Chapter 2 Summary

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

• Weather refers to the current conditions of temperature, precipitation, humidity, wind, and cloudiness, while climate is the long-term average weather at a given location.
• Climate determines the geographic ranges and physiological functioning of organisms and the resources that are available to them.
• Climate is driven by the balance of energy gains from solar radiation and reradiation from the atmosphere and energy losses due to 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 the surface of Earth.

• Latitudinal differences in the intensity of solar radiation at Earth’s surface establish atmospheric circulation cells.
• The Coriolis effect and the differential heat capacity of ocean waters and land act on atmospheric circulation patterns to determine the direction of prevailing winds at Earth’s surface.
• 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.

• Global temperature patterns are determined by latitudinal variation in solar radiation, as well as by oceanic circulation patterns and by the distribution of continents.
• Temperature decreases as the elevation of the land surface increases.
• Global patterns of terrestrial precipitation are determined by atmospheric circulation cells, but are also influenced by semipermanent pressure cells.

CONCEPT 2.4 Regional climates reflect the influence of the distribution of oceans and continents, elevation, and vegetation.

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

CONCEPT 2.5 Seasonal and long-term climatic variation are associated with changes in Earth’s position relative to the sun.

• The tilt of Earth’s axis as it orbits the sun causes seasonal changes in precipitation in tropical regions and in temperatures in temperate and polar regions.
• 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.
• Variations in climate over years to decades are caused by cyclic changes in atmospheric pressure systems, which have widespread effects beyond the regions where the pressure systems are located.
• Long-term climatic cycles over hundreds and thousands of years are associated with changes in the shape of Earth’s orbit, the angle of tilt of its axis, and its orientation to other celestial bodies.

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

• The salinity of Earth’s waters, including water in soils, is determined by the balance between inputs of salts and gains (precipitation) and losses (evapotranspiration) 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 pollutants.
• Oxygen concentrations are stable in most terrestrial ecosystems, but oxygen availability decreases as elevation increases. Concentrations of oxygen in aquatic ecosystems are low where consumption by organisms exceeds its slow rate of diffusion into water.