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Chapter 14: Climate


Ch. 14.1 Defining Climate

Climate is affected by several factors including latitude and elevation.

Annual Averages and Variations

Climatology- the study of Earth's climate and the factors that cause climate changes. Climate describes the long-term weather patterns of an area including: temperature, precipitation, wind, and other variables.


Data from thousands of locations around the world is averaged on a monthly or annual basis for a period of at least 30 years to determine the normals; the standard values for a location.

Limitations of Normals

Normals are not intended to describe usual weather conditions; they are the average values over a long period of time. Climate describes average weather conditions for a region, normals apply only to the specific place where the data were collected. Example: most data collected at airports; airports are located outside of cities.

Causes of Climate

Several factors influence climate: differences in latitude, topography, closeness of lakes and oceans, availability of moisture, global wind patterns, ocean currents, and air masses.


Different parts of Earth receive different amounts of solar radiation due to the tilt of the Earth on it's axis.

  1. Tropics- area between 23.5ºS and 23.5ºN of the equator. Receive the most solar radiation with sun's rays nearly perpendicular to Earth's surface.
  2. Temperate zones- between 23.5º and 66.5º N&S of the equator. Temperatures are moderate.
  3. Polar zones- 66.5º to the poles N&S. Solar radiation strikes the polar zones at a low angle so average temperatures are lower.

Topographic Affects

  • Large bodies of water affect the climates of coastal areas because water heats/cools more slowly than land.
  • Temperatures in lower atmosphere generally decrease with altitude so mountain climates are usually cooler than sea level.
  • Climate usually differs on opposite sides of mountains as a result of orographic lifting. Rising air cools, condenses, and drops its moisture. Windward side is usually wet and cool, Leeward side air is drier and warms as descends.

Air Masses

Air masses have distinct regions of origin; movement and interaction of air masses are two of the main causes of weather. Whether formed over land or water determines properties of air masses. Average weather conditions in/near regions of air-mass formation are similar to those exhibited by the air masses themselves.

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Ch. 14.2 Climate Classification

Koppen Classification System

Koppen classification system- a classification system for climates according to the average monthly temperatures and precipitation amounts. It also takes into account the vegetation found in different climates.

Koppen decided a good way to distinguish different climatic zones was by natural vegetation. He later modified it to include quantitative values to make his system more objective. He included the numerical values of temperature and precipitation.


Tropical Climates

Year-round high temperatures with up to 600cm of rain each year leading to rain forests. Tropical regions are almost continually influenced by maritime tropical air.

Areas that border the tropics to the N/S of the equator are transitions zones known as tropical wet and dry zones; including savannas. Savannas are areas with dry winter seasons as a result of the seasonal influx of dry continental air masses.

Dry Climates

Cover about 30% of Earth's land area. Continental tropical (cT) air dominates, precipitation is low, and vegetation is scarce. Evaporation rates exceeds precipitation rates. Two subtypes: arid (deserts) and semiarid (semideserts) which border wet climates.

Mild Climates

Classified into three subtypes:

  1. Humid subtropical- influenced by subtropical high-pressure systems; warm/muggy in summer, dry/cool in winter.
  2. Marine west-coast- constant inland air from the ocean; mild winters and cool summers with abundant precipitation.
  3. Mediterranean-nearness to dry midlatitide climates from south create warm/dry summers, cool/rainy winters created by storm systems from the north.

Continental Climates

Classified into three subtypes: warm summer, cool summer, subarctic.

Experience rapid, sometimes violent changes in weather. Polar air masses strong in winter, warm tropical air dominates in summer.

Polar Climates

Low temperatures, and low precipitation. Ice-cap polar climate at the highest latitudes of both hemispheres the land is permanently covered by ice and snow with no vegetation.
Highland climate has similar conditions to polar due to high altitudes.


A localized climate that differs from the main regional climate.

Heat Islands

Many concrete buildings and large expanses of asphalt can create a climate that is warmer than surrounding rural areas. Dark materials absorb more energy from the sun than surrounding vegetation causing it to heat the air around them.

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Ch. 14.3 Climatic Changes

Long-Term Climatic Changes

Climates have been, and currently are, in a constant state of change.

Ice Ages

Glaciers have alternately advanced and retreated over the past 2 million years.
Ice ages- periods of extensive glacial coverage which temperatures decreased by an estimated 5ºC.
Interglacial intervals- the alternation of ice ages with warm periods.

Short-Term Climatic Changes

Seasons- short-term periods with specific weather conditions caused by regular variations in daylight, temperature, and weather patterns.


The tilt of Earth on its axis as it revolves around the Sun causes different areas of Earth to receive different amounts of solar radiation; which creates the seasons. Throughout the year the seasons are reversed in the northern and southern hemisphere.

El Nino

El Nino- warm ocean temperatures that occasionally develop off the western coast of South America.
Normally a semipermanent high-pressure system, keeps warm water moving west across the Pacific Ocean. Creating a cool, dry climate along the northwestern coast of South America.

Occasionally the high pressure system weakens allowing the warm water from the western Pacific to surge eastward toward the South American coast. The warm water heats the air above it. Convection currents strengthen; normal cool and dry air gets much warmer and wetter. Changing climates.

La Nina- when trade winds blow stronger and warm water is pulled across the Pacific toward Australia causing the coast off South America to be cold and chilly.

Natural Causes of Climatic Changes

Changes in Earth's climate have been caused by natural events such as variations in solar activity, changes inEarth's tilt and orbit, and volcanic eruptions.

Solar Activity

Existence of sunspots that follow a 11 year cycle had been recognized by German scientist Samuel Heinrich Schwabe in 1843. English astronomer Edward Walter Maunder found that from 1645 to 1716 sunspots was scarce. The Maunder minimum- the term used to describe this period of low numbers of sunspots. This period corresponds with unusually cold climatic episode called the Little Ice Age.

Studies indicate that increased solar activity corresponds with warmer than normal sea surface temperatures, while periods of low solar activity coincide with colder sea surface temperatures.

Earth's Orbit

The shape of Earth's elliptical orbit appears to change, becoming more elliptical over the course of a 100,000 year cycle. More elliptical is warmer, less is colder due to change in the distance from sun.

Earth's Tilt

The angle of tilt varies from 22.1º to 24.5º every 41,000 years. Scientists theorize that changes in tilt may influence climate. A decrease in tilt could lead to: warmer, wetter winter in north; cooler mid-latitudes; build up in ice sheets.

Earth's Wobble

Earth wobbles on its axis, about 26,000 years, as it rotates. Currently the axis points at the North Star (Polaris) but in about 13,000 years will point at Vega causing a reversal of seasons at our poles.

Volcanic Activity

Scientists theorize that aerosols (dust-sized particles) released by volcanoes could affect global temperatures. Recent eruptions lowered global temperatures for a couple years following the eruptions.

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Ch. 14.4 Impact of Human Activities

Human activities can alter atmospheric conditions enough to influence changes in weather and climate.

Influence on the Atmosphere

Solar radiation that is not reflected by clouds passes freely through the atmosphere. It is then absorbed by Earth's surface and released as long wavelength radiation. This radiation is absorbed by atmospheric gases, some is reradiated back to Earth's surface.

The Greenhouse Effect

The process of absorption and radiation of energy in the atmosphere results in the greenhouse effect. Greenhouse effect- the natural heating of Earth's surface caused by certain atmospheric gases. Greenhouse effect warms Earth's surface by more than 30ºC and helps make life possible.

Scientists hypothesize it is possible to increase or decrease the greenhouse effect by changing the amount of atmospheric greenhouse gases, especially carbon dioxide and methane. This could lead to a rise in global temperatures, known as global warming.

Global Warming

Temperatures worldwide have shown an upward trend over the past 200 years. Consequences can be: melting ice caps causing a rise in sea level, spread of deserts, an increase in sea surface temperature, an increase in frequency and severity of storms.

Burning Fossil Fuels

One of the main sources of atmospheric carbon dioxide is the burning of fossil fuels: coal, oil, and natural gas. Almost any process that involves the burning of fossil fuels results in the release of carbon dioxide. Other greenhouse gases that are released are methane and nitrous oxide.


The mass removal of trees. Trees use carbon dioxide in the process of photosynthesis. Removal of trees reduces the amount of carbon dioxide that is removed from the atmosphere by photosynthesis.

Environmental Efforts

Individuals reduce the amount of carbon dioxide that is emitted by conserving energy; reducing fossil fuel consumption.

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Page last updated August 16, 2017.