climate - National Geographic Society climate Tea is harvested in the tropical foothills of Mount Kenya, Kenya. Photograph by George F. Mobley Quotable Twain The famous author Mark Twain described the difference between weather and climate like this: "Climate is what we expect, weather is what we get." The Big Chill Antarcticas frigid climate makes it the only continent on Earth with no permanent human residents. The coldest temperature ever recordedminus-89.2 degrees Celsius (-128.5 degrees Fahrenheit)was at Vostok Station, Antarctica. Climate is the long-term pattern of weather in a particular area. Weather is the state of the atmosphere over short periods of time. Weather can change from hour to hour, day to day, month to month or even year to year. A region’s weather patterns, tracked for more than 30 years, are considered its climate. Climate Features Different parts of the world have different climates. Some parts of the world are hot and rainy nearly every day. They have a tropical wet climate. Others are cold and snow-covered most of the year. They have a polar climate . Between the icy poles and the steamy tropics are many other climates that help make the Earth a unique planet.

Average temperature and precipitation are important features of a climate. So are the day-to-day, day-to-night, and seasonal variations in temperature and precipitation. For example, San Francisco, California, and Beijing, China, have similar yearly temperatures and precipitation. However, the daily and seasonal changes make San Francisco and Beijing very different. San Francisco’s winters are not much cooler than its summers, while Beijing is hot in summer and cold in winter. San Francisco’s summers are dry and its winters are wet. The wet and dry seasons are reversed in Beijing—it has rainy summers and dry winters. Climate features also include windiness, humidity , cloud cover , and fogginess. Climate Conditions A region’s climate is something like a person’s personality. It is usually constant, but there may be surprises. Just as someone with a cheerful attitude will sometimes become sad, an area with a generally mild climate will occasionally experience extreme rainfall or drought . But because climates are mostly constant, living things can adapt to them. The enormous variety of life on Earth is largely due to the variety of climates that exist and the climate change s that have occurred in the past. Climate has influence d the development of culture s and civilization s.

People everywhere have adapted in various ways to the climates in which they live. Clothing, for example, is influenced by climate. The warm clothing developed by Eskimo cultures of Asia and North America are necessary for survival in the cold, windy climate near the North Pole. Grass skirts, on the other hand, are part of many cultures in warm, humid climates, such as Tahiti, an island in the South Pacific Ocean. Climate also influences where and when a civilization constructs housing or other buildings. The ancient Anasazi people of southern North America built apartments into tall cliffs. The sheltered, shady area kept residents cool in the hot, dry desert climate. The development of agriculture was very dependent on climate. Ancient agricultural civilizations, such as those in Greece and India, flourish ed where the climate was mild. Communities could grow crops every season, and experiment with different types of foods and farming techniques. Today, farmers are still in tune with the climate. They plant certain crop s according to the expected amount of rainfall and the length of the growing season. A growing season is the time between the last frost of spring and the first frost of autumn.

When the weather does not follow the typical climate pattern, it can mean hard times for farmers and higher food costs for consumer s. Of course, no climate is uniform . Small variation s, called microclimate s, exist in every climate region. Most are caused by topographic feature s such as lakes, vegetation, and cities. In large urban area s, for example, streets and buildings absorb heat from the sun, raising the average temperature of the city higher than the average temperatures of more open areas nearby. This is known as the “ urban heat island effect.” Large bodies of water, like the Great Lakes in the United States and Canada, can also have microclimates. Cities on the southern side of Lake Ontario, for example, are cloudier and receive much more snow than cities on the northern shore. This “ lake effect ” is a result of cold wind s blowing across warmer lake water. Climate Types The most widely used system for classifying climates was proposed in 1900 by Wladimir Koppen . Koppen observed that the type of vegetation in a region depended largely on climate. He used this fact as the starting point for his classification scheme .

Studying temperature and precipitation data, he and other scientists developed a system for naming climate regions. According to this system, there are five climate group s: tropical, dry, mild, continental, and polar. These climate groups are further divided into climate type s. The following list shows the climate groups and their types: Tropical Wet and dry (or savanna ) Dry Ice cap All climates are the product of many factors, including latitude , elevation , topography , distance from the ocean, and location on a continent . The rainy tropical climate of West Africa, for example, results from the region’s location near the Equator and its position on the western side of the continent. A constant amount of sunlight keeps temperatures in the area warm and steady. West Africa is also at the site where moist trade wind s meet, an area called the intertropical convergence zone (ITCZ) (pronounced “itch”). As a result, the region’s climate is warm and rainy. Tropical Climates There are three climate types in the tropical group: tropical wet; tropical monsoon; and tropical wet and dry. Places with a tropical wet climate are also known as rain forests. Rain forests have the most predictable weather on Earth, with warm temperatures and regular rainfall.

Annual rainfall exceeds 150 centimeters (59 inches), and the temperature varies more during a day than it does over a year. The coolest temperature, about 20-23 degrees Celsius (68-73 degrees Fahrenheit), occurs just before dawn. Afternoon temperatures usually reach 30-33 degrees Celsius (86-91 degrees Fahrenheit). Rain forests experience very little seasonal change, meaning average monthly temperatures remain fairly constant. Tropical wet climates exist in a band extending about 10 degrees of latitude on either side of the Equator. This part of the globe is always under the influence of the intertropical convergence zone. The zone follows a pendulum -like path during the course of a year, moving back and forth across the Equator with the seasons. It moves north during summer in the Northern Hemisphere, and south during the northern winter. Some tropical wet climates are wet throughout the year. Others experience more rainfall during the summer or winter, but they never have especially dry season s. The U.S. state of Hawaii; Kuala Lumpur, Malaysia; and Belém, Brazil, are examples of areas with tropical wet climates. Tropical monsoon climate s are most common in southern Asia and West Africa.

A monsoon is a wind system that reverses its direction every six months. They usually flow from sea to land in the summer, and from land to sea in the winter. Summer monsoons bring large amounts of rainfall to tropical monsoon regions. People living in these regions depend on the seasonal rains to bring water to their crops. India and Bangladesh are famous for their monsoon climate patterns. The third type of climate, tropical wet and dry climate , has three seasons. These areas are just outside the ITCZ, near the Equator. One season is cool and dry when the warm, moist ITCZ is in the opposite hemisphere . Another season is hot and dry as the ITCZ approaches. The last season is hot and wet as the ITCZ arrives and the region experiences months as a tropical wet climate. Life in these tropical wet and dry regions depends on the wet season’s rains. During years when rains are light, people and animals suffer. Havana, Cuba; Kolkata, India; and Africa’s vast Serengeti Plain are in the wet and dry tropics. Dry Climates Regions lying within the dry climate group occur where precipitation is low, including cool, high latitudes.

There are two dry climate types: arid and semiarid. Most arid climate s receive 10 to 30 centimeters (4-12 inches) of rain each year, and semiarid climate s receive enough to support extensive grassland s. Often, these grasslands are known as savannas or prairie s. Temperatures in both arid and semiarid climates show large daily and seasonal variations. The hottest spots in the world are in arid climates. The temperature in the North African town of El Aziza, Libya, reached 58 degrees Celsius (136 degrees Fahrenheit) on September 13, 1922—the highest weather temperature ever recorded. Although rainfall is limited in all dry climates, there are few parts of the world where it never rains. One of the driest places on Earth is the Atacama Desert of Chile, on the west coast of South America. There, the town of Arica averages less than 0.05 centimeters (0.02 inches) of rain a year.

Semiarid regions, such as the Australian Outback , usually receive between 25 and 50 centimeters (10-20 inches) of rainfall every year. They are often located between arid and tropical climate regions. Arid and semiarid climates can occur when warm, moist air is blocked by mountain s. Denver, Colorado, next to the Rocky Mountains in the U.S., has this type of dry climate. Mild Climates Regions with mild and continental climates are also called temperate regions. Both climate types have distinct cold seasons. In these parts of the world, climate is influenced mostly by latitude and by a region’s position on the continent. The mild climate type called Mediterranean climate has a warm summer and a short, mild, and rainy winter. It is found on the west coasts of continents between 30 and 40 degrees latitude, and along the shores of the Mediterranean Sea. Mediterranean summers feature clear skies, cool nights, and little rain. The city of Jerusalem, Israel, once had no rain in July for more than 100 years. The type of mild climate known as humid subtropical climate is usually found on the eastern sides of continents.

In cities such as Savannah, Georgia, in the U.S.; Shanghai, China; and Sydney, Australia, summers are hot and humid. Winter can be severely cold. Precipitation is spread evenly through the year and totals 76 to 165 centimeters (30-65 inches). Hurricane s and other violent storms are common in these regions. Weather on both sides of a continent generally becomes cooler as latitude increases and areas are closer to the poles. The marine west coast climate , a type of mild climate typical of cities such as Seattle, Washington, in the U.S. and Wellington, New Zealand, has a longer, cooler winter than the Mediterranean climate. Drizzle falls about two-thirds of winter days, and temperatures average about 5 degrees Celsius (41 degrees Fahrenheit). Continental Climates Areas with continental climates have colder winters, longer-lasting snow, and shorter growing seasons. They are the transition zone s between mild and polar climates. Continental climate s experience extreme seasonal changes. There are three types of continental climate—warm summer, cool summer, and subarctic. All these climates exist only in the Northern Hemisphere. Usually, continental climates are found in the interior of continents.

Warm summer climate regions often have wet summer seasons, similar to monsoon climates. For this reason, this climate type is also called humid continental . Most of Eastern Europe, including Romania and Georgia, has humid continental climates. Cool summer climate s have winters with low temperatures and snow. Cold winds, sweeping in from the Arctic, dominate the winter weather. People living in these climates have grown accustom ed to the harsh weather, but those unprepared for such cold may suffer. Many of Napoleon Bonaparte’s soldiers, for example, were used to the mild Mediterranean climates of France. Thousands died in bitter cold as they retreat ed from Russia’s cool summer climate in the winter of 1812. North of regions with cool summer climates are regions with subarctic climate s. These regions, including northern Scandinavia and Siberia , experience very long, cold winters with little precipitation. Subarctic climates are also called boreal climate s or taiga . The range of weather in continental climate regions makes them among the most spectacular sites for weather phenomena . In autumn, for instance, vast forest s put on their annual show of brilliant color before shedding their leaves as winter approaches.

Thunderstorm s and tornado es, among the most powerful forces in nature, form mostly in continental climates. Polar Climates The two polar climate types, tundra and ice cap, lie within the Arctic and Antarctic Circles near the North and South Poles. In tundra climate s, summers are short, but plants and animals are plentiful. Temperatures can average as high as 10 degrees Celsius (50 degrees Fahrenheit) in July. Wildflowers dot the landscape, and flocks of birds return from their winter migration s to feed on insects and fish. Whales feed on microscopic creatures in the region’s cold, nutrient -rich waters. People have adapted to life on the tundra for thousands of years. Few living things exist in the ice cap climate s of the Arctic and Antarctic. Temperatures rarely rise above freezing, even in summer. The ever-present ice helps keep the weather cold by reflecting most of the sun’s energy back into the atmosphere. Skies are mostly clear and precipitation is low all year. In fact, Antarctica, covered by an ice cap a mile thick, is actually one of the largest, driest deserts on Earth.

High Elevation Climates Several geographer s and climatologist s have modified the Köppen classification system over the years, including geographer Glen Trewartha, who added a category for highland climates. There are two high elevation climate types: upland and highland. Upland climate s occur on high plateau s, or flat-topped mountains. The Patagonia n Plateau, in southern South America, has an upland high-elevation climate. Highland climate s occur on mountains. High-elevation climates are marked by very different temperatures and levels of precipitation. Climbing a lofty mountain or reaching a plateau can be like moving toward the poles. On some mountains, such as Mount Kilimanjaro, Tanzania, the climate is tropical at the base and polar at the summit. Often, high-elevation climate differs from one side of the mountain to the other. Changes in Climate Climate does not change from day to day like weather, but it does change over time. Climate changes happen slowly over hundreds or even thousands of years. For example, periodic ice age s have covered large portions of Earth with ice caps.

Some evidence shows that the Sahara Desert was once covered by ocean during a warm “wet age.” Climate change can happen for many reasons. The movement of tectonic plate s, volcanic activity, and the tilt of Earth’s axis all have effects on climate. After the eruption of the island volcano of Krakatoa, Indonesia, in 1883, winters and even summers in Asia and Europe were colder and darker. Volcanic ash blocked the sun. Farmers had to adjust to shorter, weaker growing seasons. Climates around the world were changed for years. More recently, human civilizations have begun to affect climate. Human activities that include burning fossil fuel s and cutting down forests release greenhouse gas es into the atmosphere. These gases hold in heat, which raises temperature. Scientists believe this “ greenhouse effect ” is increasing global temperatures. Increasing temperatures can change climate types. Low-lying island s may be flooded as sea waters rise from melting glacier s. Heat in the atmosphere may increase the interaction of diverse weather system s, resulting in more hurricanes and typhoon s. Organisms that have adapted to one climate may have to migrate or adapt to warmer temperatures. Manatee s, for instance, are marine mammal s native to tropical waters.

As temperatures increase, manatees have been migrating as far north as New York City, New York. to adjust to new surroundings or a new situation. agriculture Noun Anasazi Noun (1200 BCE-1300 CE) people and culture native to what is now the southwestern United States. Also called Ancestral Puebloans. ancient (dry climate) region that receives 10 to 30 centimeters (4-12 inches) of rain each year. atmosphere boreal climate Adjective region that experiences long, cold winters with very little precipitation. Also called a subarctic or tundra climate. city large settlement with a high population density. civilization to identify or arrange by specific type or characteristic. climate one of five classifications of the Earth's climates: tropical, dry, mild, continental, and polar. climate type division within a climate group. climatologist person who studies long-term patterns in weather. cloud cover amount of sky covered with clouds. construct person who uses a good or service. continent continental climate Noun climate group that experiences extreme seasonal change. Continental climates are only found in the Northern Hemisphere. cool summer climate region that experience cool summers and snowy winters.

crop learned behavior of people, including their languages, belief systems, social structures, institutions, and material goods. data (singular: datum) information collected during a scientific study. dependent relying on or needing something. desert Noun construction or preparation of land for housing, industry, or agriculture. diverse varied or having many different types. dominate time of year with little precipitation. elevation release of material from an opening in the Earth's crust. Eskimo Noun people and culture native to the Arctic region of eastern Russia, the U.S. state of Alaska, Canada, and Greenland. experiment to try or test an idea. extensive the art, science, and business of cultivating the land for growing crops. flourish to thrive or be successful. fog ecosystem filled with trees and underbrush. fossil fuel Noun coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals. frigid person who studies places and the relationships between people and their environments. glacier ecosystem with large, flat areas of grasses. Great Lakes Noun largest freshwater bodies in the world, located in the United States and Canada.

Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior make up the Great Lakes. greenhouse effect Noun phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape. greenhouse gas Noun gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere. growing season period in the year when crops and other plants grow rapidly. harsh climate group found in mountains and plateaus. highland climate (high-elevation climate) region found on and around mountains. housing humid continental Noun (continental climate) region that experiences cold winters and warm, wet summers. Also called a warm summer climate. humidity region that experiences cool winters and hot humid summers. hurricane Noun tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region. ice age Noun long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.

ice cap climate region where temperatures rarely rise above freezing. influence to encourage or persuade a person or organization to act a certain way. interaction relationship between two or more forces, objects, or organisms. Intertropical Convergence Zone (ITCZ) Noun belt of low-pressure air currents that circle the Earth at the Equator. Also known as the Monsoon Zone. island lake effect Noun process where cold winds blowing over a relatively warm lake cause rapid cloud formation and precipitation. latitude threatened marine mammal native to the Caribbean Sea and Atlantic Ocean. marine mammal Noun an animal that lives most of its life in the ocean but breathes air and gives birth to live young, such as whales and seals. marine west coast climate (mild climate) region that experiences rain and long, cool winters. Mark Twain (1835-1910, born Samuel Langhorne Clemens) American writer. Mediterranean climate (mild climate) region that experiences mild winters and warm summers. microclimate Noun small area where the climate differs within a larger climate region, such as "heat islands" in a city. microscopic to move from one place or activity to another.

migration movement of a group of people or animals from one place to another. mild climate climate group that experiences seasonal temperature changes. Also called a temperate climate. moist monsoon Noun seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains. landmass that forms as tectonic plates interact with each other. Northern Hemisphere half of the Earth between the North Pole and the Equator. North Pole Noun remote, sparsely populated interior region of Australia. Patagonia large plateau in southern South America, stretching from the Andes Mountains to the Atlantic Ocean. pendulum object suspended from a point, able to swing back and forth. periodic (singular: phenomenon) any observable occurrence or feature. plateau having to do with the North and/or South Pole. polar climate climate group found within the Arctic and Antarctic Circles. prairie regular or able to be forecasted. rain forest time of year when most of the rain in a region falls. region Noun any area on Earth with one or more common characteristics. Regions are the basic units of geography. to go back to a familiar or safe place.

savanna type of tropical grassland with scattered trees. Scandinavia region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark. scheme structure or diagram of the way information is studied, documented, and understood. seasonal likely to change with the seasons. semiarid climate Noun (dry climate) region that receives between 25 and 50 centimeters (10-20 inches) of rainfall every year. shore region of land stretching across Russia from the Ural Mountains to the Pacific Ocean. snow precipitation made of ice crystals. spectacular subarctic climate Noun region that experiences long, cold winters with very little precipitation. Also called a boreal or tundra climate. sunlight visible radiation from the sun. taiga tectonic plate Noun massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate. temperature cloud that produces thunder and lightning, often accompanied by heavy rains. topographic feature map representation of the Earth's surface showing elevation. topography study of the shape of the surface features of an area. tornado Noun a violently rotating column of air that forms at the bottom of a cloud and touches the ground.

trade wind Noun winds that blow toward the Equator, from northeast to southwest in the Northern Hemisphere and from southeast to northwest in the Southern Hemisphere. transition zone area between two natural or artificial regions. tropical climate climate group that experiences hot, wet summers. tropical monsoon climate region that experiences the monsoon winds, which bring heavy rain. tropical wet and dry climate Noun region that experiences three seasons: cool, hot, and wet. tropical wet climate Noun region that experiences hot temperatures and heavy rainfall all year. Also called a rain forest climate. tundra climate region that experiences short summers and long winters. typhoon Noun tropical storm with wind speeds of at least 74 miles (119 kilometers) per hour. Typhoons are the same thing as hurricanes, but usually located in the Pacific or Indian Ocean region. typical exactly the same in some way. unique (high-elevation climate) region found on and around large plateaus. urban area all the plant life of a specific place. volcanic having to do with volcanoes. volcanic ash region that experiences cool winters and warm, wet summers. Also called a humid continental climate. weather movement of warm or cold air.

wind Noun movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun. winter Noun time of year when part of the Earth receives the least daylight: December, January, and February in the Northern Hemisphere and June, July, and August in the Southern Hemisphere. Wladimir Koppen Climate and Weather | Climate Education Modules for K-12 Climate and Weather Body Weather Weather describes conditions in the atmosphere that are happening right now. It is the short term occurrence, or daily measurement, of fair or inclement weather. For dealing with weather, daily decisions are necessary. When it is raining, bring an umbrella; when it is stormy outside, take cover inside. Daily temperature, precipitation, and severe weather are all a part of everyday weather. If the meteorologist on TV says that it will be sunny today, this is defined as weather. Below are pictures describing weather conditions. Figure A is a picture of lightning during a lightning storm. Figure B is a satellite image of Hurricane Ivan as the eye approaches the Florida coast in September 2004.

Figure A: Cloud-to-Ground Lightning Image from NOAA Climate Climate describes the long-term weather patterns over a specified time frame for a specific area. Most books which describe regional or world climate use a long-term average of weather conditions to describe what typical conditions are likely to be present at a particular location and time of year. The average amount of rainfall is considered a part of climate. Climate statistics include both average conditions and frequencies of occurrence of severe weather, heavy rainfall, and other weather events which could impact health and property. The latitude of a location has a large impact on the climate for that area. This is primarily due to the amount of solar heating received, which varies as a function of latitude. However, locations with the same latitude may have different climates depending on multiple factors such as whether the location is close to the coast or if the location has significant topographic features, such as a mountain. Figure C shows annual average precipitation for the US from 1961-1990. Figure C: Annual Average Precipitation from 1961-1990. Figure D below shows the annual average temperature across the US from 1961-1990.

Figure D: Annual Average Temperature from 1961-1990. Figures E and F show similar conditions as above with emphasis on the southeast US. They show precipitation (in mm) and temperature (in degrees Celsius) averages over a 30-year period. Figure E: 30-year Average Precipitation (mm) Figure F: 30-year Average Temperature (C) You can think of differences between weather and climate as similar to differences between people's day to day moods and their personalities. A person is likely to have a consistent personality over time which is described by their long-term behavior regarding talkativeness, optimism or pessimism, and other factors. However, that person may show a lot of variation in their day to day moods, depending on outside influences, state of health, and even how much sleep they receive. Similarly, the climate of a region shows the long-term characteristic behavior of weather over that region. However, the weather on any day can be quite different depending on what weather systems are moving through the area and affecting the day's temperatures, rainfall, and wind conditions. Climate and Weather Relation to Agriculture/K-12 How does this relate to agriculture?

Weather and climate are considered by some to be the most limiting factors in crop production. Successful growers need to consider the climate AND weather conditions that are present in a certain growing area, as well as the growth requirements of the crops. For example, have you ever wondered why cranberries are only produced in Oregon, Massachusetts, New Jersey, Wisconsin and Maine? Or why cotton is only produced in the southern part of the United States? One reason is that crops have basic growth requirements for water, sunlight and temperature. For example, peanuts require 140 to 160 days of growth at temperatures above 56 degrees to reach complete maturity. These growing conditions exist in the Southern part of the US, but growing season is simply not long enough in the northern parts of the US for peanut production. Figure G: Downy Mildew in Cucumbers Figure H: Irrigation on Corn Image courtesy of Bridget Lassiter Image courtesy of Bridget Lassiter Weather plays a slightly different role in crop production. Different weather patterns can affect crops in different ways. For example, some crops can withstand long periods of drought, and then recover when rain (or irrigation) finally arrives – tobacco is one crop like this.

Other crops can withstand very high temperatures, and still produce high yields (such as corn, cotton and peanut). Still other crops can technically produce well in various weather conditions, but still might be plagued with insect or disease problems in times when the weather is not ideal. One good example would be cucumber production in North Carolina that can be plagued with yield-limiting levels of downy mildew when rainfall or relative humidity remains high for extended periods of time. For those reasons, weather AND climate play a role in where crops are grown, and how those crops must be managed. Weather and climate NSES Links to National Science Education Standards: 7th grade science: 7.E.1.4 : Predict weather conditions and patterns based on information from weather data collected through observations and measurements, weather maps, and cloud shapes and types. Earth Science: EEn.2.6.1 : Differentiate between weather and climate. CLIMATE ZONES CLIMATE ZONES Earth has three main climate zones—tropical, temperate, and polar. These zones can be further divided into smaller zones, each with its own typical climate. A region’s climate, together with its physical characteristics, determines its plant and animal life.

CLIMATE ZONE CLASSIFICATION POLAR AND TUNDRA Polar climates are cold and dry, with long, dark winters. In the tundra (a treeless region bordering the Arctic), temperatures rise above freezing for only a few months each year. BOREAL FOREST Boreal (cold coniferous) forests lie south of the tundra, stretching across much of northern Canada, Scandinavia, and Russia. Temperatures fall below freezing for 4–6 months a year. MOUNTAIN On mountains, the temperature decreases with altitude (height), and many high peaks are always covered in snow. Mountain climates are usually wetter and windier than lowland regions. TEMPERATE FOREST Temperate climates have warm summers and cool winters with year-round rain or snow. Temperate forests are characterized by deciduous trees, which lose their leaves during the winter. MEDITERRANEAN A Mediterranean climate is found in regions bordering the Mediterranean Sea, and in Australia and California. It is characterized by hot, dry summers and cool, wet winters. DESERT Earth’s deserts are hot and dry year-round, and usually receive less than 10 in (250 mm) of rainfall a year.

Deserts are often found in the center of continents, far from the sea. DRY GRASSLAND Dry grasslands are found in the center of continents where temperate variations are extreme. They have hot summers, cold winters, and little rainfall, so very few trees can grow there. TROPICAL GRASSLAND Tropical grasslands, such as the African savanna, lie between desert areas and tropical rainforests. The climate is hot all year, but with a distinct wet season and dry season. TROPICAL RAINFOREST Tropical rainforests are found in regions near the equator. Here, the climate is hot and wet all year, with temperatures remaining at around 80–82ºF (27–28ºC). WHAT IS A MICROCLIMATE? A small area with a different climate to its surroundings is said to have its own microclimate. Examples include a city or a rooftop garden. The temperature in cities may be around 11ºF (6ºC) warmer than the surrounding countryside because buildings and paved streets hold the Sun’s heat longer than vegetation. Artificial heating in buildings also contributes to higher city temperatures. HAS THE EARTH’S CLIMATE CHANGED OVER TIME?

Over the past two million years, Earth’s climate has slowly changed. Long, cold periods called ice ages, or glacials, have been interspersed with warmer periods. The last ice age ended about 10,000 years ago. At its height, all of northern Europe and parts of North America, Siberia, New Zealand, Tasmania, and the southernmost tip of South America were covered by ice sheets up to 3,300 ft (1,000 m) thick. WILL EARTH’S CLIMATE CHANGE IN THE FUTURE? Some scientists believe that Earth will enter another ice age in a few thousand years. However, almost all scientists believe that pollution caused by human activities is slowly causing the planet to grow warmer—a phenomenon called global warming. BIOGRAPHY: LOUIS AGASSIZ Swiss, 1807–1873 Naturalist Louis Agassiz studied glaciers and the effects of ice erosion in areas where glaciers no longer existed. He put forward the theory that much of Europe and North America was once covered by ice sheets. Through his work, the idea of “ice ages” became generally accepted.

FIND OUT MORE High School Earth Science/World Climates - Wikibooks, open books for an open world High School Earth Science/World Climates From Wikibooks, open books for an open world This is the latest reviewed version , checked on 13 January 2017. (+) Quality: minimal 12 Points to Consider Climate zone change results from the climate conditions of an area: its temperature, humidity, amount and type of precipitation, and the season. A climate zone is reflected in a region's natural vegetation. Perceptive travelers can figure out which climate zone they are in by looking at the vegetation, even if the weather is unusual for the climate on that day! Describe the relationship between the climate zones and the factors that influence climate. Discuss the relationship between climate zones and biomes. Discuss the different biomes based on a general description. Climate Zones and Biomes[ edit ] The major factors that influence climate also determine the different climate zones. The same type of climate zone will be found at similar latitudes and in similar positions on nearly all continents, both in the Northern and Southern Hemispheres.

The one exception to this pattern is the climate zones called the continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere land masses are not wide enough to produce a continental climate. Climate zones are classified by the Köppen classification system (Figure 17.7). This system is based on the temperature, the amount of precipitation and the times of year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is used as an indicator of climate type. A climate type and its plants and animals make up a biome. The organisms of a particular biome share certain characteristics around the world, because their environment has similar advantages and challenges. The organisms have adapted to that environment in similar ways over time. For example, different species of cactus live on different continents, but they have adapted to the harsh desert in similar ways. Figure 17.7: This world map of the Köppen classification system gives a good general idea of where the climate zones and major biomes are located. Where the groups are not represented by stripes (like in the western United States) the situation is complicated by geographic features such as mountains.

The Köppen classification system recognizes five major climate groups, each with a distinct capital letter A through E. Each lettered group is divided into subcategories. Some of these subcategories are forest (f), monsoon (m), and wet/dry (w) types, based on the amount of precipitation and season when that precipitation occurs. Tropical Moist Climates (Group A)[ edit ] Tropical Moist (Group A) climates are found in a band about 15° to 25° N and S of the equator (Figure 17.8). Intense sunshine means that the tropics are warm year-round: each month has an average temperature of at least 18°C (64°F). Rainfall is abundant—at least 150 cm (59 inches) per year. The subcategories of this zone are based on when the rain falls. Figure 17.8: Tropical Moist Climates (Group A) are shown in green. The main vegetation for this climate is the tropical rainforest, which are found in the Amazon in South America, the Congo in Africa and the lands and islands of southeast Asia.

Tropical Wet (Af)[ edit ] The wet tropics lie in a band around the equator, covering about 10% of the Earth's land. The wet tropics are consistently warm, with almost no annual temperature variation. Great amounts of rain fall year-round, between 175 and 250 cm (65 and 100 inches) per year. These conditions support the tropical rainforest biome (Figure 17.9). The forest is dominated by densely packed, broadleaf evergreen trees. Many habitats are found in rainforests, as a result of the high number of plant types and the different environments within the layers of the forest. Rainforests have the highest number of species or biodiversity of any ecosystem. Figure 17.9: The Amazon river and rainforest in Brazil. Tropical Monsoon (Am)[ edit ] The tropical monsoon climate resembles the tropical wet biome (Af) but has very low precipitation for one to two months each year. During these months, less than 6 cm (2.4 inches) of rain falls. Rainforests can grow here because the dry period is short, and the trees can be supported by moisture trapped in the soil.

This climate is found where the monsoon winds blow, primarily in southern Asia, western Africa, and northeastern South America. Tropical Wet and Dry (Aw)[ edit ] The tropical wet and dry climate lies north and south of the tropical wet climate, between about 5° and 10° latitude to around 15° to 20° latitude. The average annual temperature is similar to the wet tropics, but the temperature range is greater. This climate zone receives less rain than the wet tropics, about 100 to 150 cm (40 to 60 inches). For more than two months each year, rainfall is less than 6 cm (2.4 inches). Wet and dry seasons are related to the location of the ITCZ. In the summer, when the ITCZ drifts northward, the zone is wet. In the winter, when the ITCZ moves back toward the equator, the region is dry. This climate exists where strong monsoon winds blow from land to sea, such as in India. Rain forests cannot survive the months of low rainfall, so the typical vegetation is savanna (Figure 17.10).

This biome consists mostly of grasses, with widely scattered deciduous trees and rare areas of denser forests. Central Africa is famous for its savanna and the unique animals that live there. Figure 17.10: A male lion stalks the African savanna. Dry Climates (Group B)[ edit ] The Dry Climates (Group B) generally have less precipitation than evaporation and are further from the equator than Tropical (Group A) climates. They have cooler winters and longer, harsher dry seasons. Rainfall is irregular; several years of drought are often followed by a single year of abundant rainfall. Summer temperatures are high, and much of the rain evaporates before it reaches the ground. Dry climate zones cover about 26% of the world's land area. Low latitude deserts form as a result of the Ferrell cell high pressure zone. Higher latitude deserts occur within continents or in rain shadows where the air has little humidity. Arid Desert (Bw)[ edit ] Low-latitude, arid deserts are found between 15° to 30° N and S latitudes. This is where warm dry air sinks at high pressure zones.

True deserts make up around 12% of the world's lands. Deserts are found in southwestern North America, Africa, Australia and central Asia. Humidity is low, and as a result there are few clouds in the sky. The Sahara is the world's largest desert (Figure 17.11). Figure 17.11: The Sahara desert takes up much of northern Africa. The green band below the sandy Sahara is the Congo. Figure 17.12: The Sonora desert is home to many well-adapted plants including cacti, scrubby bushes, and perennials. In the Sonora Desert of the southwestern United States and northern Mexico, most weather stations record sunshine 85% of the time, both in summer and winter (Figure 17.12). Clear skies allow the ground to heat rapidly during the day and cool rapidly at night. The summer sun can be merciless and daytime temperatures are extremely hot. Temperatures often plunge when the Sun goes down and the daily temperature range may be 15° to 25°C (27° to 45°F). Annual rainfall is mostly less than 25 cm (10 inches).

The Sonora desert gets much of its rain in the winter, when storms come in from the Pacific. Summer monsoon rains drop a great deal of rain in some areas. The existence of two wet seasons a year allows a unique group of plants and animals to survive in the southwestern deserts. Vegetation is limited, since water is scarce. Desert plants are adapted to surviving long periods of drought. Cacti and shrubby plants have wide or deep roots to reach water after a rain. Many desert plants are able to store water. Some plants lie dormant as seeds, and bloom after rain falls. Semi-arid or Steppe (Bs)[ edit ] Deserts in continental interiors or in rain shadows are found at higher latitudes. Semi-arid deserts often receive more rain than the arid deserts, between 20 to 40 cm (8 to 16 inches) annually. Because land areas change temperature easily, these areas have lower annual average temperatures plus greater annual temperature ranges. In the winter, these climate zones get very cold under cold high pressure cells. In the summer, they heat up, allowing air to rise and rain to fall.

In the United States, the Great Plains, portions of the southern California coast and the Great Basin are semi-arid deserts. The biome is called steppe, which has short bunch grass, and scattered low bushes, or sagebrush (Figure 17.13). A steppe has few or no trees because there is not enough rain for trees to grow. Figure 17.13: This photo of the Great Basin in Utah illustrates the steppe biome. Moist Subtropical Mid-latitude (Group C)[ edit ] The Moist Subtropical Mid-latitude (Group C) climates are found along the coastal areas in the United States. Seasons are distinct, although winters are mild. The average temperature of the coldest month ranges from just below freezing to almost balmy, between -3°C and 18°C (27° to 64°F). Summers are often mild with average temperatures above 10°C (50°F). There is plentiful annual rainfall. Dry Summer Subtropical or Mediterranean Climates (Cs)[ edit ] The Dry Summer Subtropical climate is found on the western sides of continents between 30° and 45° latitude.

Annual rainfall is 30 to 90 cm (14 to 35 inches), most of which comes in the winter. This climate is also called the Mediterranean climate because it is found around the Mediterranean Sea (Figure 17.14). The climate is also typical of coastal California, which sits beneath a summertime high pressure for about five months each year. Land and sea breezes make winters moderate and summers cool. The mild winters and foggy summers of San Francisco represent a coastal Mediterranean climate. Further inland in Sacramento, summer temperatures are much higher, representing an interior Mediterranean climate. Vegetation must survive long summer droughts. This vegetation type is called chaparral. Scrubby, woody plants and trees are common (Figure 17.15). Figure 17.14: A map showing locations which have a Mediterranean climate. The areas around the Mediterranean Sea are the best representatives of this climate type. Figure 17.15: The scrubby plants that are typical of a Mediterranean climate. This photo is from southern France.

Humid Subtropical (Cfa)[ edit ] The Humid Subtropical climate zone is found mostly on the eastern sides of continents (Figure 17.16). Rain falls throughout the year with annual averages between 80 and 165 cm (31 and 65 inches). Summer days are humid and hot, from the lower 30s up to 40°C (mid-80s up to 104°F). Afternoon and evening thunderstorms are common. These conditions are due to warm tropical air passing over the hot continent. Winters are mild, but middle-latitude storms called cyclones may bring snow and rain. The southeastern United States, with its hot humid summers and mild, but frosty winters, is typical of this climate zone. Figure 17.16: The humid subtropical climate zone is shown in green. Forests grow thickly in much of this region, due to the mild temperatures and high humidity. Pine forests are common in the lower latitudes, while oak are more common at higher latitudes (Figure 17.17). Figure 17.17: Pine forests are common in the humid subtropical climate zone.

Marine West Coast Climate (Cfb)[ edit ] This climate lines western North America between 40° and 65° latitude, an area known as the Pacific Northwest (Figure 17.18). Ocean winds bring mild winters and cool summers. The temperature range between seasons and between day and night is fairly small. Rain falls year-round, although summers are drier as the jet stream moves northward. Low clouds, fog, and drizzle are typical. Snowfall is infrequent and short-lived. The mountain ranges that line the western U.S. keep this climate from extending far inland. Figure 17.18: The west coast marine climate zone. Figure 17.19: A Douglas fir forest in the Pacific Northwest. Dense forests of Douglas fir thrive in the heavy rain and mild temperatures (Figure 17.19). In Western Europe the climate covers a larger region since no high mountains are near the coast to block wind blowing off the Atlantic. Continental Climates (Group D)[ edit ] Continental (Group D) climates are found in most of the North American interior from about 40°N to 70°N.

In this climate, summers are cool-to-warm and winters are very cold and stormy. The average temperature of the warmest month is higher than 10°C (50°F) and the coldest month is below -3°C (-27°F). Snowfall is common and the cold temperatures mean that snow stays on the ground for long periods of time. Trees grow in continental climates, even though winters are extremely cold, because the average annual temperature is fairly mild. Continental climates are not found in the Southern Hemisphere due to the absence of a continent large enough to generate this effect. Humid Continental (Dfa, Dfb)[ edit ] Humid continental climates are found around the polar front at about 60°N latitude within continental North America and Europe (Figure 17.20). In the winter, middle-latitude cyclones bring chilly temperatures and snow. In the summer, westerly winds bring continental weather and warm temperatures. The average July temperature is often above 20°C (70°F). The region is typified by deciduous trees, which protect themselves in winter by losing their leaves.

Figure 17.20: The humid continental climate zone covers much of the northeastern United States, southeastern Canada, and middle Europe. The two variations of this climate are based on summer temperatures. In the humid continental climate with long, hot summers (Dfa), the long summers and high humidity foster plant growth (Figure 17.21). Summer days may be over 38°C (100°F), nights are warm and the temperature range is large, perhaps as great as 31°C (56°F)! In the humid continental climate with long, cool summers (Dfb), summertime temperatures and humidity are lower. Winter temperatures are below -18°C (0°F) for long periods. For example, Winnipeg, Canada has a 38°C (68°F) annual temperature range. Figure 17.21: Parts of South Korea lie in the humid continental climate zone. Subpolar (Dfc)[ edit ] The subpolar climate is found between the humid continental and the polar tundra climates (Figure 17.22). This climate is dominated by long, very cold winters with very little precipitation. Continental polar air masses form when air stagnates in this zone.

Snowfall is light, but temperatures are so cold that snowfall remains on the ground for months. Most of the approximately 50 cm (20 inches) of annual precipitation falls during summer cyclonic storms. The angle of the Sun's rays is low but the Sun is visible in the sky for most or all of the day, so temperatures may get warm, but are rarely hot. These continental regions have very high annual temperature ranges. The climate of Fairbanks, Alaska is a typical subarctic climate. Figure 17.22: The location of the subpolar climate. The boreal coniferous forests of this climate are called taiga (Figure 17.23). These vast forests stretch across North America from western Alaska to Newfoundland, and across Eurasia from Norway to the Pacific coast. Figure 17.23: The vast taiga is known for its small, hardy, and widely-spaced trees. This photo is of the Alaska Range in Alaska. Polar Climates (Group E)[ edit ] In the polar regions, winters are entirely dark and bitterly cold. In the summer, days are long, but the sun is low on the horizon.

Summers are cool with the average temperature of the warmest month at less than 10°C (50°F). Winters are extremely cold, so the annual temperature range is large. Polar climates receive less than 25 cm (10 inches) precipitation, mostly during the summer. This climate is found across the continents that border the Arctic Ocean, Greenland, and Antarctica. Polar Tundra (ET)[ edit ] The polar tundra climate is continental, with severe winters (Figure 17.24). Temperatures are so cold that a layer of permanently frozen ground, called permafrost forms below the surface. This frozen layer can extend hundreds of meters deep. The average temperature of the warmest months is above freezing, so summer temperatures defrost the uppermost portion of the permafrost. In winter, the permafrost prevents water from draining downward. In summer, the ground is swampy. Although the precipitation is low enough in many places to qualify as a desert, evaporation rates are also low, so the landscape receives more usable water than a desert. Figure 17.24: Tundra loses its green in the fall, as mosses and leaves turn brown.

The only plants that can survive the harsh winters and soggy summers are small ground-hugging plants like mosses, lichens, small shrubs and scattered small trees that make up the tundra (Figure 17.25). Due to the lack of ice-free land near the South Pole, there is very little tundra in the Southern Hemisphere. The area surrounding the Arctic Ocean is the only part of the globe with much tundra. Figure 17.25: The tundra biome is shown in this map. Ice Cap (EF)[ edit ] Ice caps are found mostly on Greenland and Antarctica, about 9% of the Earth’s land area (Figure 17.26). Ice caps may be thousands of meters thick. Ice cap areas have extremely low average annual temperatures, e.g. -29°C (-20°F) at Eismitte, Greenland. Precipitation is low, since the air is too cold to hold much moisture. Snow occasionally falls in the summer. Figure 17.26: A composite satellite image of Antarctica. Almost all the continent is covered with an ice cap.

Microclimates[ edit ] When climate conditions in a small area are different from those of the surroundings, the climate of the small area is called a microclimate. The microclimate of a valley may be cool relative to its surroundings since cold air sinks. The ground surface may be hotter or colder than the air a few feet above it, since rock and soil gain and lose heat readily. Different sides of a mountain will have different microclimates. In the Northern Hemisphere, a south-facing slope receives more solar energy than a north-facing slope, and so each side supports different amounts and types of vegetation. Altitude mimics latitude in climate zones. Climates and biomes typical of higher latitudes may be found in other areas of the world at high altitudes. Mt. Kilimanjaro in Africa lies near the equator in the tropics, but the top of the mountain is in the tundra biome and there is also a small glacier at the top. Lesson Summary[ edit ] A climate zone depends on a region's latitude, continental position, and relationship to prevailing winds, large water bodies, and mountains, among other factors. The temperature, rainfall, length of dry season, and other features of the climate zone determine which plants can grow.

When living organisms develop in similar climates, they must adapt to that same environment. So the organisms in similar climate zones resemble each other, no matter how geographically distant they are. Because the organisms are so similar, a climate zone and its organisms make up a biome. Climate and Weather - Occupies almost all of the land area within 15-20 degrees of the equator. Sub-groupings - Tropical Wet, Tropical Monsoonal, and Tropical Savanna Tropical Wet - Tropical wet represents the region closest to the equator. These regions have very little seasonal variation. Monthly averages are near 80 degrees; averages rarely vary more than 8 degrees year round. Warm temperatures, high humidity, and high precipitation amounts characterize this classification. Year round precipitation amounts range from 60 to 100 inches per year, and this is usually in the form of rain via near daily thunderstorm activity. The principal climatic control factor within this region is latitude. Tropical Monsoonal - Tropical monsoonal's separate classification is chiefly due to monsoonal precipitation patterns. Temperature averages and ranges do not differ greatly from the tropical wet grouping. This climatic classification is limited to Asia, specific examples can be found in India, Myanmar, and Thailand.

These areas have distinctive wet and dry seasons. Typical conditions are; a dry winter with possibly two inches of precipitation a month, and a wet winter with twenty to thirty inches of rainfall per month. Tropical Savanna -This classification can be found along the equator to approximately twenty degrees north and south. This group has a greater range than other tropical groupings and is the best example of the delineation between wet and dry seasons. The temperatures remain near the same as other tropical classifications yet has a year round range of fifteen to thirty degrees, simply a greater expression of seasons. Precipitation is concentrated within the spring and summer months when these areas may receive thirty five to seventy inches of precipitation. Fall and winter months are in many cases completely dry. Dry Climates Sub-groupings - Subtropical Desert, Subtropical Steppe, Midlatitude Desert, and Midlatitude Steppe Subtropical Desert - Generally these regions experience hot summers and mild winters. Winter month temperatures are usually an average of sixty degrees, while summer months averages usually are in the mid to upper nineties. Year round temperature ranges are between fifteen to thirty degrees, yet daily ranges can be dramatic.

Precipitation totals range from two to eight inches, with dew being an important source of moisture. Examples of this climate can be found in North Africa and Southwestern Asia. Subtropical Steppe - Subtropical Steppe is very similar to the Subtropical Desert groupings with greater amounts of precipitation and less temperature ranges. Precipitation amounts often are concentrated in one season depending upon location. Midlatitude Desert - Midlatitude deserts usually are a result of an area being on the leeward side of a mountain range. See the elevation section of climatic controls for a full depiction of orrographic precipitation patterns. Precipitation can best be described as erratic with totals ranging from zero to seven inches. These regions usually have hot summers and cold winters. They are capable of great year round and daily range. Average winter temperatures usually are below freezing, and summer averages are in the mid to upper nineties. Year round ranges can be over fifty degrees. The principle difference between Midlatitude deserts and other dry climates are the cold winters. Midlatitude Steppe - The midlatitude steppe grouping is best described as simply a buffer zone between humid and dry climates. Precipitation is usually more reliable, and temperatures are more moderate.

Temperature averages and precipitation amounts are very similar to the other dry climatic classifications. Mild Midlatitude Sub-groupings - Mediterranean, Humid Subtropical, and Marine West Coast Mild midlatitude - Generally can be described as the buffer zone between the tropics and the more severe mid latitudes. Principle factors behind the great variability of day to day and year round temperature changes, and precipitation amounts are due to movement of air masses. These areas usually experience great year round ranges, and have distinct seasonal change. Overall daily ranges are not that large. Mediterranean - Usually found at thirty-five degrees north or south, and on the western side of continents. Winter temperature averages are between fifty and fifty five degrees, with most of the precipitation received in these months, usually between fifteen to twenty five inches. Summers are dry and moderate with temperatures averaging between seventy five to eighty degrees. Examples of this climate can be found in Southern California, South Africa, and of course in the Mediterranean region. Humid Subtropical - Found between twenty and forty degrees north or south, and often on the eastern side of continents. This grouping has greater amounts of precipitation than the Mediterranean classification, receiving between forty to sixty inches of precipitation.

Usually most of this precipitation is in the form of rain falling in summer months, yet the winter months can not be described as dry. Summer temperatures usually average between seventy to eighty degrees, while winters can be described as ten to twenty degrees colder than the Mediterranean grouping. One important difference is the frequency of freezing temperatures, which leads to a much shorter growing season. An example of this classification is of course here in Houston. Marine West Coast - Marine west coast is generally found between forty and sixty five degrees north or south, and often on the western side of continents. The key factor behind this grouping is wind off the water moderates temperatures. If you simply looked at latitudinal position you would assume more extreme temperatures, yet moderate due to the marine influence. Summer temperatures average sixty to seventy degrees, while winters average thirty five to forty degrees. These regions are sometimes subject to very cold temperature, yet they often are not long in duration. Precipitation amounts usually range from thirty to fifty inches per year, most in the form of steady, gentile, frequent, and rain. These regions also have high humidity levels, a large number of cloudy and foggy days. Examples of this climate can be found within Western Europe and the Northwestern U.S.

Severe Midlatitude Sub-groupings - Humid Continental and Sub-ArcticUsually located between twenty to forty degrees north. Continentality is the principle factor behind conditions found within these regions. Continentality refers to the impact of a large landmass. It is the opposite of Marine West Coast where wind off the water moderates. In severe mid latitudes wind off the land produces extremes, leading to very cold winters, and surprisingly hot, yet short summers. Humid Continental - This grouping is usually found on eastern side of continents. These regions usually experience a great year round and daily range. Summer temperatures average near seventy degrees and are short in duration. Winter temperatures average between ten to twenty five degrees, with one to five months experiencing temperatures below freezing. Precipitation amounts average from twenty to fifty inches per year. Variations within these regions usually are dependent on a coastal or inland location. Coastal regions will have more moderate temperatures and higher precipitation amounts. Inland locations have more extreme temperatures and drier conditions. Examples of this climate can be found in the North America, Asia, and central Europe. Sub-Arctic - Sub-Arctic regions can be found between fifty to seventy degrees north.

Generally look for a long, cold, dark, winter and a short warm summer. Usually this grouping has a six to seven month period where average temperatures are below freezing. Ice formations can be found from September until May. Summer temperatures average from fifty to sixty degrees, although a reading of above eighty degrees in not uncommon. Precipitation amounts are very low, commonly from five to twenty inches, most frequently experienced in summer months. Examples of this climate can be found in Western Alaska, Canada, and Eurasia. Polar Sub-groupings - Tundra, Ice Cap, and Highland or Mountain These climatic classifications represent regions that are the most remote from the sun. Latitudinal position is the principle control. These groupings have no months that temperatures reach above fifty degrees, and are extremely dry. Temperatures and sun exposure are generally so low that evaporation is minimal, therefore holistically classified as humid. Tundra - Tundra is the warmest group within the sub-arctic classifications. These regions have the distinction of having one month of temperatures that average above freezing. Severity of the cold usually depends on an inland or coastal location. The coldest month may have an average of zero or twenty-five to thirty below zero, depending on individual location.

Total precipitation is below ten inches. Examples of this climate can be found along the fringes of the Arctic Circles, and the upper latitudes of North America. Ice Cap - Ice cap covers approximately nine percent of the earth's surface. The warmest month averages below zero, and the coldest months usually average between thirty to sixty below zero. This region may experience temperatures of one hundred below zero. Often this grouping is described as polar deserts because they receive less than five inches of precipitation per year, yet evaporation is minimal. Highland or Mountain - This classification defies many basic premises found true in climatic classifications. How do you achieve freezing temperatures, along the equator? Elevation! When determining conditions within this classification, each location must be looked at individually. The following factors should be considered; windward or leeward location, angle of mountain peak to determine sun exposure, the elevation, and location of the mountain within the range. Location within a range often determines amount of sunlight and wind variations. Elevation is also a factor in wind variation, the higher the elevation the less predictable the winds due to air pressure decreases. Links Go to Center for Ocean-Land-Atmosphere Studies and click on Climate Outlooks.

You can find temperature, precipitation, and soil moisture outlooks, for every region of the world. Climatic Controls The initial portion of this section presents a basic depiction of the climatic regions. The section described conditions as they exist worldwide; yet very little on the factors behind the variation in temperature, and precipitation amounts. The following section on climatic controls give the student the considerations behind placing a region within a specific climatic classification. The memory device of LACEMOPS depicts all of the climatic controls. L - Latitude S - Storms Latitude - Determines the amount and intensity of sunlight received in a given area. The principle factor behind most climatic classifications. Air Masses - Most directly experienced within North America. Movement of air masses result often in moderate to drastic temperature changes, precipitation, thunderstorms, and sometimes tornadic activity. Their source regions identify air masses. CP Continental Polar (Dry and Cold) MP Maritime Polar (Wet and Cold) MT Maritime Tropical (Wet and Warm) CT Continental Tropical (Dry and Warm) (See figure 3 - Cyclonic Precipitation for depiction.) If the air masses contrast greatly it can result in thunderstorms, and possible formation of tornadoes.

All this activity is common in North America, where the tropics and arctic meet. Tornadoes are most commonly seen in the central portions of the United States. States with the most tornadic activity are; Oklahoma, Texas, and Kansas. Usually tornadic formation requires the meeting of three dissimilar air masses, continental polar, maritime tropical, and continental tropical. Continentality - The impact of a large landmass on climate and weather patterns. Usually results in more severe temperatures, depending on latitudinal position, and coastal or inland location. The best example of the impact of continentality is in Asia and the monsoonal patterns found there. A local example can be used for clarification. Houston's climate is moderated by wind off the Gulf of Mexico. A comparison can be made in conditions experienced when we have wind off the land or out of the gulf. Examples can be a Canadian cold front and summer winds from the gulf. Elevation - Despite a latitudinal position along the equator, location at higher elevation can experience freezing temperatures and precipitation. (See figure 2 under Orographic Precipitation for depiction.) As air moves up on the windward side of the mountain it cools.

As air cools it loses its ability to hold water. Eventually as the air continues to move upward it will reach dew point and release moisture. If the ascent continues the air temperature will reach freezing possibly releasing snow or ice. After reaching the peak, the air will descend, warming as it travels down. The air will as it warms increase its ability to hold water. This results in warm and dry conditions on the leeward side. The release of moisture as a result of rising air due mountain barriers or topographical features is called orographic precipitation. Mountain Barriers - The title denotes the situation, the mountain serves as a barrier to moisture and cooler air. Air masses coming down a mountain on the leeward side will be dry and warm. This set of conditions is the phenomena behind a mid-latitude desert. A desert is created by a mountain blocking what would be normal temperature and precipitation patterns. Ocean Currents - This climatic control refers to the impact of air off the water. Often this factor serves as a moderating force, as seen with marine west coast climates.

(See page figure 4.16 on page 110 of your text for a map depicting world ocean currents.) Pressure Cells - This climatic control refers to semi-permanent pressure cells. Storms Cyclone - The result of two dissimilar air masses meeting. Hurricane - A cyclonic storm begins from five to twenty degrees from the equator as a tropical depression. If conditions are right, fed by warm, moist air, a hurricane will form with winds of at least 75 M.P.H. Hurricanes move in a counterclockwise direction. These storms are called a typhoon in the Pacific, and a cyclone in the Indian Ocean. The strongest hurricane to hit the U.S. was Camille with winds of over 200 M.P.H. The most lives lost via a hurricane was the "Galveston Storm of 1900", it resulted in six thousand lives lost. Often it is not the strength of the storm that results in casualties, but poor construction, improper public warnings, and flooding. Hurricanes easily can produce tornadic activity. Tornadoes - Usually small in size, yet capable of reaching winds of over 500 M.P.H.

Usually produced out of cyclonic storms, or thunderstorms. ???? What is the most destructive storm overall? The cyclonic storm due to its large size and its ability to produce not only thunderstorms, but tornadoes as well. Tree Rings & Climate - Windows to the Universe Tree Rings & Climate Tree-ring patterns provide data about past climates. Credit: UCAR Trees contain some of nature's most accurate evidence of the past. Their growth layers, appearing as rings in the cross section of the tree trunk, record evidence of floods, droughts, insect attacks, lightning strikes, and even earthquakes that occurred during the lifespan of the tree. Subtle changes in the thickness of the rings over time indicate changes in length of, or water availability during, the growing season. ï¿½ Each year, a tree adds to its girth, with the new growth being called a tree ring. Tree growth depends upon local environmental conditions. In some areas the limiting factor for growth is water availability, in other areas (especially at high latitudes) it is the length of the growing season. In areas where water is limited and the amount of water varies from year to year, scientists can use tree-ring patterns to reconstruct regional patterns of drought.

In areas where the length of the growing season is the limiting factor, the thickness of tree rings can indicate when growing seasons were longer (during warmer times) and when growing seasons were shorter (cooler times). The study of the growth of tree rings is known as dendrochronology. The study of the relationship between climate and tree growth in an effort to reconstruct past climates is known as dendroclimatology. A tree ring consists of two layers: A light colored layer which grows in the spring A dark colored layer which forms in late summer At locations where tree growth is limited by water availability, trees will produce wider rings during wet and cool years than during hot and dry years and the rings are wider. Drought or a severe winter can cause narrower rings too. If the rings are a consistent width throughout the tree, the climate was the same year after year. By counting the rings of a tree, we can pretty accurately determine the age and health of the tree and the growing season of each year. Modern dendrochronologists seldom cut down a tree to analyze its rings. Instead, core samples are extracted using a borer that's screwed into the tree and pulled out, bringing with it a straw-size sample of wood about 4 millimeters in diameter.

The hole in the tree is then sealed to prevent disease. Computer analysis and other methods have allowed scientists to better understand certain large-scale climatic changes that have occurred in past centuries. These methods also make highly localized analyses possible. For example, archaeologists use tree rings to date timber from log cabins and Native American pueblos by matching the rings from the cut timbers of homes to rings in very old trees nearby. Matching these patterns can show the year a tree was cut, thus revealing the age of a dwelling. Tree ring data is only collected outside of the tropics. Trees in temperate latitudes have annual spurts of growth in the summer and periods of dormancy in the winter, which creates the distinctive pattern of light and dark bands. Tropical trees grow year-round, and thus do not have the alternating dark and light band pattern that allows us to read tree ring records. Tree ring records can be combined to create climate records that span a timeframe longer than the life of a single tree.

For example, the data from a living, 200-year old tree could be combined with a data from wood from a tree that was felled 150 years ago (after living a couple of centuries) to produce a composite dataset spanning several hundred years. Trees, alive or dead, are not the only source of wood used to construct such extended records. Beams from old buildings or ruins, samples from wooden frames of old paintings, and slivers from violins have all been used to add wood samples from trees long dead to climate chronologies. In some cases, tree rings enshrined in petrified wood even give us some insights into climate conditions in truly ancient times. The oldest trees on Earth, the bristlecone pines of western North America, can live for more than 4,000 years. Dead bristlecone trunks, often well-preserved in the dry terrain upon which bristlecones grow, can be as much as 9,000 years old. The proxy climate record preserved by tree ring data spans a period of about 9,000 years. The resolution of tree ring data is one year.

Tree ring records are amongst the highest resolution proxy climate data types, but they also have one of the shortest time spans over which they apply as compared to other proxies. This map shows sites from which tree ring samples have been gathered. Tree ring samples are collected in temperate zones where the trees have annual growth patterns that produce rings. Credit: National Oceanic and Atmospheric Administration Paleoclimatology Program/Department of Commerce. Online activities We have developed two computer-based activities that allow you to experiment with some of the concepts related to dendrochronology. The first, "Build a Tree", allows you to specify the conditions (temperature and precipitation) in the vicinity of a tree on a yearly basis, and to see how those conditions influence tree ring growth. The second, "Splice Tree Ring Records Together to form a Longer Chronology", invites you to align the records from three samples of wood to generate a longer record of climate history. Click on the links below to go to these activities (require Moodle login).

Question: Periods of the year with distinctive climates are called what?
Answer: Seasons