Preview
IB DP ESS — Topic 6: Atmosphere and Climate Change | SL & HL | Paper 1 & Paper 2A
🎯 Learning Intentions By the end of this note, you will be able to:
- Define the ozone layer and explain its role in filtering ultraviolet (UV) radiation within the stratosphere.
- Explain the natural formation and destruction of ozone using the Chapman cycle, and describe how this equilibrium is disrupted by anthropogenic pollutants.
- Describe the role of chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODS) in catalytic ozone destruction.
- Analyse the environmental and human health consequences of ozone depletion, applying the ESS parameters of scale, perspectives, and sustainability.
- Evaluate the effectiveness of the Montreal Protocol (1987) and its amendments as an international response to ozone depletion.
- Discuss the relationship between ozone depletion and climate change, identifying both distinctions and interactions between the two issues.
- Distinguish between the ozone hole and general stratospheric ozone thinning, and explain why the Antarctic ozone hole forms seasonally.
Real-World Context & Relevance
In September 2023, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) released their biennial assessment confirming that the stratospheric ozone layer is on track to recover to 1980 levels by approximately 2066 over Antarctica — a remarkable turnaround from the crisis of the 1980s. At its worst, in 2006, the Antarctic ozone hole reached a record area of approximately 29.6 million km², larger than the entire continent of North America. Satellite instruments detected total ozone column values below 100 Dobson Units (DU) over parts of Antarctica, compared to a global average of around 300 DU — a reduction of more than two-thirds in the protective shield that absorbs harmful ultraviolet-B (UV-B) radiation.
The story of ozone depletion is one of the most instructive case studies in environmental science: a global atmospheric crisis caused by a specific class of industrial chemicals, detected through international scientific collaboration, and addressed through a landmark multilateral agreement. It demonstrates that human societies can, under the right conditions, identify a systemic environmental threat and act collectively to reverse it. Yet the story is not without complexity — the very chemicals used to replace CFCs (hydrofluorocarbons, or HFCs) turned out to be potent greenhouse gases, illustrating the trade-offs and unintended consequences that characterise real-world environmental management.
🌍 Why This Matters The ozone layer is a critical component of Earth's atmospheric system, absorbing up to 99% of the Sun's harmful UV-B and UV-C radiation. Its depletion directly increases the incidence of skin cancer, cataracts, and immune suppression in humans, while also damaging phytoplankton, amphibian populations, and terrestrial plant productivity — cascading effects that ripple through entire food webs and ecosystems. The recovery of the ozone layer, driven by the Montreal Protocol, is widely regarded as the most successful example of international environmental governance in history.
Core Concepts & Definitions
To understand ozone depletion, we must first understand what the ozone layer is, where it sits within the atmospheric system, and what it does. The atmosphere is layered — the troposphere (0–12 km), stratosphere (12–50 km), mesosphere, and thermosphere — and each layer has distinct chemical and thermal