global warming?

Question

stuffs on global warming.causes,effects,solutions....

Answer 1

Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades.

The Earth's average near-surface atmospheric temperature rose 0.6 ± 0.2 °Celsius (1.1 ± 0.4 °Fahrenheit) in the 20th century. The prevailing scientific opinion on climate change is that "most of the warming observed over the last 50 years is attributable to human activities" [1].

The increased amounts of carbon dioxide (CO2) and other greenhouse gases (GHGs) are the primary causes of the human-induced component of warming. They are released by the burning of fossil fuels, land clearing and agriculture, etc. and lead to an increase in the greenhouse effect.

The measure of the response to increased GHGs, and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational [2] and model studies. This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO2 in the atmosphere. The current literature estimates sensitivity in the range 1.5–4.5 °C (2.7–8.1 °F). Models referenced by the Intergovernmental Panel on Climate Change (IPCC) project that global temperatures may increase by between 1.4 and 5.8 °C (2.5 to 10.5 °F) between 1990 and 2100. The uncertainty in this range results from both the difficulty of estimating the volume of future greenhouse gas emissions and uncertainty about climate sensitivity.

An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of precipitation. These changes may increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences include higher or lower agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors. Warming is expected to affect the number and magnitude of these events; however, it is difficult to connect particular events to global warming. Although most studies focus on the period up to 2100, warming (and sea level rise due to thermal expansion) is expected to continue past then, since CO2 has an estimated 50 to 200 year long average atmospheric lifetime [3].

Only a small minority of climate scientists discount the role that humanity's actions have played in recent warming. However, the uncertainty is more significant regarding how much climate change should be expected in the future, and there is a hotly contested political and public debate over what, if anything, should be done to reduce or reverse future warming, and how to deal with the predicted consequences.

The term 'global warming' is a specific case of the more general term 'climate change' (which can also refer to 'global cooling', such as occurs during ice ages). In principle, 'global warming' is neutral as to the causes, but in common usage, 'global warming' generally implies a human influence. However, the UNFCCC uses 'climate change' for human-caused change, and 'climate variability' for other changes [1]. Some organizations use the term 'anthropogenic climate change' for human-induced changes.

Contents [hide]
1 Historical warming of the Earth
2 Causes
2.1 Greenhouse gases in the atmosphere
2.2 Alternative theories
2.2.1 Solar variation theory
3 Predicted effects
3.1 Effects on ecosystems
3.2 Impact on glaciers
3.3 Miniature Rock Glaciers
3.4 Destabilization of ocean currents
3.5 Environmental refugees
3.6 Spread of disease
3.7 Financial effects
3.8 Biomass production
3.9 Opening up of the Northwest Passage in summer
4 Responses
5 Climate models
6 Other related issues
6.1 Relationship to ozone depletion
6.2 Relationship to global dimming
6.3 Pre-human global warming
7 References
8 See also
9 External links
9.1 Scientific
9.2 Polar ice-related links
9.3 Other



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Historical warming of the Earth
See also: Temperature record of the past 1000 years

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.Relative to the period 1860–1900, global temperatures on both land and sea have increased by 0.75 °C (1.4 °F), according to the instrumental temperature record. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C/decade against 0.13 °C/decade (Smith, 2005). Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C per decade since 1979, according to satellite temperature measurements. Over the one or two thousand years before 1850, world temperature is believed to have been relatively stable, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.

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 Celsius. Similar estimates prepared by the World Meteorological Organization and the UK Climatic Research Unit concluded that 2005 was still only the second warmest year, behind 1998 [4][2].

Depending on the time frame, a number of temperature records are available. These are based on different data sets, with different degrees of precision and reliability. An approximately global instrumental temperature record begins in about 1860; contamination from the urban heat island effect is believed to be small and well controlled for. A longer-term perspective is available from various proxy records for recent millennia; see temperature record of the past 1000 years for a discussion of these records and their differences. The attribution of recent climate change is clearest for the most recent period of the last 50 years, for which the most detailed data are available. Satellite temperature measurements of the tropospheric temperature date from 1979.

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Causes
Main articles: Attribution of recent climate change and Scientific opinion on climate change

Carbon dioxide during the last 400,000 years and 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.The climate system varies both through natural, "internal" processes as well as in response to variations in external "forcing" from both human and non-human causes, including solar activity, volcanic emissions, and greenhouse gases. Climatologists agree that the earth has warmed recently. The detailed causes of this change remain an active field of research, but the scientific consensus identifies greenhouse gases as the primary cause of the recent warming. This conclusion can be controversial, especially outside the scientific community.

Adding carbon dioxide (CO2) or methane (CH4) to Earth's atmosphere, with no other changes, will make the planet's surface warmer; greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 30 °C (54 °F) lower, and the Earth uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the theory that adding carbon dioxide or methane to the Earth's atmosphere will, absent any mitigating actions or effects, result in warmer surface temperatures on Earth. Rather, the debate is about what the net effect of the addition of carbon dioxide and methane will be, when allowing for compounding or mitigating factors.

One example of an important feedback process is ice-albedo feedback. The increased CO2 in the atmosphere warms the Earth's surface and leads to melting of ice near the poles. As the ice melts, land or open water takes its place. Both land and open water are less reflective than ice, and so absorb more solar radiation. This causes more warming, which in turn causes more melting, and the cycle continues.

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 by increased greenhouse gases. Climate commitment studies indicate that, even if greenhouse gases were stabilized at present day levels, a further warming of perhaps 0.5 °C to 1.0 °C (0.9–1.8 °F) would still occur.

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Greenhouse gases in the atmosphere

Plots of atmospheric Carbon dioxide and global temperature during the last 750,000 yearsGreenhouse gases are transparent to shortwave radiation from the sun. However, they absorb some of the longer infrared radiation emitted as black body radiation from the Earth, making it more difficult for the Earth to cool. How much they warm the world by is shown in their global warming potential. The atmospheric concentrations of carbon dioxide and methane have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is 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 carbon dioxide values this high were last attained 40 million years ago. About three-quarters of the anthropogenic (man-made) emissions of carbon dioxide to the atmosphere during the past 20 years is due to fossil fuel burning. The rest of the anthropogenic emissions is predominantly due to land-use change, especially deforestation [3].

The longest continuous instrumental measurement of carbon dioxide mixing ratios began in 1958 at Mauna Loa. Since then, the annually averaged value has increased monotonically by approximately 21% from the initial reading of 315 ppmv, as shown by the Keeling curve, to over 380 ppmv in 2006 [4] [5]. The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend, with the maximum reached during the northern hemisphere's late spring (the growing season in the northern hemisphere temporarily removes some CO2 from the atmosphere).

Methane, the primary constituent of natural gas, enters the atmosphere both from biological production and leaks from natural gas pipelines and other infrastructure. Some biological sources are natural, such as termites, but others have been increased or created by agricultural activities, such as the cultivation of rice paddies [6]. Recent evidence suggests that forests may also be a source (RC; BBC), and if so this would be an additional contribution to the natural greenhouse effect, and not to the anthropogenic greenhouse effect (Ealert).

Future carbon dioxide levels are expected to continue rising due to ongoing fossil fuel usage, though the actual trajectory will depend on uncertain economic, sociological, technological, and natural developments. The IPCC Special Report on Emissions Scenarios gives a wide range of future carbon dioxide scenarios [7], ranging from 541 to 970 parts per million by the year 2100. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal and tar sands are extensively used.


Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.Globally, the majority of anthropogenic greenhouse gas emissions arise from fuel combustion. The remainder is accounted for largely by "fugitive fuel" (fuel consumed in the production and transport of fuel), emissions from industrial processes (excluding fuel combustion), and agriculture: these contributed 5.8%, 5.2% and 3.3% respectively in 1990. Current figures are broadly comparable.[8] Around 17% of emissions are accounted for by the combustion of fuel for the generation of electricity. A small percentage of emissions come from natural and anthropogenic biological sources, with approximately 6.3% derived from agriculturally produced methane and nitrous oxide.

Positive feedback effects, such as the expected release of methane 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. [9]. Note that the anthropogenic emissions of other pollutants—notably sulfate aerosols—exert a cooling effect; this partially accounts for the plateau/cooling seen in the temperature record in the middle of the twentieth century [10], though this may also be due to intervening natural cycles.

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Alternative theories
Various alternative hypotheses have been proposed to explain the observed increase in global temperatures, including but not limited to:

The warming is within the range of natural variation.
The warming is a consequence of coming out of a prior cool period — the Little Ice Age.
The warming is primarily a result of variances in solar irradiance.[5]
However, the strong scientific support for man-made global warming implies that such alternative opinions are not widely held. In the journal Science, an essay by Naomi Oreskes considered the abstracts of all 928 scientific articles in the ISI citation database identified with the keyword "global climate change". Dr. Oreskes concluded that none of these abstracts attempt to refute the position that man-made emissions of greenhouse gases are a substantial contributor to recent warming. [11] [12]

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Solar variation theory

30 years of solar variabilityMain article: Solar variation theory
Modeling studies reported in the IPCC Third Assessment Report (TAR) did not find that changes in solar forcing were needed in order to explain the climate record for the last four or five decades [13]. These studies found that volcanic and solar forcings may account for half of the temperature variations prior to 1950, but the net effect of such natural forcings has been roughly neutral since then [14]. In particular, the change in climate forcing from greenhouse gases since 1750 was estimated to be eight times larger than the change in forcing due to increasing solar activity over the same period [15].

Since the TAR, some studies (Lean et al., 2002, Wang et al., 2005) have suggested that changes in irradiance since pre-industrial times are less by a factor of 3 to 4 than in the reconstructions used in the TAR (e.g. Hoyt and Schatten, 1993, Lean, 2000.). Other researchers (e.g. Stott et al. 2003 [16]) believe that the impact of solar forcing is being underestimated and propose that solar forcing accounts for 16% or 36% of recent greenhouse warming. Others (e.g. Marsh and Svensmark 2000 [17]) have proposed that feedback from clouds or other processes enhance the direct effect of solar variation, which if true would also suggest that the impact of solar variability was being underestimated. In general the level of scientific understanding of the contribution of variations in solar irradiance to historical climate changes is "very low" [18].

The present level of solar activity is historically high. Solanki et al. (2004) suggest that solar activity for the last 60 to 70 years may be at its highest level in 8,000 years; Muscheler et al. disagree, suggesting that other comparably high levels of activity have occurred several times in the last few thousand years [19]. Solanki concluded based on their analysis that there is a 92% probability that solar activity will decrease over the next 50 years. In addition, researchers at Duke University (2005) have found that 10–30% of the warming over the last two decades may be due to increased solar output [20].

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Predicted effects
Main article: Effects of global warming
The predicted effects of global warming are many and various, both for the environment and for human life. These effects include sea level rise, impacts on agriculture, reductions in the ozone layer, increased intensity and frequency of extreme weather events, and the spread of disease. In some cases, the effects may already be manifest, although it is difficult to attribute specific natural phenomena to long-term global warming. In particular, the relationship between global warming and hurricanes is still being debated. [6][21] A draft statement by the World Meteorological Organization acknowledges the differing viewpoints on this issue [22].

The extent and likelihood of these consequences is a matter of considerable controversy. A summary of possible effects and recent understanding can be found in the report of the IPCC Working Group II [23]. Some scientists believe global warming is already causing death and disease across the world through flooding, environmental destruction, heat waves and other extreme weather events. (Reuters, February 9, 2006; archived)

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Effects on ecosystems
Both primary and secondary effects of global warming — such as higher temperatures, lessened snow cover, rising sea levels, and weather changes — may influence not only human activities but also ecosystems. Some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Similarly, changes in timing of life patterns, such as annual migration dates, may alter regional predator-prey balance. The effect of advanced spring arrival dates in Scandinavia of birds that overwinter in subsaharan Africa has been ascribed to evolutionary adaptation of the species to climactic warming [24].

Ocean pH is lowering as a result of increased carbon dioxide levels. Lowering of ocean pH along with changing water temperature and ocean depth will have a direct impact on coral reefs.

Another suggested mechanism whereby a warming trend may be amplified involves the thawing of tundra, which can release significant amounts of the potent greenhouse gas methane that is trapped in permafrost and ice clathrate compounds [25].

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Impact on glaciers

Global glacial mass balance in the last fifty years, reported to the WGMS and the NSIDC. The increased downward trend in the late 1980s is symptomatic of the increased rate and number of retreating glaciers.Global warming has led to negative glacier mass balance, causing glacier retreat around the world. Oerlemans (2005) showed a net decline in 142 of the 144 mountain glaciers with records from 1900 to 1980. Since 1980 global glacier retreat has increased significantly. Similarly, Dyurgerov and Meier (2005) averaged glacier data across large scale regions (e.g. Europe) and found that every region had a net decline from 1960 to 2002, though a few local regions (e.g. Scandinavia) have shown increases. Some glaciers that are in disequilibrium with present climate have already disappeared [26] and increasing temperatures are expected to cause continued retreat in the majority of alpine glaciers around the world. Upwards of 90% of glaciers reported to the World Glacier Monitoring Service have retreated since 1995 [27].

Of particular concern is the potential for failure of the Hindu Kush and Himalayan glacial melts. The melt of these glaciers is a large and reliable source of water for China, India, and much of Asia, and these waters form a principal dry-season water source. Increased melting would cause greater flow for several decades, after which "some areas of the most populated region on Earth are likely to 'run out of water'" (T. P. Barnett, J. C. Adam and D. P. Lettenmaier 2005) [28]

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Miniature Rock Glaciers
Rock glaciers - a cache of ice under a pile of boulders - are among other water signs such as drying meadows and warning lakes that scientists are studying in the Sierra's in the western United States[29]. Connie Miller searches for the rock glaciers in the Yosemite area of the Sierra crest. She hypothesizes that rock glaciers will be predictors of how ecosystems change with rising temperatures. Miller is leading an effort (the Consortium for Integrated Climate Research in Western Mountains[30])to co-ordinate the work of many scientists to see how the pieces of the Global Warming puzzle may fit.

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Destabilization of ocean currents
Main article: Shutdown of thermohaline circulation
There is also some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would affect in particular areas like Scandinavia and Britain that are warmed by the North Atlantic drift.

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Environmental refugees

The termini of the glaciers in the Bhutan-Himalaya. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. According to USGS researchers, glaciers in the Himalaya are wasting at alarming and accelerating rates, as indicated by comparisons of satellite and historic data, and as shown by the widespread, rapid growth of lakes on the glacier surfaces. The researchers have found a strong correlation between increasing temperatures and glacier retreat.Even a relatively small rise in sea level would make some densely settled coastal plains uninhabitable and create a significant refugee problem. If the sea level were to rise in excess of 4 meters (13 ft) almost every coastal city in the world would be severely affected, with the potential for major impacts on world-wide trade and economy. Presently, the IPCC predicts sea level rise of less than 1 meter (3 ft) through 2100, but they also warn that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea level many meters over the next millennia. It is estimated that around 200 million people could be affected by sea level rise, especially in Vietnam, Bangladesh, China, India, Thailand, Philippines, Indonesia and Egypt.

An example of the ambiguous nature of environmental refugees is the emigration from the island nation of Tuvalu, which has an average elevation of approximately one meter above sea level. Tuvalu already has an ad hoc agreement with New Zealand to allow phased relocation [31] and many residents have been leaving the islands. However, it is far from clear that rising sea levels from global warming are a substantial factor - best estimates are that sea level has been rising there at approximately 1–2 millimeters per year (~1/16th in/yr), but that shorter timescale factors—ENSO, or tides—have far larger temporary effects [32] [33] [34] [35].

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Spread of disease
One of the largest known outbreaks of Vibrio parahaemolyticus gastroenteritis has been attributed to generally rising ocean temperature where infected oysters were harvested in Prince William Sound, Alaska in 2005. Before this, the northernmost reported risk of such infection was in British Columbia, 1000 km to the south (McLaughlin JB, et al.).

Global warming may extend the range of vectors conveying infectious diseases such as malaria. A warmer environment boosts the reproduction rate of mosquitos and the number of blood meals they take, prolongs their breeding season, and shortens the maturation period for the microbes they disperse[36]. Global warming has been implicated in the recent spread to the north Mediterranean region of bluetongue disease in domesticated ruminants associated with mite bites (Purse, 2005). Hantavirus infection, Crimean-Congo hemorrhagic fever, tularemia and rabies increased in wide areas of Russia during 2004–2005. This was associated with a population explosion of rodents and their predators but may be partially blamed on breakdowns in governmental vaccination and rodent control programs.[37] Similarly, despite the disappearance of malaria in most temperate regions, the indigenous mosquitos that transmitted it were never eliminated and remain common in some areas. Thus, although temperature is important in the transmission dynamics of malaria, many other factors are influential [38].

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Financial effects
Financial institutions, including the world's two largest insurance companies, Munich Re and Swiss Re, warned in a 2002 study (UNEP summary) that "the increasing frequency of severe climatic events, coupled with social trends" could cost almost US$150 billion each year in the next decade. These costs would, through increased costs related to insurance and disaster relief, burden customers, tax payers, and industry alike.

According to the Association of British Insurers, limiting carbon emissions could avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s. According to Choi and Fisher (2003) each 1% increase in annual precipitation could enlarge catastrophe loss by as much as 2.8%.

The United Nations' Environmental Program recently announced that severe weather around the world has made 2005 the most costly year on record [39], although there is "no way to prove that [a given hurricane] either was, or was not, affected by global warming" [40]. Preliminary estimates presented by the German insurance foundation Munich Re put the economic losses at more than US$200 billion, with insured losses running at more than US$70 billion.

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Biomass production
The creation of biomass by plants is influenced by the availability of water, nutrients, and carbon dioxide. Part of this biomass is used (directly or indirectly) as the energy source for nearly all other life forms, including feed-stock for domestic animals, and fruits and grains for human consumption. It also includes timber for construction purposes.

A rise in atmospheric carbon dioxide can increase the efficiency of the metabolism of most plants, potentially allowing them to create more biomass.[citation needed] A rising temperature can also increase the growing season in colder regions. It is sometimes argued that these effects can create a greener, richer planet, with more available biomass. However, there are many other factors involved, and it is currently unclear if plants benefiting from global warming is a realistic scenario. Plant growth can be limited by a number of factors, including soil fertility, water, temperature, and carbon dioxide concentration.

IPCC models currently predict a possible modest increase in plant productivity; however there are several negative impacts: decreases in productivity may occur at above-optimal temperatures; greater variation in temperature is likely to decrease wheat yields; in experiments, grain and forage quality declines if CO2 and higher temperature are increased; and the reductions in soil moisture in summer, which are likely to occur, would have a negative impact on productivity.[41]

Satellite data shows that the productivity of the northern hemisphere has indeed increased from 1982 to 1991 [42]. However, more recent studies [43],[44] found that from 1991 to 2002, wide-spread droughts had actually caused a decrease in summer photosynthesis in the mid and high latitudes of the northern hemisphere.


NOAA projects that by the 2050s, there will only be 54% of the volume of sea ice there was in the 1950s.[edit]
Opening up of the Northwest Passage in summer
Melting Arctic ice may open the Northwest Passage in summer in approximately ten years, which would cut 5,000 nautical miles (9,300 km) from shipping routes between Europe and Asia. This would be of particular relevance for supertankers which are too big to fit through the Panama Canal and currently have to go around the tip of South America. According to the Canadian Ice Service, the amount of ice in Canada's eastern Arctic Archipelago decreased by 15% between 1969 and 2004 [45][46]. A similar opening is possible in the Arctic north of Siberia, allowing much faster East Asian to Europe transport.

Negative impacts of the melting of ice include a potential increase in the rate of global warming, as that ice reflects more sunlight than the open water which is replacing it. There are also ecological effects of melting polar ice: for example, polar bears use sea ice to reach their prey, and swim to another ice floe when one breaks up. Ice is now becoming further separated, and dead polar bears are being found in the water, believed to have drowned.[47] More recently, observed cannibalistic behavior in polar bears has been suggested by some scientists to be the result of food shortages brought on by global warming (Amstrup et al. 2006).

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Responses
Main articles: Mitigation of global warming and adaptation to global warming
The possibility that global temperatures will continue to significantly increase has led others to propose means to mitigate global warming. Mitigation covers all actions aimed at reducing the negative effects or the likelihood of global warming.

There are five categories of actions that can be taken to mitigate global warming:

Reduction of energy use (conservation)
Shifting from carbon-based fossil fuels to alternative energy sources
Carbon capture and storage
Carbon sequestration
Planetary engineering to cool the earth
Strategies for mitigation of global warming include development of new technologies, wind power, nuclear power, solar power, renewable energy, biodiesel, electric or hybrid automobiles, fuel cells, energy conservation, carbon taxes, enhancing natural carbon dioxide sinks, population control and carbon capture and storage. Some environmentalist groups encourage individual action against global warming, often aimed at the consumer, and there has been business action on climate change.

The world's primary international agreement on combating climate change is the Kyoto Protocol. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.

Although the combination of scientific consensus and economic incentives were enough to persuade the governments of more than 150 countries to ratify the Kyoto Protocol (notably excluding the United States and Australia), there is a continuing debate about just how much greenhouse gas emissions warm the planet. Some politicians, including President of the United States George W. Bush [48], Prime Minister of Australia John Howard [49] have argued that the cost of mitigating global warming is too large to be justified.

However, some segments of the business community have accepted both the reality of global warming and its attribution to anthropogenic causes, as well as the need for actions such as carbon emissions trading and carbon taxes.

Adaptation strategies accept some warming as a foregone conclusion and focus on preventing or reducing undesirable consequences. Examples of such strategies include defense against rising sea levels or ensuring food security.

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Climate models

Calculations of global warming from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions.
The distribution of warming (with an average of 3.0 °C or 5.4 °F) 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.Main article: General circulation model
Scientists have studied global warming with computer models of the climate (see below). For a climate model to be accepted by the scientific community as being valid it must first be shown that it does a good job of simulating known climate variations, such as the difference between summer and winter, the North Atlantic Oscillation[citation needed], or El Niño. Once models which fail these tests are rejected, the remaining models all predict that the net effect of adding greenhouse gases will be a warmer climate in the future. However, the amount of predicted warming varies by model, and there still remains a considerable range of climate sensitivity predicted by the models which survive these tests; one of the most important sources of this uncertainty is believed to be different ways of handling clouds. Part of the technical summary of the IPCC TAR includes a recognition of the need to quantify this uncertainty: "In climate research and modeling, we should recognize that we are dealing with a coupled non-linear system, and therefore that the prediction of a specific future climate is not possible. Rather the focus must be on the probability distribution of the system's possible future states by the generation of ensembles of model solutions." (see [50], page 78). An example of a study which aims to do this is the climateprediction.net project; their methodology is to investigate the range of climate sensitivities predicted for the 21st century by those models which are first shown to give a reasonable simulation of late 20th century climate change.

As noted above, climate models have been used by the IPCC to anticipate a warming of 1.4 °C to 5.8 °C (2.5 °F–10.4 °F) between 1990 and 2100 [51]. They have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models predict from various natural and human derived forcing factors. In addition to having their own characteristic climate sensitivity, models have also been used to derive independent assessments of climate sensitivity.

Climate models can produce a good match to observations of global temperature changes over the last century [52]. 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. Adding simulation of the carbon cycle to the models 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 [53].

Uncertainties in the representation of clouds are a dominant source of uncertainty in existing models, despite clear progress in modeling of clouds [54]. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability. Further, all such models are limited by available computational power, so that they may overlook changes related to small scale processes and weather (e.g. storm systems, hurricanes). However, despite these and other limitations, the IPCC considered climate models "to be suitable tools to provide useful projections of future climates" [55].

In December, 2005 Bellouin et al. suggested in Nature that the reflectivity effect of airborne pollutants was about double that previously expected, and that therefore some global warming was being masked. If supported by further studies, this would imply that existing models under-predict future global warming. [56]

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Other related issues
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Relationship to ozone depletion
Main article: Ozone depletion
Although they are often interlinked in the mass media, the connection between global warming and ozone depletion is not strong. There are four areas of linkage:

Global warming from carbon dioxide radiative forcing is expected (perhaps somewhat surprisingly) to cool the stratosphere. This, in turn, would lead to a relative increase in ozone depletion and the frequency of ozone holes.

Radiative forcing from various greenhouse gases and other sourcesConversely, ozone depletion represents a radiative forcing of the climate system. There are two opposed effects: reduced ozone allows more solar radiation to penetrate, thus warming the troposphere. But a colder stratosphere emits less long-wave radiation, tending to cool the troposphere. Overall, the cooling dominates: the IPCC concludes that observed stratospheric O3 losses over the past two decades have caused a negative forcing of the surface-troposphere system [57] of about −0.15 ± 0.10 W/m² [58].
One of the strongest predictions of the greenhouse effect theory is that the stratosphere will cool. However, although this is observed, it is difficult to use it as an attribution of recent climate change since similar cooling is caused by ozone depletion.
Ozone depleting chemicals are also greenhouse gases, representing 0.34 ±0.03 W/m², or about 14% of the total radiative forcing from well-mixed greenhouse gases [59].
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Relationship to global dimming
Main article: Global dimming
Some scientists now consider that the effects of global dimming (the reduction in sunlight reaching the surface of the planet, possibly due to aerosols) may have masked some of the effect of global warming. If this is so, the indirect aerosol effect is stronger than previously believed, which would imply that the climate sensitivity to greenhouse gases is also stronger. Concerns about the effect of aerosol on the global climate were first researched as part of concerns over global cooling in the 1970s.

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Pre-human global warming
The Earth has experienced natural global warming and cooling many times in the past, and can offer useful insights into present processes. It is thought by some geologists that a rapid buildup of greenhouse gases caused the Earth to experience global warming in the early Jurassic period, with average temperatures rising by 5 °C (9.0 °F). Research by the Open University published in Geology (32: 157–160, 2004 [60]) indicates that this caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, carbon dioxide levels dropped back to normal over roughly the next 150,000 years.

Sudden releases of methane from clathrate compounds (the Clathrate Gun Hypothesis), have been hypothesized as a cause for other past global warming events, including the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last glacial period is thought not to be due to methane release [61]. Instead natural variations in the Earth's orbit are believed to have triggered the retreat of ice sheets by changing the amount of solar radiation received at high latitude and led to deglaciation.

The greenhouse effect is also invoked to explain how the Earth made it out of the Snowball Earth period 600 million years ago. During this period all silicate rocks were covered by ice, thereby preventing them from combining with atmospheric carbon dioxide. The atmospheric carbon dioxide level gradually increased until it reached level that could have been as much as 350 times current levels. At this point temperatures were raised enough to melt the ice, even though the reflective ice surfaces had been reflecting most sunlight back into space. Increased amounts of rainfall would quickly wash the carbon dioxide out of the atmosphere, and thick layers of abiotic carbonate sediment have been found on top of the glacial rocks from this period.

Using paleoclimate data for the last 500 million years Veizer et al. (2000, Nature 408, pp. 698–701) concluded that long-term temperature variations are only weakly related to carbon dioxide variations. Most paleoclimatologists believe this is because other factors, such as continental drift and mountain building have larger effects in determining very long term climate. However, Shaviv and Veizer (2003, [62]) proposed that the biggest long-term influence on temperature is actually the solar system's motion around the galaxy, and the ways in which this influences the atmosphere by altering the flux of cosmic rays received by the Earth. Afterwards, they argued that over geologic times a change in carbon dioxide concentrations comparable to doubling pre-industrial levels, only results in about 0.75 °C (1.3 °F) warming rather than the usual 1.5–4.5 °C (2.7–8.1 °F) reported by climate models [63]. They acknowledge (Shaviv and Veizer 2004) however that this conclusion may only be valid on multi-million year time scales when glacial and geological feedback have had a chance to establish themselves. Rahmstorf et al. 2004 [64] argue that S+V have highly and arbitrarily tuned their data, and that their conclusions are unreliable.

Paleoclimatologist William Ruddiman has argued (e.g. Scientific American, March 2005) that human influence on the global climate actually began around 8,000 years ago with the development of agriculture. In his opinion, this prevented carbon dioxide (and later methane) levels falling as rapidly as they would have done otherwise. Ruddiman argues that without this effect, the Earth would be entering, or already have entered, a new ice age. However other work in this area (Nature 2004) argues that the present interglacial is most analogous to the interglacial 400,000 years ago that lasted approximately 28,000 years, in which case there is no need to invoke the spread of agriculture for having delayed the next ice age.

[edit]
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Questions about Clathrate Gun Hypothesis (source of information

Answer 2

Global warming is increased temperatures due to increased greenhouse gases produced by man.

The US must ratify the Kyoto protocal, being the first step toward doing something about this global problem which we are cheifly to blame.

CO2 is 30% higher than it has been for 650,000 years. Methane is 130% greater. These are two of the main pollutants humans put into the atmosphere in excess, and they are two of the primary greenhouse gases.

Look at the 'hockeystick', which shows a dramatic warming since 1950 after a fairly stable climate for 1000 years. In fact, the 10 hottest years in recorded history have all happened since 1990, with 2005 being the hottest, and 2006 is shaping up to maybe break that record.
(see links below)

How's that for proof of man's fault in this? There is ample proof, any real scientist will tell you that.

There has NEVER been an article doubting man's influence on global warming published in a peer-reviewed journal. A recent study of almost 1000 proved that.

Yes, the earth naturally heats and cools, but the rate and amount we are warming now is unprecedented in the recent geologic past. We are doing this, and we must stop it. This is not some political statement or rhetoric. This is science trying to educate a crass, ignorant public of the damage they are doing. The magnitude of temperature increase ALREADY is about 10x that of the 'little ice age' of the middle ages, and rate and amount are only going up.

Just to be clear, glacial and interglacial cycles are mainly controlled by astronomical fluctuations, but we have a detailed record of the last 7 cycles, and what the climate and CO2 is doing now is way different and extreme. The rate of increase is much higher than in the past AND the value itself is much higher.

HI CO2:
http://news.bbc.co.uk/1/hi/sci/tech/4467420.stm
HOCKEY STICK:
http://news.bbc.co.uk/1/hi/sci/tech/5109188.stm
General climate stuff:
http://news.bbc.co.uk/1/hi/sci/tech/3897061.stm

Answer 3

Global warming refers to an unequivocal and continuing rise in the average temperature of Earth's climate system.[2] Since 1971, 90% of the warming has occurred in the oceans.[3] Despite the oceans' dominant role in energy storage, the term "global warming" is also used to refer to increases in average temperature of the air and sea at Earth's surface.[4] Since the early 20th century, the global air and sea surface temperature has increased about 0.8 °C (1.4 °F), with about two-thirds of the increase occurring since 1980.[5] Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850.[6]

Scientific understanding of the cause of global warming has been increasing. In its fourth assessment (AR4 2007) of the relevant scientific literature, the Intergovernmental Panel on Climate Change (IPCC) reported that scientists were more than 90% certain that most of global warming was being caused by increasing concentrations of greenhouse gases produced by human activities.[7][8][9] In 2010 that finding was recognized by the national science academies of all major industrialized nations.[10][A] Affirming these findings in 2013, the IPCC stated that the largest driver of global warming is carbon dioxide (CO2) emissions from fossil fuel combustion, cement production, and land use changes such as deforestation.[11] Its 2013 report states

Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely (95-100%) that human influence has been the dominant cause of the observed warming since the mid-20th century. - IPCC AR5 WG1 Summary for Policymakers[12]

Climate model projections were summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicated that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2.0 to 5.2 °F) for their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5 °F) for their highest.[13] The ranges of these estimates arise from the use of models with differing sensitivity to greenhouse gas concentrations.[14][15]

Future climate change and associated impacts will vary from region to region around the globe.[16][17] The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well as a probable expansion of subtropical deserts.[18] Warming is expected to be strongest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent extreme weather events including heat waves, droughts and heavy rainfall; ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the loss of habitat from inundation.[19][20]

Proposed policy responses to global warming include mitigation by emissions reduction, adaptation to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),[21] whose ultimate objective is to prevent dangerous anthropogenic (i.e., human-induced) climate change.[22] Parties to the UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissions[23][24][25][26] and to assist in adaptation to global warming.[23][26][27][28] Parties to the UNFCCC have agreed that deep cuts in emissions are required,[29] and that future global warming should be limited to below 2.0 °C (3.6 °F) relative to the pre-industrial level.[29][B] Reports published in 2011 by the United Nations Environment Programme[30] and the International Energy Agency[31] suggest that efforts as of the early 21st century to reduce emissions may be inadequate to meet the UNFCCC's 2 °C target.

Emissions of greenhouse gases grew 2.2% per year between 2000 and 2010, compared with 1.3% per year from 1970 to 2000.[32]

Answer 4

There main gas is CO2 they calculate that it has increased 30% wrong. If u measure it u will find 1 to 2 parts per million ,and I know we are producing billions of cf. of CO2 where did it go???well our chief Eng. engineered a 2 part system. the other side of the system is green plants which take in the CO2 and put out oxygen. that is where it is ,if they were right people would be dieing. U cant fix something that is not broken. If u don't have an increase in CO2 we don't have global warming
Hope this helps

Answer 5

Global warming is a growing concern for the scientists.
Gl warming s caused by harmful gases such as CO2,SO2.
These gases emitted into the atmos do not allow any heat to escape from the earth.
Since,no heat escapes, temp of the earth increases.This can b very dangerous b'coz antaractic ice caps can melt and many cities along the coasts will get submerged.

Answer 6

I have asked many people about the subject and most of them don't really know so I asked my science teacher and she said yes were expiriencing the hot weather but realise the "global" part while america (western hemisphere) are expiriencing the hottest weather in recorded history The eastern hemisphere is expiriencing their coldest times at the same time so it balances out its not global warming unless its world wide

Answer 7

You notice how the global warming paranoia never provides a positive aspect to it such as it might be warmer in the winter, crops may have higher yields, elevated CO2 reduces the amount of water needed for plants, fewer starving children, etc. It demonstrates that it is paranoia and it is pseudoscience.

Answer 8

1

Answer 9

Global warming, also called climate change, is the term used to describe any weather event. For example, if the number of tornados is a few more then average, it will be said that this is due to global warming. However, if the number of tornados is a few less then average, it will be said to be because of climate change. The purposed fixes for global warming and climate change is heavy taxation of Americans and everntual transformation of America into a communist country.

Answer 10

It's a MASSIVE LIE. The government/ illuminati are trying to trick you !!!!! DON'T fall into their trap!!!!!

Answer 11

Russian professors have more recently asked, "Is it not "Global cooling"??!!