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Global warming refers to the increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.

Global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the past century. The Intergovernmental Panel on Climate Change (IPCC) concludes, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations,"[1] which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes have probably had a small warming effect from pre-industrial times to 1950, but a small cooling effect since 1950.[2][3] These basic conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. The American Association of Petroleum Geologists is the only scientific society that rejects these conclusions.[4][5] A few individual scientists disagree with some of the main conclusions of the IPCC.[6]

Climate models referenced by the IPCC project that global surface temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100.[1] The range of values reflects the use of differing scenarios of future greenhouse gas emissions and results of models with differences in climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if greenhouse gas levels are stabilized.[1] This reflects the large heat capacity of the oceans.

An increase in global temperatures is expected to cause other changes, including sea level rise, increased intensity of extreme weather events, and changes in the amount and pattern of precipitation possibly resulting in more frequent floods and drought. Other effects include changes in agricultural yields, glacier retreat, species extinctions and increases in the ranges of disease vectors.

Remaining scientific uncertainties include the exact degree of climate change expected in the future, and how changes will vary from region to region around the globe. There is ongoing political and public debate on a world scale regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences. Most national governments have signed and ratified the Kyoto Protocol, aimed at reducing greenhouse gas emissions.

Contents [hide] 1 Terminology 2 Causes 2.1 Greenhouse gases in the atmosphere 2.2 Feedbacks 2.3 Solar variation 3 Temperature changes 3.1 Recent 3.2 Pre-human climate variations 4 Climate models 5 Attributed and expected effects 5.1 Economics 6 Adaptation and mitigation 7 Issue debate, political processes and laws 8 Related climatic issues 9 See also 10 References 11 Further reading 12 External links 12.1 Scientific 12.2 Educational 12.3 Other

Terminology The term "global warming" is a specific example of the broader term climate change, which can also refer to global cooling. In common usage the term refers to recent warming and implies a human influence.[7] The United Nations Framework Convention on Climate Change (UNFCCC) uses the term "climate change" for human-caused change, and "climate variability" for other changes.[8] The term "anthropogenic climate change" is sometimes used when focusing on human-induced changes.

Causes Carbon dioxide during the last 400,000 years and (inset above) the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.Main articles: Attribution of recent climate change and scientific opinion on climate change The climate system varies through natural, internal processes and in response to variations in external forcing factors including solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming remain an active field of research, but the scientific consensus[9] identifies increased levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available. Contrasting with the scientific consensus, other hypotheses have been proposed to explain most of the observed increase in global temperatures. One such hypothesis is that the warming is caused by natural fluctuations in the climate or that warming is mainly a result of variations in solar radiation.[10]

None of the effects of forcing are instantaneous. Due to the thermal inertia of the Earth's oceans and slow responses of other indirect effects, the Earth's current climate is not in equilibrium with the forcing imposed. Climate commitment studies indicate that even if greenhouse gases were stabilized at present day levels, a further warming of about 0.5 °C (0.9 °F) would still occur.[11]

Greenhouse gases in the atmosphere Main article: Greenhouse effect Recent increases in atmospheric carbon dioxide (CO2). The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring, and declines during the northern hemisphere growing season as plants remove some CO2 from the atmosphere.The greenhouse effect was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. It is the process by which absorption and emission of infrared radiation by atmospheric gases warms a planet's atmosphere and surface.

Greenhouse gases create a natural greenhouse effect, without which mean temperatures on Earth would be an estimated 30 °C (54 °F) lower so that Earth would be uninhabitable.[12] Thus scientists do not "believe in" or "oppose" the greenhouse effect as such; rather, the debate concerns the net effect of the addition of greenhouse gases, while allowing for associated positive and negative feedback mechanisms.

On Earth, the major natural greenhouse gases are water vapor, which causes about 36–70% of the greenhouse effect (not including clouds); carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone, which causes 3–7%.[13][14] Some other naturally occurring gases contribute very small fractions of the greenhouse effect; one of these, nitrous oxide (N2O), is increasing in concentration owing to human activity such as agriculture. The atmospheric concentrations of CO2 and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750. These levels are considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that CO2 values this high were last attained 20 million years ago.[15] "About three-quarters of the anthropogenic man-made emissions of CO2 to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation."[16]

The present atmospheric concentration of CO2 is about 383 parts per million (ppm) by volume.[17] Future CO2 levels are expected to rise due to ongoing burning of fossil fuels and land-use change. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios gives a wide range of future CO2 scenarios, ranging from 541 to 970 ppm by the year 2100.[18] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[19]

Positive (reinforce) feedback effects such as the expected release of CH4 from the melting of permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes) may lead to significant additional sources of greenhouse gas emissions[20] not included in climate models cited by the IPCC.[1]

Feedbacks Main article: Effects of global warming#Further global warming (positive feedback) The effects of forcing agents on the climate are complicated by various feedback processes.

One of the most pronounced feedback effects relates to the evaporation of water. In the case of warming by the addition of long-lived greenhouse gases such as CO2, the initial warming by these gases will cause more water to be evaporated into the atmosphere. Since water vapor itself acts as a greenhouse gas, this causes still more warming; the warming causes more water vapor to be evaporated, and so forth until a new dynamic equilibrium concentration of water vapor is reached with a much larger greenhouse effect than that due to CO2 alone. (Although this feedback process involves an increase in the absolute moisture content of the air, the relative humidity stays nearly constant or even decreases slightly because the air is warmer.)[21] This feedback effect can only be reversed slowly as CO2 has a long average atmospheric lifetime.

Feedback effects due to clouds are an area of ongoing research and debate. Seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect. Seen from above, the same clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Increased global water vapor concentration may or may not cause an increase in global average cloud cover. The net effect of clouds thus has not been well modeled, however, cloud feedback is second only to water vapor feedback and is positive in all the models that were used in the IPCC Fourth Assessment Report.[21]

Another important feedback process is ice-albedo feedback.[22] When global temperatures increase, ice near the poles melts at an increasing rate. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues.

Positive feedback due to release of CO2 and CH4 from thawing permafrost is an additional mechanism contributing to warming. Possible positive feedback due to CH4 release from melting seabed ices is a further mechanism to be considered.

The ocean's ability to sequester carbon is expected to decline as it warms, because the resulting low nutrient levels of the mesopelagic zone limits the growth of diatoms in favour of smaller phytoplankton that are poorer biological pumps of carbon.[23]

Solar variation Solar variation over the last 30 years.Main article: Solar variation Variations in solar output, possibly amplified by cloud feedbacks, may have contributed to recent warming.[24] A difference between this mechanism and greenhouse warming is that an increase in solar activity should produce a warming of the stratosphere while greenhouse warming should produce a cooling of the stratosphere. Reduction of stratospheric ozone also has a cooling influence but substantial ozone depletion did not occur until the late 1970s. Cooling in the lower stratosphere has been observed since at least 1960.[25] Thus, solar activity alone is not the main contributor to recent warming. Phenomena such as solar variation combined with volcanoes have probably had a warming effect from pre-industrial times to 1950, but a cooling effect since 1950.[1] However, some research has suggested that the Sun's contribution may have been underestimated. Two researchers at Duke University have estimated that the Sun may have contributed about 40–50% of the global surface temperature warming over the period 1900–2000, and about 25–35% between 1980 and 2000.[26] Stott and coauthors suggest that climate models overestimate the relative effect of greenhouse gases compared to solar forcing; they also suggest that the cooling effects of volcanic dust and sulfate aerosols have been underestimated.[27] Nevertheless, they conclude that even with an enhanced climate sensitivity to solar forcing, most of the warming during the latest decades is attributable to the increases in greenhouse gases.

In 2006, a team of scientists from the United States, Germany, and Switzerland presented results showing no net increase of brightness over the last thousand years. Solar cycles lead to a small increase of 0.07% in brightness over the last 30 years. This effect is far too minute to contribute significantly to global warming.[28][29] A 2007 paper by Lockwood and Fröhlich further confirms the lack of a correlation between solar output and global warming for the time since 1985.[30]

Temperature changes Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.Main article: Temperature record

Recent Global temperatures on both land and sea have increased by 0.75 °C (1.35 °F) relative to the period 1860–1900, according to the instrumental temperature record. This measured temperature increase is not significantly affected by the urban heat island. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[31] Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.

Sea temperatures increase more slowly than those on land both because of the larger effective heat capacity of the oceans and because the ocean can lose heat by evaporation more readily than the land [1]. Since the northern hemisphere has more land mass than the southern it warms faster; also there are extensive areas of seasonal snow cover subject to the snow-albedo feedback. Although more greenhouse gases are emitted in the northern than southern hemisphere this does not contribute to the asymmetry of warming as the major gases are essentially well-mixed between hemispheres.

Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree.[32] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[33][34]

Anthropogenic emissions of other pollutants—notably sulfate aerosols—can exert a cooling effect by increasing the reflection of incoming sunlight. This partially accounts for the cooling seen in the temperature record in the middle of the twentieth century,[35] though the cooling may also be due in part to natural variability.

Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation.[36] Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[37]

Pre-human climate variations Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume. Today's date is on the left side of the graph.Further information: Paleoclimatology See also: Snowball Earth Earth has experienced warming and cooling many times in the past. The recent Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles timed by orbital variations with interglacial warm periods comparable to present temperatures.[38]

A rapid buildup of greenhouse gases caused warming in the early Jurassic period (about 180 million years ago), with average temperatures rising by 5 °C (9 °F). Research by the Open University indicates that the warming caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, CO2 levels dropped back to normal over roughly the next 150,000 years.[39][40]

Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as a cause for other warming events in the distant past, including the Permian-Triassic extinction event (about 251 million years ago) and the Paleocene-Eocene Thermal Maximum (about 55 million years ago).

Climate models The projected temperature increase for a range of stabilization scenarios (the coloured bands). The black line in middle of the shaded area indicates 'best estimates'; the red and the blue lines the likely limits. From the work of IPCC AR4, 2007. Calculations of global warming prepared in or before 2001 from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions. The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. In this figure, the globally averaged warming corresponds to 3.0 °C (5.4 °F).Main article: Global climate model Scientists have studied global warming with computer models of the climate. These models are based on physical principles of fluid dynamics, radiative transfer, and other processes, with some simplifications being necessary because of limitations in computer power. These models predict that the net effect of adding greenhouse gases is to produce a warmer climate. However, even when the same assumptions of fossil fuel consumption and CO2 emission are used, the amount of projected warming varies between models and there still remains a considerable range of climate sensitivity.

Including uncertainties in future greenhouse gas concentrations and climate modelling, the IPCC anticipates a warming of 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) between 1990 and 2100.[1] Models have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human derived causes.

Climate models can produce a good match to observations of global temperature changes over the last century, but cannot yet simulate all aspects of climate.[41] These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions.

Most global climate models, when run to project future climate, are forced by imposed greenhouse gas scenarios, generally one from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may be run by adding a simulation of the carbon cycle; this generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO2). Some observational studies also show a positive feedback.[42][43][44]

The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[45] There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability.

Attributed and expected effects Main article: Effects of global warming Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to the WGMS and the NSIDC.Though it is difficult to connect specific weather events to global warming, an increase in global temperatures may in turn cause other changes, including glacial retreat and worldwide sea level rise. Changes in the amount and pattern of precipitation may result in flooding and drought. There may also be changes in the frequency and intensity of extreme weather events. Other effects may include changes in agricultural yields, reduced summer streamflows, species extinctions and increases in the range of disease vectors.

Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, increased intensity and frequency of extreme weather events, are being attributed in part to global warming.[46] While changes are expected for overall patterns, intensity, and frequencies, it is difficult to attribute specific events to global warming. Other expected effects include water scarcity in some regions and increased precipitation in others, changes in mountain snowpack, adverse health effects from warmer temperatures.

Increasing deaths, displacements, and economic losses projected due to extreme weather attributed to global warming may be exacerbated by growing population densities in affected areas, although temperate regions are projected to experience some minor benefits, such as fewer deaths due to cold exposure.[47] A summary of probable effects and recent understanding can be found in the report made for the IPCC Third Assessment Report by Working Group II.[46] The newer IPCC Fourth Assessment Report summary reports that there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since about 1970, in correlation with the increase in sea surface temperature, but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations. The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.[1]

Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to 2.5 ft) between 1990 and 2100,[48] repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events, lowering of ocean pH, and the spread of diseases such as malaria and dengue fever. One study predicts 18% to 35% of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections.[49] Two populations of Bay checkerspot butterfly are being threatened by changes in precipitation, though few mechanistic studies have documented extinctions due to recent climate change.[50]

Economics Main articles: Economics of global warming and Low-carbon economy Some economists have tried to estimate the aggregate net economic costs of damages from climate change across the globe. Such estimates have so far failed to reach conclusive findings; in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon (tC) (US$-3 per tonne of carbon dioxide) up to US$350/tC (US$95 per tonne of carbon dioxide), with a mean of US$43 per tonne of carbon (US$12 per tonne of carbon dioxide).[47] One widely-publicized report on potential economic impact is the Stern Review; it suggests that extreme weather might reduce global gross domestic product by up to 1%, and that in a worst case scenario global per capita consumption could fall 20%.[51] The report's methodology, advocacy and conclusions have been criticized by many economists, primarily around the Review's assumptions of discounting and its choices of scenarios,[52] while others have supported the general attempt to quantify economic risk, even if not the specific numbers.[53][54]

In a summary of economic cost associated with climate change, the United Nations Environment Programme emphasizes the risks to insurers, reinsurers, and banks of increasingly traumatic and costly weather events. Other economic sectors likely to face difficulties related to climate change include agriculture and transport. Developing countries, rather than the developed world, are at greatest economic risk.[55]

Adaptation and mitigation Main articles: Adaptation to global warming, Mitigation of global warming, and Kyoto Protocol The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming or adjust to it. Many environmental groups encourage action against global warming, often by the consumer, but also by community and regional organizations. There has been business action on climate change, including efforts at increased energy efficiency and (still limited) moves to alternative fuels. One important innovation has been the development of greenhouse gas emissions trading through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances.

The world's primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the United Nations Framework Convention on Climate Change (UNFCCC), negotiated in 1997. The Protocol now covers more than 160 countries globally and over 55% of global greenhouse gas emissions.[56] The United States (historically the world's largest greenhouse gas emitter), Australia, and Kazakhstan have not ratified the treaty. China (which is expected to soon overtake the US in greenhouse gas emissions) and India have ratified the treaty, but as developing countries, are exempt from its provisions. Chinese Premier Wen Jiabao has called on the nation to redouble its efforts to tackle pollution and global warming.[57]

This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.[58]

The world's primary body for crafting a response is the Intergovernmental Panel on Climate Change (IPCC), a UN-sponsored activity which holds periodic meetings between national delegations on the problems of global warming, and issues working papers and assessments on the current status of the science of climate change, impacts, and mitigation. It convenes four different working groups examining various specific issues. For example, in May 2007, the IPCC held conferences in Bonn, Germany,[59] and in Bangkok, Thailand.[60]

In the absence of clear concerted action by the US Federal government, various state, local, and regional governments have begun their own initiatives to indicate support and compliance with the Kyoto Protocol, on a local basis. For example, the Regional Greenhouse Gas Initiative (RGGI),[61] is a state-level emissions capping and trading program, which was founded on January 18, 2007 and is comprised of eight Northeastern US states.

Issue debate, political processes and laws Main articles: Global warming controversy and politics of global warming Increased awareness of the scientific findings surrounding global warming has resulted in political and economic debate. Poor regions, particularly Africa, appear at greatest risk from the suggested effects of global warming, while their actual emissions have been negligible compared to the developed world.[62] At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and have been used as part of its justification for continued non-ratification.[63] In the Western world, the idea of human influence on climate and efforts to combat it has gained wider acceptance in Europe than in the United States.[64][65]

Fossil fuel organizations and companies such as American Petroleum Institute and ExxonMobil, represented by Philip Cooney, and some think tanks such as the Competitive Enterprise Institute and the Cato Institute have campaigned to downplay the risks of climate change,[66][67] while environmental groups and entertainers have launched campaigns emphasizing the risks. Recently, some fossil fuel companies have scaled back such efforts[68] or called for policies to reduce global warming.[69]

This issue has sparked debate in the U.S. about the benefits of limiting industrial emissions of greenhouse gases to reduce impacts to the climate, versus the effects on economic activity and also about the politic manipulation of scientific testimonies and reports.[70][71]

There has also been discussion in several countries about the cost of adopting alternate, cleaner energy sources in order to reduce emissions.[72]

Another point of debate is the degree to which newly-developed economies, like India and China, should be expected to constrain their emissions and change to renewable energies. China's CO2 emissions (mainly from coal power plants and cars), are expected to exceed those of the U.S. within the next few years (and according to one report may have already done so[73]). China has contended that it has less obligation to reduce emissions, since its emissions per capita are about one-fifth those of the U.S.; the U.S. contends that if they must bear the costs of reducing emissions, so should China.[74] India will also soon be one of the biggest sources of industrial emissions, and has made assertions similar to China's on this issue.[75]

Related climatic issues Main articles: Ocean acidification, global dimming, and ozone depletion A variety of issues are often raised in relation to global warming. One is ocean acidification. Increased atmospheric CO2 increases the amount of CO2 dissolved in the oceans.[76] CO2 dissolved in the ocean reacts with water to form carbonic acid resulting in acidification. Ocean surface pH is estimated to have decreased from approximately 8.25 to 8.14 since the beginning of the industrial era,[77] and it is estimated that it will drop by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO2.[1][78] Since organisms and ecosystems are adapted to a narrow range of pH, this raises extinction concerns, directly driven by increased atmospheric CO2, that could disrupt food webs and impact human societies that depend on marine ecosystem services.[79]

Another related issue that may have partially mitigated global warming in the late twentieth century is global dimming, the gradual reduction in the amount of global direct irradiance at the Earth's surface. From 1960 to 1990 human-caused aerosols likely precipitated this effect. Scientists have stated with 66–90% confidence that the effects of human-caused aerosols, along with volcanic activity, have offset some of global warming, and that greenhouse gases would have resulted in more warming than observed if not for these dimming agents.[1]

Ozone depletion, the steady decline in the total amount of ozone in Earth's stratosphere, is frequently cited in relation to global warming. Although there are areas of linkage, the relationship between the two is not strong. ????????????????????????? What does the greenhouse effect have to do with global warming?

The "greenhouse effect" refers to the natural phenomenon that keeps the Earth in a temperature range that allows life to flourish. The sun's enormous energy warms the Earth's surface and its atmosphere. As this energy radiates back toward space as heat, a portion is absorbed by a delicate balance of heat-trapping gases in the atmosphere—among them carbon dioxide and methane—which creates an insulating layer. With the temperature control of the greenhouse effect, the Earth has an average surface temperature of 59°F (15°C). Without it, the average surface temperature would be 0°F (-18°C), a temperature so low that the Earth would be frozen and could not sustain life.

"Global warming" refers to the rise in the Earth's temperature resulting from an increase in heat-trapping gases in the atmosphere.

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What is causing global warming?

offsite General emissions information Past emissions trends Emissions trends in the United States International emissions trends Scientists have concluded that human activities are contributing to global warming by adding large amounts of heat-trapping gases to the atmosphere. Our fossil fuel use is the main source of these gases. Every time we drive a car, use electricity from coal-fired power plants, or heat our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the air. The second most important source of greenhouse gases is deforestation, mainly in the tropics, and other land-use changes.

Since pre-industrial times, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, atmospheric methane has risen by 151 percent, mostly from agricultural activities like growing rice and raising cattle.

As the concentration of these gases grows, more heat is trapped by the atmosphere and less escapes back into space. This increase in trapped heat changes the climate, causing altered weather patterns that can bring unusually intense precipitation or dry spells and more severe storms.

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What is the best source of scientific information on global warming?

IPCC Highlights-Climate Science IPCC Backgrounder

offsite Intergovernmental Panel on    Climate Change

In 1988, the United Nations Environment Programme and the World Meteorological Organization set up the Intergovernmental Panel on Climate Change (IPCC) to examine the most current scientific information on global warming and climate change. More than 1,250 authors and 2,500 scientific experts reviewers from more than 130 countries contributed to the panel's most recent report, Climate Change 2007: The Fourth Assessment Report (the full report will be released in November 2007). These scientists reviewed all the published and peer-reviewed scientific information produced during the previous few years to assess what is known about the global climate, why and how it changes, what it will mean for people and the environment, and what can be done about it.

The IPCC Fourth Assessment Report is the most comprehensive and up-to-date evaluation of global warming. As the new benchmark, it serves as the basis for international climate negotiations.

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Is global warming already happening?

offsite Observed Climate Variability and Change Impacts, Adaptation, and Vulnerability to Climate Change Yes. The IPCC concluded in its Third Assessment Report, "An increasing body of observations gives a collective picture of a warming world and other changes in the climate system." The kinds of changes already observed that create this consistent picture include the following:

Examples of observed climatic changes

Increase in global average surface temperature of about 1°F in the 20th century

Decrease of snow cover and sea ice extent and the retreat of mountain glaciers in the latter half of the 20th century

Rise in global average sea level and the increase in ocean water temperatures

Likely increase in average precipitation over the middle and high latitudes of the Northern Hemisphere, and over tropical land areas

Increase in the frequency of extreme precipitation events in some regions of the world Examples of observed physical and ecological changes

Thawing of permafrost

Lengthening of the growing season in middle and high latitudes

Poleward and upward shift of plant and animal ranges

Decline of some plant and animal species

Earlier flowering of trees

Earlier emergence of insects

Earlier egg-laying in birds back to top

Are humans contributing to global warming?

offsite Climate Change 2001: The Scientific- Basis - Policymaker Summary (pdf) In 1995, the world's climate experts in the IPCC concluded for the first time in a cautious consensus, "The balance of evidence suggests that there is a discernible human influence on the global climate."

In its 2001 assessment, the IPCC strengthened that conclusion considerably, saying, "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities."

Scientists have found significant evidence that leads to this conclusion:

The observed warming over the past 100 years is unlikely to be due to natural causes alone; it was unusual even in the context of the last 1,000 years.

There are better techniques to detect climatic changes and attribute them to different causes.

Simulations of the climate's response to natural causes (sun, volcanoes, etc.) over the latter half of the 20th century alone cannot explain the observed trends.

Most simulation models that take into account greenhouse gas emissions and sulphate aerosols (which have a cooling effect) are consistent with observations over the last 50 years. back to top

How much warmer is the Earth likely to become?

offsite View past global temperature trends View U.S. and global climatic trends Latest IPCC (WG I) projections

The IPCC's Third Assessment Report projects that the Earth's average surface temperature will increase between 2.5° and 10.4°F (1.4°-5.8°C) between 1990 and 2100 if no major efforts are undertaken to reduce the emissions of greenhouse gases (the "business-as-usual" scenario). This is significantly higher than what the Panel predicted in 1995 (1.8°-6.3°F, or 1.0°-3.5°C), mostly because scientists expect a reduced cooling effect from tiny particles (aerosols) in the atmosphere.

Scientists predict that even if we stopped emitting heat-trapping gases immediately, the climate would not stabilize for many decades because the gases we have already released into the atmosphere will stay there for years or even centuries. So while the warming may be lower or increase at a slower rate than predicted if we reduce emissions significantly, global temperatures cannot quickly return to today's averages. And the faster and more the Earth warms, the greater the chances are for some irreversible climate changes.

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Would a temperature rise of a couple degrees really change the global climate?

offsite Potential impacts on the U.S.  Worldwide early warning signs An increase of a few degrees won't simply make for pleasantly warmer temperatures around the globe. Even a modest rise of 2°- 3°F (1.1°-1.7°C) could have dramatic effects. In the last 10,000 years, the Earth's average temperature hasn't varied by more than 1.8°F (1.0°C). Temperatures only 5°-9°F cooler than those today prevailed at the end of the last Ice Age, in which the Northeast United States was covered by more than 3,000 feet of ice.

Scientists predict that continued global warming on the order of 2.5°-10.4°F over the next 100 years (as projected in the IPCC's Third Assessment Report) is likely to result in:

a rise in sea level between 3.5 and 34.6 in. (9-88 cm), leading to more coastal erosion, flooding during storms, and permanent inundation

severe stress on many forests, wetlands, alpine regions, and other natural ecosystems

greater threats to human health as mosquitoes and other disease-carrying insects and rodents spread diseases over larger geographical regions

disruption of agriculture in some parts of the world due to increased temperature, water stress, and sea-level rise in low-lying areas such as Bangladesh or the Mississippi River delta. back to top

Is global warming connected to the hole in the ozone layer?

NASA image -- Ozone layer hole Global warming and ozone depletion are two separate but related threats. Global warming and the greenhouse effect refer to the warming of the lower part of the atmosphere (also known as the troposphere) due to increasing concentrations of heat-trapping gases. By contrast, the ozone hole refers to the loss of ozone in the upper part of the atmosphere, called the stratosphere. This is of serious concern because stratospheric ozone blocks incoming ultraviolet radiation from the sun, some of which is harmful to plants, animals, and humans.

The two problems are related in a number of ways, including:

Some human-made gases, called chlorofluorocarbons, trap heat and destroy the ozone layer. Currently, these gases are responsible for less than 10 percent of total atmospheric warming, far less than the contribution from the main greenhouse gas, carbon dioxide.

The ozone layer traps heat, so if it gets destroyed, the upper atmosphere actually cools, thereby offsetting part of the warming effect of other heat-trapping gases. But that's no reason to rejoice: the cooling of the upper layers of the atmosphere can produce changes in the climate that affect weather patterns in the higher latitudes.

Trapping heat in the lower part of the atmosphere allows less heat to escape into space and leads to cooling of the upper part of the atmosphere. The colder it gets, the greater the destruction of the protective ozone layer.

offsite Kyoto Protocol (greenhouse gases) Montreal Protocol (ozone) Reducing ozone-depleting gases is crucial to preventing further destruction of the ozone layer, but eliminating these gases alone will not solve the global warming problem. On the other hand, efforts to reduce all types of emissions to limit global warming will also be good for the recovery of the ozone layer.

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Is there anything we can do about global warming?

in global environment Personal global warming solutions The role of forests in protecting climate

on UCS website Clean vehicles program Clean energy program offsite Fuel-efficient cars Energy-efficient products Green-e Renewable Energy Program Yes! The most important action we can take to slow global warming is to reduce emissions of heat-trapping gases. Governments, individuals, and businesses can all help.

Governments can adopt a range of options for reducing greenhouse gas emissions, including

increasing energy efficiency standards

encouraging the use of renewable energy sources (such as wind and solar power)

eliminating subsidies that encourage the use of coal and oil by making them artificially cheap

protecting and restoring forests, which serve as important storehouses of carbon Individuals can reduce the need for fossil fuels and often save money by

driving less and driving more fuel-efficient and less-polluting cars

using energy-efficient appliances

insulating homes

using less electricity in general Businesses can increase efficiency and save substantial sums by doing the same things on a larger scale. And utilities can avoid building expensive new power plants by encouraging and helping customers to adopt efficiency measures.

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Will responding to global warming be harmful to our economy?

in publications Clean Energy Blueprint Drilling in Detroit Common Sense on Climate Change

offsite Economics of climate change

Reducing our impact on the global climate does not have to hurt the world's economies. The answer depends much on the "how" and "when."

The challenge is to strike a balance between responding early enough to avoid major negative (costly) impacts, and responding some time later in order to avoid taking big, expensive steps now which then may turn out to be unnecessary or inappropriate. This type of challenge is typical in business and industry; decision-making under uncertainty is the daily bread of most managers.

Clearly, global warming still involves many unknowns, but the remaining uncertainties in our scientific understanding no longer warrant a "wait and see" stance. Science tells us with increasing certainty that we are in for a serious long-term problem that will affect all of us.

And there is much we can do now that makes sense in terms of the economic bottom line while helping to reduce our impact on the global climate and on our local environment and health. The United States and other developed countries should seize the opportunity to take the lead in developing new, clean, energy-efficient technologies, and help developing countries take a greener path to economic prosperity. All of this can be done in a cost-effective manner, while creating jobs and new business opportunities.

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Explaining Global Warming -- What's Ozone Got To Do With It?

Frameworks research has identified several obstacles that limit people's understanding of, and willingness to do anything about, climate change. These researchers found that the general public has difficulty distinguishing between ozone depletion and climate change: When asked to describe global warming, people often responded that it is a problem with a hole in the ozone layer. The public also thinks that there is a causal link between the ozone hole and the planet warming up. This short summary explains the confusions experienced by the general public, offers suggestions for improving the public's understanding, and shows how scientists can help people adjust their mental frames about climate change.

Linking Mental Models

Misperception: "More of the sun's radiation (or heat) gets in through the ozone hole, and that's why it's warming up down here."

Many people interviewed for the Frameworks research connected what they understood about the "ozone hole" to help them understand global warming by simply using their mental model of ozone depletion as a starting point to grapple with the causes of climate change. This type of thinking—which may seem odd to experts who understand the ozone and climate change issues clearly—is a typical mechanism employed in all learning: we extend existing mental models to make sense of new information.

Misperception: "There are these heat-trapping gases that cause a hole in the ozone layer..."

The second type of confusion also inappropriately links two different mental models: the gases that destroy the ozone layer are the same as those that trap heat and cause global warming. That is, of course, partially true-chlorofluorocarbons (CFCs) and ozone itself are heat-trapping gases. But this understanding misses the primary heat-trapping gases—CO2, methane, and nitrous oxide—and therefore fails to identify the pervasive human activities underlying human-driven climate change. (Note: N2O both traps heat and reacts to form NO in the stratosphere, which leads to catalytic destruction of ozone in all but the lowest portions of the stratosphere. So, it, too, performs a dual role in both problems.)

Background

Global warming and ozone depletion are two separate but related environmental threats. Global warming and the greenhouse effect refer to the warming of the atmosphere (mostly in the lower part, also known as the troposphere) due to increasing concentrations of heat-trapping gases. By contrast, the ozone hole refers to the loss of ozone in a higher part of the atmosphere, known as the stratosphere. Ozone loss is a serious concern because stratospheric ozone blocks incoming ultraviolet radiation from the sun, some of which is harmful to plants, animals and humans.

Over the past few years, scientific inquiry has revealed a complex set of mutual interactions between these two problems, making it ever more understandable that the general public is confused about the two issues: (1) the upper-atmospheric ozone depletion contributes to shifts in climate patterns, (2) lower-atmospheric ozone formation contributes to the warming effect, and (3) the emission of certain gases and resulting climate changes lead to cooling of the stratosphere, i.e., precisely to the conditions that enhance the depletion of the ozone layer.

Because most people have no or little background in basic atmospheric science, however, it may be helpful, should questions about the ozone-climate change link arise, to precede more specific details with an overview of the layered structure of the atmosphere. This will help people understand that most of the gases that make up our atmosphere—including those that make up the heat-trapping "blanket"—are actually located in the lower-most portion of the atmosphere, the troposphere, while the ozone layer is within the layer above, the stratosphere (see graphic). Weather dynamics occur in the troposphere under the strong influence of Earth's surface and to a lesser extent under the influence of the dynamics in the stratosphere.

Figure from Lutgens and Tarbuck's The Atmosphere, 2001

The following bullets spell out the interactive relationship between ozone and climate change in some more detail.

Some human-made gases, called chlorofluorocarbons (or CFCs), trap heat and destroy the ozone layer. Currently, these gases are responsible for less than 10 percent of total atmospheric warming—far less than the contribution from the main heat-trapping gas, carbon dioxide. [Since the Montreal Protocol, which regulates the emission of ozone-depleting substances, the use of CFCs is being phased out.]

Some of the gases used to replace ozone-destroying chemicals are highly potent, if shorter-lived heat-trapping gases—HCFCs, still affecting ozone and thus considered only a temporary replacement, and HFCs. These substances will remain in the atmosphere for years or, a few of them, for decades. Thus, they resolve one problem but add at least to some extent to another. [Note: Because HFCs are powerful heat-trapping substances, the Kyoto Protocol includes them in the "basket" of regulated gases.]

Ozone itself is a heat-trapping gas, so it adds to warming wherever it is found, albeit the mechanisms differ. Near the ground, ozone is formed from air pollutants and traps heat. In the stratosphere, ozone heats the surrounding air when it is photo-dissociated by solar ultraviolet photons, but cools the surrounding air when it radiates infrared energy to space. The heating effect, which occurs only in daylight, is more effective than the cooling effect, which occurs day and night.

As the higher atmospheric (stratospheric) ozone layer gets destroyed, there is less photo-dissociative warming, and hence a cooling of the stratosphere. [Note: increases in methane and water vapor add to the cooling of the stratosphere.] This offsets part of the overall warming effect produced by other heat-trapping gases in the rest of the atmosphere. The resulting lower overall warming may be misleading, however, as it does not imply no or only little climate change. Rather, the cooling of higher layers of the atmosphere can produce changes in weather (wind) patterns in the higher latitudes. Thus, the chemical changes in the different layers of the atmosphere lead to dynamic changes that can have global and regional consequences for the climate.

The colder the stratosphere gets, the greater the destruction of the protective ozone layer, or, differently put, the slower the recovery of the ozone layer. Reducing ozone-depleting gases is crucial to prevent further destruction of the ozone layer, but eliminating these gases alone will not solve the global warming problem. On the other hand, efforts to reduce all types of emissions to limit global warming will also be good for the recovery of the ozone layer.

And while you're at it... ...Clear up a related confusion: "good" and "bad" ozone

Confusion: Given the problem of ozone depletion, how come we get ozone alerts, meaning high levels of ozone?

You may want to help people distinguish between the two primary "ozone problems."

A simple way to distinguish between the two is to label them with qualifiers that connect to human health impacts. Stratospheric ("upper air") ozone is "good ozone" or "protective ozone" in that it shields us from ultraviolet radiation, which can cause eye and skin damage in humans, impact the immune system, damage crops and destroy phytoplankton in the oceans, the basis of the marine food web.

While ground-level ozone also protects us from the sun's ultraviolet radiation, this benefit is overwhelmed by its contribution to air pollution. Ground-level ozone is "bad ozone" or "destructive ozone" because as an air pollutant in the air we breathe, it contributes to smog and damages lung tissue, especially in the young, old, and in people with heart and lung problems. Bad ozone also causes damage to plants, crops, and plankton in the ocean, and reacts with other air pollutants that are damaging lung, eye and throat irritants.

Episodes of elevated ozone concentrations near the ground occur particularly on hot days. Thus the prospects of global warming suggest that the conditions for ozone alerts will be met more frequently, especially during the summer in urban and coastal areas, but even in rural areas. The fact that global warming will likely worsen existing air pollution and related health problems is yet another reason why many people confuse the two issues.

The Explaining Mechanism

Interestingly, Frameworks research also shows that the general public has a much better grasp of the mechanism of ozone depletion than of the causes of climate change. The "simplifying model" used to explain stratospheric ozone depletion—i.e., the hole in the ozone layerihelped explain that abstract scientific issue to the average person. As a result, many Americans understand the problem of a thinning ozone layer as being akin to a hole in Earth's roof, and were thus motivated to take political action to fix the hole. Frameworks claims that ozone depletion is an example of a complicated scientific issue that was framed well and suggest that a similar technique could work to improve the public's understanding of climate change and what it will take to solve the problem.

Further information:

Overview of ozone and the atmosphere (including the evolution of the atmosphere, ozone layer formation and destruction, and the structure of the atmosphere) http://daac.gsfc.nasa.gov/

Connections between climate change and ozone depletion http://www.ndsc.ncep.noaa.gov/climchng.html

Other misconceptions about climate change and ozone depletion: http://www.gcrio.org/gwcc/misconceptions.html (note, this is slightly dated; scientists now see a number of connections between the two models; see first link)

Climate change may become major cause of ozone loss http://www.gsfc.nasa.gov/topstory/20020422greengas.html

The effect of climate change on ozone depletion http://www.msc-smc.ec.gc.ca/education/arcticozone/change_e.cfm

Ozone recovery delayed by global warming http://www.giss.nasa.gov/gpol/abstracts/1998/ShindellRindL.html

Kirk-Davidoff et al., 1999. "The effect of climate change on ozone depletion through changes in stratospheric water vapour." Nature, 402, 25 November, pp. 399-401.

This science primer was written by former UCS Staff Scientist Susanne Moser and reviewed by Dr. Mario Molina, Massachusetts Institute of Technology, and Dr. Charles Kolb, Aerodyne Research Inc. This document cannot be reprinted or reposted to electronic networks without permission and acknowledgement. AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA From Wikipedia, the free encyclopedia Jump to: navigation, search Ozone

General Systematic name Trioxygen Molecular formula O3 Molar mass 47.998 g·mol-1 Appearance bluish colored gas CAS number [10028-15-6] Properties Density and phase 2.144 g·L-1 (0 °C), gas Solubility in water 0.105 g·100mL-1 (0 °C) Melting point 80.7 K, -192.5 °C Boiling point 161.3 K, -111.9 °C Thermodynamic data Standard enthalpy of formation ?fH°solid +142.3 kJ·mol-1 Standard molar entropy S°solid 237.7 J·K-1.mol-1 Hazards EU classification not listed NFPA 704 Supplementary data page Structure and properties n, er, etc. Thermodynamic data Phase behaviour Solid, liquid, gas Spectral data UV, IR, NMR, MS Regulatory data Flash point, RTECS number, etc. Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references For other uses, see Ozone (disambiguation). Ozone (O3) is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic species O2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals. Ozone in the upper atmosphere filters potentially damaging ultraviolet light from reaching the Earth's surface. It is present in low concentrations throughout the Earth's atmosphere. It has many industrial and consumer applications. Ozone therapy is a controversial alternative medicine practice; mainstream scientific medicine has found ozone to be harmful to humans, and equipment intended to be used for ozone therapy is banned in the United States.[1]

Ozone, the first allotrope of a chemical element to be described by science, was discovered by Christian Friedrich Schönbein in 1840, who named it after the Greek word for smell (ozein), from the peculiar odor in lightning storms.[2] The odor from a lightning strike is from ions produced during the rapid chemical changes, not the ozone itself.[3]

Contents [hide] 1 Physical properties 2 Structure 3 Chemistry 4 Ozone in Earth's atmosphere 4.1 Ozone layer 4.2 Low level ozone 4.2.1 Ozone as a greenhouse gas 5 Ozone and health 5.1 Ozone in air pollution 5.2 Physiology of ozone 6 Production techniques 6.1 Corona discharge method 6.2 Ultraviolet light 6.3 Cold plasma 6.4 Special considerations 6.5 Incidental production 6.6 Laboratory production 7 Applications 7.1 Industrial applications 7.2 Consumer applications 7.3 Ozone therapy 8 See also 9 Notes and references 10 External links

[edit] Physical properties Undiluted ozone is a pale blue gas at standard temperature and pressure; it forms a dark blue liquid below -112 °C and a violet-black solid below -193 °C.[4] At concentrations found in the atmosphere it is colorless.[5] The concentration above which it can be smelled (odor threshold) is between 0.0076 and 0.036 ppm.[6] It is said to smell faintly of geraniums.

[edit] Structure The structure of ozone, according to experimental evidence from microwave spectroscopy, is bent, with C2v symmetry (similar to the water molecule), O – O distance of 127.2 pm and O – O – O angle of 116.78°.[7] The central atom forms an sp2 hybridization with one lone pair. Ozone is a polar molecule with a dipole moment of 0.5337 D.[8] The bonding is single bond on one side and double bond on the other side, and these bonds are blended to become known as resonance structures. The bond order is 1.5 for each side.

[edit] Chemistry Ozone is a powerful oxidizing agent. It is also unstable at high concentrations, decaying to ordinary diatomic oxygen (in about half an hour in atmospheric conditions[9]):

2 O3 ? 3 O2. This reaction proceeds more rapidly with increasing temperature and decreasing pressure. Ozone will oxidize metals (except gold, platinum, and iridium) to oxides of the metals in their highest oxidation state:

2 Cu2+(aq) + 2 H3O+(aq) + O3(g) ? 2 Cu3+(aq) + 3 H2O(l) + O2(g) Ozone also increases the oxidation number of oxides:

NO + O3 ? NO2 + O2 The above reaction is accompanied by chemiluminescence. The NO2 can be further oxidized:

NO2 + O3 ? NO3 + O2 The NO3 formed can react with NO2 to form N2O5:

NO2 + NO3 ? N2O5 Ozone reacts with carbon to form carbon dioxide, even at room temperature:

C + 2 O3 ? CO2 + 2 O2 Ozone does not react with ammonium salts but it reacts with ammonia to form ammonium nitrate:

2 NH3 + 4 O3 ? NH4NO3 + 4 O2 + H2O Ozone reacts with sulfides to make sulfates:

PbS + 4 O3 ? PbSO4 + 4 O2 Sulfuric acid can be produced from ozone, either starting from elemental sulfur or from sulfur dioxide:

S + H2O + O3 ? H2SO4 3 SO2 + 3 H2O + O3 ? 3 H2SO4 All three atoms of ozone may also react, as in the reaction with tin(II) chloride and hydrochloric acid:

3 SnCl2 + 6 HCl + O3 ? 3 SnCl4 + 3 H2O In the gas phase, ozone reacts with hydrogen sulfide to form sulfur dioxide:

H2S + O3 ? SO2 + H2O In an aqueous solution, however, two competing simultaneous reactions occur, one to produce elemental sulfur, and one to produce sulfuric acid:

H2S + O3 ? S + O2 + H2O 3 H2S + 4 O3 ? 3 H2SO4 Iodine perchlorate can be made by treating iodine dissolved in cold anhydrous perchloric acid with ozone:

I2 + 6 HClO4 + O3 ? 2 I(ClO4)3 + 3 H2O Solid nitryl perchlorate can be made from NO2, ClO2, and O3 gases:

2 NO2 + 2 ClO2 + 2 O3 ? 2 NO2ClO4 + O2 Ozone can be used for combustion reactions and combusting gases in ozone provides higher temperatures than combusting in dioxygen (O2). Following is a reaction for the combustion of carbon subnitride:

3 C4N2 + 4 O3 ? 12 CO + 3 N2 Ozone can react at cryogenic temperatures. At 77 K (-196 °C), atomic hydrogen reacts with liquid ozone to form a hydrogen superoxide radical, which dimerizes:[10]

H + O3 ? HO2 + O 2 HO2 ? H2O4 Ozonides can be formed, which contain the ozonide anion, O3-. These compounds are explosive and must be stored at cryogenic temperatures. Ozonides for all the alkali metals are known. KO3, RbO3, and CsO3 can be prepared from their respective superoxides:

KO2 + O3 ? KO3 + O2 Although KO3 can be formed as above, it can also be formed from potassium hydroxide and ozone:[11]

2 KOH + 5 O3 ? 2 KO3 + 5 O2 + H2O NaO3 and LiO3 must be prepared by action of CsO3 in liquid NH3 on an ion exchange resin containing Na+ or Li+ ions:[12]

CsO3 + Na+ ? Cs+ + NaO3 Treatment with ozone of calcium dissolved in ammonia leads to ammonium ozonide and not calcium ozonide:[13]

3 Ca + 10 NH3 + 6 O3 ? Ca•6NH3 + Ca(OH)2 + Ca(NO3)2 + 2 NH4O3 + 2 O2 + H2 Ozone can be used to remove manganese from the water, forming a precipitate which can be filtered:

2 Mn2+ + 2 O3 + 4 H2O ? 2 MnO(OH)2 (s) + 2 O2 + 4 H+ Ozone will also turn cyanides to the one thousand times less toxic cyanates:

CN- + O3 ? CNO- + O2 Finally, ozone will also completely decompose urea:[14]

(NH2)2CO + O3 ? N2 + CO2 + 2 H2O

[edit] Ozone in Earth's atmosphere The distribution of atmospheric ozone in partial pressure as a function of altitude. Concentration of ozone as measured by the Nimbus-7 satellite. Total ozone concentration in June 2000 as measured by EP-TOMS satellite instrument.The standard way to express total ozone levels (the volume of ozone in a vertical column) in the atmosphere is by using Dobson units. Concentrations at a point are measured in parts per billion (ppb) or in µg/m³.

[edit] Ozone layer Main article: Ozone layer The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer between about 10 km and 50 km above the surface (or between 6.21 and 31.1 miles). Here it filters out the shorter wavelengths (less than 320 nm) of ultraviolet light (270 to 400 nm) from the Sun that would be harmful to most forms of life in large doses. These same wavelengths are also among those responsible for the production of vitamin D, which is essential for human health. Ozone in the stratosphere is mostly produced from ultraviolet rays reacting with oxygen:

O2 + (radiation < 240 nm) ? 2 O O + O2 ? O3 It is destroyed by the reaction with atomic oxygen:

O3 + O ? 2 O2 (See Ozone-oxygen cycle for more detail.)

The latter reaction is catalysed by the presence of certain free radicals, of which the most important are hydroxyl (OH), nitric oxide (NO) and atomic chlorine (Cl) and bromine (Br). In recent decades the amount of ozone in the stratosphere has been declining mostly due to emissions of CFCs and similar chlorinated and brominated organic molecules, which have increased the concentration of ozone-depleting catalysts above the natural background. See ozone depletion for more information.

[edit] Low level ozone Main articles: Tropospheric ozone and Photochemical smog Low level ozone (or tropospheric ozone) is regarded as a pollutant by the World Health Organization.[15] It is not emitted directly by car engines or by industrial operations. It is formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides that react to form ozone directly at the source of the pollution or many kilometers down wind. For more details of the complex chemical reactions that produce low level ozone see tropospheric ozone.

Ozone reacts directly with some hydrocarbons such as aldehydes and thus begins their removal from the air, but the products are themselves key components of smog. Ozone photolysis by UV light leads to production of the hydroxyl radical and this plays a part in the removal of hydrocarbons from the air, but is also the first step in the creation of components of smog such as peroxyacyl nitrates which can be powerful eye irritants. The atmospheric lifetime of tropospheric ozone is about 22 days and its main removal mechanisms are being deposited to the ground, the above mentioned reaction giving OH, and by reactions with OH and the peroxy radical HO2· (Stevenson et al, 2006).[16]

As well as having an impact on human health (see below) there is also evidence of significant reduction in agricultural yields due to increased ground-level ozone and pollution which interferes with photosynthesis and stunts overall growth of some plant species.[17][18]

[edit] Ozone as a greenhouse gas Although ozone was present at ground level before the industrial revolution, peak concentrations are far higher than the pre-industrial levels and even background concentrations well away from sources of pollution are substantially higher.[19][20] This increase in ozone is of further concern as ozone present in the upper troposphere acts as a greenhouse gas, absorbing some of the infrared energy emitted by the earth. Quantifying the greenhouse gas potency of ozone is difficult as it is not present in uniform concentrations across the globe. However, the most recent scientific review on the climate change (the IPCC Third Assessment Report[21]) suggests that the radiative forcing of tropospheric ozone is about 25% that of carbon dioxide.

[edit] Ozone and health

[edit] Ozone in air pollution There is a great deal of evidence to show that high concentrations (ppm) of ozone, created by high concentrations of pollution and daylight UV rays at the earth's surface, can harm lung function and irritate the respiratory system.[15][22] A connection has also been shown to exist between increased ozone caused by thunderstorms and hospital admissions of asthma sufferers.[23] Air quality guidelines such as those from the World Health Organization are based on detailed studies of what levels can cause measurable health effects.

A common British folk myth dating back to the Victorian era holds that the smell of the sea is caused by ozone, and that this smell has "bracing" health-giving effects.[24] Neither of these is true. The characteristic "smell of the sea" is not caused by ozone, but by the presence of dimethyl sulfide generated by phytoplankton, and dimethyl sulfide, like ozone, is toxic in high concentrations.[25]

The U.S. Environmental Protection Agency has developed an Air Quality index to help explain air pollution levels to the general public. 8-hour average ozone concentrations of 85 to 104 ppbv are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy".[26] The EPA has designated over 300 counties of the United States, clustered around the most heavily populated areas (especially in California and the Northeast), as failing to comply with the National Ambient Air Quality Standards.

[edit] Physiology of ozone Ozone, along with reactive forms of oxygen such as superoxide, singlet oxygen (see oxygen), hydrogen peroxide, and hypochlorite ions, is naturally produced by white blood cells and other biological systems (such as the roots of marigolds) as a means of destroying foreign bodies. Ozone reacts directly with organic double bonds. Also, when ozone breaks down to dioxygen it gives rise to oxygen free radicals, which are highly reactive and capable of damaging many organic molecules. Ozone has been found to convert cholesterol in the blood stream to plaque (which causes hardening and narrowing of arteries). Moreover, it is believed that the powerful oxidizing properties of ozone may be a contributing factor of inflammation. The cause-and-effect relationship of how the ozone is created in the body and what it does is still under consideration and still subject to various interpretations, since other body chemical processes can trigger some of the same reactions. A team headed by Dr. Paul Wentworth Jr. of the Department of Chemistry at the Scripps Research Institute has shown evidence linking the antibody-catalyzed water-oxidation pathway of the human immune response to the production of ozone. In this system, ozone is produced by antibody-catalyzed production of trioxidane from water and neutrophil-produced singlet oxygen.[27] See also trioxidane for more on this biological ozone-producing reaction.

Ozone has also been proven to form specific, cholesterol-derived metabolites that are thought to facilitate the build-up and pathogenesis of atherosclerotic plaques (a form of heart disease). These metabolites have been confirmed as naturally occurring in human atherosclerotic arteries and are categorized into a class of secosterols termed “Atheronals”, generated by ozonolysis of cholesterol's double bond to form a 5,6 secosterol as well as a secondary condensation product via aldolization.[28]

[edit] Production techniques Information in this article or section has not been verified against sources and may not be reliable. Please check for inaccuracies and modify as needed, citing the sources against which it was checked. This article has been tagged since July 2007. Ozone used in industry is measured in g/Nm3 or weight percent. The regime of applied concentrations ranges from 1 to 5 weight percent in air and from 6 to 13 weight percent in oxygen.

Ozone generators currently on the market generate ozone molecules by employing one of the methods below.

[edit] Corona discharge method This is the most popular type of ozone generator for most industrial and personal uses. While variations of the "hot spark" coronal discharge method of ozone production exist, including medical grade and industrial grade ozone generators, these units usually work by means of a corona discharge tube. They are typically very cost-effective, and do not require an oxygen source other than the ambient air. However, they also produce nitrogen oxides as a by-product. Use of an air dryer can reduce or eliminate nitric acid formation by removing water vapor and increase ozone production. Use of an oxygen concentrator can further increase the ozone production and further reduce the risk of nitric acid formation due to removing not only the water vapor, but also the bulk of the nitrogen.

[edit] Ultraviolet light UV ozone generators work by employing a light source that generates the same narrow-band ultraviolet light that is responsible for the sustenance of the ozone layer in the stratosphere of the Earth (via the bombardment of the Earth's atmosphere by the sun's radiation). While standard UV ozone generators tend to be less expensive, they usually produce ozone with a concentration of about 2% or lower. Another disadvantage of this method is that it requires the air to be exposed to the UV source for a longer amount of time, and any air that is not exposed to the UV source will not be treated. This makes UV generators impractical for use in situations that deal with rapidly moving air or water streams (in-duct air sterilization, for example).

[edit] Cold plasma In the cold plasma method, pure oxygen gas is exposed to a plasma created by dielectric barrier discharge. The diatomic oxygen is split into single atoms, which then recombine in triplets to form ozone.

Cold plasma machines utilize pure oxygen as the input source, and produce a maximum concentration of about 5% ozone. They produce far greater quantities of ozone in a given space of time compared to ultraviolet production. However, because cold plasma ozone generators are very expensive, and still require occasional maintenance, they are found less frequently than the previous two types.

The discharges manifest as filamentary transfer of electrons (micro discharges) in a gap between two electrodes. In order to evenly distribute the micro discharges, a dielectric insulator must be used to separate the metallic electrodes and to prevent arcing.

Some cold plasma units also have the capability of producing short-lived allotropes of oxygen which include O4, O5, O6, O7, etc. These anions are even more reactive than ordinary O3.

[edit] Special considerations Ozone cannot be stored and transported like other industrial gases (because it quickly decays into diatomic oxygen) and must therefore be produced on site. Available ozone generators vary in the arrangement and design of the high-voltage electrodes. At production capacities higher than 20kg per hour, a gas/water tube heat-exchanger is utilized as ground electrode and assembled with tubular high-voltage electrodes on the gas-side. The regime of typical gas pressures is around 2 bar absolute in oxygen and 3 bar absolute in air. Several megawatts of electrical power may be installed in large facilities, applied as one phase AC current at 600 to 2000 Hz and peak voltages between 3000 and 20000 volts.

The dominating parameter influencing ozone generation efficiency is the gas temperature, which is controlled by the cooling water temperature. The cooler the water, the better the ozone synthesis. At typical industrial conditions, almost 90 percent of the effective power is dissipated as heat and needs to be removed by a sufficient cooling water flow.

Due to the high reactivity of ozone, only few materials may be used like stainless steel (quality 316L), glass, polytetrafluorethylene, or polyvinylidene fluoride. Viton may be used with the restriction of constant mechanical forces and absence of humidity.

[edit] Incidental production Ozone may be formed from O2 by electrical discharges and by action of high energy electromagnetic radiation. Certain electrical equipment generate significant levels of ozone. This is especially true of devices using high voltages, such as ionic air purifiers, laser printers, photocopiers, and arc welders. Electric motors using brushes can generate ozone from repeated sparking inside the unit. Large motors that use brushes, such as those used by elevators or hydraulic pumps, will generate more ozone than smaller motors.

[edit] Laboratory production In the laboratory ozone can be produced by electrolysis using a 9 volt battery, a pencil graphite rod cathode, a platinum wire anode and a 3M sulfuric acid electrolyte.[29] The half cell reactions taking place are

3 H2O ? O3 + 6 H+ + 6 e-; ?Eo = -1.53 V; 6 H+ + 6 e- ? 3 H2; ?Eo = 0 V; 2 H2O ? O2 + 4 H+ + 4 e-; ?Eo = -1.23 V; so that in the net reaction three equivalents of water are converted into one equivalent of ozone and three equivalents of hydrogen. Oxygen formation is a competing reaction.