Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

Environment and Additional Topics for UPSC Prelims

UPSC : Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

The document Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev is a part of the UPSC Course Environment and Additional Topics for UPSC Prelims.
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ENVIRONMENTAL CHANGE: CLIMATE CHANGE AND POLLUTION


Introduction

Environmental change is usually defined as a change or disturbance of the environment most often caused by human influences and natural ecological processes. Environmental change does not only encompass physical changes, but also biotic changes in the ecosystem, such as those caused by infestation of invasive species.

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

As depicted in the figure above environmental change can be of the following types:

5.1. CLIMATE CHANGE
Climate change is a long-term shift in weather conditions identified by changes in temperature, precipitation, winds, and other indicators. Climate change can involve both changes in average conditions and changes in variability, including, for example, frequency of extreme events.
When we speak about climate change, most people think about global warming. And if we speak about global warming, most of us think about the greenhouse effect. The greenhouse effect is actually a naturally occurring process which has been accelerated by human activity.

5.1.1. CAUSES OF CLIMATE CHANGE
Any factor that causes a sustained change to the amount of incoming energy or the amount of outgoing energy can lead to climate change. Different factors operate on different time scales, and not all of those factors that have been responsible for changes in earth's climate in the distant past are relevant to contemporary climate change. Factors that cause climate change can be divided into two categories - those related to natural processes and those related to human activity.

Natural Causes
The Earth's climate can be affected by natural factors that are external to the climate system, such as changes in volcanic activity, solar output, and the Earth's orbit around the Sun. Of these, the two factors relevant on timescales of contemporary climate change are changes in volcanic activity and changes in solar radiation. In terms of the Earth's energy balance, these factors primarily influence the amount of incoming energy.
Volcanic eruptions are episodic and have relatively short-term effects on climate. Changes in solar irradiance have contributed to climate trends over the past century but since the Industrial Revolution, the effect of additions of greenhouse gases to the atmosphere has been about ten times that of changes in the Sun's output.

Human Causes
 Increase in the level of greenhouse gases has led to considerable heating of Earth leading to global warming. During the past century, the temperature of Earth has increased by 0.8o Celsius, most of it during the last three decades.

 Deforestation is the conversion of forested areas to non-forested ones. A number of human activities contribute to it. One of the major reasons is the conversion of forest to agricultural land so as to feed the growing human population. Trees are axed for timber, firewood, cattle ranching and for several other purposes. Since forests are major consumers of Carbon Dioxide, therefore deforestation is a major contributor to global warming.

5.1.2. GREENHOUSE EFFECT AND GLOBAL WARMING
The term ‘Greenhouse effect’ has been derived from a phenomenon that occurs in a greenhouse. In a greenhouse the glass panel lets the light in, but does not allow heat to escape. Therefore, the greenhouse warms up, very much like inside a car that has been parked in the sun for a few hours.
The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere. Sunlight warms the surface of the Earth. Since the earth cannot store this heat forever, the warm Earth sends energy back into space. The sunlight which hits the Earth's surface is made up of high energy ultra-violet and visible radiation. The energy emitted from the surface of the Earth is infra-red or 'longwave radiation' and is less energetic than sunlight.

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

Particles and gases in the air absorb infrared heat radiation. The gases are called greenhouse gases. They let the sunlight in, but they don't let the heat radiation from Earth back out into space. They trap the heat near the ground. The greenhouse effect is very important for life on Earth. The average temperature of the Earth is 15 degree Celsius and if there were no greenhouse gases in the air, the average temperature of the Earth would be about 30 degree Celsius lower.
We need a natural greenhouse effect. But by putting more and more greenhouse gases into the air, humans have enhanced the natural greenhouse effect and are making the Earth warmer. It's not the natural greenhouse effect which is causing global warming, it's the additional greenhouse effect caused by humans which is causing the main culprit.

Greenhouse Gases and their Contribution
Greenhouse gases (GHGs) warm the Earth by absorbing energy and slowing the rate at which the energy escapes to space; they act like a blanket insulating the Earth. Different GHGs can have different effects on the Earth's warming. Two key ways in which these gases differ from each other are their ability to absorb energy (their "radiative efficiency"), and how long they stay in the atmosphere (also known as their "lifetime"). The most important greenhouse gas is water vapour (which accounts for about 60% of the greenhouse effect) but the concentrations of water vapour in the atmosphere have changed much over the past few centuries. So it is unlikely that water vapour is responsible for the observed warming of our planet.

However, human activity has dramatically increased the concentration of carbon dioxide in the atmosphere. Carbon dioxide is the most important greenhouse gas in the atmosphere, contributing about 60% of the greenhouse effect (if water vapour is not counted). Methane is the second most important greenhouse gas in the atmosphere, contributing about 20% of the greenhouse effect. Concentrations of methane and ozone, which are also strong greenhouse gases, have also increased dramatically since the industrial revolution.

The Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2). The larger the GWP, the more that a given gas warms the Earth compared to CO2 over that time period. The time period usually used for GWPs is 100 years. GWPs provide a common unit of measure, which allows analysts to add up emissions estimates of different gases (e.g., to compile a national GHG inventory), and allows policymakers to compare emissions reduction opportunities across sectors and gases. CO2, by definition, has a GWP of 1 regardless of the time period used, because it is the gas being used as the reference.

Methane (CH4) is estimated to have a GWP of 28–36 over 100 years. CH4 emitted today lasts about a decade on average, which is much less time than CO2. But CH4 also absorbs much more energy than CO2. The net effect of the shorter lifetime and higher energy absorption is reflected in the GWP. The CH4 GWP also accounts for some indirect effects, such as the fact that CH4 is a precursor to ozone, and ozone is itself a GHG.

GHGs

Lifetime in atmosphere (years)

Sources

Sink

GW Potential over-

share

Natural

Anthropogenic

 

20 Years

100 years

CO2

Variable

---

Burning fossil fuels, deforestation, aerobic fermentation of solid waste and wastewater

Oceans, Forests

1

1

60%

CH4

12

Wetlands, Oceans

Animal waste, paddy fields, burning fossil fuels, anaerobic fermentation of solid waste & wastewater

Earth bacteria and chemical reactions in the atmosphere

56

21

20%

N2O

120

Microbial processes in oceans’ waters and natural soil

Fertilized soil, biomass and fossil fuel burning

Soil Photochemical reactions in the atmosphere

280

310

6%

O3

 

Complex photochemical reactions in the atmosphere

---

Reaction with free radicals in the atmosphere and complex photochemical reactions

Several hours to days

 

 

CFCs

45

---

Industrial activities, refrigerators, pesticides, artificial solvents, and foam products

Chemical reactions in ozone layer

7020

5350

14%

HFC-23

264

 

 

9100

11700

 

 

CO2 Emission Worldwide
About a third of the world's Carbon Dioxide emissions come from Asia, Australia and Oceania and 28% comes from North America – almost 60% of the global CO2 emissions come from these two regions. However, even though both regions emit almost the same amount of CO2 per year, the causes are quite different. About 3.9 billion people live in Asia, Australia and Oceania, that's 61% of the world population, whereas only about 323 million people live in North America (U.S.A. and Canada).
High CO2 emissions in Asia, Australia and Oceania are simply the result of the huge number of people living in the region, in North America it is the very high consumption of energy which is the cause.19.7 tonnes of CO2 are emitted per citizen in the USA, while in India it is only 1.1 tonnes. Such huge differences result from the different degree of economic development. Higher the standard of living in a country, higher is the energy consumption.

5.1.3. OZONE HOLE AND GLOBAL WARMING
Chlorofluorocarbons (CFCs) play a role in both global warming and ozone-hole formation. In the troposphere, they act as greenhouse gases. They absorb infra-red radiation coming from the surface of the Earth and, by trapping this heat close to the Earth they contribute to global warming. In the stratosphere they are broken down by high intensity ultra-violet radiation from the Sun into chlorine radicals and these have the ability destroy ozone. Other greenhouse gases, such as carbon dioxide and methane, do not have a comparable role in ozone depletion.
Since ozone prevents high intensity ultra-violet radiation from reaching the surface of the Earth and causes stratospheric warming, it can be assumed that formation of the ozone hole changes the total radiation budget of the Earth. This is, indeed, the case. However, ozone depletion and the formation of the polar ozone holes don’t lead to a further warming of the troposphere, but to a slight cooling. It can be discussed as under:

1. Absorption of ultra-violet radiation by ozone molecules causes warming in the stratosphere. Some of this heat emitted in the stratosphere is transferred to the troposphere causing slight tropospheric warming as well. This warming gets lessened due to formation of ozone hole.

2. In the lower stratosphere, ozone can still act as a greenhouse gas and absorb infra-red radiation coming from the Earth's surface. So absorption of both ultra-violet and infra-red radiation by ozone leads to a warming of the upper troposphere. If ozone levels decrease, the upper troposphere will, therefore, get cooler.

3. Backscattering of solar radiation is particularly strong over the Antarctic where the strongest ozone depletion occurs. This is because the snow and ice covered ground has a very high albedo. Because of this high backscattering, only a small fraction of the extra ultra-violet radiation that enters the troposphere from ozone loss causes heating.

Overall, the cooling effect of ozone loss is the highest and decreases in ozone levels cause cooling not only in the stratosphere but also slight cooling in the troposphere.

5.1.4. FEEDBACK EFFECTS
When the Earth warms up, a large number of changes take place in the atmosphere, the oceans and on the land surface. Some of these changes can, in turn, affect the temperature. These are called feedback effects. Some of these feedback effects increase global warming, while others reduce it.

Feedback from water vapor
Water vapor is one of the most important feedback effects. A slight warming of the Earth due to more sunlight or an increased greenhouse effect, will lead to an increase in the amount of water vapor in the atmosphere. As water vapor is also a greenhouse gas, the extra water vapor will increase the greenhouse effect even more, leading to even greater warming. Thus water vapor has an amplifying effect on global warming.

Feedback from snow and ice cover
The feedback effects from ice and snow-covered surfaces are similar. When the climate is cold, there is a lot of ice and snow on Earth. These shiny surfaces reflect sunlight away from the ground and make it even colder. A warmer climate means less ice and snow. This leads to less reflection of solar radiation to outer space and increased warming.

Feedback from clouds
When it gets warmer on Earth, the amount of water vapor in the atmosphere increases and more clouds may be formed. This can either increase or decrease warming, depending on what type of clouds they are. All clouds both cool the Earth by reflecting sunlight back into space and warm it up by absorbing heat from the surface in the same way that greenhouse gases do. Thin cirrus clouds (which appear high up in the atmosphere when the weather is fine) generally have a warming effect. Low cumulus and stratus clouds, on the other hand, have a cooling effect.

5.1.5. CLIMATE CHANGE AND OCEANS
Water has a very high specific heat capacity. This means that a lot of energy is needed to increase its temperature. As the Earth is 71% water, energy from the sun causes only small changes in the planet's temperature. This stops the Earth getting too hot or too cold and makes conditions possible for life. Heat is stored by the ocean in summer and released back to the atmosphere in winter. Oceans, therefore, moderate climate by reducing the temperature differences between seasons.

The largest carbon store on Earth is in sediments, both on land and in the oceans, and it is held mainly as calcium carbonate. The second biggest store is the deep ocean where carbon occurs mostly as dissolved carbonate and hydrogen carbonate ions. About a third of the carbon dioxide from fossil fuel burning is stored in the oceans and it enters by both physical and biological processes:

1. Physical Process: Carbon dioxide dissolves more easily in cold water than in warm water. It also dissolves more easily in seawater compared to pure water because seawater naturally contains carbonate ions.
Cold waters sink to the deep ocean at high latitudes in the Southern Ocean and in the Nordic and Labrador Seas in the North Atlantic Ocean. These regions are therefore the major physical carbon dioxide removal areas of the ocean.

2. Biological Process: Carbon dioxide is also taken up by phytoplankton in photosynthesis and converted into plant material. Land plants and marine phytoplankton take up about the same amounts of carbon dioxide as each other but marine phytoplanktons grow much faster than land plants.

By burning fossil fuels, we are releasing carbon about a million times faster than natural biological cycles do. Forests and phytoplankton can't take up the carbon dioxide fast enough to keep up with the increases in emissions and atmospheric carbon dioxide levels have, therefore, risen dramatically over the past few decades.

Consequences of Global Warming on Oceans
Global warming is likely to have a number of effects on the ocean:

 Carbon dioxide dissolves more easily in cold water than in warm water so warmer temperatures will reduce the ability of the oceans to take up carbon dioxide and this will further enhance the greenhouse effect.

 Higher temperatures are also predicted to increase the input of freshwater into the high latitude oceans. Computer models suggest that this additional freshwater comes from increased rain at mid and high latitudes and from the melting of ice sheets.

 Ocean circulation is very sensitive to the amount of freshwater entering the system. Freshwater controls the density of seawater and therefore the ability of seawater to sink when it is cooled. If the water is too fresh, cooling won't make it dense enough to sink into the deep ocean. If water doesn't sink at high latitudes there is only wind driven forcing and therefore reduced water circulation around the oceans.

 Warmer temperatures also cause expansion of water and, along with the additional water from ice melt, will result in a rise in sea level and may cause flooding.

 Excess CO2 absorbed by the oceans will lead to formation of carbonic acid. This acidification will have detrimental effect shell forming creatures like the corals because it will reduce the ability of carbonate ions in the ocean needed to form shell.

 Will lead to migration of tropical marine creatures towards temperate areas thus disturbing the food chain, food availability and biodiversity of a region.

 Researchers have found that rising temperatures in the world’s oceans will affect the development of the plankton on which most marine life feeds. It has been demonstrated that the increasing warmth caused by a changing climate will upset the natural cycles of carbon dioxide, nitrogen and phosphorous. This will affect the plankton, making it scarcer and so causing problems for fish and other species higher up the food chain.

5.1.6. AGRICULTURE AND GLOBAL WARMING
Intensive ploughing of agricultural land and deforestation are also ways to increase CO2 emissions. Soil contains a large amount of organic matter and is, therefore, also an important carbon store. When the soil is intensively ploughed, more oxygen can get into it. This extra oxygen increases the rate at which the organic matter is broken down into CO2.
Nitrous oxide (N2O) is produced biologically in soils, water and animal wastes. Over the last two centuries, human activities have increased N2O concentrations by 13%. The main sources of N2O are fossil fuel combustion, agricultural soil management, industry and the use of nitrogen based fertilizers.

The main sources of methane (natural gas) (CH4) are ruminant livestock (cows and sheep) and rice cultivation. Methane is produced by microscopic organisms which grow in anaerobic conditions. Anaerobic means that there is no oxygen present. Anaerobic conditions occur in waterlogged soils. Rice is grown in flooded fields so rice paddies are an ideal environment for these methane producing organisms to grow. About a third of the total amount of methane in the atmosphere comes from agricultural sources. Other natural sources of methane are coal and petroleum fields.

Agriculture can help to reduced greenhouse gas emissions by adopting practices that allow more CO2 to be stored in soils, crops and trees by ploughing less and slowing the rate of deforestation. More effective use of chemicals would lead to "cleaner" agriculture.

Climate Smart Agriculture
 

Climate-smart agriculture (CSA) is an approach that helps to guide actions needed to transform and reorient agricultural systems to effectively support development and ensure food security in a changing climate. CSA aims to tackle three main objectives:
 Sustainably increasing agricultural productivity and incomes
 Adapting and building resilience to climate change
 Reducing and/or removing greenhouse gas emissions, where possible.

CSA is an approach for developing agricultural strategies to secure sustainable food security under climate change. CSA provides the means to help stakeholders from local to national and international levels identify agricultural strategies suitable to their local conditions.

Developing the potential to increase the productivity and incomes from smallholder crop, livestock, fish and forest production systems will be the key to achieving global food security over the next twenty years. Climate change is expected to hit developing countries the hardest. Its effects include higher temperatures, changes in precipitation patterns, rising sea levels and more frequent extreme weather events. All of these pose risks for agriculture, food and water supplies. Resilience is therefore a predominant concern. Agriculture is a major source of greenhouse gas emissions. Mitigation can often be a significant co-benefit of actions to strengthen adaptation and enhance food security, and thus mitigation action compatible with national development priorities for agriculture is an important aspect of CSA.

Different elements of climate-smart agricultural systems include:
 Management of farms, crops, livestock, aquaculture and capture fisheries to balance near-term food security and livelihoods needs with priorities for adaptation and mitigation.
 Ecosystem and landscape management to conserve ecosystem services that are important for food security, agricultural development, adaptation and mitigation.
 Services for farmers and land managers to enable better management of climate risks/impacts and mitigation actions.
 Changes in the wider food system including demand-side measures and value chain interventions that enhance the benefits of CSA.

CSA is not a set of practices that can be universally applied, but rather an approach that involves different elements embedded in local contexts. CSA relates to actions both on-farm and beyond the farm, and incorporates technologies, policies, institutions and investment.

5.2. CONSEQUENCES OF CLIMATE CHANGE
Because the Earth’s climate system is too large to undertake controlled experiments, scientists use mathematical models, known as Global Circulation Models (GCMs) to forecast climate trends over the coming decades. Major predictions are as below:
● Global climate models predict an increase in average global rainfall ranging from about 5 to 20% because a warmer atmosphere can hold more water vapour.
● High latitude regions (particularly the Polar Regions) and high elevations are likely to experience greater warming than the global mean warming, especially in winter.
● Winter time and night time minimum temperatures will continue to rise faster than average temperatures.
● The hydrological cycle is likely to further intensify, bringing more floods and more droughts.
● More winter precipitation is predicted to fall as rain, rather than snow. This will decrease snow pack and spring runoff, potentially worsening spring and summer droughts.
● Global warming will also affect sea level. There have been a range of estimates for sea level rise based on greenhouse gas emissions and temperature projections that affect the expansion of the water in the oceans and glacial melting. Recent estimates suggest that average sea levels will rise by around half a metre by 2100.

● The amount of oxygen dissolved in the oceans may decline, with adverse consequences for ocean life.

● Ocean acidification and climate change would impair a wide range of planktonic and shallow benthic marine organisms that use aragonite to make their shells or skeletons, such as corals and marine snails (pteropods), with significant impacts particularly in the Southern Ocean.

● Will lead to earlier leafing of trees and plants over many regions; movements of species to higher latitudes and altitudes in the Northern Hemisphere; changes in bird migrations in Europe, North America and Australia; and shifting of the oceans' plankton and fish from cold to warm-adapted communities.

● Climate change will impact agriculture and food production around the world due to: the effects of elevated CO2 in the atmosphere, higher temperatures, altered precipitation and transpiration regimes, increased frequency of extreme events, and modified weed, pest, and pathogen pressure. In general, low-latitude areas are at most risk of having decreased crop yields.

5.2.1. METHODS TO HINDER CLIMATE CHANGE
People can slow down and eventually stop the climate change we have already started. The steps that can be helpful in doing so are:
● Burn less fossil fuel so that we emit less carbon dioxide. Technological improvements and lifestyle changes can reduce the amount of energy we use on transportation, heating, cooling, lighting, appliances that run on electricity, industrial production and so on. Alternative energy resources such as wind, solar, hydro, biomass and nuclear power should be exploited.
● Stop deforestation to prevent release of stored Carbon. Today deforestation is especially prevalent in developing countries, where forests are cut down for agriculture, industrialization and real estate.
● Garbage dumps (landfills) release methane (CH4) from rotting organic waste. By capturing this gas and using it as fuel, we get both heat and reduced emissions of greenhouse gases.
● Building an energy and resource efficient economy- especially the polluting agriculture and industrial sector.

5.2.2. CARBON SEQUESTRATION
Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric CO2.
It can be done in the following ways:
 Afforestation
 Wetland Restoration
 Sustainable Agriculture
 Growing Seaweed that can be used to produce bio-methane.
 Bio-char produced by pyrolysis of bio waste. It can be used as landfill and increase soil fertility.
 Subterranean injection which involves injecting CO2 into depleted oil and gas reservoirs and other geological features, or into the deep ocean.
 Iron Fertilization of Oceans encouraging the growth of planktons and thus capturing CO2.

Geo-Engineering
It is large-scale intervention in the Earth’s climatic system with the aim of limiting climate change. Theoretically, there are two major types of interventions – Carbon Sequestration and solar radiation management. Solar Radiation Management techniques include firing sulphur dioxide into atmosphere, putting huge mirrors in the space, creating pale coloured rooftop and other structures which have high albedo.

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

 

5.3. STRATOSPHERIC OZONE DEPLETION
A higher than normal concentration of Ozone molecules, called the Ozone layer, is found in Stratosphere. It acts as a shield absorbing ultraviolet radiation from the sun. UV rays are highly injurious to living organisms since DNA and proteins of living organisms preferentially absorb UV rays, and its high energy breaks the chemical bonds within these molecules.

The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU). 1 DU is equivalent to a layer of pure ozone molecules 0.01mm thick.

Ozone gas is continuously formed and destroyed by the action of UV rays on molecular oxygen, resulting in a dynamic equilibrium. Briefly, the process is:

1. Oxygen molecules photodissociate after intaking an ultraviolet photon whose wavelength is shorter than 240 nm. This converts a single O2 into two atomic oxygen radicals.
2. The atomic oxygen radicals then combine with separate O2 molecules to create two O3 molecules.
3. These ozone molecules absorb UV light between 310 and 200 nm, following which ozone splits into a molecule of O2 and an oxygen atom.
4. The oxygen atom then joins up with an oxygen molecule to regenerate ozone.
5. This is a continuing process that terminates when an oxygen atom "recombines" with an ozone molecule to make two O2 molecules : 2 O3 → 3 O2

However, due to addition of chlorofluorocarbons (CFCs) in the atmosphere because of Human activity, this equilibrium has been disturbed.

CFCs were widely used as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, their life-cycle is depicted below:

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

The main source of these halogen atoms in the stratosphere is photo-dissociation of man-made halocarbon refrigerants, solvents, propellants, and foam-blowing agents (CFCs, HCFCs, freons, halons) – popularly called as ODS (Ozone Depleting Substance). These compounds are transported into the stratosphere by winds after being emitted at the surface. UV rays act on them releasing Chlorine atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts. Thus Cl atoms are not consumed in the reaction. Hence, whatever CFCs are added to the stratosphere, they have permanent and continuing effects on Ozone levels.

Although ozone depletion is occurring widely in the stratosphere, the depletion is particularly marked over the Antarctic region. This has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole. It is only under certain meteorological conditions that ozone holes form. The conditions required to form the ozone hole are:
● cold temperatures during the polar winter
● ice cloud formation
● special meteorological conditions to form the polar vortex
● followed by the polar sun rise in the spring

The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this polar vortex, over 50% of the lower stratospheric ozone is destroyed during the Antarctic spring.

Reactions that take place on polar stratospheric clouds (PSCs) dramatically enhance ozone depletion. PSCs form more readily in the extreme cold of the Arctic and Antarctic stratosphere. Sunlight-less polar winters contributes to a decrease in temperature and the polar vortex traps and chills air. These low temperatures form cloud particles. These clouds provide surfaces for chemical reactions whose products will, in the spring lead to ozone destruction.

Ordinarily, most of the chlorine in the stratosphere resides in "reservoir" compounds, primarily chlorine nitrate (ClONO2) as well as stable end products such as HCl. The formation of end products essentially removes Cl from the ozone depletion process. During the Antarctic winter and spring, however, reactions on the surface of the polar stratospheric cloud particles convert these "reservoir" compounds into reactive free radicals (Cl and ClO). The clouds remove NO2 from the stratosphere by converting it to nitric acid in the PSC particles. These are then lost by sedimentation. This prevents newly formed ClO from being converted back into ClONO2.

The role of sunlight in ozone depletion is the reason why the Antarctic ozone depletion is greatest during spring. During winter, even though PSCs are at their most abundant, there is no light over the pole to drive chemical reactions. During the spring, however, the sun comes out, providing energy to drive photochemical reactions and melt the polar stratospheric clouds, releasing considerable ClO, which drives the whole mechanism. Warming temperatures near the end of spring break-up the vortex around mid-December. As warm, ozone and NO2-rich air flows in from lower latitudes, the PSCs are destroyed, the enhanced ozone depletion process shuts down, and the ozone hole closes.

Role of Volcanoes and Ocean in Ozone Depletion
The main causes or events that pump excess Chlorine and ODS in the stratosphere are those that are human caused. Volcanoes and oceans contribute to some extent, but these are natural causes and they are taken care of by the natural production of Ozone in the stratosphere.

The vast majority of volcanic eruptions are too weak to reach the stratosphere, around 10 km above the surface. Thus, any HCl emitted in the eruption begins in the troposphere. Sea salt from the oceans is also released very low in the atmosphere. These compounds would have to remain airborne for 2-5 years to be carried to the stratosphere. However, both sea salt and HCl are extremely soluble in water, as opposed to CFCs which do not dissolve in water.

Researchers have also examined the potential impacts of other chlorine sources, such as swimming pools, industrial plants, sea salt, and volcanoes. However, chlorine compounds from these sources readily combine with water and rain out of the troposphere very quickly before they have a chance to reach the stratosphere. In contrast, CFCs are very stable and do not dissolve in rain. There are no natural processes that remove the CFCs from the lower atmosphere. Over time, winds drive the CFCs into the stratosphere.

5.3.2. CONSEQUENCES OF OZONE DEPLETION

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

Humans
Research confirms that high levels of UV rays cause non-melanoma skin cancer. Additionally, it plays a major role in malignant melanoma development. UV is also linked to cataract.

Tropospheric Ozone
Increased surface UV leads to increased tropospheric ozone. Ground-level ozone is generally recognized to be a health risk, as ozone is toxic due to its strong oxidant properties. The risks are particularly high for young children, the elderly, and those with asthma or other respiratory difficulties. Ozone at ground level is produced mainly by the action of UV radiation on combustion gases from vehicle exhausts.

Plants
Plant growths as well as its physiological and developmental process are all affected negatively. These include the way plants form, timing of development and growth, distribution of plant nutrients and metabolism, etc. these changes can have important implications for plant competitive balance, animals feeding on these plants, plant diseases and biogeochemical cycles.
P.S. - Plants do not use UV rays for photosynthesis. They may well have negative overall impact on photosynthesis.
 

Marine Ecosystems
Phytoplankton forms the foundation of aquatic food webs. These usually grow closer to the surface of water, where there is enough sunlight. A change in UV levels is known to affect the development and growth of phytoplankton and naturally, the fish that feed on them. UV radiation is also known to have affected the development stages of fish, shrimp, crab, amphibians and other animals. When this happens, animals in the upper food chain that feed on these tiny fishes are all affected. Whales’ skin is also damaged due to exposure to high intensity of UV rays.

Biogeochemical Cycle
The power of higher UV level affects the natural balance of the gases including the greenhouse gases in the biosphere. Changes in UV level can cause biosphere atmospheric feedback resulting from the atmospheric build-up of these gases.

Crops

An increase of UV radiation would be expected to affect crops. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV radiation and would be affected by its increase.

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

5.3.3. REMEDIAL MEASURES
 A very easy way to control ozone depletion would be to limit or reduce the amount of driving as vehicular emissions eventually result in smog which is a culprit in the deterioration of the ozone layer. (Smog is discussed in Air pollution section further).

 Usage of eco-friendly and natural cleaning products for household chores- many of these cleaning agents contain toxic chemicals that interfere with the ozone layer.

 Avoiding use of pesticides and using bio-control agents or exploring pest resistant GM crops.

 A study shows that the harm caused by rocket launches would outpace the harm caused due to CFCs. At present, the global rocket launches do not contribute hugely to ozone layer depletion, but over the course of time, it will become a major contributor to ozone depletion. All types of rocket engines result in combustion by products that are ozone-destroying compounds that are expelled directly in the middle and upper stratosphere.

 Putting N2O under the Montreal Protocol as it is currently significant contributor to Ozone depletion while the contribution of others has decreased.

__________________

NASA Reports have claimed that Ozone layer over Antarctica is thickening again and would half close in the next five years.

__________________

5.4. DEFORESTATION
Forest clearance or Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use.
Deforestation occurs for many reasons: trees are cut down to be used or sold as fuel (sometimes in the form of charcoal) or timber, while cleared land is used as pasture for livestock, agriculture, plantations of commodities, industrialisation and settlements. Deforestation has also been used in war to deprive the enemy of cover for its forces and also vital resources. Disregard of ascribed value, lax forest management and deficient environmental laws are some of the factors that allow deforestation to occur on a large scale.

5.4.1. CONSEQUENCES OF DEFORESTATION
Climate Change: Forests are some of the largest reserves of carbon. Amazon rainforests are called lungs of the earth because of their ability absorb carbon dioxide and release fresh oxygen.

Pollution of Air, Water and Soil: Toxic gases and chemicals released into the environment are absorbed by the forests. Deforestation reduces this capacity and increases the impact of the pollution.

Water Cycle: Forests intercept moisture and cause rainfall. They play an important part in water cycle through transpiration and facilitation of cloud formation.

Soil: Deforestation generally increases rates of soil loss, by increasing the amount of runoff and reducing the protection of the soil from tree litter. Tree roots bind soil together, and if the soil is sufficiently shallow they act to keep the soil in place by also binding with underlying bedrock. Tree removal on steep slopes with shallow soil thus increases the risk of landslides, which can threaten people living nearby. Deforestation reduces soil cohesion, so that erosion, flooding and landslides ensue. It eventually leads to soil degradation as well.

Biodiversity: Deforestation on a human scale results in decline in biodiversity, and on a natural global scale is known to cause the extinction of many species. The removal or destruction of areas of forest cover has resulted in a degraded environment with reduced biodiversity. Forests support biodiversity, providing habitat for wildlife; moreover, forests foster medicinal conservation. With forest biotopes being irreplaceable source of new drugs (such as taxol), deforestation can destroy genetic variations (such as crop resistance) irretrievably.

5.5. LAND DEGRADATION AND DESERTIFICATION

Land degradation is caused by multiple forces, including extreme weather conditions particularly drought, and human activities that pollute or degrade the quality of soils and land utility. It negatively affects food production, livelihoods, and the production and provision of other ecosystem goods and services. Land degradation has accelerated during the 20th and 21st century due to increasing and combined pressures of agricultural and livestock production (over-cultivation, overgrazing, forest conversion), urbanization, deforestation, and extreme weather events such as droughts and coastal surges which salinate land. Desertification, is a form of land degradation, by which fertile land becomes desert.

5.5.1. CONSEQUENCES OF LAND DEGRADATION
These social and environmental processes are stressing the world's arable lands and pastures essential for the provision of food, water and quality air. Land degradation and desertification can affect human health through complex pathways. As land is degraded and in some places deserts expand, food production is reduced, water sources dry up and populations are pressured to move to more hospitable areas. The potential impacts of desertification on health include:
 Higher threats of malnutrition from reduced food and water supplies;
 More water- and food-borne diseases that result from poor hygiene and a lack of clean water;
 Respiratory diseases caused by atmospheric dust from wind erosion and other air pollutants;
 Spread of infectious diseases as populations migrate.

5.6. WETLANDS LOSS AND DAMAGE
Wetlands are defined as lands transitional between terrestrial and aquatic eco-systems where the water table is usually at or near the surface or the land is covered by shallow water. The land area is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem.
Wetlands are the most productive ecosystems that provide many services and commodities to humanity. Regional wetlands are integral parts of larger landscapes; their functions and values to the people in these landscapes depend on both their extent and their location. Each wetland thus is ecologically unique. Some important uses of wetlands:
 Aquaculture: Wetlands are used to harvest fish/aquatic animals for human consumption and pharmaceuticals.
 Flood control
 Groundwater replenishment: The surface water which is the water visibly seen in wetland systems only represents a portion of the overall water cycle which also includes atmospheric water and groundwater. Wetland systems are directly linked to groundwater and a crucial regulator of both the quantity and quality of water found below the ground.
 Shoreline stabilisation and storm protection: Tidal and inter-tidal wetland systems protect and stabilize coastal zones. Coral reefs and mangroves provide a protective barrier to coastal shoreline.
 Nutrient retention: Wetland vegetation up-take and store nutrients found in the surrounding soil and water.
 Sediment traps
 Water purification: Many wetland systems possess biofilters, hydrophytes, and organisms that in addition to nutrient up-take abilities have the capacity to remove toxic substances that have come from pesticides, industrial discharges, and mining activities.
 Reservoirs of biodiversity
 Wetland products: Apart from aquaculture products, wetland systems naturally produce an array of vegetation and other ecological products that can harvested for personal and commercial use. Some important products: rice, sago palm, nipa palm, honey from mangroves, Fuel wood, Salt (produced by evaporating seawater), Animal fodder, Traditional medicines (e.g. from mangrove bark), Fibres for textiles, Dyes and tannins.
 Cultural values
 Recreation and tourism
 Climate change mitigation and adaptation: Wetlands perform two important functions in relation to climate change. They have mitigation effects through their ability to sink carbon, and adaptation effects through their ability to store and regulate water. However, coastal wetlands, such as tropical mangroves and temperate salt marshes are also emitters of nitrous oxide (N2O). In Southeast Asia, peatswamp forests and soils are source of CO2. Rice fields are source of methane.

5.6.1. CAUSES OF WETLAND LOSS IN INDIA
Human Causes:
 Drainage for agriculture, forestry and mosquito control
 Dredging and stream channelization for navigation and food protection
 Filling for solid waste disposal, roads
 Conservation for aquaculture/mariculture
 Construction of dykes, dams and seawalls for flood control
 Discharge of pesticide, herbicide, nutrients from domestic sewage
 Mining of wetlands for peat, coal, gravel, phosphate and other minerals
 Ground water abstraction
 Sediment diversion by dams, deep channels
 Hydrological alterations by canals, roads and other structures
 Subsidence due to extraction of ground water oil, gas and other minerals

Natural Causes:
 Subsidence
 Sea level rise
 Drought
 Hurricane and other storms
 Erosions
 Biotic effects
(Kindly refer to Wetlands Document where the topic has been discussed elaborately)

5.7. URBANIZATION
Urbanization is the gradual increase in proportion of people living in urban areas and ways in which each society adapts to the change. It is mostly driven by rural-urban migration, which is more often than not based on environmental and economic distress. Rapid, unplanned and unsustainable patterns of urban development are making developing cities focal points for many emerging environment and health hazards. As urban populations grow, the quality of global and local ecosystems, and the urban environment, will play an increasingly important role in public health with respect to issues ranging from solid waste disposal, provision of safe water and sanitation, and injury prevention, to the interface between urban poverty, environment and health.

Chapter - 5 - Environmental Change: Climate Change and Pollution( Part -1) - Environment UPSC Notes | EduRev

 

5.8. DAMAGE TO CORAL REEFS
Coral reefs are some of the most diverse ecosystems in the world, housing tens of thousands of marine species. Thousands of identical polyps live together and form a coral colony. Each polyp excretes a calcium carbonate exoskeleton beneath it and, over long periods of time, the skeletons of many coral colonies add up to build the structure of a coral reef. Reefs only occur in shallow areas that are reachable by sunlight because of the relationship between coral and algae. Various types of microscopic algae live inside of the coral, providing them with food and helping them to grow faster. In many ways, reef-building corals are animals that act like plants- they stay in one place and get some of their energy from the sun. Coral reefs cover an area of over 280,000 km2 and are described as the “rainforests of the seas” because of the biodiversity they support.

Coral reefs benefit the environment and people in numerous ways. For example, they
 Through the photosynthesis carried out by their algae, coral serve as a vital input of food into the tropical/sub-tropical marine food-chain, and assist in recycling the nutrients too.
 The reefs provide home and shelter to over 25% of fish and up to two million marine species.
 They are also a nursery for the juvenile forms of many marine creatures.
 Protect shores from the impact of waves and from storms;
 Provide benefits to humans in the form of food and medicine; economy through tourism.
 The World Meteorological Organization says that tropical coral reefs yield more than US$ 30 billion annually in global goods and services, such as coastline protection, tourism and food.

Threat to coral reefs
 According to a 2004 report, 20% of the world’s coral reefs have been effectively destroyed and show no immediate prospects of recovery;
 The report predicts that 24% of the world’s reefs are under imminent risk of collapse through human pressures; and a further 26% are under a longer term threat of collapse.
The 2004 edition of Status of Coral Reefs around the World lists the following top 10 emerging threats in these three categories:

Global Change Threats

 

 Coral bleaching—caused by elevated sea surface temperatures due to global climate change;

 Rising levels of CO2 causing ocean acidification

 Diseases, Plagues and Invasives—linked to human disturbances in the environment.

 

Direct Human Pressures

 

 Over-fishing (and global market pressures)—including the use of damaging practices (bomb and cyanide fishing);

 Sediments—from poor land use, deforestation, and dredging;

 Nutrients and Chemical pollution

 Development of coastal areas—for urban, industrial, transport and tourism developments, including reclamation and mining of coral reef rock and sand beyond sustainable limits.

 

The Human Dimension- Governance, Awareness and Political Will

 

 Rising poverty, increasing populations, alienation from the land

 Poor capacity for management and lack of resources

 Lack of Political Will, and Oceans G

 

 __________________________________

In 1995, France started testing its Nuclear weapons in the Pacific despite huge protests. It is now emerging that the coral in the French Polynesia regions where many Nuclear tests have been carried out have been harmed, as the French atomic energy commission has admitted.

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