People participation in forest management

Definition of Forest

•If tree canopy covers more than 10% of a 1-hectare plot it is called as forest. (FSI 2001 Report)

•As of 2010, the Food and Agriculture Organization of the United Nations estimates India’s forest cover to be about 68 million hectares, or about 20 percent of the country’s area.

•At 692,000 sq km, forests covered 23% of India’s land, and were directionally headed to reach the targeted 33%. (FSI 2012 Report)

•Forest can be classified into state-owned forest, collective forest,

 and household forest, in accordance with timber ownership.

• The variety and distribution of forest vegetation is large: there are 600 species of hardwoods.

•India is one of the 12 mega biodiverse regions of the world.

Forest Classification

•Very Dense Forest: All lands, with a forest cover with canopy density of 70 percent and above

•Moderately Dense Forest: All lands, with a forest cover with canopy density of 40-70 percent

•Open Forest: All lands, with forest cover with canopy density of 10 to 40 percent

•Mangrove Cover: Mangrove forest is salt tolerant forest ecosystem found mainly in tropical and sub-tropical coastal and/or inter-tidal regions. Mangrove cover is the area covered under mangrove vegetation as interpreted digitally from remote sensing data. It is a part of forest cover and also classified into three classes viz. very dense, moderately dense and open.

•Non Forest Land: defined as lands without any forest cover

Forest management

•Forest management is a branch of forestry concerned with the overall administrative, economic, legal and social aspects and with the essentially scientific and technical aspects, especially silviculture, protection, and forest regulation.

•Management of forest lands is the sharing of the products, responsibilities, control and decision-making authority over forest lands between Forest Department and local user groups.

•It involves a contract specifying the distribution of authority, responsibility and benefits between villages and State Forest Departments with respect to land allocated for forest Management.

•India was one of the first in the world to introduce scientific forest management.

Community Forest

•community forests are usually administered by a locally elected body, usually called the Forest Protection Committee, Village Forest Committee or the Village Forest Institution.

• The issues of such communities were addressed in the Indian Forest Act, 1927, which initiated the development of village forests for sustainable use by villagers dwelling in or on the fringes of the forest

• Legislation pertaining to communal forests vary from state to state, but typically the state government retains some administrative control over matters like staff appointment, and penalization of offenders.

•Such forests typically conform to the IUCN Category VI Protected Areas, but protection may be enforced by the local communities or the government depending on local legislation.

• communal forests are formed in two ways: Joint forest management program and Social forestry program

Fundamental of ground water, water quality and

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Understanding Heat Budget

The Earth’s climate is a solar powered system. Globally, over the course of the year, the Earth system—land surfaces, oceans, and atmosphere—absorbs an average of about 240 watts of solar power per square meter (one watt is one joule of energy every second). The absorbed sunlight drives photosynthesis, fuels evaporation, melts snow and ice, and warms the Earth system. The state of the global climate depends upon the balance of energy fluxes (flows) into and out of the climate system (made up of the atmosphere, oceans, ice masses, biosphere and geosphere). The most important component in this respect is the atmosphere, and the major energy fluxes of incoming sunlight and outgoing terrestrial radiation from the Earth, which must balance. The nature of the Earth’s atmosphere, with its greenhouse gases, also affects the state of the global climate.

The Sun doesn’t heat the Earth evenly. Because the Earth is a sphere, the Sun heats equatorial regions more than polar regions. The atmosphere and ocean work non-stop to even out solar heating imbalances through evaporation of surface water, convection, rainfall, winds, and ocean circulation. This coupled atmosphere and ocean circulation is known as Earth’s heat engine.

The climate’s heat engine must not only redistribute solar heat from the equator toward the poles, but also from the Earth’s surface and lower atmosphere back to space. Otherwise, Earth would endlessly heat up. Earth’s temperature doesn’t infinitely rise because the surface and the atmosphere are simultaneously radiating heat to space. This net flow of energy into and out of the Earth system is Earth’s energy budget. The Earth’s heat or energy budget is determined by the amount of sunlight that is either absorbed or reflected by the Earth’s varied surfaces.

When the flow of incoming solar energy is balanced by an equal flow of heat to space, Earth is in radiative equilibrium, and global temperature is relatively stable. Anything that increases or decreases the amount of incoming or outgoing energy disturbs Earth’s radiative equilibrium; global temperatures rise or fall in response.

The earth absorbs Insolation (it is a measure of solar radiation energy received on a given surface area in a given time) and re-emits outgoing terrestrial radiation and these two are in balance.

Radiation from the Sun and Earth

The Earth’s atmosphere has an important influence on the heat budget of the global climate system. This is determined by the processes involved in solar (Sun) and terrestrial (Earth) energy transfers. Radiation emitted from the Sun has a temperature of approximately 6000°C. The radiation is emitted over a spectrum of wavelengths, with a specific quantity of energy for each wavelength. Most solar energy is emitted with a wavelength of approximately 0.5 microns. This represents radiation in the visible part of the spectrum. The total energy output of the Sun is approximately 64 million Wm^-2.

The solar radiation disperses uniformly in all directions. After travelling 93 million miles, only a tiny fraction of the energy emitted by the Sun is intercepted by the Earth. Therefore, the energy arriving at the top of the Earth’s atmosphere is many orders of magnitude smaller than that leaving the Sun. The latest satellite measurements indicate a value of 1368Wm^-2 for the energy received at the top of the atmosphere. This is known as the solar constant.

The Earth also emits radiation, but since it is much cooler than the Sun, its radiating energy is in the longer wavelength, invisible infrared or heat part of the spectrum. Sometimes, we can indirectly see heat radiation, for example the heat shimmers rising from a tarmac road on a hot sunny day. The energy received by the Earth from the Sun balances the energy lost by the Earth back into space.

Heat / Energy Budget

Earth’s heat engine does more than simply move heat from one part of the surface to another; it also moves heat from the Earth’s surface and lower atmosphere back to space. This flow of incoming and outgoing energy is Earth’s energy budget. For Earth’s temperature to be stable over long periods of time, incoming energy and outgoing energy have to be equal. In other words, the energy budget at the top of the atmosphere must balance. This state of balance is called radiative equilibrium.

About 29 percent of the solar energy that arrives at the top of the atmosphere is reflected back to space by clouds, atmospheric particles, or bright ground surfaces like sea ice and snow. This energy plays no role in Earth’s climate system. About 23 percent of incoming solar energy is absorbed in the atmosphere by water vapor, dust, and ozone, and 48 percent passes through the atmosphere and is absorbed by the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth system.

Processes in Atmosphere and surface of Earth

The atmosphere and the surface of the Earth together absorb 71 percent of incoming solar radiation, so together, they must radiate that much energy back to space for the planet’s average temperature to remain stable. However, the relative contribution of the atmosphere and the surface to each process (absorbing sunlight versus radiating heat) is asymmetric. The atmosphere absorbs 23 percent of incoming sunlight while the surface absorbs 48. The atmosphere radiates heat equivalent to 59 percent of incoming sunlight; the surface radiates only 12 percent. In other words, most solar heating happens at the surface, while most radiative cooling happens in the atmosphere. How does this reshuffling of energy between the surface and atmosphere happen?

Three processes of scattering, reflection and absorption take place in the atmosphere and surface of Earth

1. Scattering – It accounts for about 7% of insolation
   • Short wavelengths (insolation is of a short wavelength) are most easily scattered by gas and dust molecules in the atmosphere. This process involves redirecting the insolation towards a different direction.
2. Reflection – It accounts for about 27% of insolation, of which clouds 21% and ground 6%
   • Reflected insolation simply returns to space, wavelength unchanged. Clouds are especially effective in reflecting insolation
   • Reflection is dependent on albedo

• Albedo: the ratio of the light reflected by a body to the light received by it. Albedo values range from 0 (pitch black) to 1 (perfect reflector).
  • absorption of short-wave ultraviolet radiation by oxygen and nitrogen in the thermosphere and
  • absorption of longer-wave Ultra Violet radiation by ozone in the stratosphere

1. • Albedo of snow can reach 90%, and when the sun is at a low angle (e.g. sunrise/set) albedo of water can reach 80%. OTOH when the angle > 40° albedo is about 2-4% (see notes)
2. Absorption – It accounts for about 19% of insolation
   • Gases, clouds, dust and haze all absorb certain wavelengths of insolation, which is transformed into molecular motion resulting in a rise in temperature
   • Absorption is especially pronounced in the thermosphere and stratosphere which are warmer than expected because of the

1. • Water vapour is another main absorber of insolation
     

     Energy Budget of Surface of Earth

     For the energy budget at Earth’s surface to balance, processes on the ground must get rid of the 48 percent of incoming solar energy that the ocean and land surfaces absorb. Energy leaves the surface through three processes: evaporation, convection, and emission of thermal infrared energy.

     About 25 percent of incoming solar energy leaves the surface through evaporation. Liquid water molecules absorb incoming solar energy, and they change phase from liquid to gas. The heat energy that it took to evaporate the water is latent in the random motions of the water vapor molecules as they spread through the atmosphere. When the water vapor molecules condense back into rain, the latent heat is released to the surrounding atmosphere. Evaporation from tropical oceans and the subsequent release of latent heat are the primary drivers of the atmospheric heat engine

     An additional 5 percent of incoming solar energy leaves the surface through convection. Air in direct contact with the sun-warmed ground becomes warm and buoyant. In general, the atmosphere is warmer near the surface and colder at higher altitudes, and under these conditions, warm air rises, shuttling heat away from the surface.

     Finally, a net of about 17 percent of incoming solar energy leaves the surface as thermal infrared energy (heat) radiated by atoms and molecules on the surface. This net upward flux is actually the result of two large but opposing fluxes: heat flowing upward from the surface to the atmosphere and heat flowing downward from the atmosphere to the ground. Remember that the peak wavelength of energy a surface radiates is based on its temperature. The Sun’s peak radiation is at visible and near-infrared wavelengths. The Earth’s surface is much cooler, only about 15 degrees Celsius on average. The peak radiation from the surface is at thermal infrared wavelengths around 12.5 micrometers.

   • The Energy Budget of the Atmosphere

     The Earth, however, has an atmosphere, consisting mostly of nitrogen (78%), oxygen (21%) and a number of greenhouse gases, which affect the Sun-Earth energy balance. The average global temperature is in fact 33°C higher than it should be. Certain atmospheric gases absorb radiation at some wavelengths but allow radiation at other wavelengths to pass through unimpeded. The atmosphere is mostly transparent (little absorption) in the visible part of the spectrum, but significant absorption of solar ultra-violet radiation by ozone, and terrestrial infra-red radiation by water vapour, carbon dioxide and other trace gases occurs.

     The absorption of terrestrial infra-red radiation is particularly important to the energy budget of the Earth’s atmosphere. Such absorption by the trace gases heats the atmosphere, and so the Earth stores more energy near its surface than it would if there was no atmosphere. Consequently the temperature is higher by about 33°C.

     This process is popularly known as the greenhouse effect.

     Conclusion

     The fluxes or flows of energy within the Earth’s atmosphere determine the state of our climate. Factors which influence these on a global scale may be regarded as causes of global climate change. Basic principles determine the state of the Earth-Atmosphere energy budget, and consequently the global climate. The atmosphere’s greenhouse gases influence this energy balance by absorbing outgoing energy from the Earth, thereby increasing the global average surface temperature. This process is called the natural greenhouse effect. Through man-made emissions of greenhouse gases since 1765, this natural phenomenon is being enhanced with possible consequences of global warming

     References

     http://en.wikipedia.org/wiki/Earth%27s_energy_budget

     http://okfirst.mesonet.org/train/meteorology/EnergyBudget2.html

     http://earthobservatory.nasa.gov/

     http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1a.html

     http://www.solarenergygreenlifestyleforyou.com/2008/04/solar-energy-from-sun-to-earth.html

     http://www.greenpeace.org/international/photosvideos/photos/greenhouse_effect

Water Pollution

Drinking Water:

Drinking water or potable water is water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm

Although water covers about 70 percent of the Earth, less than 1 percent is available as freshwater for human use. The vast majority of the water on this “blue planet” is found in the ocean, too salty to drink and unfit for many other applications. Of the freshwater available on Earth, about two-thirds is frozen in ice caps and glaciers, which leaves only a small fraction accessible for human use.

Surface water—such as that in lakes, reservoirs, rivers, and streams—is the primary water source for humans.

Groundwater—that is, water underground in aquifers (highly permeable rocks, soil, and sand)—can be extracted through wells or found as springs. Technically speaking, groundwater resources exceed salt-free surface water on Earth, but humans use surface water more often because it is easier to access in large quantities. Groundwater is stored in the tiny open spaces between rock, sand, soil, and gravel under the land’s surface. It is found in two zones.

1. The unsaturated zone is immediately below the land surface and contains

both water and air in the open spaces.

1. The saturated zone, under the unsaturated zone, contains water in all the

open spaces.

WHO’s (World Health Organization) Guidelines for Drinking-water Quality, set up in Geneva, 1993, are the international reference point for standard setting and drinking-water safety.

Eutrophication

Eutrophication  is a natural process that occurs in an aging lake or pond as that body of water gradually builds up its concentration of plant nutrients. Cultural or artificial eutrophication occurs when human activity introduces increased amounts of these nutrients, which speed up plant growth and eventually choke the lake of all of its animal life.

In nature, eutrophication is a common phenomenon in freshwater ecosystems and is really a part of the normal aging process of many lakes and ponds. Some never experience it because of a lack of warmth and light, but many do. Over time, these bodies of freshwater change in terms of how productive or fertile they are. While this is different for each lake or pond, those that are naturally fed rich nutrients from a stream or river or some other natural source are described as “eutrophic,” meaning they are nutrient-rich and therefore abundant in plant and animal life. Eutrophication is not necessarily harmful or bad, and the word itself is often translated from the Greek as meaning “well nourished” or “good food.” However, eutrophication can be speeded up artificially, and then the lake and its inhabitants eventually suffer as the input of nutrients increases far beyond what the natural capacity of the lake should be.

In natural lakes a distinction is sometimes made between ‘natural’ and ‘cultural’ (anthropogenic) eutrophication processes. Natural eutrophication depends only on the local geology and natural features of the catchment.

Cultural eutrophication is associated with human activities which accelerate the eutrophication process beyond the rate associated with the natural process (e.g. by increasing nutrient loads into aquatic ecosystems).

Natural eutrophication

Natural eutrophication is usually a fairly slow and gradual process, occurring over a period of many centuries. It occurs naturally when for some reason, production and consumption within the lake do not cancel each other out and the lake slowly becomes overfertilized. While not rare in nature, it does not happen frequently or quickly.

Cultural eutrophication:

One of the most important types of water pollution, cultural eutrophication describes human-generated fertilization of water bodies. Cultural denotes human involvement, and eutrophication means truly nourished, from the Greek word eutrophic. Key factors in cultural eutrophication are nitrates and phosphates, and the main sources are treated sewage and runoff from farms and urban areas. The concept of cultural eutrophication is based on anthropocentric values, where clear water with minimal visible organisms is much preferred over water rich in green algae and other microorganisms.

Nitrates and phosphates are the most common limiting factors for organism growth, especially in aquatic ecosystems. Most fertilizers are a combination of nitrogen, phosphorus, and potassium. Nitrates are key components of the amino acids, peptides, and proteins needed by all living organisms. Phosphates are crucial in energy transfer reactions within cells. Natural sources of nitrates (and ammonia) are more readily available than phosphates, so the latter is often cited as the crucial limiting factor in plant growth. Nitrates are supplied in limited quantities by decaying plant material and nitrogen-fixing bacteria, but phosphates must come from animal bones, organic matter, or from the breakdown of phosphate-bearing rocks. Consequently, the introduction and widespread use of phosphate detergents, combined with excess fertilizer in runoff, has produced a near ecological disaster in some waters.

In ecosystems, there is a continuous cycling of matter, with green algae and plants making food from chemicals dissolved in water via photosynthesis; this provides the food base needed by herbivores and carnivores. Dead plant material and animals are then decomposed by aerobic (oxygen using) and anaerobic decomposers into the simple elements they came from. Natural water bodies are usually well-suited for handling this matter cycling; however, human impacts often inject large amounts of additional nutrients into the system, changing them from oligotrophic (poorly nourished) to eutrophic water bodies. Once present within a relatively closed body of water, such as a lake or estuary, these extra nutrients may cycle numerous times before leaving the system.

Lake Classification

Lakes in which most of the organic matter is from autochthonous sources are referred to as “autotrophic”, whereas those dominated by the input of paralimnetic particulate organic matter (POM) and dissolved organic matter (DOM) are termed “allotrophic”.

Rodhe’s scheme included Oligotrophic (low in both auto- and allotrophic organic sources), eutrophic (dominated by autotrophy), dystrophic (dominated by allotrophy, brown coloured water), and mixotrophy (high in both auto- and allotrophic organic source).

Trophic classification is most commonly performed using parameters which reflect pelagic phytoplanktonic autotrophy (total phosphorus [TP], Chlorophylla [Cha], Secchi [SD]). In lakes dominated by paralimnetic or littoral organic sources, the TSI will be low because autochthonous (pelagic, phytoplanktonic) production is low, e.g. dystrophic lakes.

• Oligo-Eutro classification scheme:
  • Oligotrophic lakes are poorly supplied with plant nutrients and support little plant growth. As a result, biological productivity is generally low, the waters are clear, and the deepest layers are well supplied with oxygen throughout the year.
  • Mesotrophic lakes are intermediate in characteristics. They are moderately well supplied with plant nutrients and support moderate plant growth.
  • Eutrophic lakes are richly supplied with plant nutrients and support heavy plant growths. As a result, biological productivity is generally high, the waters are turbid because of dense growths of phytoplankton, or contain an abundance of rooted aquatic plants; deepest waters exhibit reduced concentrations of dissolved oxygen during periods of restricted circulation.
  • Dystrophic (dominated by allotrophy, brown coloured water)
  • The boundary categories of the above are ultraoligotrophy and hypereutrophy.

Some general characteristics of Oligotrophic and eutrophic lakes.

Characteristic	Oligotrophic	Eutrophic
primary production	Low	High
diversity of primary producers	high species diversity,with low population densities	low species diversity,with high population densities
light penetration into water column	High	Low
toxic blooms	Rare	frequent
plant nutrient availability	Low	High
animal production	Low	High
oxygen status of surfacewater	High	Low
fish	salmonid fish (e.g.trout, char)often dominant	coarse fish (e.g. perch, roach, carp) often dominant

Trophic bands for standing waters. (Phosphorus concentrations tend to be higher in running waters that carry suspended sediment.)

Trophic band	Total phosphorus/mg l–1
dystrophic	<0.005
oligotrophic	0.005–0.01
mesotrophic	0.01–0.03
eutrophic	0.03–0.1
hypertrophic	>0.1

Point and Non Point sources of water Pollution

Pollution originating from a single, identifiable source, such as a discharge pipe from a factory or sewage plant, is called point-source pollution. Pollution that does not originate from a single source, or point, is called nonpoint-source pollution. Liquid, solid, and airborne discharges from point sources as well as pollutants from nonpoint sources may go either into surface water or into the ground. (Airborne pollutants can be assimilated into rainwater and can affect water quality: acid rain is an example.) The ability for these pollutants to reach surface water or groundwater is enhanced by the amount of water available from precipitation (rain) or irrigation.

Point Sources

Point-source pollutants in surface water and groundwater are usually found in a plume that has the highest concentrations of the pollutant nearest the source (such as the end of a pipe or an underground injection system) and diminishing concentrations farther away from the source. The various types of point-source pollutants found in waters are as varied as the types of business, industry, agricultural, and urban sources that produce them.

Commercial and industrial businesses use hazardous materials in manufacturing or maintenance, and then discharge various wastes from their operations. The raw materials and wastes may include pollutants such as solvents, petroleum products (such as oil and gasoline), or heavy metals . Point sources of pollution from agriculture may include animal feeding operations, animal waste treatment lagoons, or storage, handling, mixing, and cleaning areas for pesticides, fertilizers, and petroleum. Municipal point sources might include wastewater treatment plants, landfills, utility stations, motor pools, and fleet maintenance facilities.

For all of these activities, hazardous materials may be included in the raw materials used in the process as well as in the waste stream for the facility. If the facility or operator does not handle, store, and dispose of the raw materials and wastes properly, these pollutants could end up in the water supply. This may occur through discharges at the end of a pipe to surface water, discharges on the ground that move through the ground with infiltrating rainwater, or direct discharges beneath the ground surface.

Non Point Sources

Nonpoint-source pollution occurs as water moves across the land or through the ground and picks up natural and human-made pollutants, which can then be deposited in lakes, rivers, wetlands, coastal waters, and even groundwater. The water that carries nonpoint-source pollution may originate from natural processes such as rainfall or snowmelt, or from human activities such as crop irrigation or lawn maintenance.

Nonpoint-source pollution is usually found spread out throughout a large area. It is often difficult to trace the exact origin of these pollutants because they result from a wide variety of human activities on the land as well as natural characteristics of the soil, climate, and topography.

The most common nonpoint-source pollutants are sediment , nutrients, microorganisms and toxics. Sediment can degrade water quality by contaminating drinking water supplies or silting in spawning grounds for fish and
Nonpoint sources of pollution in urban areas may include parking lots, streets, and roads where stormwater picks up oils, grease, metals, dirt, salts, and other toxic materials. In areas where crops are grown or in areas with landscaping (including grassy areas of residential lawns and city parks), irrigation, and rainfall can carry soil, pesticides, fertilizers, herbicides, and insecticides to surface water and groundwater. Bacteria, microorganisms, and nutrients (nitrogen and phosphorus) are common nonpoint-source pollutants from agricultural livestock areas and residential pet wastes. These pollutants are also found in areas where there is a high density of septic systems or where the septic systems are faulty or not maintained properly. Other pollutants from nonpoint sources include salt from irrigation practices or road de-icing, and acid drainage from abandoned mines.

MLCs

Drinking water standards are called maximum contaminant levels (MCLs)

Primary Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. Primary MCLs are set as close to the PHGs (or MCLGs) as is technologically, and conomically feasible.

Secondary Maximum Contaminant Level (SMCL): Threshold levels for aesthetic concerns; taste, odor, and staining.

Maximum Contaminant Level Goal (MCLG): The level of a contaminant in

drinking water below which there is no known or expected risk to health.

References:

http://openlearn.open.ac.uk/mod/resource/view.php?id=171939

http://www.chebucto.ns.ca/ccn/info/Science/SWCS/eutro.html

http://www.dwa.gov.za/iwqs/eutrophication/NEMP/02Eutrophication.pdf

http://www.waterencyclopedia.com/Po-Re/Pollution-Sources-Point-and-Nonpoint.html

http://www.tcoek12.org/~stjusd/5305107.pdf

Community Structure in Ecology

Presentation on Global Warming

Views From Mongolia

Understanding Global Warming

Definition:

Global warming is an average increase in the temperature of the atmosphere near the Earth’s surface and in the troposphere, which can contribute to changes in global climate patterns. Global warming can occur from a variety of causes, both natural and human induced. In common usage, “global warming” often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities.

Introduction:

It is the phenomenon of increasing average air temperatures near the surface of earth over the past one to two centuries. Since the mid-20th century, climate scientists have gathered detailed observations of various weather phenomena (such as temperature, precipitation, and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that, since at least the beginning of the Industrial Revolution, the influence of human activities has been deeply woven into the very fabric of climate change.

Giving voice to a growing conviction of most of the scientific community, the Intergovernmental Panel on Climate Change (IPCC) reported that the 20th century saw an increase in global average surface temperature of approximately 0.6 °C (1.1 °F). The IPCC went on to state that most of the warming observed over the second half of the 20th century could be attributed to human activities, and it predicted that by the end of the 21st century the average surface temperature would increase by another 1.8 to 4.0 °C (3.2 to 7.2 °F), depending on a range of possible scenarios. Many climate scientists agree that significant economic and ecological damage would result if global average temperatures rose by more than 2 °C [3.6 °F] in such a short time. Such damage might include increased extinction of many plant and animal species, shifts in patterns of agriculture, and rising sea levels.

The scenarios referred to above depend mainly on future concentrations of certain trace gases, called greenhouse gases that have been injected into the lower atmosphere in increasing amounts through the burning of fossil fuels for industry, transportation, and residential uses. Modern global warming is the result of an increase in magnitude of the called greenhouse effect, a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour, carbon dioxide, methane, and other greenhouse gases. Of all these gases, carbon dioxide is the most important, both for its role in the greenhouse effect and for its role in the human economy.

Causes of global warming

The greenhouse effect

It is the warming effect that results from short wave (infrared, visible, and ultraviolet) solar radiation being largely able to pass unhindered to the surface of the Earth, where it is re-radiated as longer wave (infrared) radiation (as happens in a greenhouse). This outgoing long wave radiation is partially absorbed by Green House Gases (especially water vapor and carbon dioxide) in the atmosphere. The failure of most of the radiant energy to escape means that it is ‘recycled’ and retained as heat in the lowest part of the atmosphere, an important component in maintaining the Earth’s surface temperature. Without greenhouse warming the Earth’s average surface temperature would be around –18°C (0°F) and unable to support life. The natural effect of the recycling of radiant energy is, however, being enhanced by increases in the concentration of greenhouse gases particularly carbon dioxide (CO2), owing to human activity, notably since the beginning of the Industrial Revolution (around 1700 AD). The burning of fossil fuels (oil, coal, and natural gas) and the clearing of land and burning of vegetation, in particular, contribute to the rise of carbon dioxide concentrations. It is predicted that the enhanced greenhouse effect resulting from the increased concentrations of greenhouse gases will generate increased Global Warming and contribute to global climate change. Computer models have been used to attempt to predict the amount of warming that may result from further increases in greenhouse gas levels

The influences of human activity on climate

Human activity has influenced global surface temperatures by changing the radiative balance governing the Earth on various timescales and at varying spatial scales. The most profound and well-known anthropogenic influence is the elevation of concentrations of greenhouse gases in the atmosphere. Humans also influence climate by changing the concentrations of aerosols and ozone and by modifying the land cover of Earth’s surface.

Some of the human activities which change the climate are:

• Industrial activities, which emit a variety of atmospheric pollutants including SO2, particulate matter, photochemically reactive hydrocarbons, chlorofluorocarbons, and inorganic substances (such as toxic heavy metals)
• Burning of large quantities of fossil fuel, which can introduce CO₂, CO, SO₂, NO_x, hydrocarbons (including CH₄), and particulate soot, polycyclic aromatic hydrocarbons, and fly ash into the atmosphere
• Transportation practices, which emit CO₂, CO, NO_x, photochemically reactive (smog forming) hydrocarbons, and polycyclic aromatic hydrocarbons
• Alteration of land surfaces, including deforestation
• Burning of biomass and vegetation, including tropical and subtropical forests and savanna grasses, which produces atmospheric CO₂, CO, NO_x, and particulate soot and polycyclic aromatic hydrocarbons
• Agricultural practices, which produce methane (from the digestive tracts of domestic animals and from the cultivation of rice in waterlogged anaerobic soils) and N₂O from bacterial denitrification of nitrate-fertilized soils.

Greenhouse gases

We know that the earth is surrounded by a mixture of gases. The Earth’s atmosphere consists of roughly 79.1% nitrogen, 20.9% oxygen, 0.03% carbon dioxide, and trace amounts of other gases Greenhouse gases are a natural part of the atmosphere. Greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, halogenated fluorocarbons, ozone, perfluorinated carbons, and hydrofluorocarbons. Water vapor is the most important greenhouse gas, but human activity doesn’t have much direct impact on its amount in the atmosphere.

Global warming is caused by an increase in the levels of these gases brought about by human activity. The greatest impact on the greenhouse effect has come from industrialization and increases in the amounts of carbon dioxide, methane, and nitrous oxide. The clearing of land and burning of fossil fuels, for example, have raised atmospheric gas concentrations of soot and other aerosols (fine particles in the air). Manufactured greenhouse gases and particles, rather than the occasional volcanic eruption, now account for higher gas concentrations. The planet has begun to warm at a steep rate, and future temperature increases are predicted by climatic models programmed with the volumes of gases released yearly into the atmosphere. Some scientists are already seeing the consequences of global warming, such as the melting of the polar ice sheets and rising sea levels. Greenhouse gases warm Earth’s surface by increasing the net downward longwave radiation reaching the surface. The relationship between atmospheric concentration of greenhouse gases and the associated positive radiative forcing of the surface is different for each gas. A complicated relationship exists between the chemical properties of each greenhouse gas and the relative amount of longwave radiation that each can absorb. What follows is a discussion of the radiative behaviour of each major greenhouse gas.

Radiative Forcing

Radiative forcing is a measure of how the energy balance of the Earth-atmosphere system is influenced when factors that affect climate are altered.

Some Green House Gases

Water Vapour

Water vapour is the most potent of the greenhouse gases in Earth’s atmosphere, but its behaviour is fundamentally different from that of the other greenhouse gases. The primary role of water vapour is not as a direct agent of radiative forcing but rather as a climate feedback—that is, as a response within the climate system that influences the system’s continued activity. This distinction arises from the fact that the amount of water vapour in the atmosphere cannot, in general, be directly modified by human behaviour but is instead set by air temperatures. The warmer the surface, the greater the evaporation rate of water from the surface. As a result, increased evaporation leads to a greater concentration of water vapour in the lower atmosphere capable of absorbing longwave radiation and emitting it downward.

Carbon dioxide

Carbon dioxide (CO₂) is one of the most significant Green house gases. Natural sources of atmospheric CO₂ include outgassing from volcanoes, the combustion and natural decay of organic matter, and respiration by aerobic (oxygen-using) organisms. These sources are balanced, on average, by a set of physical, chemical, or biological processes, called “sinks,” that tend to remove CO₂ from the atmosphere. Significant natural sinks include terrestrial vegetation, which takes up CO₂ during the process of photosynthesis. A long-term balance between these natural sources and sinks leads to the background, or natural, level of CO₂ in the atmosphere.

Methane

Methane (CH₄) is the second most important greenhouse gas. CH₄ is more potent than CO₂ because the radiative forcing produced per molecule is greater. In addition, the infrared window is less saturated in the range of wavelengths of radiation absorbed by CH₄, so more molecules may fill in the region. However, CH₄ exists in far lower concentrations than CO₂ in the atmosphere, and its concentrations by volume in the atmosphere are generally measured in parts per billion (ppb) rather than ppm. CH₄ also has a considerably shorter residence time in the atmosphere than CO₂ (the residence time for CH₄ is roughly 10 years, compared with hundreds of years for CO₂).

Natural sources of methane include tropical and northern wetlands, methane-oxidizing bacteria that feed on organic material consumed by termites, volcanoes, seepage vents of the seafloor in regions rich with organic sediment, and methane hydrates trapped along the continental shelves of the oceans and in polar permafrost. The primary natural sink for methane is the atmosphere itself, as methane reacts readily with the hydroxyl radical (OH^-) within the troposphere to form CO₂ and water vapour (H₂O). When CH₄ reaches the stratosphere, it is destroyed. Another natural sink is soil, where methane is oxidized by bacteria.

Surface-level ozone and other compounds

The next most significant greenhouse gas is surface, or low-level, ozone (O₃). Surface O₃ is a result of air pollution; it must be distinguished from naturally occurring stratospheric O₃, which has a very different role in the planetary radiation balance. The primary natural source of surface O₃ is the subsidence of stratospheric O₃ from the upper atmosphere (see below Stratospheric ozone depletion). In contrast, the primary anthropogenic source of surface O₃ is photochemical reactions involving the atmospheric pollutant carbon monoxide (CO). The best estimates of the concentration of surface O₃ are 50 ppb, and the net radiative forcing due to anthropogenic emissions of surface O₃ is approximately 0.35 watt per square metre.

Nitrous oxides and fluorinated gases

Additional trace gases produced by industrial activity that have greenhouse properties include nitrous oxide (N₂O) and fluorinated gases (halocarbons), the latter including sulfur hexafluoride, hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs). Nitrous oxide is responsible for 0.16 watt per square metre radiative forcing, while fluorinated gases are collectively responsible for 0.34 watt per square metre. Nitrous oxides have small background concentrations due to natural biological reactions in soil and water, whereas the fluorinated gases owe their existence almost entirely to industrial sources.

Aerosols

The production of aerosols represents an important anthropogenic radiative forcing of climate. Collectively, aerosols block—that is, reflect and absorb—a portion of incoming solar radiation, and this creates a negative radiative forcing. Aerosols are second only to greenhouse gases in relative importance in their impact on near-surface air temperatures. Aerosols have the ability to influence climate directly by absorbing or reflecting incoming solar radiation, but they can also produce indirect effects on climate by modifying cloud formation or cloud properties.

Perhaps the most important type of anthropogenic aerosol in radiative forcing is sulfate aerosol. It is produced from sulfur dioxide (SO₂) emissions associated with the burning of coal and oil. Since the late 1980s, global emissions of SO₂ have decreased from about 73 million tons to about 54 million tons of sulfur per year.

Nitrate aerosol is not as important as sulfate aerosol, but it has the potential to become a significant source of negative forcing. One major source of nitrate aerosol is smog (the combination of ozone with oxides of nitrogen in the lower atmosphere) released from the incomplete burning of fuel in internal-combustion engines. Another source is ammonia (NH₃), which is often used in fertilizers or released by the burning of plants and other organic materials. If greater amounts of atmospheric nitrogen are converted to ammonia and agricultural ammonia emissions continue to increase as projected, the influence of nitrate aerosols on radiative forcing is expected to grow.

Land-use change

There are a number of ways in which changes in land use can influence climate. The most direct influence is through the alteration of Earth’s albedo, or surface reflectance. Land-use changes can also influence climate through their influence on the exchange of heat between Earth’s surface and the atmosphere.

Stratospheric ozone depletion

Since the 1970s the loss of ozone (O₃) from the stratosphere has led to a small amount of negative radiative forcing of the surface. This negative forcing represents a competition between two distinct effects caused by the fact that ozone absorbs solar radiation. In the first case, as ozone levels in the stratosphere are depleted, more solar radiation reaches Earth’s surface. In the absence of any other influence, this rise in insolation would represent a positive radiative forcing of the surface. However, there is a second effect of ozone depletion that is related to its greenhouse properties. As the amount of ozone in the stratosphere is decreased, there is also less ozone to absorb longwave radiation emitted by Earth’s surface. With less absorption of radiation by ozone, there is a corresponding decrease in the downward re-emission of radiation. This second effect overwhelms the first and results in a modest negative radiative forcing of Earth’s surface and a modest cooling of the lower stratosphere by approximately 0.5 °C (0.9 °F) per decade since the 1970s.

Natural influences on climate

There are a number of natural factors that influence Earth’s climate. These factors include external influences such as explosive volcanic eruptions, natural variations in the output of the Sun, and slow changes in the configuration of Earth’s orbit relative to the Sun. In addition, there are natural oscillations in Earth’s climate that alter global patterns of wind circulation, precipitation, and surface temperatures. One such phenomenon is the El Niño/Southern Oscillation (ENSO), a coupled atmospheric and oceanic event that occurs in the Pacific Ocean every three to seven years.

Effects of Global Warming

There are two major predicted effects of global warming:

• Increase of temperature on the earth by about 3° to 5° C (5.4° to 9° Fahrenheit) by the year 2100.

• Rise of sea levels by at least 25 meters (82 feet) by the year 2100.

Increasing global temperatures are causing a broad range of changes. Sea levels are rising due to thermal expansion of the ocean, in addition to melting of land ice. Amounts and patterns of precipitation are changing. The total annual power of hurricanes has already increased markedly since 1975 because their average intensity and average duration have increased (in addition, there has been a high correlation of hurricane power with tropical sea-surface temperature).

Changes in temperature and precipitation patterns increase the frequency, duration, and intensity of other extreme weather events, such as floods, droughts, heat waves, and tornadoes. Other effects of global warming include higher or lower agricultural yields, further glacial retreat, reduced summer stream flows, species extinctions. As a further effect of global warming, diseases like malaria are returning into areas where they have been extinguished earlier.

References:

http://www.eoearth.org/article/Global_warming

http://en.wikipedia.org/wiki/Global_warming

http://www.nrdc.org/globalwarming/brief.asp

http://www.epa.gov/climatechange/

http://www.ipcc.ch/

http://www.britannica.com/

Manahan, Stanley, 2000, Environmental Chemistry, Lewis Publishers, London