1.3.1. GREENHOUSE GASES

Recently, scientific studies conducted indicate that both natural or anthropogenic factors are the primary cause of global warming. Greenhouse gases are also important in understanding earth’s climatic history. According to these studies, the greenhouse effect, the warming of the climate as a result of heat trapped by atmospheric gases, plays a significant role in regulating earth’s temperature (Fig. 1.1).

Over the last 600 million years, concentrations of greenhouse gases have varied from 5000 parts per million (ppm) to less than 200 ppm owing primarily to the effects of geologic processes and biologic interventions. Studies also have shown that there is a direct correlation between carbon dioxide (CO ₂) gas and global warming. Several historic examples of rapid change in greenhouse gas concentrations indicate a strong correlation with global warming during various geologic events, such as the end of the Varangian glaciation.

According to the Intergovernmental Panel on Climate Change (IPCC) in 2007, the atmospheric concentration of CO ₂ in 2005 was 379 ppm ³, compared with preindustrial levels of 280 ppm ³. These measurements have been substantiated by verifying the dynamic equilibrium of vast amounts of CO ₂ gas held in the world’s oceans, which move into and return from the atmosphere (Figs. 1.2 and 1.3).

Figure 1.1Greenhouse effect. Courtesy of United Nations Environmental Program/GRID-Arendal.

Figure 1.2Temperature and CO 2 concentration in the atmosphere over the past 400,000 years (from the Vostok Ice Core). Courtesy of United Nations Environmental Program/GRID-Arendal.

1.3.2. SOLAR VARIATION

Variations in sunspots and solar flare activity, which significantly affect the earth’s temperature, also have been observed and studied for several centuries. As we know, the sun is the ultimate source of essentially all heat in the climate system. The energy output of the sun, which is converted to heat at the earth’s surface, is the most significant factor controlling the earth’s climate. Ever since the Big Bang, the sun, which is a nuclear fusion reactor furnace, has been burning by converting hydrogen into helium and is getting brighter by outputting higher amounts of energy. In its earlier days, the earth went through several extreme cold and hot periods when liquid water at its surface was completely frozen and liquefied several times, a phenomenon referred to as the faint young sun paradox.

Recent climatology studies have determined that the sun undergoes 11-year cyclic modulations. The 11-year sunspot cycle, however, has so far not been established as having a definitive effect on the global climate. Solar intensity variations, though, did have influence in triggering the global warming effect recorded from 1900 to 1950.

Figure 1.3Global atmospheric concentration of CO 2. Courtesy of United Nations Environmental Program/GRID-Arendal.

1.3.3. ORBITAL VARIATIONS

Orbital variation patterns of the earth’s movement around the sun result in solar energy absorption variability because small variations in the earth’s orbit lead to much more considerable changes in the distribution and abundance of sunlight reaching the earth’s surface. Such orbital variations are a consequence of basic physics owing to the mutual interactions of the earth, its moon, and the other planets. These variations are considered the driving factors underlying the glacial and interglacial cycles of the last ice age. Some of the most notable climatic variations observed, such as the repeated advance and retreat of the desert, have been the result of these orbital variations.

1.3.4. VOLCANISM

Large volcanic activities that occur several times per century also have had a significant effect on climate, causing cooling for periods of a few years. For instance, the 1991 eruption of the Mount Pinatubo in the Philippines affected the global climate substantially. The huge eruptions that have taken place a few times every hundred million years can be verified based on the magmatic variations in rocks and have reshaped the climate for millions of years. It has been speculated that the dust emitted into the atmosphere from large volcanic eruptions in the past has been responsible for cooling owing to the fact that the dust particles have partially blocked transmission of the sun’s rays to the earth’s surface. However, recent studies of and measurements taken from volcanic eruptions indicate that most of the dust thrown in the atmosphere returns to the earth’s surface within 6 months.

Volcanoes also contribute to the extended atmospheric pollutants because over millennia of geologic time periods, they release carbon dioxide from the earth’s interior, counteracting the uptake by sedimentary rocks and other geologic carbon sinks. However, CO ₂ contribution resulting from volcanic eruptions is considered relatively insignificant compared with current anthropogenic emissions. Recent estimates indicate that anthropogenic activities generate more than 130 times the amount of carbon dioxide emitted by volcanoes.

1.3.5. GLACIATION

Glaciers are one of the most sensitive indicators of climate change. They advance substantially during climate cooling, as in ice ages, and retreat during climate warming on moderate time scales, a climatic cycle that has been repeating through the ages (Fig. 1.4). Glaciers are dynamic in nature; they grow in winter and collapse in summer, contributing to natural climatic variability. These are generally referred to as externally forced changes. However, in the last couple of centuries, glaciers have been unable to regenerate enough mass during the winter to make up for ice lost during summer months. The most significant climate processes that have taken place in the past several million years have been the glacial cycles that result from planetary gravitational forces and cause the formation of ice sheets.

1.3.6. OCEAN VARIABILITY

Climate changes also result from the interaction between the atmosphere and oceans. Many climatic fluctuations are a result of heat accumulation and storage in the oceans that cause water currents to move between different heat reservoirs. The movement process of oceanic water, thermoline circulation, plays a key role in redistributing and balancing heat and, consequently, climatic conditions throughout the globe.

Figure 1.4Trend in global average surface temperature. Courtesy of United Nations Environmental Program/GRID-Arendal.

Figure 1.5Great ocean conveyer belt. Courtesy of United Nations Environmental Program/GRID-Arendal.

1.5.1. THE USE OF SEQUESTERED SOLAR ENERGY AND ANTHROPOGENIC CAUSES OF ATMOSPHERIC POLLUTION

Anthropogenic factors are acts by humankind that affect the environment and influence climate. Various theories of human-induced climate change have been debated for many years. The biggest factor of present concern is the increase in CO ₂ levels owing to emissions from combustion. Other concerns are particulate matter in the atmosphere that exerts a cooling effect. Other factors, such as land use, animal husbandry, agriculture, and deforestation, also affect climate.

1.5.2. FOSSIL FUELS

Carbon dioxide variations over the last 400,000 years have shown a rise since the industrial revolution. Beginning in the 1850s and accelerating ever since, the human consumption of fossil fuels has elevated CO ₂ levels from a concentration of 280 ppm to more than 380 ppm today. These increases have been projected to reach more than 560 ppm before the end of the twenty-first century. It is known that CO ₂ levels are substantially higher now than at any other time in the last 800,000 years. Along with rising levels of atmospheric pollutants, it is anticipated that there will be an increase in global temperature by 1.4–5.6°F between 1990 and 2100 (Fig. 1.6).

1.5.3. MILLENNIAL PERSPECTIVE OF CARBON DIOXIDE VARIATIONS

Organic materials such as plants (mainly formed from hydrocarbons and water molecules) under certain conditions, such as natural disasters, fires, volcanic activity, tectonic plate displacement, and extreme geoclimatic changes, lose significant amounts of their water content and are left with solely carbon and mineral materials. It is because of the sun’s energy that organic life, in accordance with certain chemical processes, is transformed into various forms of hydrocarbon organic structures.

Figure 1.6Projected changes in CO 2 and global temperature: summary of assumptions in the IPCC 1992 alternative scenarios. Courtesy of United Nations Environmental Program/GRID-Arendal.

Through the passage of millennia, these remains of organic carbonized material are manifested in the form of solid coal or liquid crude oils, referred to as fossil fuels. Fossil fuels, therefore, are considered to be sequestered forms of concentrated solar energy.

One of the most common sources of energy known to humans is the chemical combination of carbon molecules with oxygen. At a certain kindling point (elevated temperature), one atom of carbon (C) combines with two atoms of oxygen (O ₂), giving rise to a carbon dioxide molecule (C + O ₂ = CO ₂). During this chemical combination, a certain amount of heat energy is released. We normally refer to this as a burning process.

Carbon dioxide, in its normal state, is a gas that is heavier than air. Under certain atmospheric pressures and temperatures, it liquefies. This liquid form of CO ₂ is used in common fire extinguishers. Under normal temperature conditions, CO ₂, when present in the air, displaces oxygen and ceases the spread of fire by preventing oxygen present in the air from reacting or combining with other forms of hydrocarbon-based material. This is referred to as oxygen starvation.

When heated, CO ₂ molecules, owing to thermal agitation, distance themselves from each other, rendering the gas lighter than air. Large quantities of CO ₂ result from burning fossil fuels. When heated by the sun’s energy, CO ₂ rises to higher elevations and surrounds the planet in a blanket of gas referred to as the inversion layer (Fig. 1.7).

When solar rays impinge on the earth, they are repelled from its surface and the north and south polar ice caps. The reflection of solar energy back into the earth’s outer stratosphere moderates global temperature to levels that promote the existence of various life forms. Minor elevations in the earth’s climatic conditions, in turn, affect the organic life and the reproductive cycles of all species.

As discussed earlier, global climatic temperature is moderated not only by the reflection of solar rays but also by the heat-absorption capability of the earth’s oceans. Two-thirds of the earth’s surface is covered by oceans, which absorb significant amounts of solar energy. Owing to earth’s relative rotational tilt angle to the sun (23.5 degrees), the oceanic water at the equator and poles absorbs unequal amounts of solar energy, giving rise to a water temperature gradient differential that creates convective water circulation within the oceans. The movement or displacement of lighter warm waters from the equator to the north and cold water from the north pole to the south is referred to as the gulf stream or the belt current and regulates continental climatic conditions.

Figure 1.7CO 2 emissions of various countries in 1995. Courtesy of United Nations Environmental Program/GRID-Arendal.

When fossil fuels are burned, the resulting blanket of CO ₂ gas, referenced earlier, thickens, thus elevating the earth’s temperature through energy entrapment. The entrapment of higher energy within this reflective blanket elevates the surface temperature of the oceans, thus increasing evaporation and water particulate release into the atmosphere. Water molecules, when released into the atmosphere, in turn, act as supplemental reflective shields, further reflecting the sun’s rays and expanding the inversion layer, exacerbating global warming.

1.6.1. WOOD BURNING

From the dawn of civilization until the mid-eighteenth century, humans used wood burning as their primary source of energy. It was used mainly for heating but also, to a lesser degree, for smelting and distillation. Owing to a smaller global population, the CO ₂ gas generated did not saturate the absorption capacity of plants and the oceans. Consequently, it did not have a significant negative effect on the environment.

1.6.2. COAL BURNING

With the invention of the steam engine in 1750, historically cited as the dawn of industrial revolution, the use of coal as the primary source of energy turned the wheels of industries, shortened intercontinental travel time, enabled significant transcontinental transportation, displaced cultures, gave rise to significant advancements in farming automation, and increased farm production and manufactured goods.

The industrial revolution also resulted in a better standard of living for certain privileged populations in the Western world, improving levels of hygiene and life expectancy. As a result of the deployment of steam-driven farming equipment and the availability of larger amounts of food stock, population growth accelerated in an unprecedented manner.

Owing to greater energy demand and the global proliferation of the industrial revolution, the use of coal created significant atmospheric and environmental pollution in industrial centers such as London and Paris, causing major human health problems. Death from pulmonary and respiratory diseases, such as black lung and tuberculosis, were the norm of the times.

1.6.3. CRUDE OIL AND NATURAL GAS

At the beginning of the twentieth century, the advent of the internal combustion engine, the discovery of vast crude oil reservoirs in Texas, and the proliferation of electrical energy generation and distribution brought the industrial revolution into a new era of accelerated expansion.

Mass production of automobiles necessitated the construction of roadways (facilitating rapid land transportation), the creation of new suburban communities, unprecedented real estate development, and the production of new goods and services, all of which became possible owing to the abundance of fossil fuels. Advances in aviation technology furthered the demand for gasoline and created an acute increase in dependency on fossil fuels.

The rapid expansion of urban dwellings and technology created an ever-extensive demand for electrical energy and necessitated the massive construction of coal- and crude oil–fired steam turbines, which have contributed significantly to atmospheric pollution and deterioration of the global environment. In the past century, global dependency on crude oil has increased to such an extent that it has become the most significant commodity sustaining modern life. Without fossil fuel energy, hydroelectric and nuclear power plants would not have sufficient power production capacity to sustain the minimal energy requirements of 6.6 billion people globally.

1.6.4. FOSSIL FUEL DEPENDENCY

Dependency on fossil fuels over the last century has shaped our way of life, customs, moral standards, population distribution, demographics, hygiene, life expectancy, standard of living, global economies, security, and international politics. Control of global fossil fuel resources has caused political upheavals and international strife, defined international geographic boundaries, displaced multitudes of populations, caused wars, and resulted in the destruction of property and human life. However, the most significant effect has been the deterioration of the global habitat for all living species.

Control of fossil fuel resources, particularly crude oil and natural gas, has significantly shifted the international balance of trade and power, polarized ideologies, and created a divide between the resources of rich and poor countries.

1.6.5. IMPACT OF CLIMATE CHANGE ON HUMAN HEALTH

There is a close link between the increase in anthropogenic atmospheric pollution, increases in the size of the inversion layer, global temperature rise, and the occurrences of diseases related to elevated temperatures. It is well known that extreme global temperature rise can directly cause loss of life and promote environments for the growth of pathogens that cause serious diseases. Global temperature elevation, whether owing to natural or anthropogenic causes, increases air and water pollution, both of which harm human health.

The most significant effect of climate change is the increase in human causalities owing to dehydration and heat stroke. People with cardiovascular impairments become extremely vulnerable in hot weather because their cardiovascular systems overwork in order to regulate and maintain normal body temperature. In addition, higher temperatures exacerbate respiratory problems because increased temperature increases the concentration of ozone at ground level. The natural layer of ozone in the troposphere blocks harmful ultraviolet radiation from reaching the earth’s surface. However, in the lower atmosphere, ozone becomes a significantly harmful pollutant that can damage lung tissue and cause pulmonary dysfunction and severe cases of asthma and other lung-related diseases. Even modest exposure to ozone can cause healthy individuals to experience chest pains, nausea, and pulmonary congestion.

A recent statistical analysis of mortality and hospital admissions showed that death rates in the United States increased during extreme temperatures, seriously endangering the old and very young urban populations. In July 1995, a heat wave in Chicago killed more than 700 people. Worse yet, a heat wave in 2005 killed 15,000 elderly in France, 7000 in Germany, 8000 in Spain and Italy, and 2000 in the United Kingdom. Recently, the BBC announced 25,000 deaths in England and Wales owing to cold weather, all of which went relatively unnoticed. It is also estimated that each year 200,000 people die from excess heat in Europe. However, an astonishing 1.5 million Europeans die annually from excess cold.

Global warming also increases the risk of some infectious diseases, particularly those that appear only in warm areas. Deadly diseases often associated with hot weather, such as West Nile viral infection, cholera, and Lyme disease, are spreading rapidly throughout North America and Europe because increased temperatures in these areas allow disease carriers such as mosquitoes, ticks, and mice to thrive. In the past decade, West Nile virus–carrying mosquitoes in the United States and Canada have increased significantly. It is a general consensus among scientists that global temperature rise will increase the frequency of disease outbreaks, particularly in areas with polluted waters.

Heat-related deaths can be prevented by emergency measures such as moving vulnerable people to air-conditioned buildings and by reducing the emissions of photochemical oxidants that cause ground-level ozone. Many of the impacts of climate change on health could be avoided through the maintenance of strong public health programs that monitor, quarantine, and treat the spread of infectious diseases and respond to other health emergencies as they occur.

1.6.6. IMPACT OF AIR POLLUTION AND ULTRAVIOLET RADIATION ON HUMAN HEALTH

It is estimated that air pollution, even with the U.S. Clean Air Act (among the most stringent air-quality laws in the world), causes as many as 50,000 Americans to die prematurely annually. Perhaps the leading cause of air pollution–related death in both industrialized and developing countries is particulate matter, such as soot and dirt particles, causing respiratory failure. Another significant health concern, aside from ground-level ozone, is lead emissions from gasoline, which cause neurologic damage and impairment to the intelligence of children. Sulfur dioxide emissions from coal-burning steam plants are a significant factor as well in respiratory diseases. Air pollution today poses a risk to millions worldwide, especially children in the world’s urban areas.

Increased ultraviolet (UV) radiation, which results from depletion of the stratospheric ozone layer, has had numerous adverse effects on human health, including an increased risk of various forms of skin cancer, a weakening of the human immune system, and an increased risk for eye disorders such as cataracts.

1.6.7. CLIMATE PROTECTION POLICIES THAT COULD ENHANCE HUMAN HEALTH

Policies and measures that enforce the reduction of emissions of greenhouse gases are the only viable solutions to ameliorate human health problems. Measures that could improve air quality significantly include the extensive use of green energy and enhanced energy-efficiency movements that promote the use of noncarbon fuels. It is estimated that an international adoption of increased carbon emission control policies worldwide would reduce deaths from air pollution by about 8 million between 2000 and 2020.

1.6.8. AIR POLLUTION AND STRATOSPHERIC OZONE DEPLETION MITIGATION MEASURES

It is a well-established fact that human, industrial, and agricultural activity in the last century has been a significant factor in contributing to atmospheric pollution. Another family of human-made chemical compounds, chlorofluorocarbons (CFCs), which also are considered to be one of the leading causes of stratospheric ozone depletion and which result in the production of greenhouse gases, has been banned recently. This measure will help in climate protection as well as in preserving the stratospheric ozone layer.

It should be noted that the deployment of smoke stack scrubbers, used for reducing air pollution on coal-fired power plants, has resulted in more energy consumption and an increase in greenhouse emissions. Therefore, their use must be banned.

1.7.1. CEMENT MANUFACTURE

Ever since the Roman discovery of concrete and the subsequent patenting of the cement manufacturing processes in the eighteenth century, concrete has become one of the most used building materials. Cement manufacturing, which involves the excessive burning of coal, is the third largest source of human-made CO ₂ emissions. While fossil fuel combustion and deforestation each produce significantly more CO ₂, cement making is responsible for approximately 2.5 percent of total worldwide emissions from industrial sources.

1.7.2. LAND USE

Prior to the widespread use of fossil fuels, humanity’s largest effect on local climate likely resulted from changes to the environment. For example, human activities change the amount of water going into and out of a given location. They also change the local ecology by influencing ground cover and altering the amount of sunlight that is absorbed.

Historical evidence suggests that the climates of Greece and other Mediterranean countries were permanently changed between 700 BC and 1 AD because of widespread deforestation (the wood was used for shipbuilding and construction). This finding is supported by the archeologic discovery of a species of tree that was used for shipbuilding in the ancient world but which can no longer be found in the area.

There are also hypotheses that suggest that the rise of agriculture and the accompanying deforestation led to increases in CO ₂ and methane gases during the period 5000–8000 years ago. The increases in CO ₂ may have been responsible for delaying the onset of a more severe glacial period (Fig. 1.8).

In 2007 it was found that the average temperature has risen about 2°F over the past 50 years, with a much larger increase in urban areas. This change was attributed mainly to extensive human development of the landscape.

1.7.3. LIVESTOCK

According to a 2006 United Nations report, livestock is responsible for 18 percent of the world’s greenhouse gas emissions, as measured in CO ₂ equivalents. This includes land deforestation in order to create grazing land. In the Amazon Basin, 70 percent of deforestation has been to make way for grazing land. In addition to CO ₂ emissions, livestock produces 65 percent of human-induced nitrous oxide, which has 296 times the global-warming potential of CO ₂, and 37 percent of human-induced methane, which has 23 times the global-warming potential of CO ₂.

Figure 1.8The main greenhouse gases.Courtesy of United Nations Environmental Program/GRID-Arendal.

1.7.4. ARGUMENT ABOUT THE GLOBAL CLIMATIC TEMPERATURE BALANCE

As discussed earlier, the glacial and interglacial cycles of the last ice age provide important information. It is believed that orbital variations of the earth around the sun result in the growth and retreat of ice sheets. However, the ice sheets reflect sunlight back into space and therefore cool the climate, a phenomenon referred to as the ice-albedo feedback. Moreover, an increase in polar ice plates results in falling sea levels. It should be noted that the expansion of ice caps also indirectly diminishes the growth of plant life and therefore leads to reductions in CO ₂ and methane. This causes further cooling of the atmosphere.

Using a similar argument, rising temperatures caused by anthropogenic emissions of greenhouse gases could lead to retreating snow lines, revealing darker ground underneath. Consequently, the result would be increased absorption of sunlight and thus excess water vapor, methane, and CO ₂ generation. This eventually would act as significant positive feedback because increases in these levels would create an accelerated warming trend. Water vapor, unlike other major greenhouse gases, can act as a driving force, resulting in changing circulation patterns in the ocean or atmosphere. For instance, a significant melting of glacial ice from Greenland would interfere with sinking waters in the North Atlantic and inhibit the thermohaline circulation discussed earlier. This could significantly affect the distribution of heat to in the Atlantic Ocean (Fig. 1.9).

Figure 1.9Sea level rise owing to global warming. Courtesy of United Nations Environmental Program/GRID-Arendal.

Figure 1.10Great weather and flood and catastrophes over 40 years. Courtesy of the United Nations Environmental Program/GRID-Arendal.

Other potential effects of global warming that have not yet been fully studied include the potential to either inhibit or promote certain natural processes. For instance, we do not know whether rising temperatures promote or inhibit vegetative growth, which, in turn, could either absorb more or have a saturation level that will decrease carbon dioxide levels. It should be noted that evidence for climate change in the past has been taken from a number of sources, allowing for the reconstruction of past climatic variations (Fig. 1.10). Most of the evidence gathered has been based on indirect climatic changes inferred from changes in indicators that reflect climate, such as pollens and fossilized remains of species.

1.8.1. DATING OF THE LITTLE ICE AGE

As mentioned earlier, there is mixed concurrence by scientists about the beginning year of the little ice age. However, scientific discovery has shown that a series of events preceded the downward trend of climatic conditions. It has been established that in the thirteenth century, north polar ice and Greenland glaciers began advancing southward. It also has been recorded that from 1315 through 1318, torrential rains ushered in an era of extremely unstable weather conditions in northern Europe that lasted through the mid-nineteenth century. The following is a timeline of climatic change during the 400 years of the little ice age:

It is believed that the little ice age lasted until the mid-nineteenth century

1.8.2. NORTHERN HEMISPHERE

The following are anecdotal accounts of the effect of the little ice age on the northern hemisphere:

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  Cold weather was experienced throughout many parts of the world.

  
  
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  As a result of severe climatic conditions in the fourteenth century, most springs and summers were so cold and wet that common farming crops such as cereals could not yield sufficient sustenance.

  
  
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  As a consequence, Europe experienced a severe famine from 1315 to 1317, resulting in new crops such as rye and barley that were better suited for shortened, less reliable growing seasons.

  
  
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  The Thames River often froze over during the winter, and people skated and even held parties on the ice.

  
  
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  In 1622, waters around the Potomac River froze in the winter.

  
  
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  In the sixteenth century, vine growing completely disappeared from some northern regions of Europe, resulting in a severe reduction in wine production and increased use of beer as a substitute.

  
  
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  In the early sixteenth century, violent storms caused massive flooding and loss of life. Some of these resulted in permanent losses of large tracts of land from the Danish, German, and Dutch coasts.

  
  
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  In the mid-sixteenth century in southern Europe, warm weather crops, such as oranges, were abandoned in provinces where they had been grown for centuries.

  
  
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  In the mid-seventeenth century, glaciers advanced, gradually engulfing farms and crushing entire villages.

  
  
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  In 1758, General Washington’s army marched across the Potomac River to invade the British garrison.

  
  
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  In the winter of 1794–1795, the French army invaded Holland by marching over the frozen rivers of the Netherlands.

  
  
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  The first Thames frost fair was recorded in 1607, and the tradition lasted through 1814.

  
  
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  In the eighteenth century, owing to a lack of harvest, the population of Iceland fell by half.

  
  
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  It has been said that the famous violin maker Stradivari produced his outstanding instruments during the little ice age, when the colder climate meant the wood used in his violins had denser growth rings (which are otherwise larger in warmer periods).

  
  
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  It also has been speculated that severe mortality rates in Europe, East Asia, and the Middle East attributed to a decrease in agricultural output and deterioration of nutrition and immune systems were consequences of the little ice age. Ruddiman,

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  who first theorized the correlation, further suggests that massive depopulation in the New World during the 1500s was a result of the Americas being in contact with Europe.

1.8.3. PRINCIPAL CAUSES OF THE LITTLE ICE AGE

At present, scientists have identified two probable causes for the little ice age: a decrease or increase in volcanic eruptions. In essence, some researchers are of the opinion that anthropogenic atmospheric pollution that affects climate is extremely minor compared with natural events. As a matter of fact, some scientists consider glaciations to be normal cycles for earth, as in the medieval warm period and the interglacial glaciations period.

1.8.4. VOLCANIC ACTIVITY

Throughout the little ice age, the world also experienced severe volcanic eruptions, which spewed enormous amounts of ash that reached high into the atmosphere and covered the entire earth. In some instances, large amounts of volcanic ash can block out incoming solar radiation, leading to worldwide cooling that can last up to several years. Emitted volcanic ashes, in addition to large amounts of CO ₂, contain significant amounts of sulfur dioxide (SO ₂) gas. When the SO ₂ gas reaches the upper atmosphere, it combines with water particulates and turns into sulfuric acid, which amplifies the reflection of the sun’s rays, further reducing the amount of radiation reaching earth’s surface.

1.8.5. OCEAN CONVEYOR SHUTDOWN

Another possible cause of the little ice age is related to the disruption or slowing of ocean conveyor, also known as the gulf stream. It could have been interrupted by the introduction of large amounts of freshwater in the North Atlantic, possibly caused by melting of glaciers during the medieval warming period. According to documented records, around 1850 the global climate began warming, and the little ice age ended. Notwithstanding, scientific opinion of the effects of the little ice age on climate change is that warming over the last 50 years has increased proportions of CO ₂ in the atmosphere, stemming from human, or anthropogenic, activity.