Why Does Burning Fossil Fuels Enhance the Greenhouse Effect?

Burning fossil fuels enhances the greenhouse effect because combustion releases additional carbon dioxide into the atmosphere. The increased carbon dioxide concentration causes more outgoing infrared radiation to be absorbed and re-emitted, reducing the rate at which Earth loses energy to space.

The Mechanism

This is part of B.2 Greenhouse effect, studied by both SL and HL students.

1. Coal, oil and natural gas contain carbon. During combustion, carbon combines with oxygen and produces carbon dioxide: $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$.
2. Human activity adds carbon dioxide faster than natural processes can remove all of it, so its atmospheric concentration increases.
3. Earth absorbs incoming solar radiation and emits energy mainly as longer-wavelength infrared radiation.
4. Carbon dioxide molecules have specific molecular energy levels. They absorb particular infrared wavelengths when the radiation matches allowed changes in their vibrational energy.
5. The molecules subsequently re-emit infrared radiation in all directions. Some returns toward Earth's surface, so less energy escapes directly to space.
6. This creates an energy imbalance: absorbed power temporarily exceeds outgoing power. Earth's surface and lower atmosphere warm until outgoing radiation again balances incoming radiation at a higher equilibrium temperature.

A common misconception is that greenhouse gases mainly block incoming sunlight. In fact, their key role is absorbing and re-emitting Earth's outgoing infrared radiation. The greenhouse effect is also not the same as ozone depletion.

Exam Technique

For an IB Explain question, link cause and effect: fossil-fuel combustion increases $\text{CO}_2$ concentration, more outgoing infrared is absorbed and re-emitted, less energy escapes to space, and Earth's equilibrium temperature rises. Do not merely state that carbon dioxide “traps heat” without describing radiation and molecular energy levels.