Global Climate Models (HL) (DP IB Environmental Systems & Societies (ESS))

Climate Models

• Climate models are highly complex mathematical tools used to understand and predict Earth’s climate

  • They simulate climate processes by using complex equations to represent the interactions within Earth’s atmosphere, oceans, land, and ice

  • Climate models predict possible outcomes by manipulating different inputs and observing potential changes

Inputs to climate models

• There can be a very large number of different inputs to climate models

  • This depends on the specific model being used

• Some common inputs include:

  • Greenhouse gas concentrations

  • Solar radiation levels

  • Volcanic activity

  • Land surface changes

• Some inputs are known accurately, while others, like past GHG levels, may use proxy data (e.g. ice cores)

How climate models work

• Climate models create predictions based on equations that represent key processes, such as:

  • Atmospheric circulation, which includes wind and heat flow

  • Ocean currents, which distribute heat across the planet

  • Water cycle processes, such as evaporation, precipitation, and condensation

• Models can be highly complex, integrating thousands of variables to simulate climate changes over time

Testing climate models: hindcasting

• Hindcasting is a technique used to test the accuracy of climate models

  • Models are run backwards in time from the present

  • By comparing modelled past climate data with actual recorded data, scientists can test the reliability of the model

• Hindcasting helps identify inaccuracies and improves model reliability for future predictions

Limitations and uncertainty in climate models

• There is some uncertainty in models due to:

  • Limited or imperfect input data, especially from ancient proxies

  • Simplified representations of complex natural processes

• These limitations mean that models predict a range of outcomes rather than a single precise forecast

• Models are updated as more accurate data and advanced computing methods become available

Climate Model Predictions

• Climate models provide future climate scenarios based on different inputs and assumptions

• They predict future impacts of climate change in several key areas, including:

  • temperature

  • sea levels

  • precipitation

Temperature change predictions

• Climate models predict global temperature changes under different greenhouse gas emission scenarios:

  • Higher emissions scenarios predict greater temperature increases

  • Predictions often give a range of possible temperature rises by the end of the century

    • For example, some models predict a temperature rise between 1.5°C and 4°C by 2100, depending on emissions

Sea-level rise predictions

• Climate models show possible scenarios for sea-level rise due to:

  • Melting polar ice and glaciers

  • Thermal expansion, where warmer water expands

    • For example, some models suggest that sea levels could rise by 0.5 to 1 metre by 2100 under high-emission scenarios

Precipitation pattern predictions

• Climate models predict changes in rainfall patterns:

  • Some regions may experience more frequent and intense rainfall

  • Other regions may become drier, leading to drought conditions

    • For example, some models predict increased rainfall in the northern hemisphere but drier conditions in parts of Africa

Uncertainty in predictions

• Different models may produce slightly different outcomes for the same scenario

• This range helps scientists understand possible outcomes and prepare for various future conditions