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Fundamental drivers of climate
- 1. Solar radiation
- 2. Atmospheric gases and particulates
- 3. The adiabatic process
a. Light varies in energy based on wavelength.
b. Gamma (shortest) – UV – visible light – Near infrared – far infrared (longest)
c. The different wavelengths produce color within the visible range (for us). Shorter wavelengths are blue, then green, yellow, and the longest wavelengths produce red.
d. Solar energy is either absorbed or reflected back into space.
Atmospheric gases and particulates
a. Ozone below the stratosphere absorbs most of the UV radiation.
b. Clouds and atmospheric gases reflect about 25% of the incoming solar radiation back out to space.
c. Another 25% is absorbed by dust, water vapor, and carbon dioxide in the atmosphere.
- d. Solar radiation reflected from the earth’s surface is also partially absorbed by the
- atmosphere creating a “heat blanket.”
The Adiabatic process
a. As gas expands it cools; as gas is compressed, it heats.
b. Atmospheric pressure is greater near the ground than at high altitudes.
c. As air near the ground warms, it rises; cool air at higher altitudes sinks.
d. Warm air can hold more water vapor than cold air.
e. As warm wet air rises and cools it loses its ability to hold water vapor; water condenses and forms clouds and, if moist enough, rain.
a. Why do water droplets form on the outsides of cold drinks?
b. During the winter in a heated home, your skin tends to be dry. Why?
- Warm air can hold more water than cold air.
- A cold glass cannot hold much water vapor so the warm moist air around the glass condenses. While the warm room can hold more water and due to the removal of vapor though heating, water is removed from the body to level out the gradient between the environment.
The earth is spinning at a rate of
one revolution per day
a. Areas near the equator must cover more distance than areas near the poles
i. At the equator the earth moves at a rate of 1000 miles per hour.
ii. At 60o latitude, the earth is moving at a mere 522 mph. This leads to a clockwise motion of air masses and oceans in the northern hemisphere and a counterclockwise motion in the southern hemisphere (Coriolis effect)
The earth is round leading to a difference in the intensity or density of solar radiation striking the earth’s surface between the equator and the poles.
- a. When the sun is directly in line with a region it receives the maximum solar
b. When the sun is striking at an angle, the solar radiation is less.
The amount of atmosphere that the solar radiation must travel through before striking the earth’s surface is also greater near the poles than near the equator.
The earth’s axis is tilted with
respect to the sun
- a. The number of hours in a day varies as a function of where the earth is in its
- orbit around the sun
i. Longer days (summer) occur in California when the sun is preferentially striking the Northern Hemisphere.
ii. Shorter days (winter) occur when the sun is preferentially striking the Southern Hemisphere.
- b. Climate patterns on a geologic time scale were greatly influenced by the positions of
- the landmasses with respect to the equator.
1. Air currents
- a. Air near the equator is heated and rises until it hits the stratosphere where
- further heating ceases.
b. Air below pushes the stratospheric air outward, north and south.
c. Once the air hits the stratosphere it continues cooling as it flows north and south.
d. At some point it cools enough to begin to sink.
e. As it sinks, it warms and picks up water vapor, drying the environment.
f. This occurs around 30o latitude, north and south.
The entire process is repeated at 60o
1. Ocean currents
a. Ocean currents are primarily driven by wind.
b. The earth’s oceans are divided into two major bodies, the Pacific and the Atlantic.
- c. The Coriolis force causes a clockwise motion in the north and a counterclockwise
- current in the south.
The temperature of the ocean adjacent to a landmass can have a great effect on the region’s climate
1. The effect of mountains
- a. Rain shadow effect occurs as water-laden air moves up a mountain slope, cools and
- loses most of its water as rain or snow. As this same air descends down the opposite slope it is cold and dry. It warms and picks up water from the environment.
b. Climate changes as one goes up slope analogous to traveling further from the equator.
c. North and south-facing slopes differ because they receive different amounts of solar radiation. The slope receiving the most sun tends to be drier and the extremes greater.
- d. In the Northern Hemisphere, south-facing slopes receive more sun than north-facing
- e. In the Southern Hemisphere, north-facing slopes receive more sun than south-facing
a. The east coast of North America commonly experiences hurricanes yet the west coast
very rarely gets hurricanes that reach the borders of the USA. Why?
Ocean Currents due to the coriolis effect
1. The effects of vegetation. Vegetation
a. decreases wind flow
b. increases humidity
c. decreases temperature
d. moderates temperature fluctuations
a. The climates associated with very small areas are termed microclimates and are often associated with specific habitats.
b. Some examples of specific habitats with special climates are
ii. Forest litter
iv.North-facing edge of a tree or shrub
c. Both plants and animals are sensitive to microclimate.
A. The effects of moisture and temperature on biomes
1. Whittaker's ecoregions
Plant formations are depicted as a function of mean annual temperature and precipitation.
1. Local influences
- a. Soil type influences how deep roots can grow and the availability of water and
i. Organic horizon contains organic material like fallen leaves, dead animals.
- ii. The A horizon is a mixture of organic material and minerals (clay, silt, sand,
- iron, silicates, etc.)
- iii. The B horizon, or depositional horizon, contains materials that have been leached
- from the A and O horizons.
- iv. The C horizon consists of fragments of rock and often lies on top of the parent
- b. The frequency and intensity of natural disturbances like fire and hurricanes can
- also play an important role in determining the types of plants growing in a
Mountains can have several biomes occurring on their slopes because both temperature and rainfall are influenced by altitude.
A. Major Biomes
1. Problems with defining biomes
a. A biome is a vegetation ‘type’ characteristic of a given region.
b. Usually the vegetation type is driven by regional and local influences on climate.
c. Difficult to define, they may encompass several sub-biomes.
1. Tropical rain forest
a. Three major regions support tropical rain forests, all within 100 north and south of the equator.
b. Temperature varies very little throughout the year and every month generally receives at least 100 mm of rainfall (about three feet!).
c. Soils are generally nutrient-poor, acidic, thin, and low in organic matter. This is primarily caused by the heavy rains characteristic of the region.
d. Tropical rain forests have the greatest diversity of species of all the biomes. For example, one hectare (about a square football field, 100 yards by 100 yards) in the temperate forests may have a few dozen species of tree while a tropical rain forest may contain over 300 species.
e. Due to the height of the trees, the forest is very three-dimensional with many species being found only in certain heights within the forest.
Specific adaptations for both plants and animals have evolved for living in such a biologically dense environment.
1. Tropical dry forest
a. Tropical dry forests are found primarily between 100 and 250 north and south of the equator.
- b. The dry season typically lasts from 6 to 7 months followed by 5 or 6 months of
- heavy rainfall.
- c. The soils tend to be less acidic and contain more nutrients than tropical rain
- forest soils.
- a. Plants
- are often deciduous with flowering occurring before the new leaves grow.
- b. Wind pollinated plants are more common in the tropical dry forest than in the rain
- a. Tropical savannas are generally found between 10 and 20 north and south from
- the equator.
b. Like the tropical dry forest, there is a dry and wet season. However, the rains come with intense lightning leading to fires at the end of the dry season. These fires kill young trees but allow grasses to thrive. The dry season is longer and drier than in the tropical dry forest.
c. The soils tend to have a low permeability to water allowing for seasonal pools of water to form and keeping water within reach of plants' roots. Trees cannot thrive in areas with water-logged soils; hence the soils help maintain the dominance of the grass species.
d. The tropical savanna is home to enormous herds of wandering animals. The African savanna hosts elephants, giraffes, zebras, etc.
a. Desert occupy about 20% of the land surface of the earth. They are found around 300 north and south from the equator.
- b. Deserts have both cold and hot periods, sometimes within the same 24-hour period. Of all the biomes, deserts have the lowest
- amount of precipitation.
- c. Desert soils are generally low in organic matter and may contain high concentrations
- of salt.
Plants are typically sparsely distributed and many are deciduous. Plants and animals have specific adaptations for preventing water loss.
Much of animal activity occurs at night when it is cooler and the air is moister.
Temperate woodland and shrub land
a. This biome is typically found between 30 and 40 latitude.
b. The climate is generally cool and moist in the fall, winter, and spring with the summer being hot and dry. Frosts may occur but are usually not severe. Hot dry summers lead to frequent and intense fires.
Water conservation is common in both plants and animals. Many plants are fire-adapted and some require fire for nutrient cycling.
1. Temperate grassland
a. Approximately 24% of the Earth's vegetation is grassland. Much of North America and temperate Eurasia is dominated by grasslands.
b. Climate is characterized by summer rainfall and cold dry winters.
c. Soils are generally deep and fertile (The vast agricultural fields of corn, wheat, etc., of the USA are converted grasslands.)
- d. These grasslands once supported huge herds of roving herbivores like bison and
a. These forests are typically between 30 and 55 latitude.
b. Temperatures are generally not extreme with ample rainfall. Some temperate forests receive enough rainfall to be called rain forests.
c. The soils tend to be very fertile and rich in both organic and inorganic nutrients.
Species diversity and plant biomass is the greatest of all of the temperate biomes. Many forests exhibit high degrees of stratification.
- a. Eleven percent of the earth's land surface is covered with boreal forests and
- typically these forests are found between 50 and 65 latitude.
b. The winter is long and the summer is short. The growing season lasts only a few months. Winter temperatures can be very extreme (-70C) and summer temperatures can reach over 30C. Precipitation is moderate.
c. Soils tend to have low fertility and are thin and acidic. In many regions the subsoil is permanently frozen (permafrost) excluding deep roots.
d. Generally these forests are dominated by evergreen conifers.
a. Tundra is commonly found at greater latitudes than the boreal forests.
- b. The climate is cold and dry; however, the extremes are less than those seen in the
- boreal forest. Because evaporation is
- limited, the summers are soggy and the tundra hosts ponds and streams.
c. Soil building is exceedingly slow and permafrost is common.
The tundra is dominated by a thick spongy network of short shrubs and dwarf trees, primarily willows and birch. Huge herds of caribou and musk ox are common.
- a. Increasing elevation is analogous to increasing latitude. The climate becomes colder and the plant formations change
- b. Mountain ranges located near the equator tend to have greater precipitation than those
- further away from the equator.
c. Mountain ranges can also influence the amount of rainfall that reaches the leeward side via the rain shadow effect.