Summary of Chapter Concepts

Earth is warmed by the greenhouse effect. Much of the ultraviolet and visible light emitted by the Sun passes through the atmosphere and strikes clouds and the surface of Earth. Clouds and the planet begin to warm and emit infrared radiation back toward the atmosphere. The gases in the atmosphere absorb the infrared radiation, become warmer, and re-emit infrared radiation back toward Earth. These greenhouse gases allow the planet to become warmer than would otherwise be possible. The increase in production of greenhouse gases due to human activities increases the greenhouse effect and leads to global warming.

There is an unequal heating of Earth by the Sun. Each year, high latitude regions of the world receive solar radiation that is weaker in intensity due to a longer path through the atmosphere with a less direct angle, which causes the energy of the Sun to be spread over a larger area. In addition, the axis of Earth is tilted 23.5° and this causes seasonal changes in temperature.

The unequal heating of Earth drives air currents in the atmosphere. Due to the properties of air, the warmer temperatures near the equator drive atmospheric convection currents known as Hadley cells between approximately 0° to 30° latitude in the Northern and Southern Hemispheres. Polar cells are at higher latitudes, between approximately 60° to 90°. These air convection currents cause the distribution of heat and precipitation around the globe. Their path is also influenced by Coriolis forces that are created by the rotation of Earth.

Ocean currents also affect the distribution of climates. Ocean currents are driven by the unequal warming of Earth combined with Coriolis effects, atmospheric convection currents, and differences in salinity. Gyres exist on both sides of the equator and help distribute heat and nutrients to higher latitudes. El Niño–Southern Oscillation (ENSO) events represent a disruption in normal ocean currents in the South Pacific and the impacts on climates can be felt around the world. Thermohaline circulation is a deep and slow circulation of the world’s oceans driven by changes in salt concentration in the waters of the North Atlantic.

Smaller-scale geographic features can affect regional and local climates. Increased land area of continents reduces the amount of evaporation possible, which causes the Northern Hemisphere to experience less precipitation than the Southern Hemisphere. Proximity to the coast can also affect climates; regions that are more distant from coastlines typically have lower precipitation and higher variation in temperature. Mountain ranges force air to rise over them, causing higher precipitation on one side of the mountain range and rain shadows on the opposite side.

Climate and the underlying bedrock interact to create a diversity of soils. Soils are comprised of horizons that contain different amounts of organic matter, nutrients, and minerals. Soils can be weathered by processes including freezing, thawing, and leaching. In acidic soils of cool, moist regions, soils can experience podsolization, a process that breaks down clay particles and reduces fertility. In warm, humid climates, soils can experience laterization, a process that breaks down clay particles and leaches nutrients from the soil.