Set 1 — Lecture 14 + 15

Global climate

The average climate of the whole Earth. It is assessed using things like globally averaged temperature, sea-surface temperature, sea ice, and greenhouse gases. If a question is about the whole planet, think global climate.

Regional climate

The climate of a specific area. It is classified mostly by temperature and precipitation. If a question is about one location or one climate type, think regional climate.

Global climate vs regional climate

Global climate is the average climate of the whole Earth, while regional climate is the climate of a specific place. If a question asks about climate classification, that is regional climate.

Climate classification uses

Temperature and precipitation are the two main variables used to classify regional climates. If a graph has those two axes, it is likely a climate classification question.

Köppen-Geiger Climate Classification System

A system that groups regional climates based on temperature and precipitation. If a question asks how climates are classified, this is the system.

Main climate classes

The five main climate classes are A tropical, B arid, C warm temperate, D continental, and E polar.

Tropical climate (A)

A climate that is hot year-round, with the coldest month above 64°F. If a clue says near the equator, hot all year, and humid, think A.

Arid climate (B)

A climate that is dry with little precipitation. It is dry because it forms where air sinks, so there are fewer clouds and less rain. If a question asks why B is dry, think downward motion and subsidence.

Warm temperate climate (C)

A moderate mid-latitude climate with enough precipitation to support diverse agriculture. If a question says neither hottest nor coldest, heavily populated, and good for agriculture, think C.

Continental climate (D)

A climate with large seasonal temperature differences, warm summers, and cold winters. If a clue says only in the Northern Hemisphere and strong seasonality, think D.

Polar climate (E)

A very cold and dry climate near the poles with limited vegetation. If the clue is tundra or ice cap, think E.

Where tropical climates are found

Near the equator, mostly under the Hadley cell. If a map clue is equatorial and rainy, think A.

Where arid climates are found

Near 30° north and 30° south where air sinks between the Hadley and Ferrel cells. If the clue is dry belts around 30°, think B.

Where warm temperate climates are found

In the mid-latitudes, often near coasts in the Ferrel cell. If the clue is moderate climate with many people, think C.

Where continental climates are found

Mainly in the Northern Hemisphere between about 40° and 60° north. If the clue is only Northern Hemisphere, think D.

Where polar climates are found

Mostly above 60° north and south near the poles. If the clue is extreme cold, think E.

Why climate B is dry

B is dry because it forms in a part of global circulation with downward motion, so there is a lack of clouds and precipitation. If “all of the above” includes wrong circulation logic, do not pick it.

Most populated climate

Warm temperate climate (C) is the most populated. If the question asks which climate is most populated, pick C.

Population order from least to most populated

E, D, B, A, C. If a question asks for ranking, start with polar and end with warm temperate.

Regional climate controls

Topography, ocean currents, and atmospheric weather patterns all help shape regional climate. If a true/false asks this, it is true.

Which climates do not support forests

Arid and polar climates generally do not support forests well. If a question tries to make continental the answer, be careful, because continental can support trees.

ENSO

El Niño Southern Oscillation is a short-term ocean-atmosphere climate cycle in the Pacific. If a question mentions Pacific sea-surface temperature, pressure, winds, and currents together, think ENSO.

La Niña

The cool ENSO phase. It has stronger trade winds, stronger upwelling, and cooler eastern Pacific water. If the clue is strong trade winds plus upwelling, think La Niña.

El Niño

The warm ENSO phase. It has weaker or reversed trade winds, suppressed upwelling, and warm water moving east. If the clue is weak winds and warm eastern Pacific water, think El Niño.

Walker Circulation

The east-west air circulation across the tropical Pacific tied to ENSO. If a diagram shows air, pressure, and water movement across the Pacific, think Walker circulation.

Equatorial Counter Current

An eastward-flowing current tied especially to transition into and establishment of El Niño. If a question asks which ENSO phase is associated with it, think El Niño.

La Niña weather effect

La Niña usually shifts the jet stream north and brings drier and warmer conditions across much of the U.S. If the clue is warmer and drier across much of the U.S., think La Niña.

El Niño weather effect

El Niño usually shifts the jet stream south and brings wetter and cooler conditions across much of the southern U.S. If the clue is wetter and cooler in the southern U.S., think El Niño.

NAO

The North Atlantic Oscillation depends on the pressure difference between the Bermuda or Azores high and the Icelandic low. If the question mentions those two pressure centers, think NAO.

Positive NAO

A stronger pressure difference that shifts the jet stream northward and makes it more zonal. If the clue is stronger gradient and northward jet stream, think positive NAO.

Negative NAO

A weaker pressure difference that shifts the jet stream southward and makes it more meridional. If the clue is southward jet stream and colder eastern U.S. winters, think negative NAO.

Teleconnection

A climate link where conditions in one region affect weather in another faraway region. If a question asks how ENSO and NAO can affect distant places, think teleconnection.

Volcanic eruptions and climate

Explosive eruptions can cause short-term global cooling because aerosols reflect sunlight. If the clue is cooling for 1 to 3 years, think explosive eruptions.

Composite volcano clue

A large explosive composite volcano can inject ash and aerosols into the stratosphere and cool the surface. If a multiple-choice asks volcano type plus effect, this is the answer.

11-year solar cycle

A natural cycle tied to sunspot activity and small changes in solar radiation. If the clue is sunspots and slight warming or cooling, think solar cycle.

More sunspots means

More sunspots means slightly more solar radiation reaching Earth. If asked what is true about the solar cycle, this is the safe clue.

Milankovitch cycles

Long-term orbital changes that affect solar radiation and help drive glacial and interglacial cycles. If a question asks what causes glacial/interglacial periods, think Milankovitch.

Eccentricity

A 100,000-year cycle in how elliptical Earth’s orbit is. A more eccentric orbit means greater seasonal variability.

Precession

A 26,000-year wobble of Earth that gradually shifts the seasons. If the question asks which cycle shifts the seasons, think precession.

Obliquity

A 41,000-year cycle in Earth’s tilt. Greater tilt means stronger seasonal contrast.

Milankovitch cycle order

From shortest to longest: precession, obliquity, eccentricity.