• The general condition of temperature and
precipitation for an area for an extended period of
• The climate of any region of the world is
determined by 2 factors: 1) temperature and 2)
Factors that Affect Temperature
• Areas close to the equator receive direct rays
• In Polar Regions, sun’s rays are not as direct.
• As elevation increases, the
• Air is less dense.
3. Ocean Currents
• Some currents are warm.
• Surface temperature of water affects the
temperature of the air above it.
• Land near warm currents has warmer
temperatures. Ex: Ireland
Land near cold currents has cooler temperatures.
Ex: California coast.
Major Ocean Currents:
California surfer during the summer…wearing a wetsuit!!!
Factors that Affect Precipitation (2 factors)
1) Prevailing winds
They tend to blow from one direction
Moisture content may vary:
a) Warm air holds more moisture than cold air.
b) Winds from rising warm air tend to bring precipitation
c) Winds from rising cold air tend to bring little precipitation.
Direction form which wind blows
a) land breeze – dry Ex. Sahara desert in Africa
b) sea breeze – moisture Ex. England, Scotland, Ireland.
2. Mountain Ranges
Act as a barrier to winds and precipitation
a) Windward side – side facing wind receives more
b) Leeward side – side facing awy from wind receives less
1) Moist Air moves up windward side – cools, dropping
Moves over mountaintop to leeward side bringing dryer air.
There is little precipitation.
Example: Sierra Nevada mountain range: western side is moist, east side is
Changes in Climate
What causes the climate to change?
3 natural factors:
1) slow drifting of continents
2) changes in the sun’s energy output
3) variations in the position of the Earth relative to the sun,
collectively known as the “Milankovitch Cycles.”
1. Ice Ages
• Periodically, the Earth’s surface
have been covered enormous sheets
• 4 major ice ages (major glaciations)
during the past 2 million years.
• Average temperature was about 6° C
below today’s avg. temp.
• Lasts about 100,000 or more. The
most recent began about 1.75 mya
and ended 10,000 ago.
• Time period between major
glaciations are called interglacials.
(warm period - today)
What kind of life existed?
2. Drifting Continents
• Approximately 200
mya, Pangaea started to
• Temp and precip
• Moves only a few
cm/yr. So, climate
changes will happen
over millions of years.
3. Extinction of Dinosaurs
1) Dinosaurs could not adapt to
the slow change in climate.
2) Many plants became extinct.
3) Asteroid struck the Earth 65
mya. This resulted in
enormous clouds and dust
worldwide blocking the sun’s
rays. Temperatures dropped.
Actually, the real reason why
dinosaurs became extinct is
4. Variations in Radiant Energy
Some scientists believe the sun’s energy output changes over time,
affecting the Earth’s temperature. But there is no evidence.
5. Global Warming
Human activity may have influenced the climate.
• Fossil fuels – coal, oil, and natural gas. These release a
greenhouse gas - CO2 (Carbon Dioxide) which traps heat in the
• In the past 25 years, CO2 levels have increased by 8%. If this
continues, an increase of 2° C can be drastic.
6. El Nino
• Normally, tradewinds off the coast of South America
flow east-to-west and pile up warm water in the western
• Every few years, the tradewinds change direction,
allowing the pool of warm water to move east where it
blocks the rising cold water.
• These changes help trigger the global weather changes
associated with El Niño. EX. Increased rainfall in the
southern half of the U.S. & droughts in Indonesia.