Visualizing Environmental Science

The Atmosphere and Climate

LEARNING OBJECTIVES

However, only two of these factors change over years

or decades: solar intensity and atmospheric composition.

Solar intensity changes in cycles, and over the past de-

cade, the sun has been slightly less intense than over the

previous century. We would expect this to lead to a slight

cooling of the atmosphere.

As we explore later in this chapter, however, changes

in the atmosphere’s composition have caused Earth’s

temperature to increase—along with other local and

global changes—over the past century. Across Earth, the

two most important factors that define an area’s overall

climate are temperature—both average temper-

ature and temperature variability—and both

average and seasonal precipitation. Latitude,

elevation, topography, quantity and types of

vegetation, distance from the ocean, and geo-

graphic location all influence climate. Other climate fac-

tors include weather conditions such as wind, humidity,

fog, cloud cover, and, in some areas, lightning. Un-

like weather, which changes rapidly, climate generally

changes slowly, over hundreds or thousands of years.

Because each region’s climate is relatively constant

for many years, organisms have adapted to them. The

1. Distinguish between weather and climate, and
   explain what determines Earth’s climate.


2. Summarize the effects of solar energy on
   Earth’s temperature.


3. Provide several reasons for regional
   precipitation differences.

W

eather refers to the conditions in the atmo-

sphere at a given place and time; it includes

temperature, atmospheric pressure, precipi-

tation, cloudiness, humidity, and wind.

Weather changes from one hour to the next

and from one day to the next.

Earth’s overall climate is determined by

several factors: the sun’s intensity, Earth’s dis-

tance from the sun, tilt of the Earth relative

to its rotational axis, distribution of water and

landmasses across Earth’s surface, and composition of

gases in Earth’s atmosphere. Most of these factors change

very slowly—for example, millions of years ago, Earth’s

surface had only one landmass, while now it has several.

A few billion years ago, the sun was only about 25 percent

as intense as it is now.

climate The typical

weather patterns that

occur in a place over

a period of years.

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Tropical climates occur in a region that spans the equator, from 15 to 25° latitude north to 15 to 25° latitude south.

Photographed at the Na Pali Coast, Kauai, Hawaiian Islands.

Equator

30° Tropic of Cancer

30°

60°

60°

Hawaiian

Islands

Kauai

Niihau Oahu

Molokai

Lanai Maui

Kahoolawe Hawaii

Tropic of Capricorn

Diane Cook and Len Jenshel/NG Image Collection