The role of the carbon cycle in the greenhouse effect and the Earth's energy balance; positive and negative feedbacks; and strategies to mitigate climate change.

What this dot point is asking

Eduqas wants you to explain how the carbon cycle regulates climate through the greenhouse effect and the Earth's energy balance, distinguish positive and negative feedbacks and their link to tipping points, and evaluate strategies to mitigate climate change.

The answer

The carbon cycle and the energy balance

Climate is set by the Earth's energy balance: incoming shortwave solar radiation is balanced over time by outgoing longwave radiation to space. Greenhouse gases, regulated by the carbon cycle, intercept some of the outgoing longwave radiation and re-emit it, keeping the surface habitable. By transferring carbon from the slow cycle to the atmosphere, human emissions raise greenhouse-gas concentrations, trap more longwave radiation and warm the surface, the enhanced greenhouse effect, shifting the energy balance until a warmer equilibrium is reached.

Feedbacks and tipping points

Feedbacks make the climate response non-linear. The ice-albedo feedback is the clearest: warming melts reflective ice and snow, exposing darker ocean and land that absorb more solar energy, causing further warming and more melting. Thawing permafrost releases stored methane and carbon dioxide, adding to warming. A warmer ocean absorbs less carbon dioxide, leaving more in the atmosphere. Some negative feedbacks exist (increased low cloud reflecting sunlight, faster plant growth taking up carbon), but they are generally weaker, so the net effect amplifies warming and raises the risk of crossing tipping points such as ice-sheet collapse or Amazon dieback.

Mitigation and adaptation

Mitigation reduces the cause by cutting emissions and protecting sinks: decarbonising energy (renewables, nuclear), carbon capture and storage, energy efficiency, protecting and restoring carbon sinks (forests, peatlands, REDD+), carbon pricing and international agreements such as the Paris Agreement. Adaptation manages the consequences that are now unavoidable: flood defences, drought-resistant crops, water management and managed retreat. Eduqas expects a judgement that mitigation tackles the root while adaptation copes with committed change, that effectiveness depends on combining strategies, and that the central obstacle is securing enforceable global cooperation when costs and benefits fall unevenly between countries.

Examples in context

Example 1. Arctic amplification and the ice-albedo feedback. The Arctic is warming roughly two to four times faster than the global average, the clearest real-world case of the ice-albedo positive feedback. As sea ice and snow melt, dark ocean and tundra absorb more solar energy, accelerating regional warming and further ice loss, while thawing permafrost releases methane and carbon dioxide, a second positive feedback. The Arctic demonstrates how feedbacks turn a modest forcing into rapid, amplified change and why it is treated as an early-warning region for tipping points, a powerful Eduqas example linking the carbon cycle to climate dynamics.

Example 2. The Paris Agreement and the limits of global mitigation. The 2015 Paris Agreement committed nearly all countries to limit warming to well below $2$ degrees Celsius, ideally $1.5$, through nationally determined contributions. It shows both the promise and the limits of mitigation governance: it created near-universal participation and a shared target, but its pledges are voluntary and not legally enforceable, and current commitments fall short of the goal. Paris is the standard Eduqas case for evaluating mitigation strategy, illustrating that effective climate action depends on enforceable cooperation, not just agreed targets, and links this topic directly to global governance.

Try this

Q1. Define the enhanced greenhouse effect. [2 marks]

• Cue. The strengthening of the natural greenhouse effect by human greenhouse-gas emissions, which trap more outgoing longwave radiation and warm the surface further.

Q2. Explain one positive feedback in the climate system. [3 marks]

• Cue. The ice-albedo feedback: warming melts reflective ice, exposing darker ocean and land that absorb more solar energy, causing further warming and more melting, amplifying the initial change.