Common section

Chapter 10

From Rainforests to Ice Caps: The Geography of Climates

In This Chapter

bulletClassifying climates

bulletGetting sticky with humid tropical climates

bulletDrying out with dry climates

bulletStaying comfortable with humid mesothermal climates

bulletChilling out with humid microthermal climates

bulletFreezing with polar climates

T he ancient Greeks divided the world climatically into a tropical torrid zone, two mid-latitude temperate zones (one in each hemisphere), and two high-latitude frigid zones. The Greeks lived in the temperate zone of the Northern Hemisphere and never sojourned to the frigid zone to their north or torrid zone to their south. That suited them just fine, for what they knew — or rather believed to be true — about those areas was fearsome.

The torrid zone in particular inspired dread. It was believed that the sun could literally burn people to death or set fire to a ship. The Greeks’ direct experience with Saharan temperatures reinforced that perception, while observation of black-skinned Africans confirmed that fatal frying awaited one who ventured too close. These ideas persisted for nearly two thousand years, until 1434, when the Portuguese captain Gil Eannes rather clandestinely navigated into the area without ill effect to any of his crew.

Nowadays the study of climate, the average temperature and precipitation conditions that occur at a location over a long period of time, is looked upon more as a source of useful information than of fear. Knowledge of climates and their distribution help us to understand, for example, why particular patterns of agriculture are practiced in particular parts of the world. This may prove very useful in devising development scenarios aimed at increased food production. In addition, knowledge of climate helps us to understand why people live where they do (as well as where they could live), the problems and potentials of various regions, and the geographies of architecture and dress.

Obviously, therefore, climate is an immensely important geographic variable. Accordingly, climatology is a major sub-field of study and research within geography, and the subject of this chapter.


I’d like to throw in my own two cents here. Although each chapter is designed to stand on its own, I advise you to read Chapter 9, which recounts the reasons why particular climates occur in particular regions, prior to this one in order to grasp the full meaning of weather and climates. Global warming and climate change are important, timely, and controversial topics. While this is a logical place to discuss them, I’m going to hold off until Chapter 18, which focuses on current issues of human-environment interaction.

Giving Class to Climates

One thing that has not changed since ancient Greece is the need to classify climates. Because no two areas have exactly the same average temperature and rainfall regimes, Earth is a climatic crazy quilt. To make sense of it, various categories — climate types — have been defined on the basis of maximum and/or minimum temperature and precipitation data.

In 1898, Vladimir Köppen, a German geographer and climatologist, developed the climate classification system that is most in use today. He identified about 25 specific climates and used a rather arcane letter code (using codes such as BWh, Dfb) to identify and define them. If this book were Climate for Dummies, then it would be appropriate to discuss the Köppen system ad nauseum. But because this book’s title is Geography For Dummies, and because I’m a nice guy and don’t feel it necessary to bog you down with unnecessary information, I’m going to forego the letter code and several of Köppen’s climate-types and aim for just enough descriptive treatments of just enough climates to provide a global overview consistent with the goals of this book.


Before getting down to the nitty-gritty of classifying climates, we must keep in mind a common thread among climates. Each climate type has an associated assemblage of natural vegetation that is likely to occur provided human beings and natural catastrophes do not interfere. Thus, if one could journey overland from the equator to the North Pole, different natural vegetation assemblages would be encountered with every change in climate. This is illustrated in Figure 10-1. In reality, of course, people have modified or eliminated natural vegetation in many areas, as by converting grasslands and rainforests to farms. When one visits a particular climatic realm, therefore, purely natural vegetation may or may not dominate the landscape, or be present at all. In any event, the climate-natural vegetation connection is so strong that some climates are named for the plant cover that is associated with them (including the tropical rainforest, steppe, and tundra.)

In general terms, the world’s climates may be grouped into five classes. They are humid tropical climates, dry climates, humid mesothermal climates, humid microthermal climates, and polar climates. Each is discussed in the following sections.

Mixing Sun and Rain: Humid Tropical Climates


In humid tropical climates, the average temperature of each month is 64° F or higher. The warmth is a function of vertical rays (see Chapter 9) and near-vertical rays that strike the tropical latitudes pretty much throughout the year. All that sunshine, in turn, generates high evapotranspiration (for more on this, see Chapter 8), producing a moisture-laden atmosphere, and also creates convection currents (see Chapter 9 for more details) that cause the air to rise, cool, condense, and cause rain. In consequence, annual precipitation is abundant and may occur year-round or in distinctive wet seasons that vary in intensity and duration. This variation in precipitation distinguishes the three principal climates in the Humid Tropical category (see Figure 10-2): tropical rainforest, tropical monsoon, and savanna — the latter is also known as tropical wet and dry.


As “tropical” suggests, these climates generally occur between Latitudes 23 1/2° North and South. Figure 10-2 shows, however, a few decidedly non-equatorial areas where a tropical humid climate prevails due to warm water currents, orographic rainfall (see Chapter 9 for more details), or some other mechanism. Conversely, “non-tropical” climates are occasionally seen between The Tropics of Cancer and Capricorn thanks to the cooling effects of elevation, cold-ocean-surface currents, or predominant wind directions.

Tropical rainforest


In areas of Tropical Rainforest climate all months average above 64° F and the driest month of the year averages above 2.4 inches (6 cm) of rain. For all intents and purposes, therefore, this climate may be described as warm and wet year-round. Although the equatorial low-pressure belt shifts north and south with the seasons, it never wanders far enough afield to result in a genuine dry period.

Incredible forests!

Tropical rainforest vegetation is the definitive natural-landscape feature. This plant assemblage is dominated by broadleaf evergreen species that grow to about 150 feet in height. Their adjoining tree tops create a “closed canopy” that in turn give rise to vertically arranged ecological zones between the ground and tree tops, each comprised of different plant species. Add to that the following:

bulletA year-round growing season (which accommodates a wide range of species)

bulletThe lack of frost and drought (which also accommodates a wide range of species )

bulletThe great age of the rainforest (which has encouraged mutation and genetic drift)

The result is the greatest concentration of living things (especially as regards to plants) to be found anywhere on Earth. How great, you ask? Well, in a square mile of forest in Vermont, you may find 12 to 15 different species of plants. In tropical rainforests, 300 to 400 different species are not unknown in comparable-size areas.

Not only is the variety of plants found here great. So, too, is their potential as sources of food and medicine. The latter is particularly important because a high percentage of medicinal drugs — including anti-carcinogens — utilize chemical compounds derived from tropical plants. Thus far, however, only a relatively small percentage of rainforest plants have been analyzed for their food and medicinal values. Also, because plants take in carbon dioxide and give off oxygen, the tropical forests are important to maintaining global atmospheric balance.

Endangered forests

Despite their real and potential benefits, tropical rainforests have been disappearing at an alarming rate. Reasons include:

bulletRapidly rising populations in rainforest countries, which encourage conversion of forests to farmlands

bulletGlobal demand for timber coupled with technological developments that make rainforests more harvestable than ever before

bulletGovernment programs that encourage settlement of rainforests either to assert ownership of remote areas or to relieve population pressure in other parts of the country

Fortunately, countries that contain rainforests have created national parks and preserves that will save millions of acres for posterity. But millions of acres more stand to be lost unless preservation efforts are greatly expanded.

Poor soils


Despite the lush forest cover, the tropical rainforest realm is underlain by infertile soils called latosols. These are products of warm temperatures and high rainfall, which respectively encourage high microbial activity that breaks down topsoil nutrients, and wash them away (a process called leaching) by means of runoff or downward percolation of water through the soil. Either way, the effect on soil nutrients is much like what happens to the contents of a tea bag after it has been used a couple of times — it becomes weak.

If the soil is so bad, then why (you may ask) is the natural plant cover so lush? The answer is found in root systems that tend to fan out laterally from the bases of plants rather than dig vertically into the soil. This allows trees to effectively absorb nutrients in the topsoil before leaching does its thing.

Shifting cultivation

A large percentage of the people who live in rainforest countries farm for a living, many of who practice shifting cultivation, which has a particularly devastating effect on rainforests. In this form of agriculture, farmers (and their extended families) clear an area of forest, grow crops on the plot for a year or two, and then abandon it, only to move on (hence, shift) to a new area of forest and repeat the process.

Soil infertility explains this practice. When farmers remove the trees, they also remove the sources of leaf-fall that contribute to productive topsoil. With the nutrient source literally cut off and the soil exposed to direct sunlight and rainfall, leaching is swift and sure.

When a plot of land has been abandoned, the forest reclaims it and the fertility of the soil gradually improves. After lying fallow (plowed land that’s not being farmed) for a number of years, it may be used again. But population growth in most rainforest countries is so high that “recycled” land alone is insufficient to meet local food needs. As a result, new areas of virgin rainforest must be annually cut down and the acreage added to the inventory of land that is used for occasional shifting cultivation.

Tropical monsoon

Unlike the rainforest realm, tropical monsoon regions experience a distinct dry season. That is because tropical monsoon regions generally lie in the area located between Latitudes 5° and 10° North and South, where the drying effect of the sub-tropical high-pressure belts are felt for part of the year. Despite high annual rainfall, the periodic dryness is sufficient to prevent the presence of many plant species that grow under tropical rainforest climatic conditions. Other than that, the characteristics and problems facing the world’s monsoon lands are rather similar to the rainforest realm. In fact, expect for the monsoon’s wet and dry seasons, the characteristics are so similar that many climate maps include tropical monsoon regions within the tropical rainforest category — as is done in Figure 10-2.

Malaria: A case study in climate and disease

Each year about 300 to 500 million cases of malaria occur globally and some 1.1 million people — mainly residents of sub-Saharan Africa — die from the disease or related complications. The disease is caused by a parasite that consumes red blood cells, causing high fever and other side effects. Species of mosquitoes that belong to the genus Anopheles are responsible for malaria in humans.

When a mosquito “bites,” it actually sticks a syringe-like appendage into its victim and sucks up some blood. (Mosquitoes have no teeth, so they literally couldn’t bite if their lives depended on it.) This rather antisocial behavior is necessary for mosquito reproduction, blood being required to produce eggs. Accordingly, and with no disrespect intended, it is only the females that bite. When a mosquito sucks up blood from a person or animal that has malaria, it may also suck up the malarial parasite. Hundreds of species of mosquitoes exist; and fortunately for humans, in just about every case, sucked-up malarial parasites die soon after entering the insect’s body. For whatever reason, however, in the body of an Anopheles mosquito, the parasite remains viable, and thus is capable of being spread to the next human or animal that the insect “bites.” The geography of malaria, therefore, is largely determined by the geography of the Anopheles mosquito, which is in turn is determined by the geography of the environmental conditions that the mosquito requires in order to live and reproduce. The principal criteria are temperatures that stay above about 75° F, and standing, shaded fresh water in which the insect can lay its eggs. In other words, it requires conditions that exist in abundance in areas that experience humid tropical climates.

People used to think that tropical air was unhealthy (hence, mal aria — “bad air”), and in many circles, belief persists that tropical climates are dangerous to humans. In truth, nothing is innately harmful about a warm and humid atmosphere. But what does occasionally happen is that climate gives rise to environmental conditions that are ideal for the proliferation of an insect or critter that is instrumental to the spread of a particular disease. The connection between humid tropical climates and malaria is a case in point.

Savanna (tropical wet and dry)

Savanna climate is distinguished from its tropical climatic kin by pronounced wet and dry seasons. The rather even duration and importance of these seasons have given rise to a self-explanatory climatic alias, tropical wet and dry. Most of the savanna realm is located between latitudes 5° and 20° North and South. These regions are alternately affected by passing low- and high-atmospheric pressure belts, which bring with them the wet and dry seasons respectively.

“Savanna” refers to the natural vegetation that occurs under these conditions: a mix of trees and grasses (see Figure 10-1). The relative abundance of these elements generally varies, however, with annual precipitation. Accordingly, trees dominate where rainy seasons are relatively long. Grasses dominate under opposing conditions. In some parts of the world — Africa in particular — the grasses attract large herds of grazing animals (herbivores) and the meat-eating animals (carnivores) that prey upon them. But the grasses and relatively fertile soil that underlie them also attract herdsmen and farmers. The result, as described in Chapter 2, has been a steady decline in wild-animal habitat.

Going to Extremes: Dry Climates

“Dry climate” would seem to be a pretty straightforward concept. Wrong. Technically, it occurs where warm temperatures cause potential evaporation to exceed rainfall. Don’t worry if that leaves you scratching your head. It’s kind of complex, and gets worse. Herr Koeppen stipulated that the boundary between “dry” and “humid” climatic zones occurs where R < 2T + 28 when 70 percent of the rainfall occurs during . . . Like I said, it’s kind of complex.


So for the sake of convenience, I choose to lose the formula and settle for the notion that a dry climate is characterized by no more than 20 inches of precipitation during the course of a year. Climatologists, true and exacting scientists that they are, may scream and rip their clothing upon reading this, but I think they will agree that the 20-inch threshold is pretty close to accurate, and entirely appropriate for the purposes of this book. The geography of dry climates (see Figure 10-3) is made up of two areas: desert and semi-dessert (or steppe).

Hot times in Al-Azizia

Earth’s all-time recorded high temperature — 136° F in the shade — occurred at Al-Azizia, Libya on September 13, 1922. That eclipsed the previous record, 134° F, recorded in Death Valley, California, on July 10, 1913. In all likelihood, higher temperatures have occurred on Earth but have gone unrecorded. In any event, these two numbers are testimony to the fact that by far the world’s highest temperatures occur in sub-tropical deserts.

Given the discussion of sun angles in Chapter 9, this may surprise you. The equator receives higher concentrations of solar energy than Al-Azizia, so you’d figure the equator would be warmer. However, in the equatorial realm the atmosphere tends to be somewhat cloudy and contain lots of water vapor. These respectively reflect a good portion of incoming solar energy back into space and directly absorb solar energy, both before the sunshine touches Earth. Moreover, much of this area is covered by vegetation instead of bare ground, so the “Earth as frying pan” analogy simply does not work to anything near maximum efficiency at the equator.

However, the likes of Al-Azizia are a different matter. The lack of cloud cover and scarcity of vapor in the clear desert air means that a very high percentage of the solar energy that strikes this area reaches the surface, much of which is bare ground. Thus the frying pan analogy works to near perfection. The bottom line is that even though Al-Azizia receives less intense “dosages” of solar energy than does a point on the equator, it heats up to a much greater extent.


Desert climate pertains to areas that average less than 10 inches of precipitation per year. As noted in Chapter 9, cold ocean currents, persistent high-atmospheric pressure, and mountain ranges that produce rain shadows (leeward slopes that lack rain) create dry, desert conditions. These causative factors occur over a wide latitudinal range, which explains why deserts are rather widely distributed.


Hollywood movies have a penchant for depicting deserts as seemingly never-ending seas of sand dunes. People who live in desert areas or who have traveled through them know different, however. Most deserts are covered mainly by gravel, with enough sand and soil mixed in to support plant life. The descriptive term for this is reg, a word that English-speaking students of desert environments have borrowed from Arabic, a language which was born in desert surroundings and therefore has a much richer desert-related vocabulary than does English. Contrary to what Hollywood might have you believe, about 65 percent of the Sahara is reg. Another 30 percent is erg, the classic sand dune landscape. The remaining 5 percent is hammada, or rock-covered.

The natural vegetation of deserts consists of xerophytes (“dry-loving” species), which are plants that have adapted to dry conditions. To help conserve internal moisture, and thus live in lands where they would otherwise transpire to death, most xerophytes have defense mechanisms. These may include tough (even waxy) exteriors often complemented by thorns that ward off birds and other animals that might peck away at their exteriors and expose fleshy innards to the hot dry air. Because it takes a rather specialized plant to thrive in desert conditions and usually a very long time to grow to maturity in these regions of low-moisture availability, some xerophytes of the American Southwest (such as the giant saguaro cactus) are now protected by law.

Semi-desert (steppe)

Areas with semi-desert climate receive between 10 and 20 inches of precipitation per year. They normally are located between deserts and humid climate-types of either the tropical or middle latitudes. Semi-desert owns the record for the greatest latitudinal range. Instances of it are found on the equator in East Africa and in Western Canada at about Latitude 52° North. The same climatic determinants that explain the rather broad distribution of deserts also generally explain the geography of semi-desert. The natural vegetation of this climate is steppe — short grasses that grow in clumps with bare earth in between. Steppe is Russian in origin and describes what one sees in the vast, treeless, semi-arid plains of south-central Eurasia.

Crop-growing without irrigation in semi-desert areas is an iffy proposition. During those years when precipitation is average to above average, some production is possible. Below-average years, however, bring with them the high likelihood of crop failure and famine. Agriculturally, the steppe realm is marginal land, meaning that it’s on the fringe (or margin) of that portion of Earth that is suitable for crops.

In contrast, the raising of livestock on the natural grasses has long been a principal activity. Accordingly, traditional pastoral nomads are associated with steppe environments, as are cowboys and cattle drives of the United States and gauchos (cowboy-like herdsmen) of South America. Nowadays, each of these is much more in the realm of lore than life, thanks to economic and political forces that have turned stock-raising into a rather sedentary endeavor. But raising livestock on steppe is risky. Wise resource management is essential, lest too many animals feed on the grasses, resulting in overgrazing and potential desertification — the conversion of non-desert lands to desert.

Applied Geography: Drought mitigation

Droughts have long been a source of human misery and death. The most horrendous ones typically occur in regions of steppe climate when the characteristic dry season is drier than usual and just won’t quit. Areas to the south of the Sahara Desert have been particularly prone to these occurrences in recent decades. Adding to their devastation is the relative remoteness of this region, which hampers awareness of the drought in the outside world, thus inhibiting the ability of relief agencies to mount an effective response.

Thanks to remote sensing, the use of satellite imagery to monitor Earth’s surface, it’s now possible to monitor the onset of drought as it happens. This is made possible by satellite-based infrared imaging, which is somewhat like picture taking. Lush, healthy vegetation has lots of chlorophyll, which is an excellent reflector of the infrared energy that is a part of sunshine. In color infrared imaging, such vegetation registers as bright red. In contrast, dry vegetation (which is low on chlorophyll) appears as brown. Thus, when the dry season ends and the rainy season begins, the landscape rather immediately changes from brown to red, at least as far as an infrared sensor is concerned. If however, brown persists, then that means that the rains have not arrived, possibly indicating the onset of drought.

Enjoying the In-between: Humid Mesothermal Climates


Humid mesothermal (moderate temperature) climates are located in the low-middle latitudes. They typically receive more than 20 inches of precipitation per year and therefore are not “dry.” Also, the coldest month is less than 64° F but above 27° F, which places these climates between the tropical and polar temperature thresholds (see Figure 10-4). Mild winters and natural vegetation that is dominated by deciduous trees (which shed their leaves annually, as opposed to evergreens) are definitive characteristics of these areas, which include the Humid Subtropical, Mediterranean, and Marine West Coast climates.

Humid subtropical

This climate type is characterized by year-round precipitation, warm summers, and cool winters. Much of the Southeastern United States is in this category, which helps explain why balmier parts of that region are favored nowadays by so many people as a desirable place to live and retire. Other parts of the world that experience this climate include Southern China and the sub-Himalayan lands, Southeastern South America, and parts of eastern Australia.

The short winter of this climate-type makes for a long growing season, the average number of days between the last frost of spring and the first frost of fall. As a result, agriculture tends to be an important activity. In the lower latitudes, where freezing temperatures are rare, citrus and other frost-sensitive tree crops may be plentiful. But most anything can grow here to good effect. That includes a majority of the Earth’s rice crop (mainly in Asia), arguably the world’s most important staple food.


The principal characteristic of this climate is its dry summer. Though found on all continents, Mediterranean climate is most associated with — you guessed it — the land around the Mediterranean Sea. The natural vegetation consists of grasses and scrubs of various sorts, which may become a tinderbox during the dry season. Much of California (save the mountains, deserts, and northern coast) experiences this climate, which explains why wildfires are a common dry-season hazard in that state.

Various fruits prized for their sweetness and/or juices (grapes in particular) dominate agricultural land use. Lack of rain during summer, when the fruits ripen, deprives plants of moisture that would be taken up by root systems and dilute the natural juices. This is a very big deal for the wine industry, for which valuable vintages have everything to do with lack of rain while grapes mature. As to why this kind of climate happens in the first place, predominant wind systems (associated with shifting atmospheric pressure belts) blowing from the land to the sea during summer is the culprit.

Marine west coast

This climate is characterized by mild to cool summers and cool winters. Its name pretty much tells you where you’ll find it — on the west coast of continents in the middle to high-middle latitudes. For virtually every occurrence, the principal determining factor is a warm ocean surface current immediately offshore. Coastal mountain ranges prevent this climate from spreading inland and occupying large areas in North America, South America, and Australia. Conversely, lack of Atlantic coastal mountains in much of Europe allows the marine atmosphere to uninterruptedly waft eastward and characterize most of that region.

The natural vegetation of this climate is mixed coniferous (needle-leaf) and deciduous forests, the two types respectively dominating in the higher and lower latitudes. Over the centuries humans have deforested much of that portion of Europe where this climate is found and converted the land to agricultural use — the warm temperatures attendant to the warm currents serving as a boon for agriculture. The same is generally true of the marine west coast areas of Australia, New Zealand, and South Africa.

In North America, relatively little conversion of forests to farms occurred in areas of marine west coast climate because of the prevalence of mountainous terrain. As a result, the natural vegetation serves as the preferred crop — which is to say that forestry is a major endeavor. And what forests they are! The relatively high temperatures and abundant precipitation wrought by the warm-water current offshore created lush and majestic stands, including the redwoods of Northern California. As demand for timber — much of it emanating from Asian markets — has grown, so has controversy between loggers and environmentalists regarding the extent and nature of cutting. The future of the relatively few remaining “old-growth forests” is a particularly contentious flash point.

Cooling Off: Humid Microthermal Climates


Humid microthermal (low temperature) climates are found in the high-middle latitudes. Sun angles are rather low in these areas. As a result, the average temperature of the warmest month only surpasses 50° F while the average temperature of the coldest month is 27° F or less. The two principal climates in this group are humid continental and subarctic (see Figure 10-5). Summertime differences distinguish the two climates. In humid continental regions at least four months of the year average above 50° F. In subarctic climatic regions, in contrast, fewer than four months average above 50° F. Forest is the dominant natural vegetation in both areas. Lack of land in the high latitudes explains the absence of these climates in the Southern Hemisphere.

Humid continental

This climate is found principally in Northeastern China, Eastern Europe, and, in North America, the Northeastern and Upper Midwestern parts of the United States and adjacent areas of Canada. Over much of these lands, the natural vegetation has given way to farmland. In the United States, dairy farming and the corn-soy complex (popularly called the corn belt) dominate the more humid east, while wheat and other hardy grains dominate the drier west. Much of the more northerly part of this realm is a bit too cool for agriculture, so forestry is intact. Coniferous softwoods, highly prized sources of pulp, dominate and support locally important logging economies.


This climate is generally found immediately north of the humid continental realm. Temperatures are too cold for too long for deciduous trees to thrive, and therefore coniferous forest (called taiga, a word of Russian origin) dominates the natural vegetation. Indeed, for the most part these forests are intact because the same chilly climes that discourage deciduous tree-growth also preclude agriculture. As a result, the broad belt of subarctic climate that extends all across the northerly portions of North America and Eurasia represents the largest expanse of forest on Earth. Generally, however, these forests are well removed from markets and mills and are therefore relatively untapped. On the whole, the subarctic realm is lightly populated. Mining is locally important and accounts for most towns’ economies.

Vertical zonation and “highlands climate”

Vertical zonation refers to the changes in climatic conditions and their associated vegetation that are observed between the base of a high mountain and its summit. To take an example from East Africa, the base of Mount Kilamanjaro lies in tropical savanna climate. Its summit, however, which is 19,430 feet above sea level, is covered partly by snow and ice. For all intents and purposes, therefore, a hike from the base to the summit is tantamount to traveling from the tropics to the poles, experiencing enroute climate and vegetation change that would normally require a journey of several thousand miles. On some world climate maps, mountain ranges are shown as having highlands climate. This refers to the presence of the multiple climates of vertical zonation, instead of a singular climate type that is unique to mountains.

Dropping Below Freezing: Polar Climates


Cold temperatures are the dominant characteristic of polar climates. The average temperature of the warmest month is less than 50° F, and most months typically average below freezing. The very small doses of solar energy that occur at these polar latitudes, despite the long daylight hours of summer, explain the frigidity. The resulting natural vegetation (if any) consists of short grasses, mosses, lichens, and an occasional stunted tree or shrub. The two climates that make up the geography of polar climates (see Figure 10-6) are tundra and ice cap.


In areas with tundra climate, at least one month of the year averages above freezing (32° F), but not above 50° F. Like the humid microthermal climates, and for the same reason, tundra is almost exclusively a Northern Hemisphere phenomenon (small parts of Antarctica experience it). Tundrais a Russian word that refers to the vast, nearly treeless landscapes that are characteristic of this climatic region.

Lack of forest is not a function of cold air temperatures per se, but rather the frozen soil that persists for nearly the entire year, and which prohibits tree roots from taking in sufficient nutrients. Thus, grasses that grow in abundance during the long daylight hours of the short and chilly summer dominate the natural landscape. This vegetation, in turn, attracts huge herds of caribou that annually migrate to the tundra to feast and fatten up for the long winter ahead. This relationship between plant and animal is the principal reason why, in Alaska at least, large portions of the tundra region have been designated as National Parks or National Wildlife Refuges.

Because the growing season is so short, agriculture is virtually unknown. Thus, the livelihood of the traditional societies who have long inhabited this realm — the Inuit (formerly known as Eskimos), and neighboring Native Americans in the Western Hemisphere, and the Lapps and neighboring peoples of the Russian Arctic, have relied on hunting or herding. In the last couple of decades, however, the economic importance of the tundra has increased dramatically as a result of the discovery of significant quantities of petroleum and natural gas. Serious and sometimes acrimonious debate has resulted, pitting proponents of resource exploitation and pristine wilderness.

Keeping permafrost frozen

A peculiar environmental phenomenon that has a powerful and direct bearing on debate between drilling for natural resources and providing for wildlife is permafrost, permanently frozen soil that underlies the tundra. If you drill for oil in the tundra and send it through a pipeline to wherever, then the oil needs to be warm. That is because crude oil, which is thick and viscous, flows very haltingly through cold pipe. And cold pipe is something that Alaska’s climate virtually guarantees for most of the year. Fortunately, crude oil is hot as it comes out of the ground, and the warmth helps make it less viscous as it flows through the pipe. But the warm oil warms the pipe, which can melt the permafrost underneath, causing the pipe to sink into the ground and break, resulting in oil spills. For that reason, and at great expense, the Trans-Alaska Pipeline is elevated on stanchions for much of its route. This and other permafrost-related problems are at the heart of debate concerning possible future oil exploration and drilling in the tundra.

Ice caps: Hollywood-style

Virtually every movie you have ever seen about the Arctic or Antarctic contains the obligatory blizzard scene in which the attendant “white out” easily lends the impression of copious snowfall. Indeed, big snowfalls may occasionally happen, but ice cap blizzards more typically result from high winds kicking up loose snow that never melted and has yet to become consolidated with the ice cap.

Ice cap

In areas of ice cap climate, every month averages below freezing. As the name suggests, its distribution generally coincides with the ice caps that overlie Greenland and Antarctica. At low temperature air can contain very little water. Also, due to the cold temperatures, relatively little evaporation takes place in the polar realm. On both accounts, therefore, the air has a rather low supply of vapor, which in turn depresses the possibility of precipitation. Thus, ice cap climate technically qualifies as desert because it receives less than 10 inches of precipitation per year. The astonishing and uniquely low temperatures, however, result in its being granted its separate climatic status.

As noted in Chapter 8, the ice caps in Greenland and Antarctica are a couple of miles thick, and all of it is the result of precipitation, which would seem to contradict what I just wrote. But all of that ice, however, is the product of thousands of years’ worth of small annual accumulations of snow, which, due to the year-round cold temperatures, tend not to melt, but instead accumulate, compact, and add to the ice cap.

These facts mean that boring down into the ice cap is rather like going back in time. The deeper you bore, the older the ice — and thus the older the precipitation (snow) of which the ice is made. Moreover, because precipitation captures minute but measurable amounts of atmospheric gases, it constitutes a record of the nature of the atmosphere at the time that it fell. Thus, the ice caps are important sources of information about the atmosphere and climates long ago, which figures prominently in contemporary inquiry concerning global warming and its causes.

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