BIOLOGY · Stage 9 · Chapter 12: The Carbon Cycle and Climate Change
Biology 12.4 Predicting the future — Computer Climate Models
5 min read 6 parts Lesson 4 of 6
Lesson summary
12.4 Predicting the future — Computer Climate Models — Alhussan International Academy — Biology (Stages 7–9) notes: Describe predicted impacts of future climate change and how computer climate models are built, tested and evaluated.Svante Arrhenius — in the 1890s he calculated th…
- IPCC (Intergovernmental Panel on Climate Change)
- Prediction
- Droughts and heat waves
- Wetter regions
- Temperature changes
- Extreme weather
Section 1 of 6IPCC and the greenhouse effect
- Svante Arrhenius
- in the 1890s he calculated that doubling atmospheric carbon dioxide would make the Earth's surface 5 °C warmer, seriously affecting the climate.
- His predictions are coming true in the 21st century.
- IPCC (Intergovernmental Panel on Climate Change)
- it studies evidence from thousands of scientists worldwide and advises governments.
- It states that global warming is happening because of human activities such as burning fossil fuels and deforestation,
- which raise carbon dioxide and other greenhouse gases.
- Prediction
- by the middle of the 21st century global temperatures will rise by another 1.3-1.8 °C.
Section 2 of 6Predicted impacts
- Sea level
- as oceans warm and land ice melts, some scientists predict a rise of between 26 and 82 cm by the end of the 21st century.
- Low-lying countries such as Tuvalu, and areas of many other countries, will disappear beneath the sea.
- Droughts and heat waves
- as temperatures rise and rainfall patterns change, huge areas will become infertile and dry and arid land will expand.
- Species will die out where there is no water, people will starve and fires will destroy whole ecosystems.
- Wetter regions
- many parts will get more rain and snow than ever before, often as extreme storms or blizzards.
- This will cause floods that wash away fertile soil and cause loss of homes and lives.
- Temperature changes
- some countries will get hotter and others colder.
- Warmer places will support pests such as mosquitoes, ticks and crop pests, affecting health and agriculture.
- Plant life, animal migration patterns and local species will change, and many species will become extinct.
- Extreme weather
- hurricanes and storms will happen more often, and a single storm can badly damage power supplies, buildings, roads and railways.
- Hope
- only a third of the predicted temperature rise for the next half century will happen for certain,
- so changing how we live may stop climate change before it cannot be undone.
Section 3 of 6What a climate model is
- Climate model = a computer program that uses mathematical equations to represent the processes that control the climate.
- Grid
- the Earth is divided into a three-dimensional grid of boxes covering atmosphere, ocean, land and ice.
- For each box the model calculates temperature, pressure, humidity, wind and other quantities,
- and how energy and water move between neighbouring boxes through time.
- Computing
- there are billions of calculations, so very powerful supercomputers are needed.
Section 4 of 6Inputs and outputs
- Inputs
- energy from the Sun, greenhouse gas concentrations, aerosols from volcanoes and pollution, land use and ocean currents.
- Scenarios
- scientists run the model with different assumptions about future emissions, such as emissions that keep rising or fall sharply by 2050.
- Outputs
- predicted temperature, rainfall, sea level and ice cover for each region over coming decades.
Section 5 of 6Testing the model
- Hindcasting
- the model is started at a past date, such as 1900, to see whether it reproduces the known temperature record up to the present.
- Models with both natural and human factors match observed warming well, while models with only natural factors do not.
- Comparison
- many independently built models giving similar predictions increases confidence.
Section 6 of 6Strengths and limitations
| Strengths | Limitations |
|---|---|
| Can test what might happen without risk or cost | The climate is very complex; some processes, such as clouds, are hard to represent |
| Can test different future scenarios | The future depends on human choices that are unknown |
| Improve as data and computers improve | Grid boxes are large, so small-scale detail is missing |
- Uncertainty
- predictions are given as a range, such as 1.5 to 4.5 °C of warming by 2100 depending on the scenario.
- Uses
- governments plan sea defences, farming and energy supply and set emission targets.
- Weather forecasts
- they use similar models but are reliable for only a few days, while climate models predict long-term averages.
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