Chapter 4—Global Climates and Biomes

CORE CASE STUDY:Floods, Droughts, and Famines

I.Global processes determine weather and climate

  • Weather is a local area’s short-term physical conditions such as temperature and precipitation.
  • Average temperature and average precipitation are the two major factors that determine climate of a region, together with the related factors of latitude and elevation.
  • Climate refers to long term general patters of atmospheric conditions.
  • Water vapor, carbon dioxide, and other gases influence climate by warming the lower atmosphere and the earth’s surface.
  • These gases (water vapor, carbon dioxide, methane, and nitrous oxide) are known as greenhouse gases. They allow mostly visible light, some infrared radiation, and ultraviolet radiation to pass through the troposphere. This natural warming is the greenhouse effect.
  1. Earth’s Atmosphere

Five layers of gases kept in place by gravity that weakens as you move farther away from Earth.

  1. Troposphere: closest, densest, circulation & mixing of gases, weather
  2. Temperature decreases with distance from Earth
  3. Stratosphere: less dense, UV radiation heats the higher altitudes first, ozone layer
  4. Mesosphere (middle)
  5. Thermosphere: block harmful X-rays and UV rays, aurora borealis & aurora asustralis
  6. Exosphere
  1. Unequal Heating of the Earth
  2. Variation in the angle at which the sun’s rays strike earth; perpendicular at the equator, more oblique north and south.
  3. Variation in the amount of surface area over which the Suns’ rays are distributed; smaller, more concentrated area at the equator, more oblique north and south.
  4. Some areas reflect more solar energy than others. Tropical regions have 10-20% albedovalues, polar regions have 80-95%.

C. Atmospheric Convection Currents

1. Density

  • Warm air has a lower density, rises, has a higher capacity for water vapor

2. Water vapor capacity

  • When air temperature falls, saturation point decreases, precipitation

3. Adiabiatic heating and cooling

  • Air pressure decreases with altitude, allowing air to expand in volume
  • When air sinks, increasing air pressure causes the air to decrease in volume

4. Latent heat release

  • Condensing water releases energy absorbed during evaporation
  • Hadley cells are convection currents that cycle between the equator and 30N and S.
  • The Intertropical Convergence Zone (ITCZ) receives the most intense sunlight, where the two rising Hadley cells converge. Dense clouds, thunderstorms
  • Polar cells are convection currents that cycle between 60N and S and the poles.

D. Earth’s Rotation and the Coriolis Effect

  • Rotation of the earth on its axis results in the earth moving faster beneath air masses at the

equator and slower at the poles.

  • Belts of prevailing winds are the result of atmospheric convection currents and the Corioliseffect.
  • The Corioliseffect deflects winds east and west.

E. Earth’s Tilt and the Seasons

  • Earth’s axis is tilted 23.5o
  • When one hemisphere is tilted towards the sun, the other is tilted away.

F. Ocean Currents

  1. Ocean currents influence climate by distributing heat from place to place and mixing and distributing nutrients.
  2. Gyres redistribute absorbed solar heat from one place to another, influence vegetation and climate near coastal regions.
  3. Upwelling helps mix ocean waters to distribute nutrients and dissolved oxygen needed for

aquatic organisms.

  1. Thermohaline circulation caused by differences in water density (salinity) and heat create ocean currents that are warm/cold.
  2. Ocean currents can affect the temperature of nearby landmasses.
  1. Every 3-7 years, the atmosphere and ocean interact in a way that reverses surface currents in the Pacific Ocean. (El Nino-Southern Oscillation)
  2. Trade winds near S. America weaken
  3. Warm equatorial water moves eastward toward Peru, suppressing upwelling and decreasing productivity
  4. Cooler and wetter weather in SE US, dry weather in southern African & SE Asia

G. Rain Shadows

1.Interactions between land and oceans and disruptions of airflows by mountains and cities affect local climates. Various topographic features can create local and regional microclimates.

a.One example of this is the rainshadow effect.

  • Air moves inland from the ocean with lots of water vapor.
  • Water vapor is dropped on the windward side of the mountain.
  • Cold, dry air travels to the leeward side where it descends and heats.

II. Variations in climate determine the dominant plant growth forms of terrestrial biomes

Different climates lead to different communities of organisms, especially vegetation. Differences in average temperature and precipitation due to global air and water circulation lead to differences in climate.

1.Average annual precipitation, temperature, and soil type are the most important factors in producing tropical, temperate, or polar deserts, grasslands, and forests.

2.Biomes are actually a mosaic of different biological communities.

3.Climate and vegetation vary with latitude and elevation of an area.

  1. Tundra
  2. Polar grasslands are covered with ice and snow except during a brief summer.
  3. Under the snow there is a thick, spongy mat of low-growing vegetation (grasses, mosses, dwarf
  4. woody shrubs).
  5. Permafrost is a permanently frozen layer of soil when water freezes.
  6. Global warming is causing some parts of the permafrost in parts of Alaska to melt.
  7. Another type of tundra, alpine tundra, occurs above tree line, but below permanent snow line.
  8. This area gets more sunlight than arctic tundra and has no permafrost.
  9. Boreal Forest
  10. Forests have enough precipitation to support stands of trees and are found in tropical, temperate, and polar regions. There are three main types of forest—tropical, temperate, and boreal (polar).
  11. Evergreen coniferous forests or boreal forests are located in areas just south of arctic tundra around the northern sub-arctic regions of the earth. These forests consist mostly of cone-bearing evergreen trees that keep their needles year-round to help the trees survive long, cold winters.
  • Long, dry, extremely cold winters are the norm. Summers are short.
  • Dominant trees are coniferous (cone-bearing) spruce, hemlock, fir, cedar, and pine.
  • There is low plant diversity.
  1. Temperate Rainforest
  2. Coastal areas support huge cone-bearing evergreen trees such as redwoods and Douglas fir in a cool and moist environment. Coastal coniferous forests or temperate rain forests are located along the western coast of Canada to northern California. Cool temperatures, abundant rain, and dense fog are the norm.
  3. Mountains are high-elevation forested islands of biodiversity and often have snow-covered peaks that reflect solar radiation and gradually release water to lower-elevation streams and ecosystems. Mountains are places with dramatic changes in altitude, climate, soil, and vegetation within very short distances.
  • Mountains have important ecological roles such as habitats for endemic species, biodiversity, and sanctuaries for animal species driven from other habitats.
  • Mountains play a major role in the hydrologic cycle.
  1. Temperate Seasonal Forest
  2. Temperate deciduous forests grow in areas with moderate average temperatures, abundant rainfall, and long, warm summers.
  • Broadleaf, deciduous trees dominate this biome. Leaves drop in fall, trees become dormant, and new leaves grow in spring.
  • More sunlight penetrates the canopy so there is richer diversity of ground level plant life.
  • On a worldwide basis, this biome has been disturbed by human activity more than any other

terrestrial biome as a result of establishing settlements, industrialization, and urbanization.

  1. Woodland/Shrubland
  2. Chaparral has a moderate climate but its dense thickets of spiny shrubs are subject to periodic fire. Chaparral, or temperate shrubland, is found in coastal areas that border deserts.
  3. The winter rainy season is longer than in desert; fog during spring/fall reduces evaporation.
  4. Low-growing evergreen shrubs with occasional trees is the vegetation type.
  5. Fires move swiftly when started in these areas. Chaparral is adapted to occasional fires.
  6. Floods/mudslides occur after fires at times.
  7. Temperate Grassland/Cold Desert
  8. Grasslands have enough precipitation to support grasses but not enough to support large stands of trees.Temperate grasslands with cold winters and hot, dry summers have deep and fertile soils that make them widely used for growing crops and grazing cattle.
  • Organic matter accumulates, producing fertile soil, as aboveground plant parts die each year.
  • North American grasslands are tall-grass prairies and short-grass prairies.
  • Temperature/cold deserts have cold winters and warm summers, with low rainfall. Do not support cacti and euphorbs.
  1. Tropical Rainforest
  2. Tropical rain forests have heavy rainfall on most days and a rich diversity of species occupying a variety of specialized niches in distinct layers. Tropical rain forests are near the equator and have hot, humid conditions.
  • Dominant plants are broadleaf evergreens with shallow roots.
  • A dense canopy blocks most sunlight from reaching lower levels.
  • Vines often drape individual trees.
  • Tropical forests cover about 2% of the land surface, but are habitat for about half the terrestrial species of earth.
  • Very little litter is on the forest floor because of rapid recycling of dead materials.
  • So far, at least half of these forests have been destroyed or disturbed by human activities.
  1. Tropical Seasonal Forest/Savanna
  2. Tropical seasonal forests & savannas have warm temperatures with dry and wet seasons. Trees drop their leaves during the dry seasons.
  3. Savannas are tropical grasslands with scattered trees and enormous herds of hoofed animals. Large herds of grazing and browsing animals feed here. Grazing & fire discourage woody plant growth.
  4. Soils are fairly fertile, warm temperatures promote decomposition but little rainfall constrains plants from using soil nutrients.
  5. Subtropical Desert
  1. Deserts have little precipitation and little vegetation.
  2. Tropical deserts are hot and dry most of the year with few plants, rocks, and sand.
  3. Cacti, euphorbs, and succulents are common and grow slowly. Annual plants grow quickly after rain.

III. Aquatic biomes are categorized by salinity, depth, and water flow

  • Saltwater and freshwater aquatic zones cover about 71% of the earth’s surface.
  • Salinity, depth, and flow of the water determines the major types of organisms found in an aquatic environment.
  • In aquatic systems, the key factors determining the types and numbers of organisms are temperature,

dissolved oxygen, sunlight availability, and nutrient availability.

  • Freshwater life zones include standing (lentic) bodies—such as lakes, ponds, and wetlands—and flowing (lotic) systems such as streams and rivers.
  1. Streams and Rivers
  • Three aquatic life zones, each with different conditions, can be identified along stream flow.
  • The source zone is narrow and fast moving. It dissolves large amounts of oxygen from air, and most plants are attached to rocks. Light is available, but is not very productive.
  • The transition zone forms wider, deeper streams that flow down gentler slopes. The water is warmer, with more nutrients, which supports more producers, but has slightly lower dissolved oxygen.
  • The floodplain zone has wider, deeper rivers. Water temperature is warmer; less dissolved oxygen is present and flow is slower.
  1. Lakes and Ponds
  • Lakes are large natural bodies of standing water found in depressions.
  • Rainfall, runoff, groundwater seepage and stream drainage feed lakes.
  • Generally consist of four distinct zones depending on depth and distance from shore.
  • Littoral zone is open, sunlit surface water away from shore and is the most productive area for food and oxygen production.
  • The limnetic zone is the open sunlit surface away from the shore that extends to the depth that sunlight reaches.
  • Profundal zone is deep oven water too dark for photosynthesis. Oxygen levels are lower.
  • Benthic zone consists of decomposers and detritus feeders. Fish swim from one zone to another. Sediment washing and dropping detritus feed this area.
  1. Freshwater Wetlands
  • Inland wetlands cover the land for a part of all of each year. Wetlands include swamps, marshes, prairie potholes, floodplains, and arctic tundra in summer.
  • Wetlands provide a variety of ecosystem services, including filtering waste, reducing flooding, replenishing stream flows, recharging aquifers, maintaining biodiversity, supplying valuable products, and providing recreation opportunities.
  1. Salt Marshes
  • Estuaries and coastal wetlands are subject to tidal rhythms, runoff from land, and seawater that mixes with freshwater and nutrients from rivers and streams.
  • Coastal wetlands/estuaries make nutrients available due to constant stirring of bottom sediment.
  • These areas filter toxic pollutants and excess plant nutrients, reduce storm damage, and provide nursery sites for aquatic species.
  1. Mangrove Swamps
  • Mangrove forest swamps grow in sheltered regions of tropical coasts.
  1. Intertidal Zone
  • Organisms living in the intertidal zone have adapted ways to survive the daily changes in wet/dry conditions and changes in salinity.
  • There is ample sunlight, and nutrients flow from land and wind/currents distribute them.
  • The coastal zone extends from the high-tide mark on land to the edge of the continental shelf.
  1. Coral Reefs
  • Coral reefs are home to ¼ of all marine species. Most diverse marine biome.
  • Symbiotic relationship between corals & algae mean they must live in warm, shallow, sunlit waters.
  • Coral bleaching is a growing concern worldwide.
  1. The Open Ocean
  • The open sea is divided into three vertical zones based primarily on penetration of light.
  • The photic zone is lighted, has floating phytoplankton carrying on photosynthesis, and has low nutrient levels except at upwellings.
  • Dissolved oxygen level is high.
  • The aphotic zone is the dimly lit middle zone; no producers are in this zone. Zooplankton and smaller fish live in this zone.
  • Organisms in this area are deposit feeders, or filter feeders.
  • Hydrothermal vents are present in some areas with specialized bacteria that generate energy via chemosynthesis and are food for other organisms.
  • Low average primary productivity and NPP occurs, but oceans are so large they make the largest contribution to NPP overall.

WORKING TOWARD SUSTAINABILITY: Is Your Coffee Made in the Shade?

Instructor's Manual: Chapter 71