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Earth's Geography
and Climate

Explore how latitude, axial tilt, and atmospheric circulation shape Earth's diverse climate zones and biomes.

AP Environmental Science

What is Climate?

Climate is the long-term average of weather patterns in a region, typically measured over 30 years or more. It differs from weather, which describes short-term atmospheric conditions at a specific time and place.

Weather
Short-term: hours to days. "It's raining today."
Climate
Long-term: decades. "This region averages 100 cm of rain per year."

Axial Tilt: \(23.5^\circ\) That Changes Everything

Sun Axis
\(23.5^\circ\)
 Equator Tropic of Cancer Tropic of Capricorn N S

Solar Intensity and Latitude

0° Equator Direct rays 45°N Angled rays 90°N Pole Oblique rays

The angle of incidence determines how much solar energy a surface receives per unit area. At the equator, sunlight strikes nearly perpendicular, concentrating energy. At the poles, rays spread over a larger area, delivering less energy.

Atmospheric Circulation Cells

\(90^\circ\text{N}\)
\(60^\circ\text{N}\)
\(30^\circ\text{N}\)
\(0^\circ\text{ Eq}\)
\(30^\circ\text{S}\)
 Hadley Cell Ferrel Cell Polar Cell Trade Winds (NE) Westerlies Polar Easterlies

Explain why seasonal displacement of rainfall belts can create wet and dry seasons.

Use this illustration to explore the concept described in its caption.

Two schematic globes show selected northern ITCZ position in boreal summer and southern position in boreal winter, with Equator and10°N reference markers; local rainfall responses vary.
Seasonal movement of tropical convergence can alter rainfall at a location. Regional geography and atmospheric circulation modify the simplified seasonal pattern.

The Coriolis Effect

Earth's rotation causes moving air and water to be deflected: to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere. This deflection shapes wind patterns, ocean currents, and storm rotation.

Northern Hemisphere
Deflects right: hurricanes spin counterclockwise, westerlies blow SW to NE.
Southern Hemisphere
Deflects left: cyclones spin clockwise, westerlies blow NW to SE.

Rain Shadows and the Orographic Effect

Windward Leeward Moist air rises • • • Precipitation Dry air descends Rain Shadow Wet Biome

Key Distinction: Weather vs Climate vs Biome

Weather
Atmospheric conditions at a specific time and place. Changes hour to hour. Example: "Today's high is 28°C with rain."
Climate
Statistical average of weather over 30+ years for a region. Example: "Average annual rainfall is 120 cm."
Biome
A large ecological community defined by climate and dominant vegetation. Example: "Tropical rainforest biome."

Earth's Major Climate Zones

Polar (\(60^\circ\)-\(90^\circ\))
Temperate (\(30^\circ\)-\(60^\circ\))
Subtropical (\(23.5^\circ\)-\(30^\circ\))
Tropical (\(0^\circ\)-\(23.5^\circ\))
\(90^\circ\text{N}\)
\(60^\circ\text{N}\)
\(30^\circ\text{N}\)
\(23.5^\circ\)
\(0^\circ\)
 Cold Hot

Climate zones are primarily determined by latitude and the resulting angle of solar insolation. The tropics receive the most energy, while the polar regions receive the least.

Ocean Currents and Heat Distribution

Ocean currents act as a global heat conveyor belt, transferring thermal energy from the tropics toward the poles. The thermohaline circulation is driven by differences in water temperature (thermo) and salinity (haline).

Warm Currents
Flow from equator toward poles. Carry heat, moderate coastal climates. Example: Gulf Stream warms Western Europe.
Cold Currents
Flow from poles toward equator. Cool coastal areas, bring nutrient-rich upwelling. Example: California Current cools the U.S. West Coast.

El Nino and La Nina

ENSO (El Nino-Southern Oscillation) is a periodic climate pattern in the tropical Pacific that affects weather globally. It alternates between two phases:

El Nino
Weakened trade winds allow warm water to pool in the eastern Pacific. Results in: increased rainfall in South America, droughts in Australia and Southeast Asia, warmer global temps.
La Nina
Strengthened trade winds push warm water westward. Results in: flooding in Australia, droughts in South America, cooler global temps, stronger Atlantic hurricanes.

How to Analyze Climate Factors

1
Identify the latitude. Higher latitudes receive less direct solar radiation: colder baseline climate.
2
Check proximity to water. Coastal regions have maritime climates (moderate temps). Inland regions have continental climates (extreme temps).
3
Assess elevation. Temperature drops roughly \(6.5\,{}^\circ\text{C}\) per 1,000 m of altitude gain (environmental lapse rate).
4
Look for mountain barriers. Rain shadows create dry leeward sides. Windward sides are wet.
5
Consider ocean currents. Warm currents raise temperatures; cold currents lower them and may bring fog.

Ocean influence and mountain lifting modify the same latitude

A cold-coast mountain landscape with fog,lush windward slopes and drier inland terrain accompanies a checked air-path schematic.Ocean influence and mountain lifting can produce contrasting climates at the same latitude. A rain shadow develops when moisture-bearing air rises across a mountain and descends on the leeward side.

Wind and topography shape climate

Wind and topography shape climate. Ocean influence and mountain lifting can produce contrasting climates at the same latitude. A rain shadow develops when moisture-bearing air rises across a mountain and descends on the leeward side.Ocean influence and mountain lifting can produce contrasting climates at the same latitude. A rain shadow develops when moisture-bearing air rises across a mountain and descends on the leeward side.

Example: Latitude and Temperature

Question: Why is Quito, Ecuador (\(0^\circ\) latitude, 2,850 m elevation) cooler than Miami, Florida (\(25^\circ\text{N}\), sea level), even though Quito is closer to the equator?

1
Latitude factor: Quito at \(0^\circ\) receives more direct sunlight than Miami at \(25^\circ\text{N}\). This alone would make Quito warmer.
2
Elevation factor: Quito is at 2,850 m. Using the lapse rate: \(2.85 \times 6.5 = 18.5\,{}^\circ\text{C}\) cooler than sea level.
3
Result: Elevation effect dominates latitude. Quito averages \(15\,{}^\circ\text{C}\) while Miami averages \(25\,{}^\circ\text{C}\).

Example: Rain Shadow in the Pacific Northwest

Question: Seattle, WA receives ~950 mm of annual precipitation, while Ellensburg, WA (just 150 km east) receives only ~230 mm. Why?

1
Prevailing westerlies push moist Pacific air inland.
2
The Cascade Range forces air to rise. As it rises, it cools adiabatically and drops ~950 mm of precipitation on the windward (west) side.
3
Descending dry air on the leeward (east) side warms and absorbs moisture: Ellensburg receives only ~230 mm.

Example: The Gulf Stream Effect

Question: London, UK (\(51.5^\circ\text{N}\)) has milder winters than Winnipeg, Canada (\(49.9^\circ\text{N}\)), despite being farther north. Why?

London (\(51.5^\circ\text{N}\))
January average: \(5\,{}^\circ\text{C}\). Warmed by the Gulf Stream/North Atlantic Drift. Maritime climate: mild, wet winters.
Winnipeg (\(49.9^\circ\text{N}\))
January average: \(-16\,{}^\circ\text{C}\). No warm ocean current. Continental climate: extreme cold, dry winters.

Common Mistakes

✕ Confusing Weather and Climate
A cold winter day does not disprove global warming. Weather is short-term; climate is the 30+ year average.
✕ Ignoring Elevation
Assuming all equatorial locations are hot. High-altitude tropical cities (like Bogota or Nairobi) can be quite cool.
✕ Reversing Coriolis
Forgetting the direction: right in the Northern Hemisphere, left in the Southern. This applies to wind and ocean currents, not drain water.

Climate Factor Summary

Factor Effect on Temperature Effect on Precipitation
Latitude Higher lat = cooler Varies by circulation cell
Elevation \(-6.5\,{}^\circ\text{C}\) per km up More orographic rain at altitude
Ocean Currents Warm currents warm coast, cold cool Warm currents add moisture
Proximity to Water Maritime: moderate; Continental: extreme Coastal areas wetter
Rain Shadow Minimal direct effect Windward wet, leeward dry
ENSO El Nino warms globally Shifts rainfall patterns

Question 1 of 5

Which of the following best explains why equatorial regions receive more solar energy per unit area than polar regions?

Question 2 of 5

A city at \(30^\circ\text{N}\) latitude on the western side of a continent is likely to have which climate characteristics?

Question 3 of 5

During an El Nino event, which of the following changes occurs in the tropical Pacific Ocean?

Question 4 of 5

Using the environmental lapse rate (\(\approx 6.5\,{}^\circ\text{C/km}\)), if the temperature at sea level is \(30\,{}^\circ\text{C}\), what is the approximate temperature at 3,000 m elevation?

Question 5 of 5

A coastal city warmed by a major ocean current has mild winters despite being at \(55^\circ\text{N}\) latitude. If that current were to weaken significantly, which outcome is most likely?