02-06-2012, 04:02 PM
Greenhouse Effect And Carbon Dioxide Capture Technique
Greenhouse Effect And Carbon Dioxide Capture Technique.doc (Size: 249.5 KB / Downloads: 44)
Global Warming is the increase in the average temperature of the earth’s near surface air and oceans since the mid-twentieth century and its projected continuation. The anthropogenic greenhouse gases are responsible for such a temperature rise and solar variations and volcanoes has a small warming effect. A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C colder than at present
In order, the most abundant greenhouse gases in Earth's atmosphere are:
• water vapor
• carbon dioxide
• methane
• nitrous oxide
• ozone
• chlorofluorocarbons
When these gases are ranked by their contribution to the greenhouse effect, the most important are:
Gas
Formula
Contribution
(%)
Water Vapor H2O 36 – 72 %
Carbon Dioxide CO2 9 – 26 %
Methane CH4 4 – 9 %
Ozone O3 3 – 7 %
The major non-gas contributor to the Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the greenhouse gases.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential but is only present in very small quantities.
Atmospheric absorption and scattering at different electromagnetic wavelengths. The largest absorption band of carbon dioxide is in the infrared.
The increasing concentrations of greenhouse gases in the atmosphere are causing an unprecedented rise in global temperatures, with potentially harmful consequences for the environment and human health. Although contributing to many other physical and chemical reactions, the major atmospheric constituents, nitrogen (N2), oxygen (O2), and argon (Ar), are not greenhouse gases. This is because molecules containing two atoms of the same element such as N2 and O2 and monatomic molecules such as have no net change in their dipole moment when they vibrate and hence are almost totally unaffected by infrared light. Late 19th century scientists experimentally discovered that N2 and O2 do not absorb infrared radiation (called, at that time, "dark radiation") while, at the contrary, water, as true vapour or condensed in the form of microscopic droplets suspended in clouds, CO2 and other poly-atomic gaseous molecules do absorb infrared radiation. It was recognized in the early 20th century that the greenhouse gases in the atmosphere caused the Earth's overall temperature to be higher than it would be without them.
Natural and anthropogenic sources
The 2007 Fourth Assessment Report compiled by the IPCC (AR4) noted that "changes in atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the climate system", and concluded that "increases in anthropogenic greenhouse gas concentrations is very likely to have caused most of the increases in global average temperatures since the mid-20th century".
Gas Preindustrial level Current level Increase since 1750 Radiative(W/m2)
Carbon dioxide
280 ppm 388 ppm 108 ppm 1.46
Methane
700 ppb 1745 ppb 1045 ppb 0.48
Nitrous oxide
270 ppb 314 ppb 44 ppb 0.15
CFC-12
0 533 ppt 533 ppt 0.17
Ice cores provide evidence for variation in greenhouse gas concentrations over the past 800,000 years. Both CO2 and CH4 vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature. Direct data does not exist for periods earlier than those represented in the ice core record, a record which indicates CO2 levels staying within a range of between 180ppm and 280ppm throughout the last 800,000 years, until the increase of the last 250 years. Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing which raised the CO2 concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.
Since about 1750 human activity has increased the concentration of carbon dioxide and other greenhouse gases. Measured atmospheric concentrations of carbon dioxide are currently 100 ppm higher than pre-industrial levels. Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity but over periods longer than a few years natural sources are closely balanced by natural sinks, mainly photosynthesis of carbon compounds by plants and marine plankton. As a result of this balance, the atmospheric concentration of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era.
It is likely that anthropogenic warming, such as that due to elevated greenhouse gas levels, has had a discernible influence on many physical and biological systems. Warming is projected to affect various issues such as freshwater resources, industry, food and health.
The main sources of greenhouse gases due to human activity are:
• burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations in the air. Land use change (mainly deforestation in the tropics) account for up to one third of total anthropogenic CO2 emissions. livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.
• use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
• agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N2O) concentrations.
CO2 and global warming
CO2 is a heat-trapping greenhouse gas The scientific consensus is that human-induced greenhouse gas emissions are the primary cause of global warming, and that carbon dioxide is the most important of these gases. Worldwide, 27 billion tonnes of carbon dioxide are produced by human activity annually. The physical effect of CO2 in the atmosphere can be measured as a change in the Earth-atmosphere system's energy balance – the radiative forcing of CO2 Carbon taxes are one of the policies available to governments to reduce GHG emissions.
Kyoto Protocol- It is an international agreement setting targets for industrialised countries to cut their greenhouse gas emissions. These gases are considered at least partly responsible for global warming
Carbon sequestration
Carbon sequestration is 'The process of removing carbon from the atmosphere and depositing it in a reservoir. When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering. The term carbon sequestration may also be used to refer to the process of carbon capture and storage, where CO2 is removed from flue gases, such as on power stations, before being stored in underground reservoirs. The term may also refer to natural biogeochemical cycling of carbon between the atmosphere and reservoirs, such as by chemical weathering of rocks.
Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon to either mitigate or defer global warming. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels. Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes..
CO2 may be captured as a pure by-product in processes related to petroleum refining or from flue gases from power generation. CO2 sequestration includes the storage part of carbon capture and storage, which refers to large-scale, permanent artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks.
Agriculture
Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon, more than the amount in vegetation and the atmosphere.
Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of 2010 carbon dioxide emissions annually
Carbon emission reduction methods in agriculture can be grouped into two categories: reducing and/or displacing emissions and enhancing carbon removal. Some of these reductions involve increasing the efficiency of farm operations (i.e. more fuel-efficient equipment) while some involve interruptions in the natural carbon cycle. Also, some effective techniques (such as the elimination of stubble burning) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning).
Reducing Emissions
Increasing yields and efficiency generally reduces emissions as well, since more food results from the same or less effort. Techniques include more accurate use of fertilizers, less soil disturbance, better irrigation, and crop strains bred for locally beneficial traits and increased yields.
Replacing more energy intensive farming operations can also reduce emissions. Reduced or no-till farming requires less machine use and burns correspondingly less fuel per acre. However, no-till usually increases use of weed-control chemicals and the residue now left on the soil surface is more likely to release its CO2 to the atmosphere as it decays, reducing the net carbon reduction
Enhancing Carbon Removal
All crops absorb CO2 during growth and release it after harvest. The goal of agricultural carbon removal is to use the crop and its relation to the carbon cycle to permanently sequester carbon within the soil. This is done by selecting farming methods that return biomass to the soil and enhance the conditions in which the carbon within the plants will be reduced to its elemental nature and stored in a stable state. Methods for accomplishing this include:
• Use cover crops such as grasses and weeds as temporary cover between planting seasons
• Concentrate livestock in small paddocks for days at a time so they graze lightly but evenly. This encourages roots to grow deeper into the soil. Stock also till the soil with their hooves, grinding old grass and manures into the soil.
• Cover bare paddocks with hay or dead vegetation. This protects soil from the sun and allows the soil to hold more water and be more attractive to carbon-capturing microbes. Restore degraded land, which slows carbon release while returning the land to agriculture or other use.
Ocean-related
Iron fertilization
Ocean iron fertilization is an example of such a geoengineering technique. Iron fertilization attempts to encourage phytoplankton growth, which removes carbon from the atmosphere for at least a period of time. This technique is controversial due to limited understanding its complete effects on the marine ecosystem including side effects and possibly large deviations from expected behavior. Such effects potentially include release of nitrogen oxides, and disruption of the ocean's nutrient balance.