Lesson 5 of 9 / Organisms and their environment
Carbon dioxide and global warming
How do human activities change the balance, and which actions address it?
In this lesson: Explain increased atmospheric carbon dioxide and connect mitigation actions to their mechanisms.
About 6 min
The key ideaFossil-fuel use and deforestation increase atmospheric carbon dioxide. Reducing emissions and protecting carbon uptake can limit additional warming.
The greenhouse effect keeps Earth warmer than it would otherwise be. Global warming involves an increase in average global temperature as this effect is strengthened.
Explore the idea
Connect an action to the mechanism
Combustion adds long-stored carbon. More carbon dioxide absorbs and re-emits outgoing infrared radiation, strengthening the greenhouse effect.
Original causal models. Mitigation addresses emissions or uptake; adaptation addresses effects. Their benefits and limitations need to be evaluated separately.
Explanation
Burning coal, oil and natural gas adds carbon dioxide to the atmosphere. Deforestation can add more when cleared vegetation burns or decomposes. Removing trees also reduces the photosynthetic uptake that would otherwise remove carbon dioxide from the air.
Earth absorbs sunlight and emits energy as infrared radiation. Carbon dioxide and other greenhouse gases absorb and re-emit some outgoing infrared radiation, reducing the rate at which energy escapes to space. Increasing their concentration strengthens this greenhouse effect and raises average global temperature until a new energy balance is reached.
Actions that reduce fossil-fuel combustion address the input of carbon. More efficient buildings and transport reduce energy demand; low-carbon energy sources reduce emissions for a given energy supply. An answer should identify what changes, not simply say that technology solves warming.
Protecting forests avoids loss of stored carbon and preserves uptake. Restoration can increase carbon storage over time while supporting habitats. It complements emissions reduction but cannot instantly cancel unlimited fossil-fuel emissions; establishment takes time and stored carbon can be released by disturbance.
People can also adapt to effects already occurring, for example by protecting coastal habitats that reduce erosion or designing for heat and flood risks. Adaptation reduces harm from a changing climate; it does not automatically reduce the greenhouse-gas cause. Useful decisions combine a clear mechanism with practical limits and effects on ecosystems and people.
Step by step
- 1
Identify the carbon change
Does the activity add emissions, remove a sink, or do both?
- 2
Explain the warming mechanism
More greenhouse gas changes the escape of outgoing infrared energy, strengthening warming.
- 3
Evaluate a proposed action
Link it to lower emissions, greater uptake or reduced harm, then identify an important limitation.
Worked example
Planting trees beside a new power station
A proposal claims that planting trees immediately cancels any amount of fossil-fuel use. Evaluate the claim.
One way to explain it
Growing trees can take up carbon dioxide and store carbon, but uptake takes time and depends on growth, land and survival. Fossil-fuel burning releases carbon immediately and may exceed that uptake. Tree planting can support mitigation but does not justify unlimited emissions or replace direct reductions.
Why this answer works
- Acknowledge the valid uptake mechanism.
- Compare rates, timescales and scale.
- Explain why a useful action is not an unlimited solution.
Is this true? "Carbon dioxide warms Earth by making a hole in the ozone layer."
The enhanced greenhouse effect concerns absorption and re-emission of outgoing infrared radiation. Ozone depletion is a different environmental process.