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IB DP ESS — Topic 2: Ecology | SL & HL | Paper 1 & Paper 2A/2B
🎯 Learning Intentions By the end of this note, you will be able to:
- Define climate, biome, and atmospheric circulation using IB-aligned ESS terminology.
- Explain how the unequal heating of Earth's surface drives atmospheric circulation cells and global wind patterns.
- Describe how latitude, altitude, ocean currents, and continentality interact to determine regional climate.
- Explain the relationship between climate and the distribution of major terrestrial and aquatic biomes.
- Analyse how human activities are altering climate patterns and, consequently, shifting biome boundaries at regional and global scales.
- Evaluate the implications of biome shifts for biodiversity, ecosystem services, and human well-being.
- Discuss contrasting worldviews (ecocentric, technocentric, anthropocentric) in relation to climate-driven biome change and conservation responses.
Real-World Context & Relevance
In 2019, satellite imagery revealed that the Sahara Desert had expanded southward by approximately 10% over the previous century, encroaching on the semi-arid Sahel region of sub-Saharan Africa. This process — known as desertification — has displaced millions of people, collapsed pastoral livelihoods, and triggered cascading biodiversity loss across one of the world's most biodiverse transition zones. The Sahel sits at the boundary between two biomes: the Sahara Desert and the tropical savanna. Its position is not fixed — it shifts in response to rainfall patterns driven by the West African Monsoon, which is itself controlled by large-scale atmospheric circulation systems thousands of kilometres away.
Meanwhile, in the boreal forests of Siberia and Canada, rising temperatures linked to anthropogenic climate change are causing the treeline — the boundary between the boreal forest biome and the Arctic tundra — to migrate northward at rates of up to 50 kilometres per decade in some regions (IPCC, "Climate Change 2021: The Physical Science Basis"). These two examples, separated by continents, share a common driver: the disruption of the atmospheric and oceanic circulation systems that have, for millennia, determined where on Earth particular climates — and therefore particular biomes — exist. Understanding how these systems work is not merely academic; it is the foundation for predicting, and potentially managing, some of the most consequential environmental changes of the 21st century.
🌍 Why This Matters Biomes are not static features on a map — they are dynamic expressions of climate. As atmospheric circulation patterns shift under anthropogenic forcing, biome boundaries move, ecosystem services are disrupted, and the species that depend on specific climate envelopes face extinction pressure. Understanding the link between atmospheric circulation, climate, and biome distribution is essential for predicting ecological futures and designing effective conservation and land-use policy.
Core Concepts & Definitions
Before we can understand why tropical rainforests exist near the equator and deserts cluster around 30° latitude, we need to understand what drives the patterns of temperature and precipitation that make these environments possible. The term we use to describe the long-term average conditions of temperature, precipitation, humidity, and wind in a region is climate — and it is fundamentally different from weather, which describes short-term atmospheric conditions.
📖 Key Definition — Climate Climate is the long-term average pattern of weather conditions (including temperature, precipitation, humidity, wind speed, and solar radiation) in a region, typically measured over a minimum of 30 years. It is distinct from weather ,