SUMMARY

CONCEPT 2.1 Climate is the most fundamental component of the physical environment.

2.1.1 Outline the difference between weather and climate, with specific reference to their temporal scales.

Weather refers to the current conditions of temperature, precipitation, humidity, wind, and cloud cover. Climate is the long­term average and variation in weather at a given location.

2.1.2 Explain the importance of weather variability for ecological processes.

Through their impact on mortality, extreme weather events influence the geographic distributions of organisms.

2.1.3 Summarize how temperature is determined by the gains and losses of energy at Earth's surface.

The climate system is driven by the balance between energy gains from solar radiation and reradiation by the atmosphere and energy losses due to infrared radiation from Earth's surface, latent heat flux, and sensible heat flux.

CONCEPT 2.2 Winds and ocean currents result from differences in solar radiation across Earth's surface.

2.2.1 Draw connections between differential heat gain across Earth's surface and the development of atmospheric circulation cells.

Latitudinal differences in the intensity of solar radiation at Earth's surface establish atmospheric circulation cells.

The Coriolis effect and the difference in heat capacity between the oceans and the continents act on atmospheric circulation cells to determine the pattern of prevailing winds at Earth's surface.

2.2.2 Explain how surface winds and ocean currents move heat between the tropics and the poles.

Ocean currents are driven by surface winds and by differences in water temperature and salinity.

Winds and ocean currents transfer energy from the tropics to higher latitudes.

CONCEPT 2.3 Large-scale atmospheric and oceanic circulation patterns establish global patterns of temperature and precipitation.

2.3.1 Outline the determinants of global temperature and precipitation patterns.

Global temperature patterns are determined by latitudinal variation in solar radiation, but they are also influenced by oceanic circulation patterns and by the distribution of continents.

Global patterns of terrestrial precipitation are determined by atmospheric circulation cells, but they are also influenced by

semipermanent pressure cells.

2.3.2 Explain how a region's seasonal changes in temperature are affected by its location, whether it is near a large body of water or at the center of a large continent.

Seasonal variation in temperature is greater in the middle of a continent than on the coast because ocean water has a higher heat capacity than land.

2.3.3 Summarize how air density and air exchange cause a decrease in air temperature with increases in elevation on a mountain.

The heating of air by the ground surface is less effective in the highlands because of the lower air density; therefore, temperature decreases as the elevation of the land surface increases.

CONCEPT 2.4 Regional climates reflect theinfluence of oceans and continents, mountains, and vegetation.

2.4.1 Describe the changes in an air mass that moves from a maritime zone across mountains, on both the leeward and windward slopes.

Mountains force air masses passing over them to rise and drop most of their moisture as precipitation, resulting in moister environments on windward slopes and drier environments on leeward slopes.

2.4.2 Illustrate how energy exchange components are influenced

by vegetation and subsequently affect climate.

Vegetation influences regional climates through its effects on energy exchange associated with albedo, evapotranspiration (latent heat transfer), and surface winds (sensible heat transfer).

CONCEPT 2.5 Seasonal and decadal climate variation are associated with changes in Earth's position relative to the sun and the strength of atmospheric pressure cells.

2.5.1 Explain how the tilt of Earth's axis influences (1) seasonal changes in air temperature in temperate and polar zones and (2) seasonal changes in precipitation in the tropics.

The tilt of Earth's axis as it orbits the sun causes seasonal temperature changes in temperate and polar regions and precipitation changes in tropical regions.

2.5.2 Outline how seasonal changes in surface heating in temperate and polar lakes influence water density and result in the stratification of water.

Temperature-induced differences in water density result in nonmixing layers of water in oceans and lakes. In temperate- zone lakes, these layers break down in fall and spring, allowing the movement of oxygen and nutrients.

2.5.3 Describe how cyclic change in the position and strength of high- and low-pressure cells influences weather and climate variability.

Variations in climate over years to decades are caused by cyclic changes in atmospheric pressure cells. The oscillation in the

position of high- and low-pressure cells can lead to a weakening of the easterly trade winds or a shift to westerly winds. These changes have widespread effects beyond the regions where the pressure cells are located.

CONCEPT 2.6 Salinity, acidity, and oxygen concentrations are major determinants of the chemical environment.

2.6.1 Outline what determines the salinity and acidity of soils and waters.

The salinity of Earth's waters, including water in soils, is determined by the balance between inputs of salts and gains (by precipitation) and losses (by evaporation) of water.

The pH of soils and surface waters is determined by inputs of salts from the breakdown of rock minerals, organic acids from plants, and acidic pollutants.

2.6.2 Explain why oxygen concentrations vary depending on elevation, the influence of water on diffusion, and biological consumption.

Oxygen concentrations are stable in most terrestrial ecosystems, but oxygen availability decreases as elevation increases.

REVIEW QUESTIONS

1. Why is the variability of physical conditions potentially more important than average conditions as a determinant of ecological patterns, such as species distributions?

2. Describe the factors that determine the major latitudinal climate zones (the tropic, temperate, and polar zones).

3. Why are deserts more prone to salinization from irrigation than areas with greater precipitation?

HONE YOUR PROBLEM-SOLVING SKILLS

As we will see in Chapter 3, information presented in this chapter describing variation in climate can be useful in predicting where specific collections of plant types can be found. For the following descriptions, draw a graph that portrays the following important climate features.

1. Draw a graph that shows the seasonal change in temperature for both the center of the Australian continent and the center of Eurasia, with time (12 months) on the x- axis and temperature on the ó-axis. Use Figure 2.15 as a guide, and don't worry about the actual temperatures, but instead focus on the magnitude of the seasonal change.

2. Construct a graph showing the rain shadow effect (see Figure 2.18) along a west coast in the Northern Hemisphere. Use distance for the x-axis, spanning a location near the coastline, moving into a mountain range, and ending on the eastern side of the mountain, indicating where each is along the x-axis. Use both annual average temperature and precipitation on the ó-axis.

3. Graph the trend in annual precipitation for northern Mexico in an average year and for an El Nino year (see Figure 2.23); use time on the x-axis and precipitation on the ó-axis (hint: use Figure 2.21 as a guide).

LIST OF KEY TERMS

Acidity

albedo alkalinity

Atmospheric pressure

Climate

conduction continental climate convection Coriolis effect downwelling

El Nino Southern Oscillation epilimnion evapotranspiration

Ferrell cell

greenhouse effect

greenhouse gases

Hadley cell

heat capacity

hypolimnion hypoxic intertropical convergence zone lapse rate latent heat flux maritime climate

North Atlantic Oscillation Pacific Decadal Oscillation polar cells polar zones rain shadow effect Salinity salinization sensible heat flux stratification subsidence temperate zones thermocline tropical zone tropics turnover uplift

upwelling

weather