Introduction to the Basic Drivers of Climate
September 11 , 2012
What drives variation between climates?
Climate: Long term prevailing weather in an area. Largely determined by temperature and
precipitation. Serves as a determinant to the life in that area.
Sun: Provides energy for living organisms and rives the planet’s weather and climatic patterns
(near equator = greater solar input).
Areas in the tropics receive sunlight directly. Regions in the north and south receive
sunlight at an angle. This in turn reduces heat and energy that reaches those areas.
Earth is tiled on its axis by 23.5 . As Earth orbits the sun, its orientation to the sun
changes. Northern and southern tips of the Earth have opposite seasons and tropical
areas experience little change (rainfall).
Equinox: Both hemispheres receive equal solar input.
Sunlight intensity affects global winds, precipitation patterns, ocean circulations. These
are all the components of climate.
At the equator, Earth warms air and water. Since molecules spread apart when they are
warm, it is less dense than cold air. This causes heat to rise.
Sunlight causes water to evaporate from plants, soils and water.
Water molecules rise and condense to form clouds, then fall as precipitation.
Sunlight also creates winds. Warm air moves up and cold air fills its void. Tropicsl air
moves away from the equator, towards the north and south poles. o
As it travels, it cools, becomes denser and descends around 30 north or south latitude.
This dry air absorbs moisture from the ground, creating a dry environment. Some of the
air goes back to the equator, or to the poles.
At 60 north and south, the air rises again, cools and releases precipitation (less than
Cold air flows to the poles, absorbs moisture, which leads to cold climates of the polar
Westward and eastward winds affect ocean currents. Warm tropical waters carry heat
pole-ward along the east coast, cold water goes toward equator along the west coast (to
fill the void).
Deeper currents are driven by a combination of Earth’s rotation and temperature