Anthropocene

The notion that humankind has changed the world is not new. However, with terms such as anthropozoic, psychozoic, and noosphere proposed over the last century, the idea of humans as a new global forcing agent can be considered recent and closely linked with the proposition and dissemination of the term anthropocene. It was coined more than a decade ago by Paul Crutzen, one of the three chemists who shared the 1995 Nobel Prize for discovering the effects of ozone-depleting compounds.

The term anthropocene first appeared in the paper titled “The Anthropocene,” published in the International Geosphere–Biosphere Programme Newsletter in May 2000, where Crutzen and his colleague Eugene Stoermer—a professor at the University of Michigan—noted that many forms of human activity are now capable of undermining the natural environment. For instance, in the case in carbon and nitrogen cycles, the amount that is fixed synthetically competes with the amount that is fixed by the planet’s vegetation, land, and oceans.

In their paper, Crutzen and Stoermer argued for the appropriateness of the term anthropocene to characterize the current geological epoch, emphasizing the human footprints on the planet that have been seen in geology and ecology over the last decades. Two years later, in 2002, Crutzen restated the argument in a concise article titled “Geology of Mankind” in the prestigious journal Nature. According to him, the anthropocene could have begun in the latter part of the 18th century, based on analyses of air trapped in polar ice that showed the beginning of increasing concentrations of carbon dioxide (CO2) and methane at the global level.

After these two groundbreaking articles, the term gained popularity and began to appear more often in the scientific literature of a range of disciplines and topics, leading to a more profound and careful consideration of the term. Many consider that the term is not only vivid—as much for the public as for scientists—but that it was also coined at a time of growing realization that human activity was changing the Earth on an unprecedented scale, with changes that are now seen as permanent, even on a geological time-scale. These attributes influenced scientists to increasingly use the term anthropocene to denote the current interval of time, one dominated by human activity. However, many argue that the term remains informal and is not precisely defined.

Antarctic Ice Sheet

Ice covers much of the polar regions of Earth and is a critical component to the planet’s climate. An ice sheet is defined as a mass of ice that is greater than 31,000 mi. (50,000 km) in area, such as those of Antarctica and Greenland. Ice sheets should not be confused with ice caps, which are masses of ice covering less than 31,000 mi. (50,000 km) in area. It is estimated that approximately 90 percent of the Earth’s total ice mass is located in the Antarctic Ice Sheet, or 6.4 million cu. mi. (27 million cu. km). The Ross Ice Shelf and the Filchner–Ronne Ice Shelf are the world’s largest, both found in Antarctica. Scientists are concerned that increasing temperatures of air and sea will cause significant melting of the world’s ice, including the Antarctic Ice Sheet, and cause sea-level rise.

Ice sheets, glaciers, ice caps, permafrost, snow, and sea ice are all components of the Earth’s cryosphere (portions of the Earth’s surface that are frozen over land or water). In the Southern Hemisphere, the Antarctic Ice Sheet covers approximately 98 percent of the Antarctic continent and is the single largest mass of ice on the planet. Ice sheets form as snow and frost build up in an area, compressing the previously fallen snow into ice.

The total area of ice sheets is changed regularly by melting, primarily where the ice comes into contact with water or warmer dry land at its base; and by calving, or the falling off of large pieces of the ice sheet, which become icebergs. The Antarctic Ice Sheet covers the major landmass of the continent in the eastern Antarctic and extends over the ocean in western Antarctica, where the ice sheet is as deep as 2,500 mi. (4,023 km) below sea level. The Antarctic continent is cold year-round and is as dry as a desert, with little to no annual precipitation.

Historically, the Antarctic Ice Sheet has experienced very little melting from the surface. The oldest portions of the Antarctic Ice Sheet are estimated to be 15 million years old. Typically, the seasonal fluctuation that is experienced by the ice sheet is focused on the northern Antarctic peninsula and the northeastern regions of the ice sheet. Most ice from the Antarctic Ice Sheet is lost by calving of glaciers from the protruding ice shelves of the sheet. The total volume of the ice in this region is estimated to be 7.5 million cu. mi. (31 million cu. km).

Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC), also known as the West Wind Drift, is the only current that flows completely around the globe, unimpeded by continents. Famous explorers have often referenced the ACC in their navigational logs, including Edmond Halley (the first to note the ACC in a voyage from 1699 to 1700), James Cook, James Clark Ross, Sir Francis Drake, and James Weddell. The ACC is notably the roughest sea crossing for navigators, particularly the 497 mi. (800 km) wide Drake Passage extending around Cape Horn and the Antarctic Peninsula. The role of the ACC as “mixer of the deep oceans” also has a significant impact on global climate.

The ACC, as the name implies, flows around the continent of Antarctica in an eastward direction driven by westerly winds through the Atlantic, Indian, and Pacific oceans. The ACC is as deep as 6,562–13,123 ft. (2,000–4,000 m) and as wide as 1,243 mi. (2,000 km), accounting for the vast transport of waters, despite its relatively slow eastward current. It is estimated that some of the seawater of the ACC travels the entire circumference of the globe (24,900 mi.) in a mere eight years. For comparison, the ACC carries 150 times more water around Antarctica than flows through all of the world’s rivers combined.

While flow of the ACC is not blocked by any landmasses, it is severely constrained by them. The borders of the ACC are further defined by convergence fronts with significant temperature and salinity variability. The greatest temperature change is north of the ACC in the Subtropical Convergence (Front), where the average sea surface temperature decreases from 54 degrees F (12 degrees C) to 45–46 degrees F (7–8 degrees C) in the ACC and salinity decreases from 34.9 or greater to 34.6 or less.

The southern boundary of the ACC is defined by the westward flowing Antarctic Coastal Current with a surface temperature around 30 degrees F (minus 1 degree C). Mean ACC temperature ranges from 41 to 30 degrees F (5 to minus 1 degree C). Climate change and ocean warming will likely have a significant effect on the ACC, because of this typically narrow temperature range. Any otherwise small increases in sea surface temperatures may induce dramatic effects on the system.

Albedo

Albedo originates from a Latin word albus, which means white. Albedo is the amount of sunlight (of all wavelengths) that is reflected back from an object or a substance. The more the amount of light reflected back, the brighter the color of the object. A lesser amount of light is reflected back from darker objects. The albedo of an object varies from 0 to 1. Black objects have zero albedo, while white objects have an albedo of one. Sometimes, it is also expressed in terms of percentage, 1–100. An ideal white body thus has an albedo of 100 percent, while an ideal black body has an albedo of zero percent. Some standard amounts of sunlight reflected from certain objects.

Usually, albedo is used in the field of astronomy to describe reflective properties of planets, satellites, and asteroids. There are two types of astronomical albedo: normal and bond albedo. Normal albedo is a measure of a surface’s brightness when illuminated and observed vertically, while bond albedo is defined as the fraction of total solar light reflected back to space and is a measure of a planet’s energy balance. The value of bond is defined over the entire range of wavelengths.

Surface reflectance values vary across the globe, mainly because of variation in the presence or absence of snow, ice, or clouds, which increases albedo values in those areas. The presence of ice and snow, for example, at the poles and the absence of snow and ice at the equator reflects the difference in albedo values at the poles and the equator.

The reflectance value (and hence the albedo value) changes with the change in dust concentration, thickness of the clouds (or amount of cloud cover), and zenith of sunlight falling in that zone, which is also reflected in seasonal variation in albedo value for the same region. This can be observed best at higher altitudes, where in winter the surface is covered significantly by snow (or ice), thus increasing the surface reflectance values; while in spring, when most of this snow (or ice) melts, the surface (bare soil) absorbs a lot more sunlight, thus decreasing the albedo values for the same place.

Albedo is an important concept in climatology. When albedo is expressed in percentages, snow has an albedo of 90 percent and charcoal has an albedo of 4 percent. When seen from a distance, the ocean surface has a low albedo as do most forests, while desert has one of the higher albedo values.

The role of the concept of albedo in climate change can be seen in the following example: Ice reflects back more sun radiation than water; with the snow cover getting smaller and the water in lakes (and seas and oceans) increasing, the amount of sunlight absorbed (and, hence, heat retained) is increasing, leading to further increases in the temperature of lake, sea, and ocean water. On the other hand, if more snow is formed, a cooling cycle starts. The amount of sunlight (radiation) absorbed or reflected back causes fluctuations in temperature, wind, ocean currents, and precipitation. In a way, the hydrological cycle changes with the fluctuations in temperature (which is related to how much evapotranspiration takes place). Also, the climate system equilibrium is dependent on the balance between the amount of solar radiation absorbed and the amount of terrestrial radiation emitted back to space.

Agulhas Current

The Agulhas Current is the major western boundary current of the Southern Hemisphere. It completes the anti-cyclonic gyre of the South Indian Ocean, and because the African continent terminates at a relatively modest latitude, it becomes a mechanism for the climatologically important inter-ocean exchange between the Indian and Atlantic oceans. The southwestward flowing Agulhas Current only becomes fully constituted along the east coast of southern Africa at a latitude somewhere between Durban (South Africa) and Maputo (Mozambique). It increases in speed and volume flux downstream. On average, its volume flux is 70 × 106 m3/s, with only small temporal changes. Its depth, by contrast, can vary from 6561 ft. (2,000 m) to the sea floor at 9,842 ft. (3,000 m) over a period of months. It is underlain by an opposing undercurrent at a depth of 3,937 ft. (1,200 m), with a maximum velocity of about 0.2 m/s and carrying about 4 × 106 m3/s equatorward.

An offshore profile of the surface speed of the current shows a peak of about 1.5 m/s close inshore, slowly tapering off to about 0.2 m/s at a distance of roughly 62 mi. (100 km) offshore. The temperature of its surface waters is about 11 degrees F (6 degrees C) higher than ambient waters and decreases from 80 to 71 degrees F (27 to 22 degrees C) from summer to winter.

Afforestation

Because vegetation and climate are so strongly related, rapid changes in climate will impact plant distributions, alter the makeup of natural communities, and threaten forest sustainability. Due to increases in temperature, the limited availability of water, and other environmental factors, entire forests are disappearing and new ecosystems are taking their place. Deforestation contributes to the increasing amount of carbon dioxide (CO2) in the atmosphere and is influencing climatic change. A pragmatic and economical place to begin restoring the balance of the global carbon cycle is through the process of planting trees on open land, which is known as afforestation.

Need for Afforestation

Forests exert a strong influence on the environmentdue to their ability to slow the rate of greenhouse gas emissions by acting as a sink for CO2. Therefore, they are a critical element in mitigating climate change. Numerous studies have verified that deforestation has an influence on local, regional, and global climates. The rate of deforestation in the Amazon and elsewhere has rapidly increased in recent years. Most of the clearing is due to cattle ranching, leading to a decrease in biodiversity, weakening of the hydrologic cycle, and accelerated global warming.

Additional global warming is due to the disruption of global rainfall patterns through reduced evaporation and transpiration, which will cause a reduction in forest cover and the drying up of forests. Several options for reducing CO2 include curbing deforestation, establishing reforestation and afforestation projects, enhancing management and harvesting techniques, and maximizing urban forests. Protecting existing forests and planting new forests can help reduce the greenhouse effect, and a number of multidisciplinary mitigation options revolving around forests are surfacing as researchers collectively consider the threat of climate change.

Botany

Botany is the study of plants. Botanists study all aspects of plants, including their environment and how they grow. The discipline is one of the oldest sciences and has been closely associated with agriculture, horticulture, pharmacology, and other disciplines concerned with plants. Botany is related to many other sciences such as soil science, chemistry, geography, mathematics, and physics. All the sciences and businesses that use botanical knowledge benefit from pure botanical research.

Since prehistoric times, people have used plants for medicine, food, building materials, and making other items such as musical instruments. Plant knowledge was universal among cave dwellers or hunter-gatherers, whose folklore was passed on for generations. Medicine men or women practiced the development of remedies for diseases and injuries, as well as intoxicants. When settled farming communities arose about 12,000 years ago, horticultural plant knowledge also began to move toward a body of knowledge.

Ancient civilizations of the Egyptians, Indians, and Babylonians coined names for the plants they knew. The Greeks added to plant name descriptions. Aristotle, his student Theophrastus (An Inquiry into Plants), Galen the physician, and others gave descriptions to plant names. Aristotle sought the unique form or idea that is found in each plant. This basis would eventually aid the development of taxonomy of plants. He believed in the fixity of the species. This view was challenged by Charles Darwin’s theory of evolution of the species, which was a naturalistic explanation for the enormous plant diversity in the plant kingdom.

There are hundreds of thousand of plants in the world. They vary widely, even when related. This creates a major problem for accurate identification. For example, there are a wide variety of plants named in the Bible and in other ancient literature. However, identifying the exact plants named by biblical names is problematic. The same problem occurs when plants are named by other ancient literature; because they were given local names, the specific plants named are hard to precisely identify. For example, in the Hindu Vedas, there is frequent mention of the soma plant that was used as an intoxicant. Today, scholars are not sure which plant is the soma plant because of the absence of a universal, standard terminology of identification.

A standard nomenclature was adopted after the voyages of discovery, when a rich new variety of similar and uniquely new plants confronted botanists. Standardized nomenclature was developed using a taxonomy derived from Latin names. Latin, the language of scholarship until the 20th century, was used to assign a universal name to plants with different common names or national names in the many European languages. The use of Latin, a dead language, prevents changes in names that would occur in a living language, thereby creating lasting scientific precision. The scientific naming has a fixed pattern, in which the first name identifies the genus to which a plant belongs. The second name is the species name, which denominates precisely to which subgroup it belongs. Each genus is a unique class with each of its species being also unique groups. Many plants also have varietal names. For example, the orange tree has a scientific name of Citrus sinensis; Naval and Valencia oranges are varieties.

Blizzards

In high and mid-latitudes, blizzards are some of the most widespread and hazardous weather events. They are most common in Russia and central and northeastern Asia, northern Europe, Canada, the northern United States, and Antarctica. It is predicted that climate change will likely give rise to changes in the number, severity, and geographical occurrence of blizzards. Although it is common for the term blizzard to be employed to refer to any disruptive winter storm, there is a more precise scientific usage. Blizzards are a winter phenomenon occurring when snow is blown along the ground surface by strong winds. In different countries, official definitions of blizzard conditions vary according to high wind speed, high wind chill values, low visibility, the presence of falling or blowing snow, and the length of time the conditions persist. Although no particular temperature threshold is associated with the definitions, blizzard conditions may produce extreme wind chill values through a combination of low temperatures and high wind speeds.

There are significant inter- and intra-annual variations in blizzard frequency and severity that make statistical analysis of past trends problematic. Detailed studies are limited. Nonetheless, at least in North America, historical evidence points to a decline in the frequency and severity of blizzards on the Canadian prairies, and there has been a significant decline in the frequency of blowing snow conditions in the Canadian Arctic. On the other hand, there is evidence for the occurrence of stronger blizzards along Russia’s Pacific Coast.

An increase in the vigor of winter storms in a substantially warmer and energetic atmosphere may result in severe blizzard conditions becoming more frequent. A warmer climate may also be conducive to greater weather extremes. Regional differences in temperature variations in response to climate change (such as between ocean and continents, or between polar and mid-latitudes) may reduce or enhance temperature contrasts and thereby affect the frequency and severity of storms.

There is evidence from some regions that winter storms have increased in intensity; however, some modeling and empirical studies suggest a decrease in the frequency of winter storms. There may be considerable regional variation in the response to climate change (e.g., blizzards would be less common with declining snowfalls in the Sierra Nevada of California, but possibly more frequent and severe in western Europe). Storm tracks may also shift. Forecasts are speculative, as there is still a need to verify the conclusions derived from empirical studies of past blizzard patterns and projections from climate models.

Types of Blizzards

It is possible for blizzards to occur in conditions of clear skies when no snow is falling if conditions are conducive to the movement of existing surface snow. These are termed ground blizzards. In many storms in continental interiors, it is not uncommon for little new snow to be associated with a blizzard due to a lack of moisture associated with Arctic and Antarctic air masses in winter. In such circumstances, blizzard conditions are largely the result of winds blowing the existing snow cover. 

However, blizzards in some regions (e.g., those in western Europe and the Asian coast of the North Pacific, and “nor’easters” in the northeastern United States) are characteristically accompanied by heavy snowfall. Blizzards are produced by strong winds—katabatic winds (rushing down elevated slopes) and winds generated by steep sealevel pressure gradients associated with storms in high and mid-latitudes latitudes during winter. A single storm can occur over large areas of a continent, and a severe blizzard may persist for a week or more. A blizzard that struck Saskatchewan, Canada, in 1947, lasted 10 days, burying a train in snowdrift a kilometer long. The most severe blizzards occur in Antarctica, with winds exceeding 93 mi. per hour (150 km per hour). At some Antarctic stations, blizzard conditions occur on over half the days of the year.

Historically, high death tolls have been associated with the most severe blizzards. A spring blizzard in the United States in 1888 killed more than 400 people, and 277 died in a storm in 1993. In addition to the risks resulting from high wind chill values and exposure, blizzards generate other hazards. Whiteouts are often associated with blizzards, producing dangerous travel conditions. The blowing snow, limited visibility, absence of shadows, and lack of contrast between objects can cause a loss of depth perception and conditions in which even nearby objects may be rendered invisible. The persistent winds associated with blizzards may cause severe damage to buildings, can block transportation links, and can bury structures in massive snowdrifts. Outdoor activities may come to a standstill. The resulting economic disruption can be massive. Widespread deaths of domestic animals have occurred due to exposure and sources of feed being cut off by blizzards.

A reported 130,000 head of livestock died in Inner Mongolia as a result of a blizzard that began on New Year’s Eve in 2000. However, very disruptive winter storms may not qualify as blizzards; for example, those involving high snowfalls but without an additional defining characteristic. It may be reasonable to assume that in a warmer world there would be fewer blizzards. However, the occurrence of a blizzard is dependent on a specific combination of physical and meteorological factors. A systematic variation in any one or more of these, as influenced by future climate change— for example, storm intensity, shifting storm paths, wind velocity, ambient temperature, the amount of snowfall, and the amount and condition of snow on the ground—may affect the number, intensity, and geographical distribution of blizzards.

Cretaceous Period

The Cretaceous period spanned the time period from 144 to 65 million years ago. It was the final epoch of the dinosaurs. It ended when the dinosaurs became extinct. At its height, the Cretaceous was a period of great warmth. The poles were icefree, and warm ocean currents spread from the equator to the poles. The concentration of carbon dioxide was higher than it is today, causing a greenhouse effect. The abundance of plants was not enough to lower the amount of carbon dioxide in the atmosphere.

The vigor of their growth implies that the Cretaceous climate was warm and wet, although, curiously, rainfall in the tropics was not heavy enough to support rainforests. Plants grew as far north as the Arctic Circle, proving that high latitudes were far warmer than they are today. The climate cooled, however, and rainfall diminished during the Late Cretaceous. The Cretaceous climate reached its nadir 65 million years ago, when a meteor impacted Earth, ejecting debris, dust, and ash into the atmosphere, blocking out sunlight and cooling the Earth.

The sun was not the reason the Cretaceous period had a warmer climate than today; it produced 1–2 percent less heat. Earth was warmer during the Cretaceous period because the atmosphere contained 3–6 times more carbon dioxide than in the current era. Carbon dioxide formed from the decay of large amounts of dead plants.

Moreover, the Cretaceous, particularly the mid-Cretaceous, was a period of extreme volcanism, with the eruption of volcanoes releasing carbon dioxide into the atmosphere. The weathering of carbonaceous rocks also liberated carbon dioxide.

All of this carbon dioxide created a greenhouse effect, in which carbon dioxide trapped sunlight as heat, warming the atmosphere. A reservoir of heat, the ocean displayed the consequences of the greenhouse effect in its warmth, particularly in the tropics. During the Cretaceous period, tropical waters were between 82 and 111 degrees F (28 and 44 degrees C). At 30 degrees latitude, ocean temperatures dipped to 68 degrees F (20 degrees C). At 60 degrees latitude, ocean temperatures were 54 degrees F (12 degrees C), and at 90 degrees latitude, temperatures were a cold 40 degrees F (4.5 degrees C). Polar temperatures, thus, though cold, were nonetheless above freezing and the poles did not have ice, at least not during the Late Cretaceous, though climatologists are less certain about the earlier periods of the Cretaceous. As is true today, the Cretaceous period oceans were cooler at lower depths, yet even at great depths they were warmer than today’s oceans.

Secrets in Plants

Plants absorbed carbon dioxide during the Cretaceous, though they may not have absorbed as much of the gas as they do today, accounting for the greenhouse effect during the Cretaceous. The tropics were drier during the Cretaceous than they are today, and so did not support a rainforest. The absence of a rainforest may have meant that Cretaceous plants were not numerous enough and did not grow vigorously enough to absorb as much carbon dioxide as today. Although this may have been true of the tropics, high latitudes had forests where today there is only tundra. These forests must have taken carbon dioxide out of the atmosphere, but on balance, plants did not remove carbon dioxide in sufficient quantities during the Cretaceous to reduce the greenhouse effect.

Plants reveal that the Cretaceous had a tropical climate, even at high latitudes. The plant Heilungia grew in Alaska. Although it is extinct, its relatives grow in Mexico and the Caribbean, suggesting that Alaska had a tropical climate during the Cretaceous. Temperatures must have varied little, staying around 80 degrees F (27 degrees C) year-round at high latitude. Rainfall must have exceeded 80 in. (203 cm) a year.

The fact that Alaska had swamps during the Cretaceous also suggests that rainfall was abundant. Moreover, plants grew in profusion and density in Alaska, implying high rainfall and warm temperatures. Tree rings were wide, suggesting a warm, wet climate. Conifers grew at lower latitudes, implying that the climate was less moist and that the climate became drier toward the equator, the opposite of conditions today. 

In Siberia, plants grew in the Arctic Circle. Summer temperatures averaged 70 degrees F (21 degrees C), whereas winter temperatures averaged only 43 degrees F (6 degrees C). Arctic Siberia therefore had seasons, with summer 27 degrees F (15 degrees C) warmer than in winter. The difference between summer and winter temperatures during the Cretaceous is less than the seasonal difference today at high latitudes. The climate was warm enough this far north to permit plant growth for more than seven months each year.

Autumn was brief, with the transition from summer to winter coming rapidly. South of Siberia, in what is Czechoslovakia today, temperatures averaged 68 degrees F (20 degrees C). Summer temperatures averaged 82 degrees F (28 degrees C), whereas winter temperatures averaged 52 degrees F (11 degrees C).

Enigma

The climate of the Late Cretaceous is an enigma. The oceans remained warm and the poles ice-free, but on land, temperatures and rainfall decreased. The final blow came at the end of the Cretaceous 65 million years ago, when a meteor hit Earth, ejecting debris into the atmosphere and blocking out sunlight, cooling the Earth. The meteor impact ended the Cretaceous, temperatures continued to decrease, falling low enough to cause ice ages, the last of which ended only 10,000 years ago. As the concentration of carbon dioxide diminished and ice collected at the poles, tundra replaced forests at high latitudes. Rainfall increased in the tropics, giving rise to the rainforests.

Coriolis Force

Because Earth spins on its axis, the Coriolis force bends wind right or left from the direction of its flow. The Coriolis force, therefore, causes wind to deviate from a straight path. If Earth did not spin on its axis, wind would blow following the Earth’s curvature, with no deviation. A wind blowing from south to north would not deviate northeast or northwest. In 1835, French mathematician Gustave Gaspard Coriolis discovered the force that bears his name, and derived the mathematical equations that describe the Coriolis force.

The Coriolis force is weak, compared to other meteorological phenomena. At the equator, the Coriolis Force is nonexistent because wind does not rotate at the equator as it does at the poles. At the equator, wind follows the Earth’s curvature, without deviating right or left. The absence of the Coriolis force explains why hurricanes do not form at the equator, but rather in tropical waters, at least 5 degrees north and south of the equator.

Absent the Coriolis force at the equator, a hurricane or other tropical storm that formed in the north will not cross into the Southern Hemisphere, nor will one in the south cross into the Northern Hemisphere. The equator, therefore, acts as a barrier against the movement of tropical storms. The Coriolis force keeps tropical storms in the hemisphere of their origin. By contrast to the weakness of the Coriolis force as one nears the equator, the force gains strength as one approaches the poles and reaches a maximum at the poles, where winds experience the full effect of the Earth’s rotation on its axis. At the poles, wind rotates sharply right in the Northern Hemisphere or left in the Southern Hemisphere with maximum force.

The Coriolis force accounts for the trade winds that mariners used to navigate the ocean in past eras. So predictable are these winds in direction and force that Christopher Columbus used them in his later voyages to retrace the route of his first voyage. The winds originating in the Northern Hemisphere are called the Westerlies, whereas those that originate in the Southern Hemisphere are called the Easterlies. 

On land, the Coriolis force can form tornados. A tornado will rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The direction of rotation may seem counterintuitive, however, because wind flows to the right in the Northern Hemisphere, one might expect that it would rotate clockwise, rather than counterclockwise. The same rationale applies in the Southern Hemisphere, where the flow of wind to the left might be expected to produce counterclockwise rotation, rather than clockwise rotation. However, a countervailing force, the difference in air pressure at the center and at the periphery of a tornado, forces a tornado to rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

The counterintuitive rotation of tornados underscores the weakness of the Coriolis force. The Coriolis force could be compared to gravity; both are relatively weak, unseen forces, with existences that were undefined for centuries.

Stratus Clouds

Stratus clouds are those clouds that resemble a sheet across the atmosphere. These clouds typically rest at a low altitude, found below 6,000 ft. (2,000 m). Their color can vary between white to dark gray. A stratus cloud that rests at ground level is known more commonly as fog. Stratus clouds a bit higher than fog block the sun from view and cause a cloudy day. The name stratus is the Latin word meaning “to spread out.”

The formation of stratus clouds occurs when a sheet of cool air passes under a sheet of moist, warm air. At the layer where these two sheets meet, the warm upper air is cooled to condensation and forms a stratus cloud. The cloud will extend as far as the overlap between the sheets of air. Because stratus clouds are typically fog that has been elevated, they usually do not bode precipitation. At the most, stratus clouds might bring a drizzle. A type of stratus cloud, nimbostratus, do bring precipitation.

Weather associated with nimbostratus clouds might be rain or snow. These clouds are so named because nimbus means “rain” in Latin. They are dark gray and typically rest in lower altitudes, no higher than 8,000 ft. (2,400 m). Another form of stratus cloud is the combination of a stratus cloud and a cumulus cloud, called a stratocumulus cloud. Stratocumulus clouds bring light precipitation, often a drizzle, and are found at the same elevation as nimbostratus clouds. They are somewhat fluffy, because of their cumulus nature, but darker than typical cumulus clouds. Generally, stratocumulus clouds do not bring much in terms of weather; they are used to predict dull weather.

There are many variations of stratocumulus clouds. These variations are classified as one of two types: stratocumulus undulatus (undulated, or waved) or stratocumulus cumuliformis (cumulusshaped). The types of clouds in the stratocumulus undulatus category are tratocumulus lenticularis (lens-shaped, elongated and flat), stratocumulus opacus (dark and thick), stratocumulus perlucidus (occasionally exhibiting pockets of inconsistency that allow sunlight through), and stratocumulus translucidus (sheets of stratocumulus clouds, between which a clear sky can be seen). 

Stratocumulus cumuliformis clouds include stratocumulus castellanus (towers of clouds billowing from a common base), stratocumulus diurnalis (low altitude clouds resulting from spreading of cumulus or cumulonimbus clouds), stratocumulus mammatus (from mamma, the Latin word for “breast”; having rounded clouds hanging underneath the stratus layer), and stratocumulus vesperalis (generated by air cooling patterns that occur in the evening).

High stratus clouds are called altostratus. Altostratus clouds are also translucent for sunlight. They are formed from great patches of air that are elevated and condensed, because of the cold temperature at higher altitudes. Altostratus clouds are composed of ice crystals and, therefore, threaten to deposit layers of ice on airplanes passing through.

Altostratus undulatus clouds are similar to altostratus clouds, but with undulations, or waves, and therefore are often called billow or wave clouds. Another type of cloud, called cirrostratus, combines features of cirrus and stratus clouds. They are a sheet of wispy clouds made of ice crystals and tend to form at a higher altitude than regular stratus clouds. Because of their ice-crystal composition and high altitude, cirrostratus clouds are translucent; that is, sunlight and moonlight can be seen through them. Because of the ice crystals and their light refractive properties, cirrostratus clouds often cause a halo effect around the moon or sun when viewed from below.

Clouds can be found in the atmospheric layer called the troposphere. The troposphere is the lowest atmospheric region and is where all weather takes place. At the equator, it reaches up to 11 mi. (18 km) from the Earth’s surface. The next atmospheric layer is the stratosphere, extending to 31 mi. (50 km) from the Earth’s surface. A cloud forms when water vapor reaches its dewpoint and, thus, condenses to form a water droplet. These droplets condense around cloud condensation nuclei (CCN), which are often particles of aerosol providing a scaffold around which the cloud can form. Each CCN is approximately one one-hundredth the size of the cloud droplet, which is approximately one one-hundredth the size of a rain droplet (usually about 2 mm in diameter). The nature of the clouds allows them to reflect sunlight away from the Earth, known as the albedo effect, but also to trap infrared light beneath them on the Earth’s surface. This latter phenomenon adds to the greenhouse effect.

Cumulus Clouds

Cumulus clouds are puffy and usually have well-defined boundaries. They form from the condensation or deposition of moisture in particles known as cloud nuclei present in the moist updrafts of convective plumes. The cloud particles can be composed of liquid water, supercooled water, or ice. These cloud particles are denser than air; therefore, they increase the density of cumulus updrafts. However, water vapor is lighter than dry air, and therefore, except for the effects of the cloud particles, the moist updraft air is lighter than dry air at the same temperature and pressure. This effect of moisture on air density is known as virtual temperature. Scientists have shown that the virtual temperature effect is responsible for about 50 percent of the buoyancy of convective plumes that form cumulus clouds in the tropics and subtropics, but has negligible or even negative effects over desert and semi-desert areas.

The base of cumulus clouds is usually flat, because they form when moist air rising from the surface reaches its lifting condensation level. The height of the lifting condensation level depends only on the properties of the updraft air, therefore it is constant in updrafts mixed by turbulent eddies. The height of the cloud bases usually ranges from a few hundred meters over the oceans, to more than 16,404 ft. (5,000 m) over dry desert and semi-desert areas. The shape and size of cumulus clouds depends on the intensity of the updrafts causing them to form. Individual updrafts form the various cumulus towers that compose single cumulus clouds. The rounded tops of these towers are the boundaries of convective plumes reaching their level of neutral buoyancy. Cumulus clouds can develop into giant cumulonimbus in environments convectively unstable over large depths.

Convective circulations are heat engines because they convert heat into bulk fluid motion such as convective updrafts, downdrafts, and the complete convective circulation. The efficiency of this conversion of heat into kinetic energy depends on the depth of the convective layer. Therefore, deeper convection produces stronger updrafts and more well-defined cumulus towers than shallow convection. Cumulus clouds can cause showery rain. Over deserts and semi-arid regions, the rain evaporates before reaching the surface. This is known as virga.

Global climate warming will likely produce increases in the amount of cumulus clouds. This happens because surface warming, coupled with stratospheric cooling, increases convective instability. The height of the bases of cumulus clouds might increase over land because global warming is expected to increase the surface temperature and reduce humidity. Illumination and wind has strong effects on cumulus clouds, in particular, on their appearance and organization. Changes in illumination and background cause changes in color and the apparent surface relief of cumulus clouds. Wind shears can shred the top of cumulus clouds, forming the species known as cumulus fractus. Wind can also orient clouds into rolls or cloud streets and produce waves and lenticular clouds to form above them.

Cirrus Clouds

Cirrus clouds are the thin and wisp-like clouds seen at high altitudes (higher than 20,000 to 26,000 ft., or 6,000 to 8,000 m). The name cirrus comes from the Latin word for “curl.” They are composed predominantly of tiny ice crystals, because they form in the cold region of the troposphere. If cirrus clouds drop their ice crystals, these crystals evaporate before they arrive at the ground.

Cirrus clouds can take on a variety of formations, including a more tuft-like characteristic called cirrocumulus, which also include supercooled water droplets. Some cirrus clouds are called cirrostratus; this type of cloud formation occurs when the thin strands of clouds are so dense that they cannot be deciphered. Other formations include cirrus aviaticus (also called contrails, the artificial cirrus clouds generated by aircraft), cirrus castellanus (castle-like, with towers rising from a base), cirrus duplicatus (multiple sheets), cirrus fibratus (fibrous, and resembling a horse’s tail), cirrus floccus (rounded above), cirrus intortus (tangled), cirrus Kelvin-Helmholtz (slender and signaling atmospheric turbulence), cirrus radiatus (with horizontal banding), cirrus spissatus (thick and gray in color when in front of the sun), cirrus uncinus (hooked, and reminiscent of cirrus fibratus but with more curling at the ends), cirrus vertebratus (rib-like horizontal strips of clouds), and cirrus mammatus (rounded underneath).

Cirrus clouds are generally seen in fair weather, sometimes following a thunderstorm, and their wisps typically point in the direction of the highaltitude wind flow. In the case of cirrus Kelvin-Helmholtz, the clouds lie in the turbulent atmospheric region. Cirrus clouds usually form in the summer and winter, when opposing weather fronts meet, such as warm, dry air and cool, dry air. Some meteorologists use cirrus clouds to predict rain.

Because of the high altitude of these clouds, their albedo effect is often overridden by their greenhouse effect. This imbalance is because of the fact that lower clouds are weaker at conserving solar heat, but are very good at reflecting it back into the atmosphere. In contrast, the high cirrus clouds can both conserve heat and reflect it, but are often better at conserving it. Studies are currently being conducted at the U.S. National Aeronautics and Space Administration (NASA) to determine the role of cirrus clouds in global warming and the Earth’s climate. The modeling of these clouds and their effects is difficult, because of the irregular nature of the sizes and shapes of their ice crystals.

Clouds can be found in the atmospheric layer called the troposphere. The troposphere is the lowest atmospheric region and is where all weather takes place. At the equator, it reaches up to 11 mi. (18 km) from the Earth’s surface. The next atmospheric layer is the stratosphere, extending to 31 mi. (50 km) from the Earth’s surface. A cloud forms when water vapor reaches its dewpoint and condenses to form a water droplet. These droplets condense around cloud condensation nuclei (CCN), which are often particles of aerosol providing a scaffold around which the cloud can form. Each CCN is approximately one one-hundredth the size of the cloud droplet, which is approximately one one-hundredth the size of a rain droplet (usually about 0.08 in. or 2 mm in diameter). The nature of the clouds allows them to reflect sunlight away from the Earth, known as the albedo effect, but also to trap infrared light beneath them on the Earth’s surface. This latter phenomenon adds to the greenhouse effect.

In 2007, investigations at the University of Alabama at Huntsville found that global warming might paradoxically be leading to a thinning of these greenhouse-inducing cirrus clouds.

Cloud Feedback

Increases in surface and tropospheric temperatures produce changes in cloud properties that, in turn, produce changes in temperature. This effect is known as cloud feedback. Cloud feedback has been identified by the United Nations Intergovernmental Panel on Climate Change (IPCC) as one of the most uncertain processes in climate models. Cloud particles (hydrometers) affect both thermal and solar radiation. Cloud particle size and concentration are strongly affected by updraft velocity, humidity, temperature, and cloud nuclei concentration. In addition, the lifetime of cloud particles depends on the humidity of the ambient air. Thus, cloud properties and coverage are sensitive to climate change.

Clouds produce extremely complex climate feedbacks that lead to large uncertainty in climate simulations because cloud processes are not well understood. Clouds cool the Earth by scattering solar radiation and increasing the amount of solar radiation returned to space. That is, clouds increase the planet’s albedo. They also absorb solar radiation, increasing the atmosphere’s temperature, and cooling the surface by reducing the amount of solar radiation reaching it. In addition, clouds produce a greenhouse effect by absorbing thermal radiation and re-emitting it at their own temperature.

Clouds tend to keep nighttime surface temperatures warmer than they would be in their absence, and keep daytime temperatures cooler. Cloud feedback is the combined result of changes in cloud cover, cloud height, cloud emissivity, and cloud albedo. Because various cloud processes contribute to cloud feedback, and because different types of clouds such as cumulus, stratus, and cirrus have different effects on the budget of solar and thermal radiation, cloud feedback is complicated. Climate models cannot even determine if the overall cloud feedback is positive or negative. High clouds, such as cirrus, are optically thin and cold. Because they are reasonably opaque to thermal radiation, they scatter a relatively small amount of solar radiation when compared to the amount of thermal radiation they emit. Thus, high clouds usually have a net warming effect on the planet.

Low clouds, such as stratus, are warm and highly opaque to solar and thermal radiation. However, because low clouds are not much colder than the surface, their main effect is to increase the amount of solar radiation scattered to space. Therefore, low clouds usually produce a net cooling of the planet. On the other hand, low clouds over bright and cold surfaces such as snow or ice can have a positive climate feedback. The net result depends on details of cloud properties, such a particle size distribution and concentration.

Cloud and Climate Connection

The effects of clouds on climate are uncertain, because they depend on the cloud particle number, size distribution, phase, cloud height, temperature, and many other physical parameters. Cloud feedback is the source of the largest uncertainty in the Global Climate Models (GCMs) used to calculate human-induced global climate changes. The International Satellite Cloud Climatology Project (ISCCP), started in 1983, was the first internationally coordinated satellite cloud climatology project. This pioneering program served as a prototype for many other global satellite cloud climatology projects. The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement Program (ARM) has focused on surface and cloud measurements. These measurements are used to study cloud processes to produce solid cloud climatology.

Climate-Gate

On November 17, 2009, 1,073 e-mails, sent and received between 1996 and November 2009 by members of the Climatic Research Unit (CRU) at the University of East Anglia (UEA) in the United Kingdom (UK), were intercepted by hackers. The hackers then attempted to upload it to the Website RealClimate, which notified the CRU of their possible security breach later that day. Two days later, the e-mails began circulating on public Websites, including Wikileaks, and were eventually reported by the mainstream media. This was just a couple of weeks before the Copenhagen Summit on climate change was to begin.

The long correspondence published online primarily consists of a rather informal exchange of comments and information between CRU researchers. However, among these casual e-mails were some that at first glance appeared less neutral, in which researchers talked about data, scientific publications, and recurring rebuttals by oppositional researchers. These e-mails, taken out of context, suggested that CRU researchers were hiding, modifying, or at times even deleting data in order to make climate change seem more evident. Furthermore, they seemed to imply that CRU researchers were obstructing the publication of papers they disagreed with, thus preventing their subsequent consideration by the Intergovernmental Panel on Climate Change (IPCC).

The main researchers involved were Professor Phil Jones, director of CRU; Keith Briffa, Mike Hulme, and Tim Osborn, all climatology researchers at the UEA. Michael Mann, a professor at Pennsylvania State University and the recipient of many of the leaked e-mails, was involved in the scandal.

Allegations and E-Mails

The allegations leveled against the CRU were based on excerpts of a relatively small set of e-mails. The first and perhaps most serious allegation of data manipulation is based on e-mails such as the one dated November 16, 1999, where Jones writes: “Dear Ray, Mike and Malcolm … I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years [from 1981 onward] and from 1961 for Keith’s to hide the decline.”

The second allegation involved the ostensible concealment of data, which is a violation of the Freedom of Information Act. Some of the leaked e-mails suggested that CRU researchers were under continuous pressure to release data, but were apparently unwilling or unable to honor all of the different requests they received. An example of this behavior can be found in the e-mail dated February 2, 2005, where Jones writes to Mann, apparently referring to Steve McIntyre and Ross McKitrick, two Canadian researchers who disputed Mann’s and the CRU’s work in a journal essay: “Don’t leave stuff lying around on ftp sites—you never know who is trawling them. The two MMs have been after the CRU station data for years. If they ever hear there is a Freedom of Information Act now in the UK, I think I’ll delete the file rather than send to anyone.”

The third allegation, that of silencing dissenting research and hindering its publication and consideration by the IPCC, was based on sentences such as the following drawn from an e-mail sent by Phil Jones on July 8, 2004: “I can’t see either of these papers being in the next IPCC report. Kevin and I will keep them out somehow—even if we have to redefine what the peer-review literature is!”

Climate Thresholds

Climate change is not always a gradual process. Just as the weather includes both the ordinary passage of seasons and unpredictable, extraordinary events, such as devastating hurricanes and droughts; climate change also entails both gradual processes and the sudden, sharp changes called climate thresholds. These thresholds are hypothetical— that is, they have not been observed directly, though it is believed that they have happened in the past.

Methane is often implicated in climate threshold theories. A powerful greenhouse gas, methane is contained on the Earth in a number of forms that could be unlocked all at once by sufficiently warm temperatures. For instance, in western Siberia, permafrost peat bogs that have remained frozen since the end of the last ice age are beginning to thaw; if they continue to do so, they will release large amounts of dissolved methane in a sharp spike, rather than the gradual increase seen in the past. The clathrate gun hypothesis focuses on an even larger supply of methane: the methane clathrate (ice containing methane) found in enormous amounts on the cold ocean floor. Sufficient warming would melt the ice, releasing enough methane over a short period of time to severely accelerate global warming.

The most severe mass extinction, much greater than the extinction of the dinosaurs, is the Permian-Triassic Extinction. The event caused the extinction of over 90 percent of sea life and twothirds of terrestrial vertebrates, about 250 million years ago (before the birth of the dinosaurs). This was also the only known mass extinction of insects, at a time when they enjoyed their greatest diversity and largest size. The sudden emptying of so many niches in the ecosystem likely accounts for the success of fungi, and of bivalves such as oysters, both of which were rare before the extinction, but which survived and thrived after it.

There is evidence of an extraordinary release of methane at about this time. The only known possible cause of such a release would be the melting of oceanic methane clathrate, which could explain why the Permian sea life was affected much more than land-dwelling life forms. Seen in this light, catastrophic scenarios for global warming no longer seem unprecedented. Any positive feedback to the greenhouse effect can force a climate threshold. Such an occurrence is called a runaway greenhouse effect. Most positive feedbacks, even strong ones, are not runaway effects; it must be a self-perpetuating feedback, such that the effects are stronger every time it “loops” back around. Runaway greenhouse effects not only cause a rapid rise in temperature, they are also fed by rising temperatures until something changes the system sufficiently to reduce the effect or achieve equilibrium. The planet Venus resembles the aftermath of a runaway greenhouse effect, whether or not that is how it developed.

Climate Forcing

Climate forcing occurs when the global energy balance of the Earth is changed. There are a number of mechanisms that can force climate change. The Earth’s global climate is a dynamic system that is in equilibrium. On a planetary scale, it is steered by the amount of energy available in the system for use by its various ecosystems. If the amount of energy stored or received in the climate system changes, then climate also changes.

The global climate is affected by the sun, which provides much of the energy in the global energy balance. If the energy from the sun increases or decreases, climatic changes will likely occur. On the other hand, if the amount of energy kept by the Earth from sunlight increases, then climate changes will also occur.

The flows of energy occurring in the planetary climate system are important to the global climate system. The global climate system includes the heated core of the Earth and the parts of the Earth that receive the sun’s energy. The parts of the Earth’s climate system include the atmosphere, the oceans, the cryosphere (ice caps at the poles and the alpine glaciers), the geosphere (e.g., the reflective desert sands), the dense foliage of the tropics, the vast forests of the temperate and boreal zones, and other parts of the biosphere. All of these play a role in the convection system on the planet that transfers heat around the globe.

The atmosphere is central to the Earth’s climate, which is a mixture of gases and aerosols (suspended liquids and solid particles). Commonly known as the air, the atmosphere is mostly nitrogen and oxygen. These two gases are available in amounts of about 78 percent nitrogen, 21 percent oxygen. They total about 99 percent of the air that surrounds the planet. The remaining gases and aerosols are present in only trace amounts; however, the greenhouse gases (such as carbon dioxide, methane, and nitrous oxide) play an extremely important part in the energy dynamics of the planet’s global climate.

Greenhouse gases regulate the amount of heat that is present in the lower atmosphere. The gases capture radiant infrared energy and bounce it back to Earth. The gases act as a thin thermal blanket and have a natural greenhouse effect. As a result of greenhouse gases, the temperature of the Earth is 33 degrees C warmer than it would be otherwise. However, since the Industrial Revolution began about 200 years ago, the volume of human-made greenhouse gas emissions has increased enough to affect the greenhouse gas effect and to cause global warming.

Convection is the mechanism through which many energy transfers in the system are exchanged. The oceans are heated by the energy of sunlight. The sunlight is a system input that dynamically affects the global climate on a planetary scale. The output in the system is that most of the Earth’s sunlight warming occurs in the tropics on either side of the equator. The warm seawater evaporates and rises, forming a lower pressure over the oceans and seas of the tropics and the land. The rising warmer air is replaced by cooler, denser air flowing in from the polar regions. Movements in the atmosphere are also heat transfers. The atmosphere also stores energy. About 70 percent of the Earth’s surface is covered by water. The oceans are energy storage centers that contain, in their top 656 ft. (200 m) of ocean water, 30 times the amount of energy that is stored by the atmosphere.

The continental and alpine glaciers of the high mountains contain most of the Earth’s cryosphere. Filled with ice and snow, and frozen by subzero temperatures for much of the year, the white surfaces reflect vast quantities of energy that would otherwise be absorbed by the Earth. The global climate system would then have a major energy source that would affect the dynamics of the interrelated parts of the system, and thereby invoke major changes in its output.

The plant portion of the Earth’s biosphere (all living organisms, including humans) uses carbon dioxide and sunlight to photosynthesize food for growth. The oceans play an important role in this process because plankton, while microscopic, consume vast quantities of carbon dioxide. The gas is locked away in carbonate shells, which sink to the ocean depths. In the planetary climate system, this portion of the biological part of the system reduces the amount of carbon dioxide in the atmosphere and thereby weakens the greenhouse gas effect. Both the sunlight reflection of the cryosphere and the biosphere reduce the energy in the global climate system, thereby cooling the Earth. Clouds and the upper levels of the atmosphere also play a role in the global climate system. Clouds reflect vast volumes of sunlight into outer space. Energy in the form of x-rays, gamma rays, or ultraviolet energy is also reflected back into outer space.

The global energy balance can be affected by changes on Earth, such as an increase in volcanism. Active volcanoes send huge clouds of gases and ash into the atmosphere. If the volume is sufficiently large, the input of gases and ash to the system can affect the planetary climate system by blocking the amount of the available energy and temporarily forcing cooling of the planet. The major question is whether rising levels of anthropogenic carbon dioxide are forcing global warming.

Climate Cycles

There are identifiable cycles in the weather patterns of the Earth. There are four seasons every year in the temperate zones. In the polar regions, there are seasons of light and dark; and in the tropical regions, there are seasons of wet monsoons and dry periods. These identifiable annual cycles are like the cycles of the climate of the Earth over vast eons of the geologic eras.

Geologists estimate the age of the Earth at about 4 billion years old. For much of that time, it was a ball of gas, then the scene of enormous volcanic activity, and then weather activity dominated the whole of the Archaic or Pre-Cambrian eras of Earth’s history. During that time, repetitions of climate patterns may have occurred, but there were also dramatic changes. There was a time when oxygen came to be a major part of the atmosphere, when it was not as abundant as now. These point to cycles in the climate, or the longterm average of the weather on Earth.

The last ice age ended around 12,000 years ago. However, it was not the first ice age on Earth, nor the last. It was only the end of the most recent ice age. There were at least three others in the recent history of the Earth. These ice ages, between interglacial periods, are identifiable cycles of climate in the history of the Earth.

One possible cause of cyclical changes in Earth’s climate is its orbiting of the sun (the Milankovich cycle). The solar calendar is keyed to the annual journey of the Earth around the sun. It is a journey that occurs every year and causes seasonal change. Although there are the same seasons every year, they are never exactly alike. Astronomers and others have observed that there is a cycle that some set at roughly 24,000, or 48,000, or even 72,000 years. The cycle is believed to be responsible for climate changes because the Earth wobbles a bit as it orbits the sun because of the variations in the gravitational pull of other planets and of the sun itself. The slight changes in orbit and the tilt of the Earth in relationship to the sun’s rays means more or less sunlight hitting the Earth, increasing or reducing the amount of energy available to warm the Earth and its atmosphere.

Some scientists believe that ice ages may be caused by the variations in sunlight hitting the Earth during its solar journeys. However, the amount of sunlight during the solar journey has to be combined with solar variations. The sun goes through cycles of activity in which varying levels of energy are emitted. The solar energy variations are related to the presence and absence of sunspots. Increases in these are likely to also bring about an increase in aurora lights, in both the Northern Hemisphere and Southern Hemisphere.

The aurora lights are connected to the magnetic field of the Earth. Researchers studying the sun’s magnetic activity over 100,000-year cycles have proposed the theory that the climate of the Earth is affected by this solar activity cycle. Waldo S. Glock attempted to show a relationship between the weather as a part of a climate pattern and variations in periodic solar activity.

The pattern that paleoclimatologists have discovered is one that describes significant climatic changes with relatively small changes in the Earth’s solar orbit. The variations in sunlight have been compared to variations in weather on Earth. Instruments have been developed to measure the amount of solar energy striking the Earth. Cycles have been detected using data from weather records. Weather records have also been compared statistically with wheat prices. The higher the price of wheat in historically available data, the poorer the weather likely was. Other plant information that has been available to study climate cycles is found in the rings of trees. Dendrochronology is the study of tree rings over time. Trees grow faster in wet, warm years than in dry years or in cooler times.

The discovery of climate cycles that has been verified by a variety of sources points to the current phenomenon of global warming. However, it was preceded by an ice age in which there was global cooling. Consequently, the Earth has experienced both global cooling and global warming in its 4 billion-year-old history. Opposed to theories of climatic cycles is the fact that the climate of the Earth also changes in noncyclical ways when charted on a variety of timescales.

There are shorter cycles, such as the El Niño Southern Oscillation, the Pacific Decadal Oscillation, the Arctic Oscillation, and the North Atlantic Oscillation, the 1,500 year cycle from ice core samples, and the sunspot cycle (the Hale cycle). All of these cycles can be hypothesized from climate records. They are being used in debates over global warming to argue that either the cause is anthropogenic, or that global warming is part of a natural cycle that is only apparently anthropogenic.

Effects of Climate Change

The effects of climate change have already been observed around the planet and are expected to become more severe as global temperatures increase. Ice sheets and glaciers are rapidly melting as sea levels continue to rise, forcing the relocation of low-lying populations and threatening water supplies for millions of people. Ancient permafrost is thawing, weakening the foundations of roads and buildings and possibly triggering the release of vast amounts of trapped methane gas.

Droughts, desertification, and floods are on the increase, all of which have a detrimental impact on agriculture. Biomes from grasslands to forests are in a constant state of flux as various species of vegetation attempt to adjust to the unprecedented changes in plant distribution associated with accelerated changes in climate. The global transportation infrastructure is in jeopardy as extreme weather events buckle railroads, inundate roadways, and force the cancellation of travel plans. Heat waves are contributing to the deaths of thousands and warmer temperatures are hastening the expansion of tropical diseases. The negative effects of climate change will affect all aspects of society and the natural environment.

Ice Sheets, Glaciers, and Permafrost

In the Arctic, nearly all of the ice covering Greenland is in the form of glaciers, which are rapidly melting. On the west coast of Greenland, the average temperature in winter has increased 9 degrees F (5 degrees C) in just the past two decades. There is increasing calving of ice around the edges of the Greenland Ice Sheet as it becomes more porous because of the development of moulins, which are holes or crevasses through which melt water enters a glacier from the surface. The water pouring into the moulin can melt through the ice until it makes contact with the rock base below, causing the glacier to advance more rapidly and perhaps even slide off its base into the sea. 

While it is unlikely that the Greenland Ice Sheet will disappear altogether, continued melting could reduce it to one-third its normal size. In the Arctic basin, sea ice is on the decline, with the ice pack getting thinner and thawing farther from shore. Since the early 1900s, the ice pack has been melting faster during the summer; since the 1950s, the area of summer ice pack has declined by 40 percent. The current rate of sea ice loss during the summer is about 10 percent per decade. Forecasts had originally suggested that the Arctic Ocean could be ice free in summer by 2030. However, the Northwest Passage from the Atlantic to the Pacific was free of ice and open in the summer of 2007, and at the current rate of melting, the Arctic Ocean could be completely ice free by the end of the 21st century.

Antarctica contains the largest continental ice sheets on the planet, and they are showing signs of rapid melting and movement. The average temperature of the west antarctic peninsula has increased by more than 3.6 degrees C (2 degrees C) since the 1950s, and the midwinter temperatures have warmed by as much as 9 degrees F (5 degrees C) during the same time period. Ice shelves consist of huge areas of ice frozen onto the Antarctic land mass and play an important role in Antarctic glacial retreat. Large chunks of ice occasionally break off the edges of these floating ice masses and drift away. The second-largest iceberg ever measured broke free from the Ross Ice Shelf in March 2000. A week later, three more large pieces broke free from the same ice shelf.

In 2002, the Larsen Ice Shelf lost a 1,200 sq. mi. (3,107 sq. km) chunk of ice. While the breakup of these ice shelves may not have a major effect on sea level because they are already floating in water, many of these ice shelves hold back glaciers in the ice sheet, preventing them from advancing seaward. If the ice shelves melt, it will allow the glaciers to move forward, adding ice to the sea and raising sea level.

The Arctic and Antarctica are not the only regions where ice is melting. The Himalayan Mountains and the Tibetan Plateau are home to many of the world’s great glaciers, covering more than 70,000 sq. mi. The glaciers are the source of water for the main rivers of India, including the sacred Ganges and the Indus. During the summer, the slowly melting glaciers provide water for drinking and irrigation, and during the winter, snowfall replenishes the ice for the next summer.

However, warmer temperatures are causing the glaciers to melt faster during the summer, causing major flooding in the lowlands, while the lack of snowfall at higher elevations during the warmer winters is causing drought. The same is true of the glaciers along the equator in Africa. Mount Kenya has had glaciers throughout recorded history, but now only 20 percent of these glaciers remain. The farmers in the surrounding valleys have always depended on the glaciers for their water, but the rivers are drying up and people are starving.

The snows of Mount Kilimanjaro are world famous and have been a mainstay of the people of equatorial Africa for centuries. The glaciers on the mountain are nearly gone and will soon vanish completely, leaving the locals to fight over the limited remaining water supplies. Likewise, in the mountains of Uganda, the glaciers are disappearing at an alarming rate, with 80 percent of the glacial ice melting since 1850 and all of the glaciers expected to be gone within the next 40 years. The glaciers in the European Alps have decreased by 50 percent since the 1900s and are predicted to disappear by the middle of the 21st century. During the devastating summer heat wave of 2003, which killed at least 30,000 Europeans, the glaciers in the Alps lost 7 ft. of ice. Switzerland suffered major flooding in 2005 as a result of rapidly melting glaciers and the resultant runoff. Glacier National Park in the United States has lost 80 percent of its glacial ice since 1850 and is expected to be glacier free within 30 years.

Other types of ice are melting as well. It is estimated that 20 to 25 percent of the Earth’s global landmass consists of permafrost (some of it below the Arctic Ocean), and some areas of permafrost are softening as the climate continues to warm. Across Siberia, the temperature of the permafrost has risen by more than 1.8 degrees F (1 degree C) since 1960, causing trees in the forests to lean and buildings to crack and crumble as the underlying frozen soil begins to thaw.

In some places around Fairbanks, Alaska, drier summers have warmed the permafrost by nearly 5.4 degrees F (3 degrees C), causing the same destruction seen in Siberia as well as a rash of fires and a northward migration of bark beetle infestations that are wiping out entire evergreen forests. Melting permafrost could also potentially free the billions of tons of methane that are currently locked in the frozen soil. Many fear that a sudden release of vast amounts of methane, which is 21 times more potent as a greenhouse gas (GHG) than carbon dioxide (CO2), would cause the worst-case projected global warming scenarios to happen.

Warming Oceans and Rising Seas

There is conclusive evidence gathered from millions of data points taken around the world that the temperature of the global ocean has increased dramatically in recent years. Since the mid-1950s, the mean temperature of the global ocean rose by more than 0.9 degree F (0.5 degree C) from the surface to a depth of 9,000 ft. Because of the high specific heat of water, which is five times greater than that of land, oceans have the capacity to store large amounts of heat energy that would otherwise be released into the atmosphere. 

However, the world’s oceans cannot continue to absorb this excess heat, and by the end of the 21st century it is estimated that enough heat will be released to the atmosphere by the oceans to raise global temperatures another 0.9 degrees F (0.5 degree C) in addition to the warming caused by the greenhouse effect. Because of thermal expansion and the addition of meltwater from ice caps and glaciers, sea levels are rising.

If global temperatures increase by 3.6 degrees F (2 degrees C), there could be a rapid melting of ice and sea levels could rise by as much as 6 ft. (1.8 m). If summer temperatures across the West Antarctic Ice Sheet were to rise above freezing, there could be a rapid melting event that would cause sea level to rise 20 ft. (6 m). If the entire Greenland Ice Sheet were to melt or to slide off its base into the ocean, sea level could be 30 ft. (9 m) higher. And in the highly unlikely, worstcase scenario, if the entire Antarctic Ice Sheet were to melt, sea levels worldwide would rise 230 ft. (70 m).

Agriculture, Drought, and Desertification

Global climate change is forecast to cause major shifts in the general circulation of the atmosphere, which will lead to variations in the length of the growing season and the alteration of precipitation patterns. These changes will, in turn, affect agricultural production. Some changes will be offsetting. An increased length of growing season may be offset by lower rainfall. Crop yields could be reduced, although the combined effects of climate and carbon dioxide will depend on the severity of climate change. In many regions of the United States, climate change and higher temperatures could result in considerable heat and water stress on crops, which could reduce corn, wheat, and soybean yields. In some northern areas, warmer temperatures and a longer growing season combined with rising CO2 levels may increase crop yields, provided there is adequate irrigation.

These projected agricultural shifts will affect not only the livelihood of farmers but also infrastructure

and other support services. During the last few decades, there has been a widespread drying trend over large sections of the Northern Hemisphere. Drought is more common in the tropical and subtropical regions of the world, and it is suspected that climate change is an underlying cause. The intensity and duration of droughts are on the increase, and nearly half of the planet is experiencing some form of prolonged drought. A warmer climate is forecast to generate wetter winters and drier summers across most of the middle and higher latitudes of the Northern Hemisphere, a scenario that would lead to a higher potential for summertime drought. Many scientists expect such extended extreme events to become more prevalent as the climate continues to change.

Agriculture is a critical component of local livelihoods in many countries around the world. This sector is particularly sensitive to land degradation, which results in the loss of productivity. The unwanted expansion of desert, or desertification, involves the loss of productivity of rain-fed cropland, range, pasture, woodlands, and forest from climate change. Contributing factors include drought, soil erosion, overgrazing, deforestation, warming temperatures, and changing precipitation patterns. Areas undergoing desertification are ranked as follows: a moderate-hazard area has an average 10 to 25 percent drop in agricultural productivity; a high-hazard area has a 25 to 50 percent drop; and a very high hazard area has a greater than 50 percent decline in agricultural output. Other natural resource challenges such as pests, crop diseases, poor soil fertility, and a lack of access to water are usually aggravated by periods of prolonged droughts. As of 2011, almost half of Africa’s land area was vulnerable to desertification.

Other countries experiencing desertification include Asia, Australia, and North and South America. As land for agriculture becomes further degraded, the need for more food could likely be met by increasing yields per unit of land area, water, energy, and time. Increasing variability in hydrological characteristics will likely continue to affect grain supplies and food security in many nations.

Vegetation

For many species of vegetation, climatic changes resulting in a temperature difference of a few degrees or a slight variation in rainfall pattern may determine whether a particular species survives or becomes extinct. Because climate and vegetation are so strongly associated, it is assumed that rapid changes in climate will affect plant distributions and alter the makeup of natural communities. An intensive study was completed in 1992 by C. Russell and L. E. Morse in 1992 to determine the effect of climatic change on native vascular plant species found in North America. The analysis assumed that a doubling of CO2 would lead to a 5.4 degree F (3 degree C) increase in global temperatures, basing the study on the maximum and minimum mean annual temperature that each species experiences in its current distribution. The results suggest that with this increase in temperature, 10 percent of the species under investigation would be beyond their climatic envelope and at risk for extinction.

Rare species were especially at risk, with nearly 20 percent threatened with extinction. Because climate plays such an important role in the distribution of plant species, the predicted global and regional climatic changes will likely affect a variety of existing vegetation patterns. Some species will migrate and form new associations, while others will be lost completely.

Fire patterns are likely to be altered as well, which could affect a variety of plant species, even those that are fire resistant or require the presence of fire to regenerate. A study based on a doubling of CO2 levels reveals that wildfires in Canada would undergo a 46 percent increase in seasonal severity. There are unique species that have maintained their present locations for thousands of years despite substantial climatic change, indicating that some species have a high degree of physiological tolerance to climatic fluctuations. In fact, some stress-tolerant species could benefit from extreme climates if competitors are locally depleted or eliminated.

Transportation Infrastructure

As abnormally hot days become more frequent, the transportation infrastructure is directly affected. Railroads tend to warp and buckle during extreme heat waves, sometimes causing train derailments. Asphalt roadways are subjected to softening, while concrete highways undergo joint buckling, creating hazardous conditions for motorists. Climate change and the resultant increase in severe weather events affect aircraft operations. Airports experiencing higher temperatures undergo high-density altitude conditions, which affect aircraft performance in the form of reduced lift, longer takeoff rolls, and runway closures. This phenomenon is especially prevalent at high-altitude airports where the air is already less dense.

The vast majority of flight delays and cancellations can be attributed to bad weather. Aircraft are negatively affected by high winds, such as those accompanying severe thunderstorms. These storms are strengthened by unstable conditions, which often result from surface heating associated with higher temperatures. In more than 80 percent of accidents among commercial air carriers, turbulence and high winds were responsible.

Many scientists predict that climate change will cause more extreme weather events and therefore perpetuate this trend. Increasing temperatures also have numerous indirect impacts on transportation and associated infrastructure. With sea levels projected to continue rising at an accelerated pace accompanied by higher storm surges and flooding, more major seaports along with the connecting roadway and railway facilities will likely be inundated. Likewise, airports located along coasts are at risk of diminished operations because of rising waters and will require expensive protection measures in the near future.

Health Impacts

Human health will be significantly affected by climate change because of warmer and more extreme weather, which has a categorical influence on the distribution of certain diseases. Viruses, bacteria, and insects such as mosquitoes all tend to favor a warmer, wetter environment and are the carriers of numerous infectious diseases. The most widespread of all mosquito-borne diseases affecting humans is malaria, with more people suffering from this tropical disease today than at any time in history. It is estimated that as many as 300 to 500 million people are infected with malaria each year, and that 2.5 million will die of the disease.

Malaria is expanding its range as it moves to higher latitudes and altitudes as a result of rising temperatures, deforestation, and population growth. If global temperature increases by 3.6 degrees F (2 degrees C), the range of malaria could expand to cover 60 percent of the planet. Global warming leads to more rounds of the type of weather that creates more fertile breeding ground for mosquitoes. Some scientists claim a link between global warming and the prevalence of West Nile encephalitis virus, which is transmitted by birds that have been infected by mosquito carriers. The disease first appeared in the United States in 1999, killing seven people. After it was first detected in birds in the southeast, it took just two years for the virus to spread across the United States. According to the Centers for Disease Control (CDC), in 2010 (a year of extreme weather), the virus had infected over 800 people in the United States.

Not only do higher temperatures increase the spread of tropical diseases, they also cause increased death rates for the seriously ill, the elderly, and those with weakened immune systems. More than 30,000 people were killed during the European heat wave of 2003 as temperatures rose 9 degrees F (5 degrees C) higher than normal. Most of the deaths were among the elderly because of cardiovascular problems associated with heat stroke. As global temperatures continue to rise, more extreme summer heat waves are forecast to occur.

Climap Project

Climate, Long-Range Investigation, Mapping, and Prediction (Climap) was a significant research project established in 1971 and concluded in 1981. The project coincided with the International Decade of Ocean Exploration (IDOE) and was funded by the National Science Foundation. The goal of the IDOE was “to achieve more comprehensive knowledge of ocean characteristics and their changes and more profound understanding of oceanic processes for the purpose of more effective utilization of the ocean and its resources.” In order to achieve this broad objective, a significant cross-section of ocean sediment cores were collected and analyzed to reveal a snapshot of past ocean conditions. The objective of the Climap research project was to determine the oceanic, ice, and atmospheric factors that contributed to the global climatic changes in the past million years. In order to create a climatological map of the Earth during the Last Glacial Maximum (LGM) of approximately 18,000 years ago, the study data consisted of fossil abundance collected from sea-floor sediment cores.

The original members of the Climap project consisted of researchers from Oregon State University, the Lamont Doherty Geological Observatory, Columbia University, and Brown University. The Climap group later added scientists from Europe, which included Dr. Seibold (Germany), Dr. Dansgaard (Denmark), Dr. Van der Hammen (Netherlands), and Dr. Shackleton and Dr. Lamb (England). Collectively, more than 100 researchers participated in the project.

The focus of the original group was to study climate change that resulted from the most recent cooling period of the LGM in Antarctica, the North Atlantic, and the North Pacific. The researchers sought to reconstruct the sea-surface conditions and temperatures of the planet during the LGM and develop seasonal maps to understand the oceans’ responses to the cooling period.

The scientists were also focused on the origins of ice ages and how the planet responded to them, believing that understanding the processes related to an ice age could help provide insight into predicting future climate changes. Maps of vegetative zones across continents were also developed. The Climap data is stored at the World Data Center for Paleoclimatology at the University of Colorado–Boulder under the direction of the U.S. Department of Commerce and the National Oceanic and Atmospheric Administration (NOAA), and is operated by the National Climatic Data Center in coordination with the National Geophysical Data Center in Boulder. The sediment data files contain 18,000-year-old micropaleontology in the form of faunal counts of diatoms, planktonic foraminifera, coccoliths, radiolaria, stratigraphy, and geochemistry, and inferred sea surface temperatures for 635 ocean sediment cores. The data collected during the project also included samples from the interglacial period, dating back 120,000 years.