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The distribution of large-scale ecosystems (biomes) is determined by climate. Latitude, air pressure and winds are important factors that determine the climate of a place.

Latitude

Latitude is one of the most important factors in determining global climate patterns.

In the lower latitudes, around the Equator, temperatures are the highest. In the higher latitudes, such as the polar regions of the world, temperatures are lowest. Temperatures drop the further an area is from the equator due to the curvature of the earth.

In areas around the equator, sunlight has a smaller area of atmosphere to pass through, and the sun’s rays are concentrated in a smaller area.

In areas closer to the poles, sunlight has a larger area of atmosphere to pass through and the sun is at a lower angle in the sky. As a result, more energy is lost and temperatures are cooler.

High and low air pressure

Differences in temperature lead to variations in air pressure around the world. Low-pressure areas are created when air rises. This is called low pressure because the weight of the air above the Earth's surface is lower than average. High-pressure areas are created when air sinks. This is called high pressure because the weight of the air is above average when it sinks to the Earth's surface.

Low-pressure areas are associated with cloud and precipitation (rainfall) because:

1. as the air rises it cools, condenses and forms clouds
2. the water droplets in the clouds increase in size
3. they eventually become too heavy to be held and fall as precipitation

The air above the Equator is very hot and rises, creating an area of low pressure. The Equator experiences high amounts of rainfall due to this rising air resulting in a warm and wet equatorial climate (eg Amazon and Congo tropical rainforests).

High-pressure areas are associated with dry, warm and settled weather conditions. This is because sinking air does not result in precipitation.

Winds

The air travels in the upper atmosphere and sinks at approximately 30° north and 30° south of the Equator. When the air sinks it creates an area of high pressure.

These high-pressure areas experience very dry and warm conditions resulting in a hot desert climate (eg the Sahara and Kalahari deserts). Winds blow from areas of high to low pressure, which transfers the air from where it is sinking to where it is rising. This continual transfer of wind maintains the pressure belts of high and low pressure which creates different global climatic zones.