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Climate Change |
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The atmosphere carries out the critical function of maintaining life-sustaining conditions on Earth, in the following way: each day, energy from the sun (largely in the visible part of the spectrum, but also some in the ultraviolet and infra red portions) is absorbed by the land, seas, mountains, etc. If all this energy were to be absorbed completely, the earth would gradually become hotter and hotter. But actually, the earth both absorbs and, simultaneously releases it in the form of infra red waves. All this rising heat is not lost to space, but is partly absorbed by some gases present in very small (or trace) quantities in the atmosphere, called GHGs (greenhouse gases).
However, ever since the Industrial Revolution began about 150 years ago, man-made activities have added significant quantities of GHGs to the atmosphere. The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have grown by about 31%, 151% and 17%, respectively, between 1750 and 2000 (IPCC 2001).
An increase in the levels of GHGs could lead to greater warming, which, in turn, could have an impact on the world's climate, leading to the phenomenon known as climate change.
Climate change refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer).
Climate change may be due to natural internal processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land use. While changes in the weather may occur suddenly and noticeably, changes in the climate take a long time to settle in and are therefore less obvious. Over the last 150-200 years climate change has been taking place too rapidly
However, variations in temperature have also occurred in the past - the best known is the Little Ice Age that struck Europe in the early Middle Ages, bringing about famines, etc. It is therefore difficult to determine whether current observations of increasing temperature are due to natural variability or whether they have been forced by anthropogenic (man-made) activities. But today, climate change usually refers to changes in modern climate due to interference of man.
Scientific studies and projections are further complicated by the fact that the changes in temperature that they have been observing do not occur uniformly over different layers of the lower atmosphere or even different parts of the earth.
Climate change is thus any long-term significant change in the expected patterns of average weather of a specific region (or, more relevantly to contemporary socio-political concerns, of the Earth as a whole) over an appropriately significant period of time. Climate change reflects abnormal variations to the expected climate within the Earth's atmosphere and subsequent effects on other parts of the Earth, such as in the ice caps over durations ranging from decades to millions of years. |
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| Causes of climate change | | The earth's climate is dynamic and always changing through a natural cycle. What the world is more worried about is that the changes that are occurring today have been speeded up because of man's activities. These changes are being studied by scientists all over the world who are finding evidence from tree rings, pollen samples, ice cores and sea sediments.
Climate Change is the result of a great many factors including the dynamic processes of the Earth itself, external forces including variations in sunlight intensity, and more recently by human activities, which might in future be deliberate geo-engineering. External factors that can shape climate are often called climate forcing and include such processes as variations in solar radiation, deviations in the Earth's orbit, and the level of greenhouse gas concentrations.
VOLCANISM :
One of the possible reasons for climate change on scales of centuries and millennia, like the Little Ice Age, is increased volcanic activity. Volcanism is the process of conveying material from the depths of the Earth to the surface, as part of the process by which the planet removes excess heat and pressure from its interior. Volcanic eruptions, geysers and hot springs are all part of the volcanic process and all release varying levels of particulates into the atmosphere.
Great volcanic eruptions release huge amounts of gases and aerosol particles which impact global climate by reducing the amount of solar radiation reaching the Earth's surface, lowering temperatures and changing atmospheric circulation patterns.
Volcanoes are also part of the extended carbon cycle. Over very long (geological) time periods, they release carbon dioxide from the earth's interior, counteracting the uptake by sedimentary rocks and other geological carbon dioxide sinks.
The result is a cool summers and severe winters for the period that follows. Volcanic eruptions cause short-term climate changes and contribute to natural climate variability.
OCEAN VARIABILITY :
The oceans are a major component of the climate system. They cover about 71% of the Earth and absorb about twice as much of the sun's radiation as the atmosphere or the land surface.
On a timescale often measured in decades or more, climate changes can also result from the interaction between the atmosphere and the oceans. On longer time scales (with a complete cycle often taking up to a thousand years to complete), ocean processes such as thermohaline circulation also play a key role in redistributing heat by carrying out a very slow and extremely deep movement of water, and the long-term redistribution of heat in the oceans.
Many climate fluctuations, including the El Niño Southern oscillation, the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation, owe their existence at least in part to the different ways that heat may be stored in the oceans and also to the way it moves between various 'reservoirs'. It is shown that there have been large inter-annual and inter-decadal sea-surface temperature changes off the West Coast of North America during the past 80 years. Inter-annual anomalies appear and disappear rather suddenly and synchronously along the entire coastline. The frequency of warm events has increased since 1977. Although extensive, serial, biological observations are often incomplete, it is clear that climate-ocean variations have disturbed and changed our coastal ecosystems.
EFFECT OF CO2 AND OTHER GHG :
Carbon dioxide is undoubtedly, the most important greenhouse gas in the atmosphere. Changes in land use pattern, deforestation, land clearing, agriculture, and other activities have all led to a rise in the emission of carbon dioxide. Increased carbon dioxide levels are thought to exacerbate the heating effects of the Greenhouse Effect by reducing the re-radiation of heat from the sun and, therefore, increasing the temperature contained in the atmosphere. Carbon dioxide (CO2) is emitted in a number of ways. It is emitted naturally through the carbon cycle and through human activities like the burning of fossil fuels.
The global carbon cycle is the term used to describe the Earth’s four carbon reservoirs and the exchanges of carbon between the reservoirs by various chemical, physical, geological and biological processes –including the exchange of carbon in the form of CO2. The four reservoirs, or regions of the Earth in which carbon behaves in a systematic manner, are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans and sediments (includes fossil fuels.)
Methane is another important greenhouse gas in the atmosphere. About ¼ of all methane emissions are said to come from domesticated animals such as dairy cows, goats, pigs, buffaloes, camels, horses, and sheep. These animals produce methane during the cud-chewing process. Methane is also released from rice or paddy fields that are flooded during the sowing and maturing periods. When soil is covered with water it becomes anaerobic or lacking in oxygen. Under such conditions, methane-producing bacteria and other organisms decompose organic matter in the soil to form methane.
Over the past 200 years, but mostly in the past few decades, there have been noticeable increases in atmospheric concentrations of the greenhouse gases – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydro fluorocarbons (HFC’s), per fluorocarbons (PFC’s) and sulphur hexafluoride (SF6). Human activities that release greenhouse gases into the atmosphere have been identified as being responsible for this increase. CO2 is produced when generating energy from fossil fuels and in clearing and burning forests. CH4 and N2O are emitted from agricultural activities, changes in land use and other sources. Other activities also contribute to greenhouse gas emissions.
These greenhouse gases, mainly carbon dioxide but including others such as methane, nitrous oxide, and halocarbons, enter the air mainly as byproducts of the combustion of coal, natural gas, and petroleum, and to a lesser degree through other industrial and agricultural activities. Their rates of emission into the air are roughly proportional to the global rate of energy consumption arising from human activity. Thus, as human population and per capita energy consumption have increased, concentrations of these gases have risen in nearly direct proportions to the product of both increases.
PLATES TECTONIC :
Continental drift is the movement of the Earth's continents relative to each other. The movement of the continents has a marked effect on both local and global climate. Some of the effects are the difference in the thermal properties of land versus ocean – a continental region will be colder in winter and warmer in summer than an oceanic region at any given latitude. Moreover mountain belts formed as a consequence of plate tectonic activity dramatically modify rainfall through the effects of orography – the development of a rain shadow on the leeward side of mountain belts.
Global climate is also strongly controlled by ocean currents. The differential movement between various tectonic plates results in the formation of the ocean currents. These ocean currents have a profound effect on the climate.
For example, once in Antarctica, the climate was much more temperate – there were no glaciers and the continent was covered with lush vegetation and forests. So how did this extreme change come about? The modern climate of Antarctica depends upon its complete isolation from the rest of the planet as a consequence of the Antarctic Circumpolar Current that completely encircles Antarctica and gives rise to the stormy region. The onset of this current is related to the opening of seaways between obstructing continents. Antarctica and South America were once joined together as part of Gondwana. At some time, there was possibly a shallow seaway between Antarctica and South America, but both continents were moving together. After a few more million years, the seaway was still narrow, but differential movement between the Antarctic and South American Plates created a deeper channel between the two continents that began to allow deep ocean water to circulate around the continent. Finally there was a major shift in local plate boundaries that allowed the rapid development of a deep-water channel between the two continental masses.
Plate movement also generates a lot of volcanic activity. This increased volcanic activity results in increased CO2 emissions, finally resulting in higher temperatures throughout the world
Hence, over geological timescales the movement of plates and continents has a profound effect on the distribution of land masses, mountain ranges and the connectivity of the oceans. As a consequence, plate tectonics has a very direct and fundamental influence on global climate.
ORBITAL VARIATIONS :
The sun drives the climate. Even if the sun’s output of energy did not vary (but it does), the amount of sunlight reaching different areas of the Earth would still change because of the way the Earth moves around the sun.
One natural factor in climate change may be variation in the brightness of the sun, over decades to centuries that are in step with changes in the sun’s magnetism. These changes occur over cycles of roughly 11 years--what is known as the sunspot cycle. Climate models suggest changes of roughly 0.5 percent in the sun’s brightness would produce global average temperature changes of about 0.5º C over a century or so.
In defining the tremendous impact the sun has on climate, one must understand the movement of the Earth around the sun. There are three variables--orbit shape, tilt, and wobble--that profoundly affect weather patterns.
The earth makes one full orbit around the sun each year. It is tilted at an angle of 23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer, the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is tilted away from the sun. If there was no tilt we would not have experienced seasons. Changes in the tilt of the earth can affect the severity of the seasons - more tilt means warmer summers and colder winters; less tilt means cooler summers and milder winters.
The Earth’s orbit does not form a circle as it moves around the sun: It forms an ellipse passing further away from the sun at one end of the orbit than it does at the other end. During a 100,000-year cycle, the tug of other planets on the Earth causes its orbit to change shape. It shifts from a short broad ellipse that keeps the Earth closer to the sun, to a long flat ellipse that allows it to move farther from the sun and back again.
In their effect on climate, orbital variations are in some sense an extension of solar variability, because slight variations in the Earth's orbit lead to changes in the distribution and abundance of sunlight reaching the Earth's surface. These orbital variations, known as Milankovitch cycles, directly affect glacial activity. Eccentricity, axial tilt, and precession comprise the three dominant cycles that make up the variations in Earth's orbit. The combined effect of the variations in these three cycles creates changes in the seasonal reception of solar radiation on the Earth's surface. As such, Milankovitch Cycles affecting the increase or decrease of received solar radiation directly influence the Earth's climate system.
HUMAN INFLUENCE :
Anthropogenic factors are human activities that change the environment. Human activities are increasingly altering the Earth's climate. The unprecedented increases in greenhouse gas concentrations, together with other human influences on climate over the past century and those anticipated for the future constitute a real basis for concern.
The complexity of the climate system makes it difficult to predict some aspects of human-induced climate change: exactly how fast it will occur, exactly how much it will change, and exactly where those changes will take place.
Human impacts on the climate system include increasing concentrations of atmospheric greenhouse gases. Atmospheric carbon dioxide concentrations have increased since the mid-1700s through fossil fuel burning and changes in land use, with more than 80% of this increase occurring since 1900. Moreover, research indicates that increased levels of carbon dioxide will remain in the atmosphere for hundreds to thousands of years.
The most concerning of these anthropogenic factors is the increase in CO2 levels due to emissions from fossil fuel combustion, followed by aerosols and cement manufacture. Other factors, including land use, ozone depletion, animal agriculture and deforestation, are also of concern in the roles they play - both separately and in conjunction with other factors - in affecting climate.
FOSSIL FUELS :
Fossil fuels are among the most important contributors towards the greenhouse emissions. Combustion of fossil fuels generates sulfuric, carbonic, and nitric acids, which fall to Earth as acid rain, impacting both natural areas and the built environment. Fossil fuels also contain radioactive materials, mainly uranium and thorium that are released into the atmosphere.
Carbon dioxide levels are substantially higher now than at any time in the last 750,000 years.[15] Beginning with the industrial revolution in the 19th Century and accelerating since, the human consumption of fossil fuels has elevated CO2 levels from a concentration of approximately 280 ppm in pre-industrial times [16] to around 387 ppm today. It is suggested that these changes may possibly cause an increase of 1.4–5.6°C between 1990 and 2100. Proposals by some scientists and international coalitions, aimed at attempting to prevent drastic climate change, have suggested setting goals to try to limit concentrations to 450 or 500 ppm.
AEROSOLS :
Aerosols are tiny particles suspended in the air. Density of the basic materials of aerosols range from 1.0 g/cm3 (for soot) to 2.6 (for minerals). Some occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels and the alteration of natural surface cover, also generate aerosols.
Atmospheric aerosols influence climate in two main ways, referred to as direct forcing and indirect forcing. In the direct forcing mechanism, aerosols reflect sunlight back to space, thus cooling the planet. (Sooty aerosols from such processes as biomass burning absorb some of this solar energy, leading to a local atmospheric heating which may alter stability and convection patterns.) It has been estimated that pollution of this sort over the eastern section of the United States has effectively reduced the annual crop growing season by one week.
The indirect effect involves aerosol particles acting as (additional) cloud condensation nuclei, spreading the cloud's liquid water over more, smaller droplets. This makes clouds more reflective, and longer lasting. The formation of a cloud droplet requires two things - an excess of water vapour (super saturation), and a seed or "condensation nucleus". Computing the details of cloud microphysics requires a detailed understanding of the dynamical processes moving water vapour through the atmosphere, and the physical mechanisms involved in the formation and growth of cloud particles, including heating and cooling by solar and infrared radiation.
Aerosols affect our environment at the local, regional, and global levels. At the local level, aerosols are now becoming recognised as a significant health problem, especially in regard to respiratory illnesses, including asthma.
Aerosols can be long-lived and therefore be advected over a long distance. Four weeks of measurements of tropospheric aerosols at Mildura (in the Australian state of Victoria) showed that some came from Africa, about eight days upwind, and possibly South America, even further away. These aerosols may have come from gases generated by forest fires.
Indeed, aerosols are one of the greatest sources of uncertainty in interpretation of climate change of the past century and in projection of future climate change.
CEMENT MANUFACTURE :
Cement manufacture contributes CO2 to the atmosphere when calcium carbonate is heated, producing lime and carbon dioxide, and also as a result of burning fossil fuels in the process. It is estimated that the cement industry produces around 5% of global man-made CO2 emissions. 60 % of emissions caused by making cement are from this chemical process alone. Mitigation is difficult for the chemical process. The remainder is produced from the fuels used in production, although those emissions may be mitigated with the use of greener technology. The amount of CO2 emitted by the cement industry is more than 900 kg of CO2 for every 1000 kg of cement produced.
LIVESTOCK :
According to a new report published by the United Nations Food and Agriculture Organization, the livestock sector generates greenhouse gas emissions as measured in CO2 equivalent – 18 percent – more than transport.
When emissions from land use and land use change are included, the livestock sector accounts for 9 percent of CO2 deriving from human-related activities, but produces a much larger share of even more harmful greenhouse gases. It generates 65 percent of human-related nitrous oxide, which has 296 times the Global Warming Potential (GWP) of CO2.And it accounts for respectively 37 percent of all human-induced methane (23 times as warming as CO2), which is largely produced by the digestive system of ruminants, and 64 percent of ammonia, which contributes significantly to acid rain.
LAND USE :
Deforestation, urban sprawl, agriculture, and other human influences have substantially altered and fragmented our landscape. Such disturbance of the land can change the global atmospheric concentration of carbon dioxide, the principal heat-trapping gas, as well as affect local, regional, and global climate by changing the energy balance on Earth's surface.
Prior to widespread fossil fuel use, humanity's largest effect on local climate was land use; irrigation, deforestation, and agriculture - on large scales - may fundamentally change the environment. There is evidence to suggest that the climate of Greece and other Mediterranean countries was permanently changed by widespread deforestation between 700 BC and 1 AD (the wood being used for shipbuilding, construction and fuel), with the result that the modern climate in the region is significantly hotter and drier, and the species of trees that were used for shipbuilding in the ancient world can no longer be found in the area.
Land use and land cover are linked to climate and weather in complex ways and are critical inputs for modeling greenhouse gas emissions, carbon balance, and ecosystems. Land-use and land-cover change (LULCC) studies have provided critical inputs to large-scale biomass and forest cover assessments; future LULCC goals include reducing uncertainties in biomass estimates, understanding regional heterogeneities in changes, and quantifying linkages and feedbacks between LULCC, climate change, and other human and environmental components.
However, macro-scale interactions between deforestation, climate change and soil degradation are poorly known, and rarely assessed adequately for combined scenarios of climate change and land use. | | | Effects of climate change | | A delicate balance exists between man and his environment. The impact of changes in the surrounding atmosphere on human health was first reported by Plinius, the Younger, in 73 AD. In his documentation of fatal respiratory consequences of natural air pollution caused by the eruption of Mount Vesuvius in Pompeii, he described succinctly, the effect that the clouds of airborne matter in the atmosphere had on Plinius, the Elder, a scientist as well as the commander of the Roman fleet.
Over 100 years ago, people worldwide began burning more coal and oil for homes, factories, and transportation. Burning these fossil fuels releases carbon dioxide and other greenhouse gases into the atmosphere. These added greenhouses gases have caused Earth to warm more quickly than it has in the past.
How much warming has happened? Scientists from around the world with the Intergovernmental Panel on Climate Change (IPCC) tell us that during the past 100 years, the world's surface air temperature increased an average of 0.6° Celsius (1.1°F). This may not sound like very much change, but even one degree can affect the Earth. 11 of the 12 hottest years on record occurred between 1995 and 2006. The scientific consensus is that global temperatures could rise between 1.1 and 6.4 degrees above 1980-1999 levels by the end of the 21st century.
The effects of climate change can be seen in the UK and around the world. Already, British coastal waters have warmed and temperatures have risen. Globally, extreme weather is predicted to become more common – and animals, plants and crops are all expected to be badly affected.
GLACIATIONS :
Glacial ice can range in age from several hundred to several hundreds of thousands years, making it valuable for climate research. They are recognized as being among the most sensitive indicators of climate change [1], advancing during climate cooling (for example, during the period known as the Little Ice Age) and retreating during climate warming on moderate time scales.
Projected climate change over the next century will further affect the rate at which glaciers melt. Average global temperatures are expected to rise 1.4-5.8ºC by the end of the 21st century. Simulations project that a 4ºC rise in temperature would eliminate nearly all of the world’s glaciers (the melt-down of the Greenland ice sheets could be triggered at a temperature increase of 2 to 3ºC). Even in the least damaging scenario – a 1ºC rise along with an increase in rain and snow – glaciers will continue to lose volume over the coming century. Although only a small fraction of the planet’s permanent ice is stored outside of Greenland and Antarctica, these glaciers are extremely important because they respond rapidly to climate change and their loss directly affects human populations and ecosystems.
The most significant climate processes of the last several million years are the glacial and interglacial cycles of the present age. The present interglaciation (often termed the Holocene) has lasted about 10,000 years.[3] Shaped by orbital variations, earth-based responses such as the rise and fall of continental ice sheets and significant sea-level changes helped create the climate. Other changes, including Heinrich events, Dansgaard–Oeschger events and the Younger Dryas, however, illustrate how glacial variations may also influence climate without the forcing effect of orbital changes.
GREEN HOUSE EFFECTS :
About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet’s surface and is reflected upward again as a type of slow-moving energy called infrared radiation. As it rises, infrared radiation is absorbed by “greenhouse gases” such as water vapor, carbon dioxide, ozone and methane, which slows its escape from the atmosphere. Although greenhouse gases make up only about 1 percent of the Earth’s atmosphere, they regulate our climate by trapping heat and holding it in a kind of warm-air blanket that surrounds the planet. This phenomenon is what scientists call the "greenhouse effect."
But now due to excess greenhouse gases being present in our atmosphere, there has been excessive greenhouse effect, which has led to the rise in temperatures throughout the world.
Global warming is the increase in the average temperature of the Earth's near-surface air and the oceans since the mid-twentieth century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005.
Global warming has been caused, according to scientists mostly as a result of various human activities. Some of the activities are:
• Burning natural gas, coal and oil.
• Some farming practices and land-use changes increase the levels of methane and nitrous oxide.
• Many factories produce long-lasting industrial gases that do not occur naturally, yet contribute significantly to the enhanced greenhouse effect and “global warming” that is currently under way.
• Deforestation also contributes to global warming. Trees use carbon dioxide and give off oxygen in its place, which helps to create the optimal balance of gases in the atmosphere. As more forests are logged for timber or cut down to make way for farming, however, there are fewer trees to perform this critical function.
• Population growth is another factor in global warming, because as more people use fossil fuels for heat, transportation and manufacturing the level of greenhouse gases continues to increase. As more farming occurs to feed millions of new people, more greenhouse gases enter the atmosphere.
Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, likely including an expanse of the subtropical desert regions. Other likely effects include Arctic shrinkage and resulting Arctic methane release, shrinkage of the Amazon rainforest (already very damaged by deforestation from logging and farming), increases in the intensity of extreme weather events, changes in agricultural yields, modifications of trade routes, glacier retreat, species extinctions and changes in the ranges of disease vectors.
HYSTERESIS :
More generally, most forms of internal variability in the climate system can be recognized as a form of hysteresis, where the current state of climate does not immediately reflect the inputs. Because the Earth's climate system is so large, it moves slowly and has time-lags in its reaction to inputs. For example, a year of dry conditions may do no more than to cause lakes to shrink slightly or plains to dry marginally. In the following year however, these conditions may result in less rainfall, possibly leading to a drier year the next.
The simplest variant of a hysteresis loop is a useful tool to discuss the different possibilities for how the climate system can respond to changes in some controlling variable.
It is this hysteresis that has been mooted to be the possible progenitor of rapid and irreversible climate change.
ARCTIC CHANGE :
The Arctic region has long fascinated humankind, sparking holiday myths, motivating explorers, and inspiring people to create clever solutions for living in extreme cold. Yet Arctic dwellers from Alaska to Siberia have noticed, within their lifetimes, significant changes in local climate. The major changes are:-
Temperature: Mean annual surface air temperature over the past 50 years has increased 3.6 to 5.4°F in Alaska and Siberia and decreased by 1.8°F over southern Greenland.
Sea ice: Sea ice extent in late summer decreased 15 to 20% over the past 30 years (see above).
Glaciers: Between 1961 and 1998, North American glaciers lost about 108 cubic miles of ice—about equivalent to spreading one foot of water over California, Arizona, Nevada, Utah, and Colorado.
Vegetation: White spruce, the most valuable timber species of the North American boreal forest, experienced sharp declines as summer temperatures frequently exceeded the tree's critical threshold temperature.
Marine Animals: Almost no seal pups, dependent on sea ice, survived in Canada's Gulf of St. Lawrence during the ice-free years of 1967, 1981, 2000, 2001, and 2002.
Fisheries: Warming in the Bering Sea after 1977 has increased the herring, Pacific cod, skates, and flatfish species, and Pacific salmon commercial catches have been high since 1980. | |
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