Climate Zones and Biomes

A climate zone results from the climate conditions of an area: temperature, humidity, amount and type of precipitation, and seasonality. The significant factors that influence climate determine the different climate zones worldwide. In general, 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 continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere landmasses are not broad enough to produce a continental climate.

The most common system used to classify climatic zones is the Köppen classification system. This system is based on the temperature, amount of precipitation, and the time of the year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is often used as an indicator of climate type.

A climate type and its plants and animals make up a biome. The organisms of the biome share specific characteristics around the world because their environment has similar advantages and challenges. Furthermore, the organisms have adapted to that environment similarly over time. For example, distinct cactus species live on different continents but have adapted similarly to the harsh desert.

Köppen Classification System

The Köppen classification system was developed by the German climatologist Wladimir Köppen in 1918. The classification system focuses on a location’s average monthly and annual temperature and precipitation totals. The Köppen classification system recognizes four major climate groups based on temperature values (identified by the capital letters A, C, D, and E) and the fifth based on moisture (identified by the capital letter B) to create global climate patterns. The major climate groups can then be subdivided into more specific categories based on a combination of temperature and moisture patterns for any region worldwide. Following several modifications by geographers and climatologists over time, a newer system called the modified Köppen classification system is used today. The modified version still has the five major climate categories broken into fourteen subcategories. The modified version also has a new category for “highland,” which is represented with the capital letter H and focuses on mountainous regions.

The modified Köppen classification system is a straightforward and quick way to identify global and regional climates. The first letter (always a capital letter) represents the primary climate type. The second lowercase letter identifies the precipitation patterns for a location. Finally, the third letter, again in lowercase, is used to identify the precipitation patterns for that location.

Climatologists create climographs to identify and understand a location’s precise climate visually. Each climograph visualized average temperature and precipitation patterns for a location over a year. Temperature is a continuous line, while precipitation is a monthly bar.

There are a variety of resources available from NOAA to analyze climate data. (Visualizing Climate Data | NOAA Climate.Gov, n.d.)

• Data Snapshots
• NOAA View Data Exploration Tool
• The Climate Explore
• Panopoly
• NOAA Weather and Climate Toolkit

Climate and Human Habitation

The earth’s ability to receive and absorb sunlight is a primary factor in the earth’s environment and has a significant impact on human populations. For example, there are no large cities or human communities in Antarctica because it is so cold; most of the sunlight filtering down to Antarctica is reflected off the earth at that latitude because of the tilt of its axis and the resulting angle of incoming solar radiation. Answering the fundamental questions of where most humans live on earth and why they live there depends on understanding climate. Moderate type C climates usually provide the most significant opportunities for human habitation.

Since the region between the Tropic of Cancer and the Tropic of Capricorn receives the most direct sunlight throughout the year, it is favorable to plant, and animal life provided adequate moisture or precipitation. As a result, humans have lived in the tropics for a long time, even when the ice sheets covered midlatitude parts. The tropics’ problem is that the soils are usually of poor quality, and the nutrients have been leached out. Today, when we look at the earth and the distribution of the human population, two main factors attract human habitation: moderate climates and access to water.

More than 70 percent of the earth’s surface is covered with water. The only problem is that less than 3 percent of the water is fresh, and most of that freshwater is stored in ice caps at the North or South Pole. This leaves less than 1 percent of the world’s freshwater for human use, usually in lakes, rivers, streams, groundwater, and underground aquifers. Climate plays a vital role in where humans live because precipitation is necessary to grow crops, raise livestock, and supply fresh water to urban communities.

Several geographers have developed categories to identify climate types. Climate can be defined as a long-term average weather pattern evident in a particular region of the world. Weather is a term usually used to define short-term or even daily conditions. The two main elements in climate conditions are temperature and precipitation. For this overview of world geography, the various climate types have been broken down into six basic types—A, B, C, D, E, and H—after the Köppen-Geiger classification system. Type H climates are a subset of the type E climate category.

• Type A: Tropical or equatorial climates
• Type B: Dry or arid climates
• Type C: Moderate or temperate climates
• Type D: Cold or continental climates
• Type E: Polar or extreme climates
• Type H: (Unclassified) highland climates’

Tropical Climates (Type A)

The humid tropical type A climate, usually found in the tropics, has warm temperatures year-round with high precipitation, typically rain. Type A climates have various subgroups that indicate how varied rainfall is distributed throughout the year. Some type A climates produce a dry and wet season (monsoon), while others receive consistent rainfall throughout the year.

Dry Climates (Type B)

The earth’s desert regions exemplify the dry type B climate. Temperatures can be extreme, with little precipitation. Type B climate regions experience low rainfall and high temperatures during the day and cooler temperatures at night or during the winter season. The terrain in type B climates can range from sand deserts to prairie grasslands or steppes. Type B climates have fewer trees than most other climate areas.

There is a direct relationship between highlands and type B climates in various places in the world. This climate condition, known as the rain shadow effect, or the precipitation shadow effect, occurs when one side of a mountain range receives abundant rainfall. At the same time, the region on the other side of the mountain range is a desert or has more arid climate conditions. This phenomenon is evident wherever there is terrain with enough elevation to restrict the movement of precipitation-bearing clouds.

Rain shadows are created when prevailing winds carrying moisture rise quickly in elevation up a mountainside, where the air cools and condenses to precipitate its moisture in the form of rain or snow. When the air mass hits the top of the mountain, its moisture is much reduced. The dry air rushes down the other side of the mountain range, where it increases in temperature. The warm, dry air from the mountains continues to pull moisture out of the land, resulting in desert or arid climate conditions.

Temperate Climates (Type C)

Often described as moderate in temperature and precipitation, type C climates are the most favorable to human habitation because they host the most significant population densities on the planet. Type C climates are found mainly in the midlatitudes bordering the tropics.

Seasonal changes are pronounced, with distinct winters and summers. Winters are cool to cold, and summers are usually warm. Precipitation varies from low to high, depending on location. C climates dominate the southeast and the West Coast of the United States.

Type C climates are not the most widespread on the planet but have attracted the most abundant human populations. One reason for the attraction has been the abundance of forests, farmland, and freshwater found in type C regions. As a result, the main population centers of the planet are in type C climates. With over seven billion people on the planet growing, humans have populated most regions with type C climates and are now filling up the other areas with A, B, or D climate types.

Continental Climates (Type D)

Type D climate regions are often found in the interiors of continents away from the moderating influence of large bodies of water. They are often farther north than type C regions, resulting in colder winters. Seasonal variations exist, with cool to hot summers and cold winters. Precipitation is usually in the form of rain in summer and snow in winter. Regions with type D climates can be found in the Great Lakes region of the United States, Canada, and a large portion of Russia.

Polar Climates (Type E)

Type E is an extreme climate type found in the polar regions near or to the north of the Arctic Circle and near or to the south of the Antarctic Circle. Regions with type E climates are cold, with permanent ice or permafrost year-round. Vegetation is minimal, and there are no trees. Temperatures may warm slightly during the summer but rarely rise above 50 degrees.

Highland Climates (Type H)

Type H highland climates are usually listed as a subcategory of type E climates. Mountain ranges can create various climate types because of the elevation change from the range’s base to the summit. Different climate types can be found on the same mountain at different elevations. Type H climates designate highlands or mountain terrain. Variations in climate exist on most mountain ranges. Climates at the base of mountains will vary depending on whether the mountains are found in the tropics or the higher latitudes. For example, high mountains near the equator may have a type A climate at their base and a type E climate at their summit, with various type C and type D climates between them. Type H climates are found where elevation differences are profound enough to provide different climate zones. Higher elevation relief can reach above the tree line and have permanent snow cover at the summit. The term relief is used in geography to indicate land surface elevations. Elevation zones with permanent ice or snow can resemble a type E polar climate.

Deforestation

The planet’s growing population has increased demands on natural resources, including forest products. Humans have been using trees for firewood, building homes, and making tools for millennia. As trees are a renewable resource, deforestation occurs when they are removed faster than they can be replenished. Most people in rural areas in developing countries rely on firewood to cook their food. Many of these areas are experiencing a fast decline in the number of trees available. People living in mainly type B climates may have access to few trees to start with; therefore, when trees are cut down for firewood or building materials, deforestation occurs. In tropical areas, it is common for hardwood trees to be cut down for lumber to gain income or to clear the land for other agricultural purposes, such as cattle ranching. Countries that lack opportunities and advantages look to exploit their natural resources—in this case, trees—for either subsistence agriculture or economic gain. Deforestation has increased globally with a rapid rise in the worldwide population.

Countries that are better off economically no longer have to cut down their trees but can afford to substitute other resources or import lumber from other places. Developing regions of the world in Latin America, Africa, and Asia are experiencing severe problems with deforestation.

Tropical rainforests only make up about 5 percent of the earth’s surface but contain up to 50 percent of the earth’s biodiversity. Unfortunately, these forests are cut down for a variety of reasons. Norman Meyers, a British environmentalist, estimated that the push for cattle production causes about 5 percent of deforestation in tropical regions. The timber industry cuts down nineteen percent of these forests, 22 percent are cut down for the expansion of plantation agriculture, and 54 percent are removed due to slash-and-burn farming. Most tropical rainforests are in the Amazon basin of South America, central Africa, and Southeast Asia. All these areas are looking for advantages and opportunities to boost their economies; unfortunately, they often target their tropical rainforests as revenue sources.

Deforestation causes more than the loss of trees for fuel, building materials, paper products, or manufacturing. Another related issue in the deforestation equation is soil erosion. Soils are eroded without the trees to hold the soil during heavy rains, leaving the ground unproductive. In tropical areas, soils are often degraded and lack nutrients. Most of the nutrients in tropical areas rest in decaying material at the base of the trees that supply energy back into the ecosystem. Once the trees are removed, this energy supply has little replenishment. Soil erosion in tropical areas makes it hard for forests to grow back once removed. Landslides can be a more severe component of the soil erosion problem. After heavy rainfall, entire hillsides saturated with water can slide downward, causing severe structural damage to buildings, homes, and agricultural plots. Tree roots help hold hillsides together and therefore help prevent landslides.

Forests play an essential role in the water cycle. Trees pull up moisture with their roots from the soil and transpire it through their leaves back into the atmosphere. Moisture in the atmosphere collects into clouds, condenses, and falls back to earth. Not only do trees store water, but the organic matter at the base of the trees also stores water and makes it available to the broader ecosystem, which may slow down water runoff. In addition, forest canopies disperse water during rainfall and create another layer of moisture in their leaves and branches, either used by other organisms or evaporated back into the atmosphere. Deforestation eliminates the role that forests play in the water cycle.

Forest ecosystems provide for a diverse community of organisms. Tropical rainforests are one of the most vibrant ecosystems on the planet. Their abundant biodiversity can provide insight into untapped solutions for the future. Plants and organisms in these habitats may be critical to medical or biological breakthroughs. However, wildlife and vegetation will be lost as deforestation eliminates their habitat and accelerates the extinction of endangered species.

Trees and plants remove carbon dioxide from the atmosphere and store it in the plant structure through photosynthesis. Carbon dioxide is a significant greenhouse gas part of the climate change process. Carbon dioxide and other similar gases reduce the long-wave radiation (heat) that escapes from the earth’s atmosphere, resulting in increased temperatures on the planet. As more carbon dioxide is emitted into the atmosphere, climate change occurs. Removing trees through deforestation results in less carbon dioxide being removed from the atmosphere, which contributes to climate change. Slash-and-burn farming methods that burn forests release the carbon in the plant life directly into the atmosphere, increasing the climate change effect.

Climate Change

Climate change has been a constant activity in the planet’s evolution. However, the increase in temperature in our environment is the activity that has gained the most attention in recent years. As a result, questions have been raised about the rate and extent of climate change worldwide. Understanding the dynamics of the temperature increase can assist in understanding how it is related to human activity.

The atmosphere is the gaseous layer that surrounds the earth and marks the transition between its surface and space. The atmosphere consists of a mixture of gases composed of nitrogen (77 percent), oxygen (21 percent), and minor elements (1 percent), including argon, helium, carbon dioxide, and water vapor. The small amount of carbon dioxide is a critical component in the control of the earth’s temperature. The atmosphere extends over three hundred miles above the earth’s surface, and the lower level makes up the earth’s climatic system. This lowest level is called the troposphere and is responsible for the conditions that allow life to exist on the planet’s surface.

Since the 1960s, scientists have been concerned about the concentrations of carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons in the atmosphere. These so-called greenhouse gases can trap heat energy emitted from the earth’s surface and may increase global temperatures and cause climate change. Since the Industrial Revolution, human activity—burning fossil fuels and large-scale deforestation—has increased the amount of heat-trapping greenhouse gases in the atmosphere. Carbon dioxide and similar gases act like the glass panels of a greenhouse that allow short-wave radiation from the sun to enter but do not allow the long-wave radiation of heat to escape into space.

An increase in carbon dioxide and greenhouse gases in the atmosphere will generally cause an increase in the temperature of the planet’s climate, which may cause changes in weather conditions in various places on earth. Temperature changes may affect precipitation patterns and alter weather patterns, which may affect agricultural outputs and influence energy needs which can create increasing economic instability. Climate changes also impact environmental conditions for organisms adapted to specific habitat ranges. When climates change, an organism’s habitable zone may also change, impacting entire ecosystems.

Deforestation and the burning of fossil fuels can contribute to climate change. Fossil fuels such as coal, oil, and natural gas are created when dead plant and animal life are under pressure, decay for long periods, and retain their carbon component. Burning fossil fuels releases carbon back into the atmosphere. The increasing need for energy and lumber by human activity will continue to contribute to climate change unless alternatives can be found. In addition, the increase in temperatures may melt ice caps, raise sea levels, and impact human activity worldwide. More information about climate change is included in chapter 13 on Antarctica.