosphere (living things). These spheres interact to regulate climate, biogeochemical cycling, and energy balance.
• The Greenhouse Effect is explained as a natural process whereby greenhouse gases trap some of the infrared radiation emitted by Earth, warming the surface. Major greenhouse gases include water vapor, CO₂, CH₄, and N₂O.
• The cycle of carbon is driven by both biological processes (photosynthesis, respiration, decomposition) and physical processes (ocean uptake, sedimentation, burial, and fossil fuel formation). Carbon moves among inorganic reservoirs (CO₂ in the atmosphere, carbonates in rocks, dissolved inorganic carbon in water) and organic reservoirs (biosphere, detritus, soils).
• The concept of sources and sinks is essential: sources add carbon to a pool; sinks remove or store it. Notable global sinks include forests and the oceans; notable sources include fossil fuel combustion and decomposition.
• Human activities have increased greenhouse gas concentrations, amplifying the greenhouse effect and driving climate change, including long-term shifts in temperature, precipitation, ocean circulation, cryosphere dynamics, and sea level.
• Quantitative data provided include: atmospheric composition (O₂ ~20.9%, N₂ ~78.1%), global oxygen production by photosynthesis split among terrestrial plants, marine macroalgae, and phytoplankton; global fossil fuel energy usage in TWh; and regional per-capita energy consumption in kWh.
• Key equations to memorize (carbon cycle and energy flow):
  • Photosynthesis: 6CO2 + 6H2O
    ightarrow C6H{12}O6 + 6O2
  • Respiration (and decomposition cycle): C6H{12}O6 + 6O2
    ightarrow 6CO2 + 6H2O + ATP
  • Carbon forms: Inorganic carbon sources include CO₂, CO, CaCO₃; Organic carbon includes carbohydrates, lipids, proteins, nucleic acids, etc.
• Real-world relevance: The material links Earth system science to climate action, emphasizing how energy systems (fossil fuels), land use, oceans, forests, and atmospheric composition collectively determine climate trajectories and health outcomes.

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