Global atmospheric circulation model
The global atmospheric circulation model explains the way heat is distributed around Earth, resulting in different climates.
- The equator is hottest as the heat from the sun is most concentrated on its small area.
- The hot air rises, creating low pressure and forming clouds (rain). The air reaches the edge of the troposphere and is pushed north and south.
- As the air/clouds travel, they cool and begin to sink around the tropics, creating high pressure.
- High pressure — an anticyclone; air sinks so no clouds are formed (no precipitation).
- Low air pressure — a cyclone; air rises so clouds are formed (precipitation).
- Tropical, wet climate — found near the equator where cyclones occur.
- Desert, dry climate — found near the tropics where anticyclones occur.
Equatorial climate
- Relative humidity usually over 75%.
- Average rainfall over 1500mm, which is fairly even year round.
Types of rainfall
- Convectional rainfall — The sun heats the land and water evaporates. Warm air rises and clouds condense. Rainfall occurs.
- Relief rainfall — Warm air is forced up the high relief (e.g. a mountain). It condenses and rain occurs. The other side of the tall relief is called the rain shadow as no rain reaches that side.
- Frontal rainfall — Two bodies of air meet each other. Warm air is forced over the cold air. Condensation forms clouds. It rains heavily along the front.
Factors affecting climate
| Factor | Effect on climate |
|---|---|
| Distance from the coast (sea breeze and land breeze) | The land heats and cools faster. In summer, a colder sea breeze keeps the coast cold. In winter the warm sea breeze keeps the coast warm. |
| Prevailing winds | Prevailing winds go over long areas and seas and, for example, can bring moisture from the ocean, or bring dry air from travelling over an area of land not ocean. |
| Altitude | The higher you go, the colder it is. |
| Ocean currents | Ocean currents can be warm or cold, heating or cooling the coast. |
The rainforest
An ecosystem is a large community of living organisms.
Layers of a rainforest
- Forest floor
- Understory layer
- Canopy layer
- Emergent layer
Why rainforest soil quality is poor
- Leaching — the removal of nutrients out of the soil by excess water.
- Fast nutrient absorption rates — as the rainforest is densely populated and competitive, when a plant decomposes its nutrients are quickly absorbed by other nearby plants.
- Soil erosion — the removal of the top layer of soil due to wind, water and living plants/animals.
Rainforest case study — Borneo
Deforestation — the cutting down of large areas of trees to clear up space for other purposes.
- Malaysia has one of the fastest rates of deforestation in the tropical world.
- Borneo is 130 million years old.
Causes and effects of deforestation
| Causes | Effects |
|---|---|
| Logging — the cutting down of trees to make into commercial items. Trees act as a carbon sink, so felling them releases the stored CO2 back. | Soil erosion — the degrading of the upper layer of soil. Crops take nutrients out of the soil. The rain comes and washes the loose soil away. |
| Plantations / farming (palm oil) — 85% of the world's palm oil is from Indonesia and Malaysia together. | Climate change — loss of carbon sinks. |
| Population pressure — 1970-2000 Indonesia had to transmigrate thousands of Indonesians from Java island to Borneo. | Loss of biodiversity — e.g. pygmy elephants and orangutans. |
| Hydroelectric power — e.g. the Bakun HEP scheme in Borneo. | Indigenous tribes — deforestation displaces them. 330 tribes in 1900, now far fewer. Since they are unadjusted to urban life many die young, a lot of the time due to drugs and alcohol. |
The desert
A desert is a land of extremes that receives less than 250mm of rainfall annually.
- Caused by high pressure air and usually found at the lines of latitude where dry air starts to sink (23-30 degrees north and south). It is dry as all the moisture has been used up by precipitation.
- Characterised by dry conditions, short periods of rainfall, poor soil quality and high temperatures.
Adaptations of plants and animals
Cacti
- They store water in their leaves, stems or roots.
- They have spines instead of leaves to minimise water loss.
- Spines also protect cacti from being eaten.
- They have widespread root systems to reach water from far away.
Camels
- Slit nostrils and long double eyelashes to bat away sand.
- Humps of fat to use as energy when nourishment is not available.
- Large, tough lips to eat thorny desert plants.
- Broad flat feet to spread weight and protect from sand heat.
Fennec foxes
- Large ears to expel heat.
- They are nocturnal, which helps them with heat.
- Thick hair to insulate during cold nights and protect during the day.
- Light fur to reflect the sun.
Kangaroo rats
- They live in burrows.
- They have large back legs that can help them jump 3m away from predators.
- They get moisture from a seed diet.
Desertification
Desertification — the process in which land becomes desert, typically as a result of drought, deforestation or inappropriate agriculture.
- The Sahel in the Sahara is the edge of the desert where desertification is occurring actively.
Desert case study — Thar Desert (India and Pakistan)
- Home to 16 million people.
Challenges and opportunities of living in a desert
| Challenges | Opportunities |
|---|---|
| Extreme temperatures — can exceed 50 degrees Celsius. Livestock need shade. Working in heat is hard. | Farming — irrigation, e.g. the Gandhi Canal (1958). |
| Accessibility — some areas only accessible by camel. High temps cause tarmac to melt. Overweight public transport. Cars often break down from heat. | Energy — wind and solar farms. Jaisalmer is one of the biggest wind parks in India. |
| Water supply — low annual rainfall. High temp thus quick evaporation. Farming and population are increasing. | Mining — gypsum (construction) and phosphorite (fertilisers). |
| Tourism — camel riding and trekking. |