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IB DP ESS — Topic 6: Atmosphere and Climate Change | SL & HL | Paper 1 & Paper 2A/2B
🎯 Learning Intentions By the end of this note, you will be able to:
- Define the greenhouse effect, greenhouse gases, and radiative forcing using IB-aligned ESS terminology.
- Describe the composition and structure of Earth's atmosphere, including the role of each major layer in regulating energy flows.
- Explain the natural greenhouse effect and how it maintains conditions suitable for life on Earth.
- Explain how human activities enhance the greenhouse effect by increasing concentrations of greenhouse gases in the atmosphere.
- Identify the major greenhouse gases (CO₂, CH₄, N₂O, H₂O vapour, ozone, CFCs) and their primary anthropogenic sources.
- Analyse the relative contributions of different greenhouse gases using global warming potential (GWP) and atmospheric residence time.
- Distinguish between the natural greenhouse effect and the enhanced greenhouse effect.
- Evaluate the evidence for anthropogenic enhancement of the greenhouse effect, including ice core data, Keeling Curve data, and isotopic analysis.
- Discuss contrasting worldviews (ecocentric, technocentric, anthropocentric) in relation to responses to the enhanced greenhouse effect.
Real-World Context & Relevance
In May 2023, the Mauna Loa Observatory in Hawaiʻi recorded an atmospheric CO₂ concentration of 424 parts per million (ppm) — the highest level in at least 800,000 years of reconstructed climate history. This figure, part of the continuous dataset begun by Charles Keeling in 1958, represents a 50% increase above pre-industrial levels of approximately 280 ppm. The rate of increase has itself been accelerating: the 1960s saw annual rises of around 0.7 ppm per year; by the 2010s, that figure had grown to over 2.4 ppm per year (NOAA, "Trends in Atmospheric Carbon Dioxide").
The consequences of this shift are not abstract. The Intergovernmental Panel on Climate Change's Sixth Assessment Report (2021) concluded with "unequivocal" certainty that human influence has warmed the atmosphere, ocean, and land. Global mean surface temperature has already risen approximately 1.1°C above pre-industrial levels. In the Arctic, warming is occurring at more than twice the global average rate — a phenomenon known as Arctic amplification — with sea ice extent in September 2023 reaching its lowest recorded minimum. Understanding why these changes are happening requires a precise understanding of the atmosphere itself: its composition, its energy dynamics, and the role of greenhouse gases in regulating Earth's temperature.
🌍 Why This Matters The greenhouse effect is not merely an academic concept — it is the fundamental physical mechanism driving the most significant environmental challenge of the 21st century. Every policy decision about energy, land use, transport, and agriculture ultimately connects back to the atmospheric chemistry explored in this topic. Understanding the science with precision is the foundation for evaluating any proposed solution.
Core Concepts & Definitions
Before we can understand how the greenhouse effect works, we need to understand the medium in which it operates: Earth's atmosphere. The atmosphere is not a uniform blanket of gas. It is a layered, dynamic system with distinct chemical and physical properties at different altitudes — and these properties determine how energy moves through it.
The Structure and Composition of the Atmosphere
Earth's atmosphere is composed primarily of nitrogen (N₂, approximately 78%) and oxygen (O₂, approximately 21%), with argon (Ar) making up most of the remaining 1%. These three gases, however, play almost no role in the