................................INTERESTING FACTS ABOUT CO2

Carbon dioxide (CO2) is a slightly toxic, odorless, colorless gas with a slightly pungent, acid taste. Carbon dioxide is a small but important constituent of air. It is a necessary raw material for most plants, which remove carbon dioxide from air using the process of photosynthesis.


Today’s atmosphere contains about 40% more carbon dioxide than at the start of the industrial era. This build-up of carbon dioxide and other greenhouse gases prevents heat from leaving the earth’s surface and the increase in greenhouse gases is expected to trigger a rise in temperature of 1.4 - 5.8¡C by 2100.


A typical concentration of CO2 in air is about 0.038% or 380 ppm. The concentration of atmospheric carbon dioxide rises and falls in a seasonal pattern over a range of about 6 ppmv. The concentration of CO2 in air has also been steadily increasing from year to year for over 60 years. The current rate of increase is about 2 ppm per year.


Worldwide, seven out of ten of the warmest years since 1860 occurred in the 1990s and 1998 was the warmest year on record. By the end of the 20th century, global temperatures were 0.6°C higher than 100 years ago. In central England, 1999 was the warmest year since 1659 and 1990 was the second warmest year. Analysis of tree rings, ice cores, corals and historical records indicate that the 1990s were the warmest decade of the last millennium.


Carbon dioxide is formed by combustion and by biological processes. These include decomposition of organic material, fermentation and digestion. As an example, exhaled air contains as much as 4% carbon dioxide, or about 100 times the amount of carbon dioxide which was breathed in.


Large quantities of CO2 are produced by lime kilns, which burn limestone (primarily calcium carbonate) to produce calcium oxide ( lime, used to make cement); and in the production of magnesium from dolomite (calcium magnesium carbonate). Other industrial activities which produce large amounts of carbon dioxide are ammonia production and hydrogen production from natural gas or other hydrocarbon raw materials.


The concentration of CO2 in air and in stack gases from simple combustion sources (heaters, boilers, furnaces) is not high enough to make carbon dioxide recovery commercially feasible. Producing carbon dioxide as a commercial product requires that it be recovered and purified from a relatively high-volume, CO2-rich gas stream, generally a stream which is created as an unavoidable byproduct of a large-scale chemical production process or some form of biological process.


In almost all cases, carbon dioxide which is captured and purified for commercial applications would be vented to the atmosphere at the production point if it was not recoved for transport and beneficial use at other locations.


The most common operations from which commercially-produced carbon dioxide is recovered are industrial plants which produce hydrogen or ammonia from natural gas, coal, or other hydrocarbon feedstock, and large-volume fermentation operations in which plant products are made into ethanol for human consumption, automotive fuel or industrial use. Breweries producing beer from various grain products are a traditional source. Corn-to-ethanol plants have been the most rapidly growing source of feed gas for CO2 recovery.


CO2-rich natural gas reservoirs found in underground formations found primarily in the western United States and in Canada are another source of recoverable carbon dioxide. CO2 from both natural and industrial sources is used to enhance production of oil from older wells by injecting the carbon dioxide into appropriate underground formations. Carbon dioxide is used in selectively, primarily in wells which will benefit not only from re-pressurization, but also from a reduction in viscosity of the oil in the reservoir caused by a portion of the CO2 dissolving in the oil. (The extent to which carbon dioxide will dissolve in the oil varies with the type of petroleum present in the reservoir. If the viscosity reduction effect will be minimal, nitrogen, which is usually less expensive, may be used as the pressurant instead.)


Carbon dioxide will not burn or support combustion. Air with a carbon dioxide content of more than 10% will extinguish an open flame, and, if breathed, can be life-threatening. Such concentrations may build up in silos, digestion chambers, wells, sewers and the like. Caution must be exercised when entering these types of confined spaces.


CO2 gas is 1.5 times as heavy as air, thus if released to the air it will concentrate at low elevations. Carbon dioxide will form "dry ice" at -78.5ºC (-109.3º F). One kg of dry ice has the cooling capacity of 2 kg of ordinary ice. Gaseous or liquid carbon dioxide, stored under pressure, will form dry ice through an auto-refrigeration process if rapidly depressured.


Carbon dioxide is commercially available as high pressure cylinder gas, relatively low pressure (about 300 psig or 20 barg) refrigerated liquid, or as dry ice. Large quantities are produced and consumed at industrial sites making fertilizers, plastics and rubber.


Carbon dioxide is a versatile material, being used in many processes and applications - each of which takes advantage of one or more these characteristics: reactivity, inertness and/ or coldness.


Carbon dioxide is commonly used as a raw material for production of various chemicals; as a working material in fire extinguishing systems; for carbonation of soft drinks; for freezing of food products such as poultry, meats, vegetables and fruit; for chilling of meats prior to grinding; for refrigeration and maintenance of ideal atmospheric conditions during transportation of food products to market; for enhancement of oil recovery from oil wells; and for treatment of alkaline water.


Stabilising greenhouse gas concentrations in the atmosphere at current levels requires emissions reductions of about 70% by the end of this century at the latest. Even if the Kyoto Protocol were ratified and fully implemented it could not moderate the expected warming trend of 1.4° C by 2050 by more than 0.05°C


Carbon sink activities may well develop into future carbon bombs once climate change reduces the ability of trees to survive in their current locations: A recent study on the implications of a doubling of carbon dioxide levels in the atmosphere concluded that forest dieback, mostly in boreal forest, could release 70 to 130 billion tones of additional carbon into the atmosphere. Another study found that such a carbon pulse triggered by warmer temperatures in the boreal region could release as much as 225 billion tonnes of carbon – almost one third of all the carbon now in the Earth’s atmosphere.




To offset the emissions of a power plant the size of Drax (3.75GW) in the UK would require the establishment of 1 million hectares (10,000 km2) of new tropical forest. To offset the UK’s total carbon dioxide emissions would require the planting of a new area of tropical forest about 1.5 times the size of the UK.



Biological diversity will be threatened by rapid climate change: Observations, models and experiments demonstrate that a sustained increase of just 1°C in the global average temperature would affect the functioning and composition of forests. The species that make up today's forests may not be able to survive in their current locations as local climate conditions change beyond their tolerance levels. This could result in a major impact on the species composition of one third of the world's forests. Entire forest ecosystems may disappear, other stresses caused by global warming include more insect outbreaks and fires. Because high latitudes are expected to warm more than equatorial ones, boreal forests will be more affected than temperate and tropical forests.


Forests are a major reservoir of carbon, containing some 80% of all carbon stored in land vegetation and about 40% of the carbon residing in soils. Large quantities of carbon may be released into the atmosphere during transition from one forest type to another as a result of global warming.


Fire suppression is in part responsible for the increase in biomass documented in many European temperate and boreal forests. While fire suppression may enhance sequestration in the short term, it can also create tinderbox conditions that increase the risk of fire and subsequent release of large amounts of CO2 into the atmosphere (for details on forest fire trends in boreal forests, see The Carbon Bomb, Greenpeace International, Sept 1994, available from www.greenpeace.org).


A study in Oregon found that a 450-year-old natural forest stored 2.2 to 2.3 times more carbon than a 60-year-old douglas fir plantation on a comparable site

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