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Climate Modelling and Future Projections
IB DP Biology — D: Continuity and Change | SL | D4.3 Advanced Climate Science
📋 What You Will Learn
- Identify the key components and inputs used in climate models, including greenhouse gas concentrations, solar forcing, and feedback mechanisms
- Explain how General Circulation Models (GCMs) simulate Earth's climate system using mathematical representations of physical, chemical, and biological processes
- Analyse climate model outputs — including temperature projections, sea level rise estimates, and precipitation changes — and evaluate their reliability and uncertainty
- Describe the IPCC Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs) as scenarios for future climate change
- Evaluate the strengths and limitations of climate models as scientific tools, including model validation against historical data
- Apply understanding of feedback loops (positive and negative) to explain how they amplify or dampen projected climate change
🔍 Guiding Question How do scientists use mathematical models to project future climate change, and how confident can we be in those projections?
🌍 Why This Matters In August 2021, the IPCC Sixth Assessment Report declared it "unequivocal" that human influence has warmed the climate — a conclusion reached not from a single thermometer, but from dozens of independent climate models run on supercomputers, each simulating the entire Earth system across centuries. The projections those models produce now directly inform international policy, infrastructure design, and agricultural planning for billions of people.
What Is a Climate Model?
Here is the problem scientists faced: Earth's climate is a system of staggering complexity. The ocean absorbs heat differently at the equator than at the poles. Ice reflects sunlight back into space. Forests transpire water vapour. Methane leaks from permafrost. No single equation can capture all of this — but a network of thousands of equations, running simultaneously on a supercomputer, can come remarkably close.
A climate model is not a weather forecast. Weather prediction asks: what will happen tomorrow? Climate modelling asks: what will the average state of the atmosphere be in 2100 if we continue burning fossil fuels? The distinction matters enormously for how we interpret model outputs.
📖 Key Definition — Climate Model A climate model is a mathematical representation of Earth's climate system, using equations that describe physical, chemical, and biological processes in the atmosphere, ocean, land surface, and cryosphere. Models are run on computers to simulate past, present, and future climate states.
📖 Key Definition — General Circulation Model (GCM) A General Circulation Model (GCM) is a three-dimensional climate model that divides the atmosphere and/or ocean into a grid of cells and solves equations of fluid dynamics, thermodynamics, and radiative transfer at each grid point across time steps. GCMs are the most comprehensive type of climate model currently used.
The Grid: How Models Divide the Earth
Imagine wrapping a net around the entire planet. Each square of that net is a grid cell — a three-dimensional box of atmosphere or ocean. Inside each cell, the model calculates temperature, pressure, humidity, wind speed, and dozens of other variables at every time step (typically 30 minutes of simulated time). The smaller the grid cells, the higher the resolution — and the more computing power required.
Modern GCMs use horizontal grid cells of approximately 50–100 km across and divide the atmosphere into 20–50 vertical layers. Processes smaller than the grid cell size — such as individual clouds or convection cells — cannot be directly simulated. Instead, they are represented through parameterisation : simplified mathematical relationships that approximate their average effect on the grid cell.
Components of the Climate System
A climate model is only as good as its representation of the real system. Earth's climate is driven by five