The Rate of Deforestation
The actual rate of deforestation is difficult to determine. Scientists study the deforestation of tropical forests by analysing satellite imagery of forested areas that have been cleared. Figure 2 is a satellite image illustrating how scientists classify the landscape. Contained within the image are patches of deforestation in a distinctive “fishbone” of deforestation along roads. Forest fragments are isolated areas left by deforestation, where the plants and animals are cut off from the larger forest area. Regrowth-also called secondary forest-is abandoned farmland or timber cuts that are growing back to become forest. The majority of the picture is undisturbed, or “primary,” forest, with a network of rivers draining it. The diagram itself is actually labelled.
Figure 2. Satellite image of deforestation in the Amazon region, taken from the Brazilian state of Para on July 15, 1986. The dark areas are forest, the white is deforested areas, and the grey is re-growth. The pattern of deforestation spreading along roads is obvious in the lower half of the image. Scattered larger clearings can be seen near the centre of the image.
The Food and Agriculture Organization (FAO) estimates that 53,000 square miles of tropical forests (rain forest and other) were destroyed each year during the 1980s. Of this, they estimate that 21,000 square miles were deforested annually in South America, most of this in the Amazon Basin. Based on these estimates, an area of tropical forest large enough to cover North Carolina is deforested each year!
The rate of deforestation varies from region to region. Recent research results showed that in the Brazilian Amazon, the rate of deforestation was around 6200 square miles per year from 1978-1986, but fell to 4800 square miles per year from 1986-1993. By 1988, 6% of the Brazilian Amazon had been cut down (90,000 square miles, an area the size of New England). However, due to the isolation of fragments and the increase in forest/clearing boundaries, a total of 16.5% of the forest (230,000 square miles, an area nearly the size of Texas) was affected by deforestation. Scientists are currently analysing rates of deforestation for the current decade, as well as studying how deforestation changes from year to year.
The much smaller region of Southeast Asia (Cambodia, Indonesia, Laos, Malaysia, Myanmar, Thailand, and Vietnam) lost nearly as much forest per year as the Brazilian Amazon from the mid-1970s to the mid-1980s, with 4800 square miles per year converted to agriculture or cut for timber.
Deforestation and the Hydrologic Cycle
Tropical deforestation also affects the local climate of an area by reducing the evaporative cooling that takes place from both soil and plant life. As trees and plants are cleared away, the moist canopy of the tropical rain forest quickly diminishes. Recent research suggests that about half of the precipitation that falls in a tropical rain forest is a result of its moist, green canopy. Evaporation and evapotranspiration processes from the trees and plants return large quantities of water to the local atmosphere, promoting the formation of clouds and precipitation. Less evaporation means that more of the Sun’s energy is able to warm the surface and, consequently, the air above, leading to a rise in temperatures.
Deforestation and the Global Carbon Cycle
Deforestation causes an increase in the amount of carbon dioxide (CO2) and other trace gases in the atmosphere. The plants and soil of tropical forests hold 460-575 billion metric tons of carbon worldwide with each acre of tropical forest storing about 180 metric tons of carbon. When a forest is cut and burned to establish cropland and pastures, the carbon that was stored in the tree trunks (wood is about 50% carbon) joins with oxygen and is released into the atmosphere as CO2.
The loss of forests has a profound effect on the global carbon cycle. From 1850 to 1990, deforestation worldwide (including the United States) released 122 billion metric tons of carbon into the atmosphere, with the current rate being approximately 1.6 billion metric tons per year. In comparison, fossil fuel burning (coal, oil, and gas) releases about 6 billion metric tons per year, so it is clear that deforestation makes a significant contribution to the increasing CO2 in the atmosphere. Releasing CO2 into the atmosphere enhances the greenhouse effect.
Deforestation and Biodiversity
Biological diversity, or biodiversity, is the variety of the world's organisms, including their genetic diversity and the groups they form. It is the blanket term for the natural biological wealth that assists human life and well being. The span of the concept reflects the interrelatedness of genes, species, and ecosystems.
Worldwide, 5 to 80 million species of plants and animals comprise the “biodiversity” of planet Earth. Tropical rain forests-covering only 7% of the total dry surface of the Earth-hold over half of all these species. Of the tens of millions of species believed to be on Earth, scientists have only given names to about 1.5 million of them, and even fewer of the species have been studied in depth.
Many of the rain forest plants and animals can only be found in small areas, because they require a special habitat in which to live. This makes them very vulnerable to deforestation. If their habitat is destroyed, they may become extinct animals such as the Golden coqui, Puerto Rico, 1980s, the Web-footed coqui, Puerto Rico, 1980s and the Puerto Rican ground sloth, Puerto Rico, 1500 there is a full list of all the extincted or endangered species at the end of this essay.
Every day species are disappearing from the tropical rain forests as they are cleared. We do not know the exact rate of extinction, but estimates indicate that up to 137 species disappear worldwide each day.
The loss of species will have a great impact on the planet. We are losing species that might show us how to prevent cancer or help us find a cure for AIDS. Other organisms are losing species they depend upon, and thus face extinction themselves.
Leaching and Erosion of soils
Unfortunately deforestation has its own consequences as well as harming wild life and ruining scenery it’s also permanently damages soil, this is due to a process called leaching. This process takes place when it rains. The rain runs through the soil and ‘picks up’ vital minerals and nutrience from the soil when the rain water reaches its destination, usually a river, stream or in some cases a glacier, it deposits the ‘collected’ nutrience and minerals in to the river, stream or glacier. When this happens the rain has removed the nutrience from the soil making it less fertile and less likely to grow anything, so it is unlikely or will take a longer amount of time for the forest to grow back.
The second process which directly affects the rain forest is the erosion of soil. This takes place through much the same process as leaching but the rain washes away the top layer of soil so there is a thinner layer of soil so less nutrience for the vegetation to grow in. Both of these are a direct environmental effect of deforestation.
The Greenhouse Effect
The greenhouse effect is a naturally occurring process that aids in heating the Earth's surface and atmosphere. It results from the fact that certain atmospheric gases, such as carbon dioxide, water vapour, and methane, are able to change the energy balance of the planet by being able to absorb longwave radiation from the Earth's surface.
Without the greenhouse effect, life on this planet would probably not exist, as the average temperature of the Earth would be a chilly -18 degrees Celsius, rather than the present 15 degrees Celsius.
How does it happen?
As energy from the sun passes through the atmosphere a number of things take place, a portion of the energy is reflected back to space by clouds and particles. Some of the energy available is absorbed by clouds, gases (like ozone), and particles in the atmosphere. Of the remaining amount of the solar energy passing through the Earth's atmosphere, about 4 % is reflected from the surface back to space. On average about the rest of the sun's radiation reaches the surface of the earth. This energy is then used in number of processes including the heating of the ground surface; the melting of ice and snow, the evaporation of water; and plant photosynthesis.
The heating of the ground by sunlight causes the Earth's surface to become a radiator of energy in the longwave band (sometimes called infrared radiation). This emission of energy is generally directed to space. However, only a small portion of this energy actually makes it back to space. The majority of the outgoing infrared radiation is absorbed by a few naturally occurring atmospheric gases known as the greenhouse gases. Absorption of this energy causes additional heat energy to be added to the Earth's atmospheric system. The warmer atmospheric greenhouse gas molecules begin radiating longwave energy in all directions. Over 90 % of this emission of longwave energy is directed back to the Earth's surface where it once again is absorbed by the surface. The heating of the ground by the longwave radiation causes the ground surface to once again radiate repeating the cycle described above, again and again, until no more longwave is available for absorption.
The amount of heat energy added to the atmosphere by the greenhouse effect is controlled by the concentration of greenhouse gases in the Earth's atmosphere. All of the major greenhouse gases have increased in concentration since the beginning of the industrial revolution (about 1700 A.D.). As a result of these higher concentrations, scientists predict that the greenhouse effect will be enhanced and the Earth's climate will become warmer. Predicting the amount of warming is accomplished by computer modelling. Computer models suggest that a doubling of the concentration of the main greenhouse gas, carbon dioxide, may raise the average global temperature between 1 and 3 degrees Celsius. However, the numeric equations of computer models do not accurately simulate the effects of a number of possible negative feedbacks. For example, many of the models cannot properly simulate the negative effects that increased cloud cover would have on the radiation balance of a warmer Earth. Increasing the Earth's temperature would cause the oceans to evaporate greater amounts of water, causing the atmosphere to become cloudier. These extra clouds would then reflect a greater proportion of the sun's energy back to space reducing the amount of solar radiation absorbed by the atmosphere and Earth's surface.
A number of gases are involved in the greenhouse effect (see below). These gases include: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); chlorofluorocarbons (CFxClx); and tropospheric ozone (03). Of these gases, the single most important gas is carbon dioxide, which accounts for about 55 % of the change in the intensity of the Earth's greenhouse effect. The contributions of the other gases are 25 % for chlorofluorocarbons, 15 % for methane, and 5 % for nitrous oxide. Ozone's contribution to the enhancement of the greenhouse effect is still yet to be confirmed.
Concentrations of carbon dioxide in the atmosphere are now approaching 360 parts per million. Prior to 1700 levels of carbon dioxide were about 280 parts per million. This increase in carbon dioxide in the atmosphere is primarily due to the activities of humans. Beginning in 1700, societal changes brought about by the industrial revolution increased the amount of carbon dioxide entering the atmosphere. The major sources of this gas include fossil fuel combustion for industry, transportation, space heating, electricity generation and cooking and vegetation changes in natural prairie, woodland and forested ecosystems. Emissions from fossil fuel combustion account for about 65 % of the extra carbon dioxide now found in our atmosphere. The remaining 35 % comes from the conversion of prairie, woodland and forested ecosystems primarily into agricultural systems. Natural ecosystems can hold 20 to 100 times more carbon dioxide per unit area than agricultural systems.
Artificially created chlorofluorocarbons (CFC) are the strongest greenhouse gas per molecule. However, low concentrations in the atmosphere reduce their overall importance in the enhancement of the greenhouse effect. Current measurements in the atmosphere indicate that the concentration of these chemicals may soon begin declining because of reduced emissions. Reports of the development of ozone holes over the North and South Poles and a general decline in global stratospheric ozone levels over the last two decades. Caused many nations to cutback on their production and use of these chemicals. In 1987, the signing of the Montreal Protocol agreement by 46 nations established an immediate timetable for the global reduction of chlorofluorocarbons production and use.
Since 1750, methane concentrations in the atmosphere have increased by more than 140 %. The primary sources for the additional methane added to the atmosphere (in order of importance) is: rice cultivation, domestic grazing animals, termites, landfills, coal mining, and oil and gas extraction. Anaerobic conditions associated with rice paddy flooding results in the formation of methane gas. However, an accurate estimate of how much methane is being produced from rice paddies is difficult to obtain. More than 60 % of all rice paddies are found in India and China where scientific data concerning emission rates are unavailable. Nevertheless, scientists believe that the contribution of rice paddies is large because this form of crop production has more than doubled since 1950. Grazing animals release methane to the environment as a result of herbaceous digestion. Some researchers believe the addition of methane from this source has more than quadrupled over the last century. Termites also release methane through similar processes. Land-use change in the tropics, due to deforestation, ranching, and farming, may be causing termite numbers to expand. If this assumption is correct, the contribution from these insects may be important. Methane is also released from landfills, coalmines, and gas and oil drilling. Landfills produce methane as organic wastes decompose over time. Coal, oil and natural gas deposits release methane to the atmosphere when these deposits are excavated or drilled.
The average concentration of nitrous oxide in the atmosphere is now increasing at a rate of 0.2-0.3 % per year. Sources for this increase include: land-use conversion; fossil fuel combustion; biomass burning; and soil fertilization. Most of the nitrous oxide added to the atmosphere each year comes from deforestation and the conversion of forest, savannah and grassland ecosystems into agricultural fields and rangeland. Both of these processes reduce the amount of nitrogen stored in living vegetation and soil through the decomposition of organic matter. Nitrous oxide is also released into the atmosphere when fossil fuels and biomass are burned. However, the combined contribution to the increase of this gas in the atmosphere is thought to be minor. The use of nitrate and ammonium fertilizers to enhance plant growth is another source of nitrous oxide. How much is released from this process has been difficult to quantify. Estimates suggest that the contribution from this source represents from 50 % to 0.2 % of nitrous oxide added to the atmosphere annually.
Ozone's role in the enhancement of the greenhouse effect has been difficult to determine. Accurate measurements of past long-term (more than 25 years in the past) levels of this gas in the atmosphere are currently unavailable. Moreover, concentrations of ozone gas are found in two different regions of the Earth's atmosphere. The majority of the ozone (about 97 %) found in the atmosphere is concentrated in the stratosphere at an altitude of 15 to 55 kilometres above the Earth's surface. In recent years, the concentration of the stratospheric ozone has been decreasing because of the build-up of chlorofluorocarbons in the atmosphere (see ). Since the late 1970s, scientists have discovered that total column ozone amounts over Antarctica in the springtime have decreased by as much as 70 %. Satellite measurements have indicated that the zone from 65 degrees North to 65 degrees South latitude has had a 3 % decrease in stratospheric ozone since 1978. Ozone is also highly concentrated at the Earth's surface. Most of this ozone is created as a by-product of .
This shows the Global climate change from 1880 until 2000. The overall trend of this graph is in a positive correlation as the dashed line shows, but as we’d expect the temperature varies yearly due to the season changes.
Conclusion
Deforestation starts with the use of trees in agriculture. This normally happens because local farmers cut down the trees and burn them as the burning provides nutrience for the soil. This is called slash and burn agriculture. Larger agriculture actually contributes more to deforestation as it is estimated that 53, 000 square miles of forest are destroyed each year. Scientists are trying to introduce sustainable resources, which will have minimal effect on the environment.
The deforestation not only ruins the precious rain forest but it also contributes to the current greenhouse effect, which is plaguing the planet’s atmosphere. This ‘greenhouse effect’ basically is the way in which the sun’s radiation is unable to leave the atmosphere. The major greenhouse gases are Nitrogen (N), Carbon dioxide (CO2) and Water (H2O) these gases are responsible for the major heat change in the atmosphere. In the early 90’s CFCs were also partially to blame. These have been banned in many countries now. Water is the major problem which we have. There is too much condensation which causes clouds this then reflects much of the suns radiation back down to the earth’s surface. If there were no water in the atmosphere the earth’s temperature would be –18 degrees centigrade.
Deforestation also affects the land it and is currently taking place with no trees the precipitation (rain) is able to fall directly on to the soil this causes leaching and erosion of the soil and both these mean that the nutrience is deplenished or removed from the soil. Therefore meaning that there is not enough nutrience to sustain vegetation. This in turn causes a process called desertification to occur this is the complete drying out of the soil and thus making it desert like. Nothing is able to grow. Therefore the Antarctic can technically be called a desert.
Although deforestation mainly affects plant life it does have a substantial effect on wildlife too. By cutting down trees and plants many species become extinct cause less diversity of species so fewer ‘new animals’ can be bred. This would theoretically mean that Darwin’s theory of evolution is being compromised by deforestation.