How climate shapes where biomes are found
Big idea: Long-term patterns of temperature and rainfall determine where different ecosystems develop on Earth.
Conditions in the atmosphere influence which plants and animals can survive in a place. Over time, these conditions shape large-scale ecosystems called biomes.
Short-term weather vs long-term climate
Weather can change quickly and includes factors such as temperature, rainfall, wind, and cloud cover.
Climate describes expected patterns rather than daily changes.
- Weather = short-term and variable
- Climate = long-term averages
- Climate influences vegetation and land use
Biomes are shaped by climate, not by day-to-day weather.
What a biome is
A biome can be found in different parts of the world where conditions are alike.
Even when biomes occur on different continents, they can support similar plant and animal communities if the climate is similar.
Major biome groups on Earth
Biomes can be broadly grouped based on whether they occur on land or in water.
- Aquatic biomes – freshwater and marine ecosystems
- Terrestrial biomes – land-based ecosystems
Terrestrial biomes can be grouped into several main categories.
- Forest biomes (tropical, temperate, boreal)
- Grassland biomes (tropical and temperate)
- Desert biomes (hot and cold)
- Tundra biomes (arctic and alpine)
Why temperature and rainfall matter most
The distribution of terrestrial biomes is mainly controlled by abiotic factors, especially temperature and precipitation.
These factors affect soil conditions and plant growth, which then determine which consumers can survive in the ecosystem.
- Warm, wet conditions support dense vegetation
- Dry conditions limit plant growth
- Cold temperatures slow biological processes
Linking climate to ecosystem structure
Each biome supports a unique combination of habitats, producers, and consumers based on climate conditions.
Changes in temperature or rainfall can shift biome boundaries and alter ecosystem stability.
Big exam takeaways (SL)
- Weather is short-term; climate is long-term
- Biomes form under similar climatic conditions
- Temperature and precipitation control biome distribution
- Similar biomes occur in different regions of the world
- Abiotic factors shape ecosystem structure
How different biomes are grouped and why they change
Big idea: Biomes are large-scale ecosystems shaped mainly by climate, and they can shift when climate conditions change.
Across the Earth, ecosystems with similar temperature and rainfall develop similar plant and animal communities. These large ecosystem groupings are called biomes.
How biomes are classified
A biome is classified mainly using abiotic factors such as temperature and precipitation.
Each biome has characteristic productivity and biodiversity, influenced by limiting factors such as water availability, temperature extremes, or nutrient levels.
- Climate is the main driver of biome type
- Abiotic limiting factors shape vegetation
- Vegetation then determines animal communities
Major biome groups studied at SL
Biomes are grouped into broad categories based on whether they occur on land or in water.
- Freshwater biomes
- Marine biomes
- Forest biomes
- Grassland biomes
- Desert biomes
- Tundra biomes
Biomes can be further subdivided, but SL focuses on broad patterns rather than fine detail.
Key features of major terrestrial biomes
- Forest biomes – high rainfall, high productivity, generally high biodiversity
- Grassland biomes – moderate rainfall, seasonal growth, maintained by grazing and fire
- Desert biomes – very low rainfall, low productivity, specialised adaptations
- Tundra biomes – low temperatures, short growing seasons, low biodiversity
Within each biome, plants show adaptations to climate conditions, and animals are adapted to available food, shelter, and seasonal change.
Coastal biomes: mangrove ecosystems
Mangrove ecosystems They occur at the boundary between land and sea.
- Located in warm, tropical and subtropical climates
- Found in intertidal coastal zones
- Influenced by salinity, tides, and anaerobic soils
- Highly productive and important for biodiversity and carbon storage
In exams, mangroves are treated as a biome shaped by abiotic factors such as salinity, tidal inundation, and temperature.
Why productivity and biodiversity differ between biomes
Productivity tends to be highest where conditions allow continuous photosynthesis, such as warm temperatures and sufficient water.
Biodiversity is usually highest where conditions are stable and resources are plentiful, and lowest where conditions are extreme or highly seasonal.
- Warm and wet biomes support high biodiversity
- Cold or dry biomes limit growth and species variety
- Limiting factors restrict population size and interactions
How climate change affects biome location
Rising global temperatures and changing precipitation patterns are altering the conditions that define biomes.
As climates change, biomes can shift poleward or to higher altitudes as species move to remain within their tolerance ranges.
- Some species change migration patterns
- Growing seasons may lengthen or shorten
- Existing ecosystems may become less stable
Biome shifts are a consequence of climate change, not direct human land use.
Big exam takeaways (SL)
- Biomes are classified mainly by climate
- Temperature and precipitation control biome distribution
- Each biome has characteristic productivity and biodiversity
- Limiting factors shape ecosystem structure
- Climate change is causing biome shifts worldwide
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How the atmosphere moves energy and shapes climate
Big idea: Uneven heating of the Earth by the Sun causes large-scale air movement that creates global climate patterns.
The Sun is the main source of energy for the Earth’s climate system. However, solar energy does not heat the planet evenly.
Differences in solar input cause air to move, transferring heat around the planet and influencing weather, climate, and biome distribution.
Why solar energy is unevenly distributed
The Earth is spherical and tilted on its axis. As a result, sunlight reaches different parts of the Earth at different angles.
- Sunlight is most direct near the equator
- Sunlight is spread over a larger area near the poles
- Day length varies with latitude and season
Areas receiving more direct sunlight experience higher temperatures than areas where sunlight arrives at a low angle.
How air movement balances global temperatures
Warm air is less dense and rises, while cooler air is denser and sinks. This difference in air density drives large-scale atmospheric circulation.
As warm air rises near the equator and cooler air sinks at higher latitudes, heat is redistributed around the Earth.
Atmospheric circulation helps prevent extreme temperature differences between the equator and the poles.
The three-cell circulation pattern
Global air movement can be simplified into a tricellular model.
- The Hadley Cell (near the equator)
- The Ferrel Cell (mid-latitudes)
- The Polar Cell (near the poles)
Each cell plays a role in moving air, heat, and moisture between different latitudes.
How circulation patterns affect rainfall
Where air rises, it cools and condenses, leading to cloud formation and rainfall. Where air sinks, conditions are drier.
- Rising air near the equator creates high rainfall
- Sinking air around 30° latitude creates dry conditions
- Rising air near 60° latitude increases precipitation again
These patterns help explain why rainforests, deserts, temperate forests, and tundra occur where they do.
Linking atmospheric circulation to biomes
Long-term patterns of temperature and precipitation influence soil development, vegetation type, and ecosystem productivity.
As a result, atmospheric circulation indirectly determines the distribution of major terrestrial biomes.
- Wet equatorial regions support tropical rainforests
- Dry subtropical regions support deserts
- Mid-latitudes support temperate forests and grasslands
- Cold polar regions support tundra
Big exam takeaways (SL)
- Solar energy is unevenly distributed across the Earth
- Warm air rises and cool air sinks
- Atmospheric circulation redistributes heat
- The tricellular model explains global air movement
- Climate patterns influence biome distribution
How water ecosystems are grouped and how oceans move heat
Big idea: Aquatic biomes are shaped by water properties, while ocean currents redistribute heat around the planet.
Water covers most of the Earth’s surface and supports a wide range of ecosystems. These aquatic ecosystems are grouped based on their physical and chemical conditions.
How aquatic biomes are classified
Aquatic biomes are classified mainly by salinity.
- Freshwater biomes – low salinity
- Marine biomes – high salinity
Each type contains a range of habitats with different productivity and biodiversity.
Freshwater ecosystems
Freshwater ecosystems are found inland and include rivers, lakes, ponds, and wetlands.
- Water movement affects oxygen and nutrient availability
- Temperature varies with season and depth
- Isolated water bodies may limit species movement
Productivity and biodiversity depend on limiting factors such as nutrient availability, light penetration, and oxygen levels.
Marine ecosystems
Marine ecosystems include oceans, coral reefs, estuaries, and coastal zones.
They are generally more stable in temperature than freshwater systems and support complex food webs.
- High biodiversity in coastal and shallow waters
- Primary production driven by phytoplankton
- Currents influence nutrient distribution
How ocean currents redistribute heat
The oceans absorb large amounts of solar energy. Ocean currents move this heat around the globe, influencing regional climates.
Without ocean currents, temperature differences between regions would be much more extreme.
Surface ocean currents
Surface currents occur in the upper layers of the ocean and are driven mainly by wind.
- Warm surface currents move heat away from the equator
- Cold surface currents move cooler water toward lower latitudes
- Currents influence coastal temperatures and rainfall
Surface currents help transfer heat from warm regions to cooler regions.
Deeper water movement (SL overview)
In deeper parts of the ocean, water movement is influenced by differences in temperature and salinity, which affect water density.
Colder, saltier water is denser and sinks, helping mix ocean water vertically and transport nutrients.
At SL, focus on the idea that density differences drive deep water movement — detailed mechanisms are HL.
Why ocean currents matter for life and climate
Ocean currents influence climate patterns, marine productivity, and species distribution.
- Moderate temperatures in coastal regions
- Support productive fishing zones
- Help regulate global climate
Big exam takeaways (SL)
- Aquatic biomes are classified by salinity
- Freshwater and marine systems have different limiting factors
- Oceans absorb and store solar energy
- Surface currents redistribute heat globally
- Ocean currents influence climate and productivity