APES Chapter 5: Climate and Terrestrial Biodiversity

Major factores that determine regional climates

1. Cyclical movement of air driven by solar energy, convection. 2.Uneven heating of the earth's surface by the sun Air is heated much more at the equator where the sun's rays strike directly, than at the poles where sunlight strikes at an angle and spreads out over a much greater area. Thus, solar heating varies with latitude. 3. Tilt of the Earth's axis which results in season changes The earth's axis (an imaginary line connecting the north and south poles) is tilted with respect to the sun's rays. As a result, regions north and south of the equator are tipped upward or away from the sun at different times as the earth makes its annual revolution around the sun. This means most areas of the world experience widely varying amounts of solar energy and as a result, different season throughout the year. 4. Rotation of the earth on its axis: Coriolis effect 5. Ocean currents: help to redistribute heat from the sun, thereby influencing climate and vegetation, especially near costal areas. This solar heat, along with differences in water density (mass per unit volume), creates warm and cold ocean currents. They are driven by prevailing winds and the earth's rotation (the Coriolis effect), and continental coastlines change their directions. As a result, between the continents the currents flow in roughly circular patterns called gyres, which move clockwise in the norther hemisphere and counterclockwise in the southern hemisphere.

Concept about how climate affects nature and the location of biomes

1. Desert, grassland, and forest biomes can be tropical, temperate, or cold depending on their climate and location.

Question about factors that influence climate

1. Identify the four factors that determine regional climates around the world. 2. Explain how a rain shadow desert forms.

Concept about factors that influence climate

1. Key factors that influence an area's climate are incoming solar energy, the earth's roation, global patterns of air and water movement, gases in the atmosphere and the earth's surface features.

Concept about factors that influence weather

1. Key factors that influence weather are moving masses of warm and cold air, changes in atmospheric pressure, and occasional shifts in major winds.

Other long-term factors that affect the earth's climate

1. Slight changes in the shape of the Earth's orbit around the sun from mostly round to more elliptical over a 100,000 year cycle 2. Slight changes in the tilt of the Earth's axis over a 41,000 year cycle. 3. slight changes in the Earth's wobbly orbit around the sun over a 20,000 year cycle. These three factors are known as the Milankovitch cycles.

Key questions

1. What factors influence weather? 2. What factors influence climate? 3. How does climate affect the nature and location of biomes?

In a desert, annual precipitation is low and often scattered unevenly throughout the year. During the day, the baking sun warms the ground and evaporates water from plant leaves and from the soil. At night, most of the heat stored in the ground radiates quickly into the atmosphere. This explains why in a desert, you might roast during the day but shiver at night.

A combination of low rainfall and varying average temperatures over many decades creates a variety of desert types (tropical, temperate, and cold) In all types of deserts, plants and animals have evolved adaptation that help them to stay cool and get enough water to survive.

Thermocline

A horizontal zone of gradual temperature change which separates warm and cold water

Coastal coniferous forests/ temperate rain forests

Another type of temperate forest. Found in scattered coastal temperate areas with ample rainfall and moisture from dense ocean fogs. These forests contain thick stands of large cone bearing/coniferous trees that keep most of their leaves (or needles) year round. Most of these species have small, needle shaped, wax coated leaves that can withstand the intense cold and drought of winter. Ex: Sitka spruce, Douglas fir, giant sequoia, and redwoods that once dominated undisturbed areas of these biomes along the coast of North America (from Canada to Northern California) In this biome, the ocean moderates the temperatures so winters are mild and summers are cool. The trees in these moist forests depend on frequent rains and moisture from summer fogs. Most of the trees are evergreen because the abundance of water means that they have no need to shed their leaves. Tree trunks and the ground are frequently covered with mosses and ferns in this cool and moist environment. As in tropical rain forests, little light reaches the forest floor. Many of the redwoods, Douglas fir, and western cedar forests have been cleared for their valuable timber and there is constant pressure to cut what remains. This threatens species such as the spotted owl and marbled murrelet that depend on these ecosystems. Clear cutting also loads streams in these ecosystems with eroded sediment and threatens species such as salmon that depend on clear streams for laying their eggs.

Coriolis effect.

As the earth rotates to the east the equator spins faster than the regions to its north and south. This means that air masses moving to the north or south from the equator are deflected to the east because they are also moving east faster than the land below them. Some of this high moving mass of warm air cools as it flows northeast or southeast from the equator. It becomes more dense and heavier and sinks toward the earth's surface at about 30° north and 30° south. Because it is a convection cell it starts flowing back towards the equator in what is know as a Hadley cell. Because of the Coriolis effect, this air moving towards the equator curls in a westerly direction. In the northern hemisphere, it thus flows southwest from northeast. In the southern hemisphere, it flow northwest from southeast. These winds are known as the northeast trade winds and the southeast trade winds. They are examples of prevailing winds because they blow almost continuously The warm air that does not descend in the Hadley cells at 30° north and 30° south continues moving towards the poles and curving to the east due to the Coriolis effect. These prevailing winds that blow generally from the west in temperate regions of the globe are known as westerlies. This complex movement of air results in six huge regions between the equator and the poles in which warm air rises and cool, then falls and heats up again in great rolling patters. The two nearest the equator are the Hadley cells. These convection cells and the resulting prevailing winds distribute heat and moisture over the earth's surface, thus helping to determine regional climates.

El Nino Southern Oscillation or ENSO

Change in wind patterns that happens every few years. Because normal wind patters in the Pacific Ocean are disrupted and this affects weather around much of the globe. Winds that usually blow from east to west usually weaken or reverse direction. This allows the warmer waters of the western Pacific to move towards the coast of South America. The thermocline sinks in the eastern pacific. Changes result in drier weather in some areas and wetter weather in other areas. A strong ENSO can alter weather condition over at least two thirds of the globe especially on the coasts of the Pacific and Indian oceans. Although an ENSO is a natural weather event and not a climate event, an ENSO can raise the earth's average temperature by as much as 0.25 celsius or 0.45 fahrenheit, affecting climate for a year or two.

Temperate deserts

Daytime temperatures are high in the summer and low in the winter. There is more precipitation than in tropical deserts. The scattered/widely dispersed vegetation (can't find a lot in one area) is mostly made up of drought resistant shrubs, cacti, or other succulents adapted to the dry conditions and temperature variations. Has more vegetation than tropical and polar deserts.

Tropical deserts

Hot and dry most of the year. They have few plants and a hard, windblown surface (surface has a lot of wind) strewn with rocks and sand. Ex: Sahara and Namib desert

About 60% of the world's major terrestrial ecosystems are being degraded or used unsustainably as the human ecological footprint gets bigger and spreads across the globe, according to the 2005 Millennium Ecosystem Assessment and later updates of such research.

How long can we keep eating away at these terrestrial forms of natural capital without threatening our economies and the long term survival of our own and many other species? No one know. But there are increasing signs that we need to come to grips with this vital issue. Many environmental scientists call for a global effort to better understand the nature and state of the world's major terrestrial ecosystems and biomes and to use such scientific data to protect the world's remaining wild areas from harmful forms of development. In addition, they call for us to restore many of the land areas that have been degraded, especially in areas that are rich in biodiversity.

One major type of tropical grassland is savanna

It contains widely scattered clumps of trees and usually has warm temperatures year round with alternating dry and wet seasons. Herds of grazing and browsing animals migrate across the savanna to find water and food in response to seasonal and year to year variation in rainfall and food availability. Savanna plants (like those in deserts) are adapted to survive drought and extreme heat. Many have deep roots that tap into groundwater.

Movements of air masses are strongly influenced by what?

Jet streams

Hurricanes and Typhoons

Kill and injure people, damage property, and hinder food production.

cold front

Leading edge of an advancing mass of cold air. Because cold air is denser than warm air, an advancing cold front stays close to the ground and wedges beneath less dense warmer air. It pushes this warm, moist air up, which produces rapidly moving, towering clouds called thunderheads. As it passes through, it can cause high surface winds and thunderstorms , followed by cooler temperatures and a clear sky.

Cold grassland/arctic tundra

Lies south of the arctic polar ice cap. During most of the year, these treeless plains are bitterly cold, swept by frigid winds, and covered with ice and snow. Winters are long with few hours of daylight, and the scant precipitation falls primarily as snow. Under the snow, the biome is carpeted with a thick, spongy mat of low growing plants, primarily grasses, mosses, lichens, and dwarf shrubs. Trees and tall plants cannot survive in the cold and windy tundra because they would lose too much of their heat. Most of the annual growth of the tundra's plants occur during the short 7 to 8 week summer, when there is daylight almost around the clock. One outcome of the extreme cold is the formation of permafrost. During the brief summer, the permafrost layer keeps melted snow and ice from draining into the ground. Thus, shallow lakes, marshes, bogs, ponds, and other seasonal wetlands form when snow and frozen surface soil melt. Hordes of mosquitos, black flies, and other insects thrive in these shallow surface pools. They serve as food for large colonies of migratory birds (especially waterfowl) that migrate from the south to nest and breed in the tundra's summer bogs and ponds. Animals in this biome survive the intense winter cold through adaptations such as thick coats of fur (arctic wolf, arctic fox, and musk oxen) or feathers (snowy owl) and living underground (arctic lemming). In the summer, caribou (reindeer) and other types of deer migrate to the tundra to graze on its vegetation. Tundra is vulnerable to disruption because of the short growing season, tundra soil and vegetation recover very slowly from damage or disturbances. Human activities in the arctic tundra (primarily on and around oil and natural gas drilling sites, pipelines, mines, and military bases) leave scars that persist for centuries.

Connections: Mountains and Climate

Mountains help regulate the earth's climate. many mountains are covered with glacial ice and snow that reflect some solar radiation back into space, which helps to cool the earth. However, many mountain glaciers are melting, primarily because the atmosphere has warmed over recent decades. Whereas glaciers reflect solar energy, the darker rocks exposed by melting glaciers absorb that energy. This helps to warm the atmosphere above them, which melts more ice and warms the atmosphere more in an escalating positive feedback loop.

In many coastal regions that border on deserts, we find a biome known as temperate shrubland or chaparral. Because it is close to the sea, it has a slightly longer winter rainy season than the bordering desert has and experiences fogs during the spring and fall seasons. Chaparral is found along coastal areas of souther California, the Mediterranean Sea, central Chile, southern Australia, and southwestern South Africa. This biome consists mostly of dense growths of low growing evergreen shrubs and occasional small trees with leathery leaves. Its animal species include mule deer, chipmunks, jackrabbits, lizards, and a variety of birds. The soil is thin and not very fertile. During the long, hot, and dry summers, chaparral vegetation dries out. In the late summer and fall, fires started by lightning or human activities spread swiftly. Research reveals that chaparral is adapted to and maintained by occasional fires. Many of the shrubs store food reserves in their fire resistant roots and have seeds that sprout only after a hot fire. With the first rain, annual grasses and wildflowers spring up and use nutrients released by the fire. New shrubs grow quickly and crowd out the grasses.

People like living in the chaparral biome because of its moderate, sunny climate. As a result, humans have moved in and modified this biome so much that little natural chaparral exists. The downside is that people living in chaparral assume the high risk of frequent fires, which are often followed by flooding during winter rainy season. When heavy rains come, torrents of water pour off the unprotected burned hillsides to flood lowland areas, often causing mudslides.

Tornadoes/twisters

Swirling, funnel-shaped clouds that form over land. They can destroy houses and cause other serious damage in areas where they touch down. The U.S. is the world's most tornado prone country and Australia is the second. Tornadoes in the plains of the Midwestern United States often occur when a large, dry, cold front moving southward from Canada runs into a large mass of warm humid air moving northward from the Gulf of Mexico. As the large warm front moves rapidly over the denser cold air mass, it rises swiftly and forms strong vertical convection currents that such air upward. Scientists hypothesize that the interaction of the cooler air nearer the ground and the rapidly rising warmer air above causes a spinning, vertically rising air mass, called a vortex. Most tornadoes in the American Midwest occur in the spring and summer when cold fronts from the north penetrate deeply into the Great Plains and the Midwest.

Temperate forest

The most common type of temperate forest is temperate deciduous forest. Temperate deciduous forest have warm summers, cold winters, and abundant precipitation (rain in summer and snow in winter months). They are dominated by a few species of broadleaf deciduous trees (ex: oak, hickory, maple, aspen, and birch). Animal species living in these forests include predators such as wolves, foxes, and wildcats. They feed on herbivores such as white tailed deer, squirrels, rabbits, and mice. Warblers, robins, and other bird species live in these forests during the spring and summer, mating and raising their young. The leaves of the trees in this forest drop off after developing their vibrant colors in the fall. This allows the trees to survive the cold winters by becoming dormant. Each spring, the trees sprout new leaves and spend their summers growing and producing until the cold weather returns. Because they have cooler temperatures and fewer decomposers than tropical forests have, temperate forests also have a slower rate of decomposition. As a result, they accumulate a thick layer of slowly decaying leaf litter, which becomes a storehouse of soil nutrients. On a global basis, temperate forests have been degraded by various human activities (especially logging and urban expansion) more than any other terrestrial biome.

Grasslands occur primarily in the interiors of continents in areas that are too moist for deserts to form and too dry for forests to grow. Grasslands persists because of a combination of seasonal drought, grazing by large herbivores, and occasional fires. All of which keep shrubs and trees from growing in large numbers.

The three main types of grasslands (tropical, temperate, and cold/arctic tundra) result from long term combination of low average precipitation and varying average temperatures.

Cities also create distinct microclimates based on their weather averaged over three decades or more. Bricks, concrete, asphalt, and other building materials absorb and hold heat, and buildings block wind. Motor vehicles and the heating and cooling systems of buildings release large quantities of heat and pollutants. As a result, cities on average tend to have more haze and smog, higher temperatures, and lower wind speeds than the surrounding countryside.

These factors make cities heat islands

As energy flows from the sun to the earth, some of it is reflected by the earth's surface back into the atmosphere. Molecules of certain gases in the atmosphere, including water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), absorb some of this solar energy and release a portion of it as infrared radiation (heat) that warms the lower atmosphere and the earth's surface.

These gases are called greenhouse gasses, and they play a role in determining the lower atmosphere's average temperatures and thus the earth's climates.

Cold/ northern coniferous forest/ boreal forest/ taigas

They are found south of the arctic tundra in northern regions across North America, Asia, Europe, and above certain altitudes in the Sierra Nevada and Rocky Mountain range. In the subarctic, cold, and moist climate of the northernmost boreal forests, winters are long and extremely cold, with winter sunlight available only 6 to 8 hours per day. Summers are short, with cool to warm temperatures, and the sun shines as long as 19 hours a day during midsummer. Most boreal forests are dominated by a few species of coniferous evergreen trees or conifers such as spruce, fir, cedar, hemlock, and pine. Plant diversity is low because few species can survive the winters when soil moisture is frozen. Beneath the stands of trees in these forests is a deep layer of partially decomposed conifer needles. Decomposition is slow because of the low temperatures, the waxy coating on the needles, ad high soil acidity. The decomposing conifer needles make the thin, nutrient poor topsoil acidic, which prevents most other plants (except certain shrubs) from growing on the forest floor. Year round wildlife in this biome includes bears, wolves, moose, lynx, and many burrowing rodent species. Caribou spend winter in the taiga and summer in the arctic tundra. During the brief summer, warblers and other insect eating birds feed on flies, mosquitoes, and caterpillars.

When the drier air mass passes over the mountaintop, it flows down the leeward slopes (facing away from the wind) and warms up. This warmer air can hold more moisture, but it typically does not release much of it. This tends to dry out plants and soil below.

This process is called the rain shadow effect. Over many decades, it results in semiarid or arid conditions on the leeward side of a high mountain range. Sometimes this effect leads to the formation of deserts such as Death Valley (a part of the Mojave Desert) which lies within the U.S. states of California, Nevada, Utah, and Arizona.

The earth's surface absorbs much of the solar energy that strikes it and transforms it into longer wavelength infrared radiation, which then rises into the lower atmosphere. Some of this heat escapes into space, but some is absorbed by molecules of greenhouse gases and emitted into the lower atmosphere as even longer wavelength infrared radiation. Some of this released energy radiates into space, and some adds to the warming of the lower atmosphere and the earth's surface.

Together these processes result in a natural warming of the troposphere called the greenhouse effect. Without this natural warming effect, the earth would be a very cold and mostly lifeless planet.

Typhoons

Tropical cyclones that form in the Pacific Ocean.

Cold deserts

Vegetation is sparse/ spread out. Winters are cold, summers are warms or hot, and precipitation is low. Ex: Gobi Desert

Alpine tundra

another type of tundra, occurs above the limit of tree growth but below the permanent snow line on high mountains. The vegetation is similar to that found in arctic tundra, but it receives more sunlight than arctic vegetation gets. During the brief summer, alpine tundra can be covered with an array of beautiful wildflowers.

warm front

boundary between an advancing warm air mass and the cooler one it is replacing. Because warm air is less dense (weights less per unit of volume) than cool air, and advancing warm air mass rises up over a mass of cool air. As the warm air rises, its moisture begins condensing into droplets, forming layers of clouds at different altitudes. Gradually, the clouds thicken, descend to a lower altitude, and often release their moisture as rainfall.

La nina

cools some coastal surface water. A natural weather event that occurs every few years and leads to more Atlantic Ocean hurricanes, colder winter in Canada and the northeastern United States, and warmer and drier winters in the southeastern and southwestern U.S. It also usually leads to wetter winters in the Pacific Northwest, heavy rain in Southeast Asia, and sometimes more wildfires in Florida.

tropical cyclones

form over warm ocean water and sometimes pass over coastal land areas. Created by the formation of low-pressure cells of air over warm tropical seas. Unlike hurricanes, they take a long time to form and gain strength. This allows meteorologists to track their paths and wind speeds, and warn people in areas likely to be hit by the violent storms. For a tropical cyclone to form, the temperature of ocean water has to be at least 27 degrees celsius or 80 degrees fahrenheit up to 46 meters or 150 feet deep. Areas of low pressure over these warm ocean waters draw in air from surrounding higher pressure areas. The earth's rotation makes these winds spiral counterclockwise in the northern hemisphere and clockwise in the Southern hemisphere. Most air, warmed by the heat of the ocean, rises in a vortex through the center of the storm until it becomes a tropical cyclone. The intensities of tropical cyclones are rated in different categories, based on their sustained wind speeds. The longer a tropical cyclone stays over warm waters, the stronger it gets. Significant hurricane force winds can extend 64-161 kilometer (40-100 miles) from the center (eye) of a tropical cyclone.

Tropical rain forests

found near the equators where hot, moisture laden air rises and dumps its moisture. These lush forests have year round warm temperatures, high humidity, and almost daily heavy rainfall. this warm and wet climate is ideal for a wide variety of plants and animals. Tropical rain forests are dominated by broadleaf evergreen plants, which keep most of their leave year round. The tops of the trees form a dense canopy that blocks most light from reaching the forest floor. Many of the relatively few plants that live at the ground level have enormous leaves to capture what little sunlight filters down to them. Some trees are draped with vines (called lianas) that grow to the treetops to gain access to sunlight. In the canopy, the vines grow from one tree to another, providing walkways for many species living there. When a large tree is cut down, its network of lianas/vines can pull down other trees. Tropical rain forests have a high net primary productivity. They are teeming with life and possess incredible biological diversity. Although tropical rain forests cover only about 2% of the earth's land surface, ecologists estimate that they contain at least 50% of the known terrestrial plant and animal species. A single tree in these forests may support several thousand different insect species. Plants from tropical rain forests are a source of a variety of chemicals, many of which have been used as blueprints for making most of the world's prescription drugs. Rain forest species occupy a variety of specialized niches in distinct layers, which contribute to their high species diversity. vegetation layers are structured (for the most part) according to the plants' needs for sunlight. Much of the animal life (insects, bats, and birds) lives in the sunny canopy layer, with its abundant shelter and supplies of leaves, flowers, and fruits. Dropped leaves, fallen trees, and dead animals decompose quickly in tropical rain forests because of the warm, moist conditions and the hordes of decomposers. About 90% of the nutrients released by this rapid decomposition are quickly taken up and stored by trees, vines, and other plants. Nutrients that are not taken up are soon leached from the thin topsoil by the frequent rainfall and little plant litter builds up on the ground. The resulting lack of fertile soil helps explain why rain forests are not good places to clear and grow crops or graze cattle on a sustainable basis. At least half of the world's tropical rain forests have been destroyed or disturbed by human activities such as farming, and the pace of this destruction and degradation is increasing. Ecologists warn that without strong protective measures, most of these forests along with their rich species biodiversity and highly valuable ecosystem services could be gone by the end of this century.

Climate

general pattern of atmospheric conditions in a given area over periods ranging from at least three decades to thousands of years. Changes a lot slower than weather because it covers a larger time frame. Varies among the earth's different regions primarily because of global air circulation and ocean currents. Global winds and ocean currents distribute heat ad precipitation unevenly between the tropics and other parts of the world. Scientists have described the various regions of the earth according to their climates.

insolation

input of solar energy in a given area, varies with latitude. Partly explains why tropical regions are hot, polar regions are cold, and temperate regions generally alternate between warm and cool temperatures. The amount of solar radiation reaching the earth typically varies about every 11 years because of changes in solar magnetic activity that can warm or cool the planet.

Biomes

large terrestrial regions, each characterized by a certain type of climate and dominant forms of plant life. The variety of biomes and aquatic systems is one of the four components of the earth's biodiversity. Biomes are not uniform. They consists of a variety of areas, each with somewhat different biological communities but with similarities typical of the biome. These areas occur because of the irregular distribution of the resources needed by plants and animals and because human activities have removed or altered the natural vegetation in many areas. There are also differences in vegetation along the transition zone or ecotone between any two different ecosystems or biomes.

prevailing winds

major surface winds that blow almost continuously

Ocean currents

mass movements of ocean water.

Jet streams

powerful winds that circle the globe near the top of the troposphere. They are like fast flowing rivers of air moving west to east one in each hemisphere somewhere above and below the equator. They form because of the temperature difference between the equator and the poles, which causes air to move. As the air moves away from the equator (north and south) it is deflected by the earth's rotation and flows generally west to east. The greater the temperature difference, the faster the flow of these winds. Jet streams can influence weather by moving moist air masses from one area to another.

Atmospheric pressure

results from molecules of gases in the atmosphere (mostly nitrogen and oxygen) zipping around at very high speeds and bouncing off everything they encounter. Atmospheric pressure is greater near the earth's surface because the molecules in the atmosphere are squeed together under the weight of the air above them. An air mass with high pressured (called a high) contains cool, dense air that descends slowly towards the earth's surface and become warmer. Because of this warming, water molecules in the air do not form droplets, a process called condensation. As a result, clouds (which are made of droplets) usually do not form in the presence of a high. Fair weather with clear skies follows as long as this high remains over the area. A low-pressure air mass (called a low) contains low density, warm air at its center. This air rises, expands, and cools. When its temperature drops below a certain level (the dew point) moisture in the air condenses and forms cloud. The condensation process usually requires that the air contain suspended tiny particles of dust, smoke, sea salts, or volcanic ash (called condensation nuclei) around which water droplets can form. If the droplets in the clouds combine into larger drops or snowflakes heavy enough to fall from the sky, precipitation occurs. Thus, a low tends to produce cloudy and sometimes stormy weather.

Weather

set of physical conditions of the lower atmosphere (such as temperature, precipitation, humidity, wind speed, cloud cover, etc.) in a given area over a period of hours to day. Fluctuates daily and changes based on the season. The most important factors of weather in any area are atmospheric temperature and precipitation. Meteorologists use equipment mounted on weather balloons, aircraft, ships, and satellites, as well as radar and stationary sensors, to obtain data on weather variables. They feed these data into computer models to draw weather maps for various parts of the world. Other computer models project upcoming weather conditions based on probabilities that air masses, winds, and other factors will change in certain ways. Much of the weather we experience results from interactions between the leading edges of moving masses of warm air and old air. Weather changes when one air mass replaces or meets another. The most dramatic changes in weather occur along a front

front

the boundary between two air masses with different temperatures and densities.

latitude

the location between the equator and one of the poles. Latitudes are designed by degrees north of south of the equator. The equator is at 0°, the poles are 90° north and 90° south, and areas between range from 0° to 90°.

Convection (first major climate factor)

the movement of matter (such as gas or water) caused when the warmer and less dense part of a body of such matter rises while the cooler, denser part of the fluid sinks due to gravity. In the atmosphere, convection occurs when the sun warms the air and causes some of it to rise while cooler air sinks in a cyclical patter called a convection cell. The pattern in which warm air rises and cooler air sinks (diagram in jamboard) Ex: The air over an ocean is heated when the sun evaporates water. This transfers moisture and heat from the ocean to the atmosphere, especially near the hot equator. This warm, moist air rises, then cools and releases heat and moisture as precipitation. Then the cooler, denser, and drier air sinks, warms up, and absorbs moisture as it flows across the earth's surface to begin the cycle again.

Hurricanes

tropical cyclones that form in the Atlantic Ocean

Permafrost

underground soil in which captured water stays frozen for more than 2 consecutive years.

Temperate grassland

winters can be bitterly cold, summers are hot and dry, and annual precipitation falls unevenly throughout the year. Because the aboveground parts of most of the grasses die and decompose each year, organic matter accumulates to produce deep, fertile topsoil. This topsoil is held in place by a thick network of the grasses' intertwined roots, unless the topsoil is plowed up which exposes it to high winds found in these biomes. Grasses are adapted to droughts and fires that burn the plant parts that are above the ground but do not harm the roots. As a result, new grass can grow. In the midwestern and western areas of the U.S. there are two types of temperate grasslands, depending mainly on the average rainfall. The two types are short grass prairies and tallgrass prairies In all prairies, winds blow almost continuously and evaporation is rapid, often leading to fires in the summer and fall. This combination of winds and fires helps to maintain such grasslands by hindering tree growth. Many of the world's natural temperate grasslands have been converted to farmland, because their fertile soils are useful for growing crops and grazing cattle.