Question

What human activities could redistribute carbon loads in the cycle so that global warming
might slow or decrease? Choose two different real-world examples and explain the flux in
carbon loads that would result from an increase in that human activity. Make sure to explain
what biological, physical, or geological processes would shift the carbon load from one point in
the cycle to another

Answer 1

Below are two real-world human activities that can shift carbon between reservoirs in ways that reduce atmospheric CO2, with an explanation of the physical/biological/geochemical processes that produce the fluxes.

1) Large-scale afforestation / improved forest management
- What is done: Planting new forests (afforestation) or restoring degraded forests, and changing management so forests accumulate more biomass and soil carbon (longer rotations, reduced logging, avoiding fires).
- Net flux produced: Carbon is moved from the atmosphere into the terrestrial biosphere and soils — atmosphere → living biomass (trees, roots) → litter → soil organic carbon. Over time a portion of that carbon can be stabilized in soils or converted to long-lived wood products, reducing atmospheric CO2.
- Processes involved:
- Photosynthesis: trees use CO2 from the atmosphere to form organic matter (net primary production), directly removing CO2.
- Carbon allocation: carbon is stored in trunks, branches, roots and leaves.
- Litterfall and soil processes: leaves and woody debris become litter, are decomposed by microbes, and a fraction of that carbon becomes stabilized soil organic matter (physically or chemically protected) or forms charcoal from incomplete combustion.
- Respiration & disturbance: autotrophic and heterotrophic respiration returns some carbon to the atmosphere; disturbance (fire, pests, deforestation) can rapidly reverse the sink.
- Timescales and permanence: Uptake occurs over decades as forests grow; soil carbon can persist decades–centuries. But saturation (older forests reach steady state) and reversal risks (fire, land-use change) limit permanence.
- Real-world context & capacity: Large reforestation programs (e.g., Bonn Challenge, national tree-planting initiatives) are examples. Afforestation can sequester substantial CO2 at relatively low cost per ton in the near term, but land availability, biodiversity, water use, and albedo effects constrain scale and durability.

2) Enhanced silicate rock weathering (a geochemical approach)
- What is done: Mine and crush reactive silicate rocks (basalt, olivine) and spread the fines on agricultural soils or beaches (some projects use coastal olivine spreading). The increased surface area accelerates natural rock weathering reactions that consume CO2.
- Net flux produced: Carbon is drawn from the atmosphere and converted into dissolved inorganic carbon (mainly bicarbonate) that is transported to the ocean and stored as increased ocean alkalinity and, on long timescales, as carbonate sediments — atmosphere → dissolved inorganic carbon (river→ocean) → long-term sedimentary carbonates (or stored as stable alkalinity in seawater).
- Processes involved:
- Chemical weathering: CO2 dissolved in water (as carbonic acid) reacts with silicate minerals. Simplified net (illustrative) reaction:
Ca‑silicate + CO2 + H2O → Ca2+ + 2 HCO3- + silicic acid
The bicarbonate is carried to the ocean.
- Ocean uptake and storage: Increased riverine bicarbonate raises ocean alkalinity; much of this added inorganic carbon remains dissolved and thereby removes CO2 from the atmosphere for centuries to millennia. Some bicarbonate eventually precipitates or is biologically converted to carbonate sediments (long-term burial).
- Timescales and permanence: Weathering, transport and ocean mixing take years–centuries; storage as dissolved inorganic carbon/increased alkalinity is long-lived (centuries) and burial as carbonates is multi-millennial — generally much more permanent than terrestrial biomass.
- Real-world examples and considerations: Field trials (e.g., Project Vesta, university-led pilot studies using basalt or olivine) are testing feasibility. Advantages: large theoretical capacity and permanence. Challenges: energy and emissions from mining and grinding rock, ecological impacts of adding minerals to soils/coasts, cost, and the need to ensure net negative emissions when all lifecycle emissions are counted.

Summary of how each redistributes carbon
- Afforestation causes a biotic flux: atmosphere CO2 → plant biomass & soil carbon (biosphere reservoir increases). The main mechanism is photosynthesis; reversal risk comes from respiration and disturbances.
- Enhanced silicate weathering causes a geochemical flux: atmosphere CO2 → dissolved inorganic carbon → ocean alkalinity and ultimately sedimentary carbonates (ocean/lithosphere reservoirs increase). The main mechanism is accelerated mineral dissolution and subsequent transport/precipitation, providing more permanent locking of carbon.

Both approaches reduce atmospheric CO2 (thus lowering radiative forcing) but differ in mechanism, timescale, permanence, co‑benefits and constraints. Combining several methods with emissions reductions is the realistic pathway to slow or reverse anthropogenic warming.