Lesson 1 of 7 / Climate, biodiversity and disease ecology
Human activity changes carbon flows
Why can releasing an old carbon store change the atmosphere?
In this lesson: Explain fossil fuels, deforestation and food choices as CO2/methane sources.
About 7 min
The key ideaHuman activities increase greenhouse-gas accumulation by releasing stored carbon and altering biological sinks and methane production.
Trace the biological links
How does an activity change the carbon flow?
Burning fossil fuels transfers carbon from long-term geological stores into atmospheric CO2. The source is additional to the recent biological cycle.
Brown arrows show a carbon transfer in the first view. Yellow = incoming solar radiation and red = infrared energy in the second view. The atmospheric band and arrow widths are conceptual, not literal boundaries or quantitative fractions.
Explanation
Burning fossil fuels transfers carbon from long-term geological stores into atmospheric CO2. Increased energy use over recent centuries has increased this transfer. Greenhouse gases absorb outgoing infrared radiation and alter Earth's energy balance; they do not mainly work by making a physical lid or blocking all incoming sunlight.
Clearing forests can release carbon through burning and decomposition of biomass and disturbed soils. It also removes photosynthetic organisms that would otherwise take up carbon. The net effect depends on regrowth and subsequent land use, so count both stock loss and future changes in uptake.
Food production contributes through land conversion, energy use and methane sources. Ruminant digestion and manure management can release methane, while growing feed adds resource demands. Increasing consumption of high-emission meat products can therefore increase emissions through several linked processes.
Methane can also arise from anaerobic decomposition in waterlogged agricultural settings and waste. CO2 and methane differ in atmospheric behaviour and warming effect, so carbon-footprint comparisons often express a common CO2-equivalent measure with a stated time horizon. The syllabus emphasis here is the causal contribution of CO2 and methane, not memorising a current emissions league table.
Step by step
- 1
Locate the carbon store
Geological fuel, biomass or soil organic matter.
- 2
Name the process
Combustion, decomposition or biological methane production.
- 3
State the atmospheric consequence
Explain net accumulation rather than only a local transfer.
Worked example
Work through the evidence
Why can replacing forest with cattle pasture affect both CO2 and methane?
One way to explain it
Clearing and soil disturbance can release stored carbon and reduce forest uptake, while ruminant digestion and manure can add methane emissions.
Why this answer works
- One land-use change can alter several flows.
- Regrowth, management and system boundaries affect the total footprint.
Is this true? "Greenhouse gases warm Earth mainly by stopping sunlight from entering."
Their central greenhouse role is absorption and re-emission of outgoing infrared radiation, changing energy loss to space.