Greenhouse Effect on environment & global warming
The writer is former additional commissioner, Commercial Tax UP; member, Commercial Tax Tribunal (Retd.) and President, C-CARBONS
After rapid pace of industrialization and unsystematic urbanization, the global environment is deteriorating day by day especially due to emission and discharge of harmful and dangerous gases from industries, transportation, refrigeration, air-conditioning, manmade greenhouses and solid wastes as well as due to deforestation and loss of biodiversity.
The greenhouse effect derives its term from the manmade greenhouses to develop plants. In a greenhouse, energy from the sun passes through the glass as a ray of light. This energy is absorbed by plants, soils and other objects in the greenhouse. Much of this absorbed energy is converted into heat which warms the greenhouse. The glass helps to keep the greenhouse warm by trapping this heat. The earth’s atmosphere acts somewhat like the glass of a greenhouse. About 31% of the incoming radiation from the sun is reflected directly back into space by the earth’s atmosphere and surface (particularly by snow and ice) and another 20% is absorbed by the atmosphere. The rest of the incoming radiation is absorbed by oceans and land where it is converted into heat. Particular gases in the atmosphere – the greenhouse gases – act like the glass of a greenhouse – preventing the heat from escaping. These greenhouse gases absorb heat and re-radiate some of it back to the earth’s surface, causing surface to be warmer than that would otherwise be. This natural trapping of heat or the greenhouse effect has made the earth habitable. Without it the earth would have been a cold, lifeless planet.
Earlier this term had been used to describe the naturally occurring function of traces of gases in the atmosphere and did not have any negative connotation. It was not until mid-1950 that the term-greenhouse effect was coupled with concern over climate change. The negative concerns are related to the possible negative impacts of an enhanced greenhouse effect, especially an increase in the concentration of carbon-dioxide. Compared to pre-industrialization atmospheric concentration of around 270 ppm (parts per million) the average concentration has increased to 400 ppm in 2012. This causes the manmade portion of the greenhouse effect or the enhanced greenhouse effect and has been responsible for global warming in the past 50 years or more, endangering life on earth. China is now estimated to be the largest emitter of greenhouse gases followed by European Union, Russian, Japan, Canada and India.
Potent Greenhouse Gases
Carbon dioxide or CO2 is responsible for more than 55% of the current global warming from GHGs produced by human activities. Its concentration contribution has increased by more than 30% since pre – industrial times ie within 100 years and currently increase by 1% every year. The main sources (75%) are the excessive burning of fossil fuels particularly coal and increasing motor vehicle exhaust. Deforestation and biomass burning contribute 25%. CO2 molecules remain in the atmosphere for around 200 years.
CH4 (methane) accounts for 16% of the increase in GHGs. It can trap 23 times more heat than CO2. Its molecules remain in the atmospheres for 10-12 years. It is produced by decomposition of organic matter eg rice paddies, natural wetlands, sewage, landfills, intestines of cattle, sheep and termites. Its concentration has doubled since pre industrial times. A typical domestic cow may produce 73,000 litres of methane per year. About 1/3 of humans have methane producing bacteria in their guts as well. The increasing amount of methane is linked to the world’s population growth-more people need more food and more cattle. The largest agricultural source of methane production is linked with rice production. The warm water logged soils of paddy fields provide ideal conditions for methane production. The possible sources of methane emission from paddy fields are organic matter such as rice straw, soil, organic matter and carbon supplied by decaying rice plants.
Nitrous oxide (NO2) accounts for 6% of human inputs of GHGs. It is released during nylon production, burning of biomass and fossil fuels like coal, deforestation, fertilizers, live stock wastes and nitrate contaminated ground water. Its life span is 120-190 yrs and traps heat 200 times more than CO2 molecule.
Chlorofluorocarbons are responsible for 24% of human contribution of GHGs. They are entirely man made GHGs. They can trap 1500-1700 times more heat than CO2 mol. Its sources are refrigerants, industrial solvents, aerosol propellants and products of plastic foam.
Effect on Global Warming
There are plenty of ill-effects of global warming due to greenhouse effect, some of which may be summarized as follows:
Effects on weather – The normal temperature will increase. It is projected that by 2100, the normal temperature will increase by 30C. It will disturb the cycle of rains, there will be untimely rains. The increase in temperature may bring unusual storms, floods, and droughts and so on.
Rise in Sea level – The enhanced temperature will cause melting of glaciers, ice and snow causing increase in sea level which will in turn threaten low lying coastal areas, their population, flooding the farm land and a decrease in habitable land.
Effect on crops – It is projected that when by 2100, the normal temperature would increase by 30C. by the rise of that temperature, rice and maize yields in the tropical area are expected to decrease by 20 to 40% and there would be reduction in global food production while the population would naturally grow which may lead to malnutrition.
Damage to plants and animals – It has taken millions of years for life to become used to conditions on earth. As weather and temperature changes, the homes of plants and animals will be affected all over the world, e.g. polar bears and Seal will have to find new land for hunting and living if ice in the arctic melts. Many plants and animals may not be able to cope with these changes and could die causing loss of bio-diversity.
The Greenhouse effect is a natural process that warms the earth’s surface. The earth is wrapped in a blanket of air called the atmosphere which is made-up of several layers of gases. When the sun’s energy reaches the Earth’s atmosphere, some of it is reflected back from earth’s surface and atmospheric gases in to the space and the rest is absorbed (in the form of heat-called trapping of the heat) and re-radiated by the so called Greenhouse gases (GHG’s). These gases trap some energy (i.e. heat) and become an additional source of energy (other than the sun) and emit infrared radiations to make the surrounding warmer. Greenhouse gases include water vapors (36% - 70%) carbon-dioxide(9% - 26%), methane (4% - 9%), ozone (3% -7%), nitrous oxide and some other gases. Of these, methane has 23 times the warming potential of carbon-dioxide while the remaining major gases in the atmosphere i.e. Nitrogen and Oxygen are not able to directly absorb or emit the infrared radiations, and their radiative effect on temperature is so weak that their contribution in temperature is negligible. The absorbed energy warms the atmosphere and surface of the earth. This process maintains the Earth’s temperature at around 330 c warmer than it would otherwise have been – at about freezing – 180 c rather than the palmy 150c as it is now, allowing life on Earth. In the normal scheme of things, GHG’s ,which make up less than 1% of the atmosphere are benign and useful for life. Their levels in the atmosphere are determined by a balance between “ Sources” (that release these gases) and sinks (that absorb or remove them such as photosynthesis and carbon fixing). But the modern human activity has disrupted the optimal balance. Such disruption may happen by way of more generation of these gases or introduction of new sources of GHG’s such as CFC’s (chlorofluro carbons) and their substitutes or by interference with the natural sinks such as deforestation. One hectare of tropical forest, eg, is estimated to store 445 tonne of carbon in its biomass and soil. When a forest is cleared away and replaced by agriculture or human settlements, much of the stored carbon is released into atmosphere as carbon-dioxide. With the forest gone fewer plants are left to remove carbon-di-oxide from the atmosphere through photosynthesis . The enhanced level of GHGs accumulation in the atmosphere results is causing an increase in the temperature of the earth ,referred to as the global warming which in turn leads to ‘climate change’.
Forest, soil & ocean are natural carbon sinks
Carbon dioxide is a greenhouse gas- meaning it traps the heat of sun. The amount of carbon dioxide has increased as a result of human activity mainly by burning of fossil fuels – i.e. coal, oil and natural gas. We have released carbon dioxide that would otherwise have remained stored forever. In so doing, we have caused global warming. The forests and oceans are natural regulators of carbon dioxide content in the atmosphere as they absorb carbon dioxide. They control the amount of carbon concentration that is found in our environment and keep our lives healthy and the air that we breathe worthy of breathing. In the context of global cycle of carbon entering and being removed from the Earth’s atmosphere, it is the oceans, forests and land that take in greenhouse gases. We call these carbon sinks and throughout the past 10,000 years of our current epoch, the Holocene, they have helped to keep these gases, and by extension, Earth’s atmospheres, relatively stable. A carbon sink is a natural or artificial regulator of carbon dioxide content in the atmosphere which is a greenhouse gas. As the term suggests, it absorbs, accumulates and stores carbon dioxide from the atmosphere. The process by which carbon sinks remove carbon dioxide (CO2) from the atmosphere is known as carbon sequestration. Historically, coal, oil, natural gases, sedimentary rocks, limestone are examples of carbon sinks. In current age forests, soils and oceans are major natural carbon sinks. Together they absorb half of the carbon dioxide emissions. Currently many artificial techniques have also been evolved for carbon sequestration in industries such as carbon capture etc. In carbon capture, capture of carbon is performed on a large scale by absorption of carbon dioxide on to various amine based solvents but the natural carbons sinks are the major global carbon sinks that absorb half of the carbon dioxide emissions. Oceans: Oceans are by far the largest carbon sink in the world, absorbing 30% of the carbon dioxide from the atmosphere. In oceans mainly two processes are involved for carbon sequestration from atmosphere. Solubility or physical pump is the primary mechanism responsible for CO2 absorption by the oceans which is caused due to regular ocean circulation. The other process is the biological pump process which is the sum of a series of biological processes that transport carbon from surface to the ocean’s interior via the food web. In high latitudes water stores CO2 more easily because low temperature facilitate atmospheric CO2 dissolution, hence the importance of Polar Regions in the carbon cycle. It is difficult to determine the quality of carbon stored in oceans but it is estimated that ocean concentrates 50 times more carbon than the atmosphere. Plants and Forests: The next major carbon sink is plant and forests. Green plants play a great role in controlling CO2 levels because of the process they use to live i.e. photosynthesis. Through this process they change carbon dioxide into carbon and oxygen. Oxygen is released in the atmosphere that is needed for human and other living beings and carbon is retained in the plant and trees itself in the form of stems, trunks, branches, roots and leaves. The degree of carbon sinks that forests create varies by size of the forest, season, weather and year. The availability of light, heat and water varies and so the forests absorb different amounts of carbon in different times. Also the amount of carbon absorbed varies with the growth of the plants and trees. During growth period, they absorb more carbon. A warm, sufficiently rainy summer spurs forest growth and the carbon sink is considerable. During a dry summer, growth and carbon sink are more modest. Greater is the density and area of the forest, bigger is the carbon sink. In Canada’s boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter. A 40 year study of Asian and South American tropical forests shows tropical forests absorb about 18% of all carbon dioxide added by fossil fuels. It is estimated that Asian forest absorbs about 5 tonnes of carbon dioxide per hectare per year. At many places in the world these carbon sinks are in crisis. It looks like that the world’s largest rainforests, the vast Amazon in South America, which have been aptly described as the world’s lungs, recently lost its ability to take atmospheric carbon dioxide. Its drought stressed trees were not growing and respiring enough to on balance, draw carbon out of the air. Recently many a times fires roared through the forest, transforming trees into kindling and releasing the carbon stored in their wood back into air. In 2005 and again in 2010, the vast Amazon rainforest could not absorb carbon from the air due to drought and fires and now being hit so hard by a combination of drought and fire that the forest is starting to breed carbon. This gigantic and ancient repository of atmospheric carbon is appearing to have turned into a carbon source instead of carbon sink. Soils: Soils represent a short to long term carbon storage medium and contain more carbon than all terrestrial vegetation and the atmosphere combined. Plant litter and other biomass including charcoal accumulate as organic matter in soils and are degraded by chemical weathering and biological degradation. Soils around the world contain approximately 2000 billion tonnes of carbon in various forms. About 300 billion tonnes can be found as detritus in the top soil that decomposes at varying rates depending on factors such as temperature, rains and soil conditions. During decomposition, some of the carbon in soil detritus is respired by the decomposing organisms such as fungi and bacteria with the carbon being returned to the atmosphere as carbon dioxide and the rest is converted into modified soil carbon or inert carbon. The inert carbon can remain locked away from the atmosphere for over a thousand years. Change of land use such as converting grass lands to croplands allowing rapid oxidation of large quantities of soil organic carbon and current agricultural practices lead to carbon loss from soils. Present worldwide practice of overgrazing is also substantially reducing many grasslands’ performance as carbon sinks. It has been scientifically suggested by Rodale Institute that regenerative agriculture – i.e. organic agriculture – if practiced globally, could sequestrate up to 40% of current CO2 emission. They claim that agricultural carbon sequestration has the potential to mitigate global warming. Carbon Sinks Can’t Keep Up Though the story of human forced climate change starts with fossil fuel burning which belches heat trapping CO2 into atmosphere, sadly it does not end there. As that burning causes the earth to heat up, it puts stress on existing carbon sinks. The carbon-absorbing oceans, boreal forests, and great equatorial rain forests all feel sting of that heat. This warming causes the oceans to be able to hold less carbon in their surface water due to acidification of the water and sets of droughts and fires that can reduce a forest’s ability to take in that carbon. For a long time now human fossil fuel emissions have far exceeded the ability of world’s carbon sinks to draw-in excess carbon and keep greenhouse gas level stable. Though these sinks have taken in more than half of the great volume of carbon emitted from fossil burning the total portion of heat trapping CO2 has risen from 280 ppm to more than 400 ppm. As a result of all the excess carbon now in atmosphere, the earth has warmed by more than 1 degree Celsius above 1880s levels. In this tragic context of heat, drought, ocean acidification and deforestation, it appears that the grace period that the Earth’s carbon sinks have given us to get our act together on global warming is coming to an end. Heating the earth as significantly as we have been causing these sinks to break down to be able to braw carbon- as has been the case with vast Amazon rain forests in 2005 and 2010. It was no longer drawing carbon out of the atmosphere and storing it in trees and soil but, more ominously, in 2016 it appeared to start to release carbon back into the atmosphere. Protecting and Restoring Carbon Sinks Man continues to interfere with carbon sinks but looking at its importance we have to act in positive ways to protect and rejuvenate natural sinks that have degraded overtime. These include- Forest Conservation; Forestation; Reforestation; Open space protection including grass lands and meadows; Mangrove protection; Wetlands protection and restoration; Coral reef conservation and restoration; Sea grass habitat restoration; Reduction of emissions to lighten the load on carbon sinks; Promoting regenerative agriculture. Box With reference to forests, the term “carbon sink “means that forest store more carbon dioxide than it releases into the atmosphere. As trees grow, they store carbon in their trunks, branches, roots and leaves. Plant litter stores carbon in the soil. Carbon is released back into the air as carbon dioxide when wood and plant litter decompose or when there is fire in forest. Over the past 150 years, deforestation has contributed an estimated 30 percent of the atmospheric build-up of carbon dioxide.
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