Doing the Real Math on Climate Change

Lesson:  Quantitative Model for the Cycling of Carbon Through the Geosphere, Atmosphere, Hydrosphere, and Biosphere

Below is a simplified version of the carbon cycle model that considers key processes for each sphere, focusing on major exchanges of carbon between the atmosphere, hydrosphere, biosphere, and geosphere.

 

Carbon Stocks (Carbon Reservoirs)

1. Atmosphere (A): The amount of carbon stored as carbon dioxide (CO₂) in the atmosphere.

   • Unit: GtC (Gigatonnes of Carbon)

2. Biosphere (B): The amount of carbon stored in living organisms (plants, animals, soil organic matter).

   • Unit: GtC

3. Hydrosphere (H): The amount of carbon stored in Earth's oceans, including dissolved CO₂ and carbon in marine organisms.

   • Unit: GtC

4. Geosphere (G): The amount of carbon stored in fossil fuels, rocks, and sediments. This includes both short-term exchanges (like soil and plant matter) and long-term carbon storage (e.g., in limestone or fossil fuels).

   • Unit: GtC

 

Carbon Fluxes (Carbon Transfers Between Reservoirs)

1. Photosynthesis (P):

   • Carbon is absorbed by plants from the atmosphere as CO₂ to produce organic matter.

   • Flux: P=120 GtC/year (approximately)

2. Respiration (R):

   • Carbon is returned to the atmosphere as CO₂ from living organisms (plants, animals, microbes) through respiration.

   • Flux: R=120 GtC/year (approximately)

3. Decomposition (D):

   • The breakdown of dead organic matter releases carbon back to the atmosphere (via CO₂) or into the soil.

   • Flux: D=60 GtC/year

4. Ocean Uptake (U):

   • The oceans absorb CO₂ from the atmosphere, primarily through physical processes like diffusion and biological processes like photosynthesis by phytoplankton.

   • Flux: U=90 GtC/year

5. Ocean Release (L):

   • Carbon is released back into the atmosphere from the ocean, primarily due to warmer surface waters, ocean currents, or biological respiration in the ocean.

   • Flux: L=90 GtC/year

6. Sedimentation and Fossilization (S):

   • Carbon from the biosphere and atmosphere can be buried in sediments, eventually becoming fossil fuels or sedimentary rock over geological timescales.

   • Flux: S=0.1 GtC/year (short-term) but larger over geological timescales.

7. Weathering (W):

   • Carbon in the atmosphere reacts with minerals in rocks, leading to the formation of carbonate minerals (like limestone) that can store carbon in the geosphere.

   • Flux: W=0.05 GtC/year (a slow but continuous process)

8. Volcanic Eruptions (V):

   • Volcanic activity releases CO₂ stored in the geosphere back into the atmosphere.

   • Flux: V=0.1 GtC/year

9. Combustion (C):

   • Human activities, such as the burning of fossil fuels and biomass, release large amounts of CO₂ into the atmosphere.

   • Flux: C=9.0 GtC/year (anthropogenic flux)

10. Terrestrial Carbon Flow (T):

• Carbon moves from the biosphere to the atmosphere through terrestrial processes like respiration, combustion, and decay.

• Flux: T=2.0 GtC/year

 

Model Summary:

Carbon Stocks (in GtC):

• Atmosphere (A): 750 GtC

• Biosphere (B): 3,000 GtC

• Hydrosphere (H): 38,000 GtC (oceans are the largest carbon reservoir)

• Geosphere (G): 1,000,000 GtC (long-term storage in rocks, fossil fuels, etc.)

Carbon Fluxes (in GtC per year):

• Photosynthesis (P): 120 GtC/year (Biosphere → Atmosphere)

• Respiration (R): 120 GtC/year (Biosphere → Atmosphere)

• Decomposition (D): 60 GtC/year (Biosphere → Atmosphere)

• Ocean Uptake (U): 90 GtC/year (Atmosphere → Hydrosphere)

• Ocean Release (L): 90 GtC/year (Hydrosphere → Atmosphere)

• Sedimentation and Fossilization (S): 0.1 GtC/year (Biosphere → Geosphere)

• Weathering (W): 0.05 GtC/year (Atmosphere → Geosphere)

• Volcanic Eruptions (V): 0.1 GtC/year (Geosphere → Atmosphere)

• Combustion (C): 9.0 GtC/year (Human Activity → Atmosphere)

• Terrestrial Carbon Flow (T): 2.0 GtC/year (Biosphere → Atmosphere)

 

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