Learning Objectives

Each statement represents the primary learning objective for the corresponding major heading within the chapter. After you complete the chapter, you should be able to:

11.1 Distinguish between weather and climate and name the basic elements of weather and climate.

11.2 List the major gases composing Earth’s atmosphere and identify the components that are most important to understanding weather and climate.

11.3 Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere. Sketch and label a graph that shows atmospheric layers based on temperature.

11.4 Explain what causes the Sun angle and length of daylight to change during the year and describe how these changes produce the seasons.

11.5 Distinguish between kinetic energy and potential energy. Contrast heat and temperature.

11.6 List and describe the three mechanisms of heat transfer.

11.7 Sketch and label a diagram that shows the paths taken by incoming solar radiation. Summarize the greenhouse effect.

11.8 Summarize the nature and cause of the atmosphere’s changing composition since about 1750. Describe the atmosphere’s response and some possible future consequences.

11.9 Calculate five commonly used types of temperature data and interpret a map that depicts temperature data using isotherms.

11.10 Discuss the principal controls of temperature and use examples to describe their effects.11.11 Interpret the patterns depicted on world maps of January and July temperatures.

Concept Checks

 11.1 Distinguish between weather and climate. Write two brief statements about your current location: one that relates to weather and one that relates to climate. List the basic elements of weather and climate.

11.2 What are the two major components of clean, dry air? What proportion does each represent? Why is carbon dioxide an important component of Earth’s atmosphere? Why are water vapor and aerosols important atmospheric constituents? What is ozone? Why is ozone important to life on Earth?

11.3 Does air pressure increase or decrease with an increase in altitude? Is the rate of change constant or variable? Explain.The atmosphere is divided vertically into four layers, on the basis of temperature. List these layers in order, from lowest to highest. In which layer does practically all of our weather occur? What is the environmental lapse rate, and how is it determined? Why are temperatures in the thermosphere not strictly comparable to those experienced near Earth’s surface?

11.4 Briefly explain the primary cause of the seasons. What is the significance of the Tropic of Cancer and the Tropic of Capricorn?After examining Table 11.1, write a general statement that relates season, latitude, and length of daylight.

11.5 Define energy and contrast kinetic and potential energy. Distinguish between heat and temperature.

11.6 Describe the three mechanisms of heat transfer. Which mechanism is least important as a means of heat transfer in the atmosphere? In what part of the electromagnetic spectrum does the Sun radiate maximum energy? How does this compare to Earth? Describe the relationship between the temperature of a radiating body and the wavelengths it emits.

11.7 List the three paths taken by incoming solar radiation. What factors cause albedo to vary from time to time and from place to place? Explain why the atmosphere is heated chiefly by radiation emitted from Earth’s surface rather than by direct solar radiation. Which gases are the primary absorbers of longwave radiation in the lower atmosphere?

11.8 Why has the  level of the atmosphere been increasing for the past 200 years? How have temperatures in the lower atmosphere changed as greenhouse gas levels have increased?

11.9 How are the following temperature data calculated: daily mean, daily range, monthly mean, annual mean, annual range? What are isotherms, and what is their purpose?

11.10 List and briefly describe the major temperature controls.List four reasons why water bodies heat up and cool down slower that land surfaces. Describe the role that prevailing winds play in influencing temperatures. Contrast the daily temperature range on an overcast day with that on a clear and sunny day.

11.11 Why do isotherms generally trend east–west? Why do isotherms shift north and south from season to season? Where do isotherms shift most—over land or over water? Explain. Which area on Earth experiences the highest annual temperature range?

Concepts In Review: Heating the Atmosphere

11.1 Focus on the Atmosphere

Distinguish between weather and climate and name the basic elements of weather and climate.

Key Terms: meteorology, weather, climate

• Weather is the state of the atmosphere at a particular place for a short period of time. Climate is a generalization of the weather conditions of a place over a long period of time.

• The most important elements—quantities or properties that are measured regularly—of weather and climate are (1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4) type and amount of precipitation, (5) air pressure, and (6) speed and direction of the wind.

11.2 Composition of the Atmosphere

List the major gases composing Earth’s atmosphere and identify the components that are most important to understanding weather and climate.

Key Terms: airaerosols, ozone

• Air is a mixture of many discrete gases, and its composition varies from time to time and from place to place. If water vapor, dust, and other variable components of the atmosphere are removed, clean, dry air is composed almost entirely of nitrogen  and oxygen . Carbon dioxide , although present only in minute amounts, is important because it has the ability to absorb heat radiated by Earth and thus helps keep the atmosphere warm.

• Among the variable components of air, water vapor is important because it is the source of all clouds and precipitation. Like carbon dioxide, water vapor can absorb heat emitted by Earth. When water changes from one state to another, it absorbs or releases heat. In the atmosphere, water vapor transports this latent (“hidden”) heat from place to place; latent heat provides the energy that helps to drive many storms.

• Aerosols are tiny solid and liquid particles that are important because they may act as surfaces on which water vapor can condense and are also absorbers and reflectors of incoming solar radiation.

• Ozone, a form of oxygen that combines three oxygen atoms into each molecule , is a gas concentrated in the 10- to 50-kilometer (6- to 31-mile) height range in the atmosphere and is important to life because of its ability to absorb potentially harmful ultraviolet radiation from the Sun.

QUESTION:  This graph shows changes in one atmospheric component between January 2016 and January 2019. Which gas is it? How did you figure it out? Why is the line so wavy?

11.3 Vertical Structure of the Atmosphere

Interpret a graph that shows changes in air pressure from Earth’s surface to the top of the atmosphere. Sketch and label a graph that shows atmospheric layers based on temperature.

Key Terms: troposphere, environmental lapse rate, radiosonde, stratosphere, mesosphere, thermosphere

• Because the atmosphere gradually thins with increasing altitude, it has no sharp upper boundary but simply blends into outer space.

• Based on temperature, the atmosphere is divided vertically into four layers. The troposphere is the lowermost layer. In the troposphere, temperature usually decreases with increasing altitude. This environmental lapse rate is variable but averages about 6.5°C per kilometer (3.5°F per 1000 feet). Essentially, all important weather phenomena occur in the troposphere.

• Beyond the troposphere is the stratosphere, which exhibits warming because of absorption of UV radiation by ozone. In the mesosphere, temperatures again decrease. Upward from the mesosphere is the thermosphere, a layer with only a tiny fraction of the atmosphere’s mass and no well-defined upper limit.

QUESTION: When the weather balloon in this photo was launched, the surface temperature was 17°C. The balloon is now at an altitude of 1 kilometer. What term is applied to the instrument package being carried aloft by the balloon? In what layer of the atmosphere is the balloon? If average conditions prevail, what is the air temperature at this altitude? How did you figure this out?      

11.4 Earth–Sun Relationships

Explain what causes the Sun angle and length of daylight to change during the year and describe how these changes produce the seasons.

Key Terms: rotation, circle of illumination, inclination of the axis, Tropic of Cancer, summer solstice, Tropic of Capricorn, winter solstice, fall (autumnal) equinox, spring (vernal) equinox

• The two principal motions of Earth are (1) rotation about its axis, which produces the daily cycle of daylight and darkness; and (2) orbital motion around the Sun, which produces yearly variations.

• The seasons are caused by changes in the angle at which the Sun’s rays strike Earth’s surface and changes in the length of daylight at each latitude. These seasonal changes are the result of the tilt of Earth’s axis as it orbits the Sun.

QUESTION: Assume that the date is December 22. At what latitude do the Sun’s rays strike the ground vertically at noon? Is this date an equinox or a solstice? What is the season in Australia?

11.5 Energy, Heat, and Temperature

Distinguish between kinetic energy and potential energy. Contrast heat and temperature.

Key Terms: energy, kinetic energy, potential energy, heat, temperature

• Energy is the ability to do work. The two major categories of energy are (1) kinetic energy, which can be thought of as energy of motion; and (2) potential energy, energy that has the capability to do work.

• Heat refers to the quantity of thermal energy present in a material, whereas temperature refers to intensity—how hot the material is. Heat flows from regions of higher temperature to regions of lower temperature.

11.6 Mechanisms of Heat Transfer

List and describe the three mechanisms of heat transfer.

Key Terms: conduction, convection, radiation, electromagnetic radiation, visible light, infrared radiation, ultraviolet (UV) radiation

• The three mechanisms of heat transfer are (1) conduction, the transfer of heat through matter by molecular activity; (2) convection, the transfer of heat by the movement of a substance from one place to another; and (3) radiation, the transfer of heat by electromagnetic waves.

• Electromagnetic radiation is energy emitted in the form of electromagnetic waves, which can transmit energy through the vacuum of space. The wavelengths of electromagnetic radiation range from very long (radio waves) to very short (gamma rays). Visible light is the only portion of the electromagnetic spectrum we can see.

• Some basic laws that relate to radiation are (1) all objects emit radiant energy; (2) for a given amount of surface area, hotter objects radiate more total energy than do colder objects; (3) the hotter the radiating body, the shorter the wavelengths of maximum radiation; and (4) objects that are good absorbers of radiation are good emitters as well.

QUESTION: Describe how each of the three basic mechanisms of heat transfer is illustrated in this image.

11.7 Heating the Atmosphere

Sketch and label a diagram that shows the paths taken by incoming solar radiation. Summarize the greenhouse effect.

Key Terms: reflection, scattering, albedo, diffused light, greenhouse gases, greenhouse effect

• About 50 percent of the solar radiation that strikes the atmosphere reaches Earth’s surface. About 30 percent is reflected back to space. The remaining 20 percent of the energy is absorbed by clouds and the atmosphere’s gases. The fraction of radiation reflected by a surface is called the albedo of the surface.

• Radiant energy absorbed at Earth’s surface is eventually radiated skyward. Because Earth has a much lower surface temperature than the Sun, its radiation is in the form of long-wave infrared radiation. Because atmospheric gases, primarily water vapor and carbon dioxide, are more efficient absorbers of long-wave than short-wave radiation, the atmosphere is heated from the ground up

• The selective absorption of Earth’s long-wave radiation by water vapor and carbon dioxide that results in Earth’s average temperature being warmer than it would be otherwise is referred to as the greenhouse effect.

11.8 Human Impact on Global Climate

Summarize the nature and cause of the atmosphere’s changing composition since about 1750. Describe the atmosphere’s response and some possible future consequences.

• By adding carbon dioxide to the atmosphere, primarily by burning fossil fuels and through deforestation, humans are contributing significantly to global warming.

• As a result of the extra heat retention due to added , Earth’s atmosphere has warmed by about 0.8°C (1.4°F) in the past 100 years, with most of this warming occurring since the 1970s. Temperatures are projected to increase by another 2° to 4.5°C (3.6° to 8.1°F) by 2100.

• Some consequences of global warming include (1) shifts in temperature and rainfall patterns, (2) a gradual rise in sea level, (3) changing storm tracks and a higher frequency and greater intensity of tropical storms, and (4) an increase in the frequency and intensity of heat waves and droughts.

11.9 For the Record: Air Temperature Data

Calculate five commonly used types of temperature data and interpret a map that depicts temperature data using isotherms.

Key Terms: daily mean, daily temperature range, monthly mean temperature, annual mean temperature, annual temperature range, isotherm, temperature gradient

• Daily mean temperature is an average of the daily maximum and daily minimum temperatures, whereas the daily range is the difference between the daily maximum and daily minimum temperatures. The monthly mean is determined by averaging the daily means for a particular month. The annual mean is an average of the 12 monthly means, whereas the annual temperature range is the difference between the highest and lowest monthly means.

• Temperature distribution is shown on a map by using isotherms, which are lines of equal temperature. Temperature gradient is the amount of temperature change per unit of distance. Closely spaced isotherms indicate a rapid rate of change.

11.10 Why Temperatures Vary: Controls of Temperature

Discuss the principal controls of temperature and use examples to describe their effects.

Key Terms: temperature control, specific heat

• Controls of temperature are factors that cause temperature to vary from place to place and from time to time. Latitude (Earth–Sun relationships) is one example. Ocean currents (discussed in Chapter 10) are another example.

• Unequal heating of land and water is a temperature control. Because land and water heat and cool differently, land areas experience greater temperature extremes than water-dominated areas.

• Altitude is an easy-to-visualize control: The higher up you go, the colder it gets; therefore, mountains are cooler than adjacent lowlands.

• Geographic position as a temperature control involves such factors as mountains acting as barriers to marine influence or whether a place is on a windward or a leeward coast.

11.11 World Distribution of Temperature

Interpret the patterns depicted on world maps of January and July temperatures.

• On world maps showing January and July mean temperatures, isotherms generally trend east–west and show a decrease in temperature moving poleward from the equator. When the two maps are compared, a latitudinal shifting of temperatures is seen. Bending isotherms reveal the locations of ocean currents.

• Annual temperature range is small near the equator and increases with an increase in latitude. Outside the tropics, annual temperature range also increases as marine influence diminishes.

QUESTION: Refer to Figure 11.37. What causes the isotherms to bend in the North Atlantic?