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Дэлхийн газрын гадаргуу орчмын дундаж температур, 1850-аас 2006 он хүртэлх (19611990 оны дундажтай харьцуулав).
Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980


Дэлхийн дулаарал гэдэг нь Дэлхийн хуурай газар, далайн гадаргуу орчмын агаарын дундаж температур ихсэх үзэгдлийг хэлнэ. Агаарын дундаж температур сүүлийн хэдэн арван жилд тасралтгүй нэмэгдэж байгаа бөгөөд цаашид ч мөн үргэлжилнэ гэж үзэж байгаа болно.

Сүүлийн 100 жилийн хугацаанд Дэлхийн дундаж температур 0.74 ± 0.18°C -аар нэмэгдсэн бөгөөд "Уур амьсгалын өөрчлөлт судлах Засгийн газар хоорондын хороо" (Intergovernmental Panel on Climate Change - IPCC буюу ИПСС), "20-р зууны дундаас эхэлсэн, агаарын дундаж температурын ихсэлт нь, агаар мандал дахь антропоген хүлэмжийн хийн агуулга нэмэгдсэнтэй холбоотой байх бүрэн боломжтой юм" гэжээ[1]. Байгалийн бусад хүчин зүйлүүд, тухайлбал нарны энергийн өөрчлөлт (нарны идэвхижилт), галт уулын дэлбэрэлт нь аж үйлдвэржилтийн өмнөх үеэс одоог хүртэлх хугацаанд маш бага хэмжээний нөлөө үзүүлж байсан байна[2][3]. ИПСС-гийн энэхүү дүгнэлтийг Их 8 болон Дэлхийн өндөр хөгжилтэй 30 гаруй орны Шинжлэх ухааны академи, хүрээлэнгүүд хүлээн зөвшөөрдөг болно. Гэхдээ зарим нэг судлаачид эсрэг саналтай байдгийг дурьдах хэрэгтэй юм.

ИПСС-гийн уур амьсгалийн загварчлал, 1990-2100 оны хооронд агаарын дундаж температур 1.1 - 6.4 °C нэмэгдэж болзошгүйг харуулж байгаа [1] бөгөөд ирээдүйд агаар мандал руу цацагдах хүлэмжийн хийг хэр багасгахаас хамааран температурын дээд доод хязгаар нь тодорхойлогдож байгаа болно. Хэдийгээр ихэнхи судалгаа, 2100 он хүртэл өөрчлөлтийг голчлон анхаарч байгаа боловч, ирэх мянган жилд, агаар мандал дахь хүлэмжийн хийн агуулга одооныхоос нэмэгдэхгүй тогтвортой байхад, дэлхийн дулаарал, далайн усны төвшин ихэссээр байна гэж таамаглаж байна[1]. Энэ нь далайн усны дулаан багтаамжтай холбоотой юм.

Дэлхийн дулааралын улмаас далайн усны төвшин, цаг уурын гоц үзэгдэлүүд ихсэж[4], хур тундсын хэмжээ өөрчлөгдөнө. Мөн түүнчлэн хөдөө аж ахуй, мөсөн гол, мөнх цасны хэмжээ, амьтан ургамлын төрөл, зүйл зэрэг олон зүйлд сөргөөр нөлөөлөх болно.

Түүнээс гадна ирээдүйд болох дулаарлын хэмжээ, түүний сөрөг нөлөө нь дэлхийн бүс нутгуудад яаж нөлөөх вэ гэдэг сайн судлагдаагүй, тодорхой бус байна. Энэхүү дулаарлыг яаж бууруулах, түүний тулд ямар арга хэмжээ авах вэ гэдэг талаар олон улсын хэмжээнд улс төрийн болон олон нийтийн хэлэцүүлэг, төрөл бүрийн үйл ажиллагаа явагдаж байна. Хүлэмжийн хийг (ялгаруулалтыг) багасгах зорилготой Киотогийн протоколд дэлхийн ихэнхи улс нэгдсэн болно.

Нэр томъёо[засварлах | edit source]

"Дэлхийн дулаарал" гэдэг нэр томъёо нь сүүлийн хэдэн арван жилд явагдаж буй, хүний нөлөөнөөс үүдсэн дулаарлыг илэрхийлнэ. Эрдэмтэд энэхүү дулаарал цаашид мөн үргэлжилнэ гэж тооцож байна[5][6].НҮБ-ын Уур амьсгалын өөрчлөлтийн талаархи ерөнхий хэлэлцээрт тусгаснаар бол "уур амвсгалын өөрчлөлт" (climate change) гэдэг тодорхойлолтонд зөвхөн хүний нөлөөгөөр бий болох өөрчлөлтийг, харин "уур амьсгалийн хувьсалт" (climate variability) гэдэгт бусад хүчийн зүйлээс хамаарсан өөрчлөлтийг багтаадаг байна[7].

Шалтгаан, нөлөөлөх хүчин зүйл[засварлах | edit source]

Сүүлийн 400,000 жилийн нүүрстөрөгчийн давхар ислийн хэмжээ. Уг ислийн хэмжээ Аж үйлдвэрийн хувьсгалаас хойш огцом нэмэгдсэн байна (Дээд талын жижиг зураг). Миланковичийн цикл (нарыг тойрон эргэх Дэлхийн орбитын өөрчлөлт) нь 100,000 жилийн давтамжтай бий болдог мөстлөгийн гол шалтгаан гэж үзэж байна.

Дэлхийн уур амьсгалын өөрчлөлтөнд Дэлхий нарыг тойрон эргэх орбитын өөрчлөлт[8][9][10], галт уулын дэлбэрэлт, агаар мандал дахь хүлэмжийн хийн агуулга зэрэг хүчин зүйлүүд нөлөөлнө. Орчин үед явагдаж байгаа дулаарлын шалтгаан эрдэмтдийн дунд ихээхэн маргаантай байгаа ч[11], эрдэмтдийн дийлэнхи нь хүний үйл ажиллагаатай холбоотой ихэссэн хүлэмжийн хий хамгийн ихээр нөлөөлж байна гэж үзэж байна. Үүнийг сүүлийн 50 жилд хийгдсэн нарийвчилсан хэмжилтүүдийн үр дүнгээс харж болно. Гэхдээ зарим эрдэмтэд Дэлхийн дулаарлыг нарны идэвхижилттэй холбож бас тайлбарладаг байна. [12][13][14][15].

Эдгээр хүчин зүйлүүдийн аль нь ч хурдан хугацаанд нөлөөлж чадахгүй. None of the effects of forcing are instantaneous. The thermal inertia of the Earth's oceans and slow responses of other indirect effects mean that 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 2000 levels, a further warming of about 0.5 °C (0.9 °F) would still occur.[16]

Агаар мандал дахь хүлэмжийн хий[засварлах | edit source]

Үндсэн өгүүлэл: Greenhouse effect

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.

Existence of the greenhouse effect as such is not disputed. Naturally occurring greenhouse gases have a mean warming effect of about 30 °C (54 °F), without which Earth would be uninhabitable.[17] The debate centers on how the strength of the greenhouse effect is changed when human activity increases the atmospheric concentrations of some greenhouse gases.

On Earth, the major 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%.[18][19] 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 methane 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.[20] Fossil fuel burning has produced about three-quarters of the increase in CO2 from human activity over the past 20 years. Most of the rest is due to land-use change, in particular deforestation.[21]

The present atmospheric concentration of CO2 is about 383 parts per million (ppm) by volume.[22] 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, and 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.[23] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[24]

Positive (reinforcing) 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[25] not included in climate models cited by the IPCC.[1]

Хариу үйлдлүүд[засварлах | edit source]

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 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.)[26] 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. 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. Whether the net effect is warming or cooling depends on details such as the type and altitude of the cloud. These details are difficult to represent in climate models, in part because clouds are much smaller than the spacing between points on the computational grids of climate models (about 125 to 500 km for models used in the IPCC Fourth Assessment Report). Nevertheless, 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.[26]

Another important feedback process is ice-albedo feedback.[27] 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.[28]

Нарны идэвхижилт[засварлах | edit source]

Solar variation over the last 30 years.
Үндсэн өгүүлэл: Solar variation

Hypotheses have been proposed that variations in solar output, possibly amplified by cloud feedbacks, may have contributed to recent warming.[29] A difference between this mechanism and greenhouse warming is that an increase in solar activity should warm the stratosphere while greenhouse warming should cool the stratosphere. Cooling in the lower stratosphere has been observed since at least 1960,[30] which would not be expected if solar activity were the main contributor to recent warming. (Reduction of stratospheric ozone also has a cooling influence but substantial ozone depletion did not occur until the late 1970s.) Phenomena such as solar variation combined with changes in volcanic activity have probably had a warming effect from pre-industrial times to 1950, but a cooling effect since 1950.[1] A related hypothesis is that cosmic rays may affect climate by influencing the generation of cloud condensation nuclei.[31]

A few papers suggest that the Sun's contribution may have been underestimated. Two researchers at Duke University have estimated that the Sun may have contributed about 45–50% of the increase in the average global surface temperature over the period 1900–2000, and about 25–35% between 1980 and 2000.[32] 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.[33] 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 found no net increase of solar 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 small to contribute significantly to global warming.[34][35] A 2007 paper by Lockwood and Fröhlich found no relation between global warming and solar radiation since 1985, whether through variations in solar output or variations in cosmic rays.[36]

Температурын өөрчлөлт[засварлах | edit source]

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.
Үндсэн өгүүлэл: Temperature record

Орчин үе[засварлах | edit source]

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 effect. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[37] 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.[38] 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.[39] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[40][41]

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,[42] 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.[43] Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[44]

Өнгөрсөн үе[засварлах | edit source]

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.

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.[45]

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.[46][47]

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).

Дэлхийн уур амьсгалын загварчлал[засварлах | edit source]

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).
Үндсэн өгүүлэл: 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 effect of adding greenhouse gases is to produce a warmer climate.[48] However, even when the same assumptions of future GHG levels are used, 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.

Current climate models produce a good match to observations of global temperature changes over the last century, but do not simulate all aspects of climate.[49] 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.[50][51][52]

The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[53] 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[засварлах | edit source]

Үндсэн өгүүлэл: 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.[54] 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, and adverse health effects from warmer temperatures.[55]

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.[56] 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.[54] 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,[57] 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.[58] 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.[59]

Economics[засварлах | edit source]

Үндсэн өгүүлэл: Economics of global warming ба 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).[56] 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%.[60] 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,[61] while others have supported the general attempt to quantify economic risk, even if not the specific numbers.[62][63]

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.[64]

Adaptation and mitigation[засварлах | edit source]

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 also 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.[65].

Only the United States (historically the world's largest greenhouse gas emitter), Australia, and Kazakhstan have not ratified the treaty. In the absence of clear concerted action by the U.S. 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) is a state-level emissions capping and trading program involving eight Northeastern states, which was founded on December 20, 2005.[66]

China (which is expected to soon overtake the U.S. 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.[67]

This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.[68]

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,[69] and in Bangkok, Thailand.[70]

Issue debate, political processes and laws[засварлах | edit source]

Үндсэн өгүүлэл: Global warming controversy ба politics of global warming

Over the past several years, public perceptions and attitudes concerning the causes and importance of global warming have changed.[71] 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.[72] At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and Australia, and have been used as part of their rationale for continued non-ratification.[73] 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.[74][75]

Fossil fuel organizations and companies such as American Petroleum Institute and ExxonMobil, represented by individuals such as 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,[76][77][78][79] described by some as climate change denial. Environmental groups and public figures have launched campaigns emphasizing the risks. Recently, some fossil fuel companies have scaled back such efforts[80] or called for policies to reduce global warming.[81]

This issue has sparked debate regarding the benefits of limiting industrial emissions of greenhouse gases versus the effects on economic activity. In the U.S., the political manipulation of scientific testimonies and reports has also become an issue.[82][83] There has also been discussion in several countries about the cost of adopting alternate, cleaner energy sources in order to reduce emissions.[84]

Another point of debate is the degree to which newly-developed economies, such as India and China, should be expected to constrain their emissions. 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[85]). 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.[86] India will also soon be one of the biggest sources of industrial emissions, and has made assertions similar to China's on this issue.[87]

In an interview with the BBC, President Bush´s advisor and director of the Office of Science and Technology Policy, John Marburger said that climate change is taking place and there is more than 90 percent certainty that it is due to man-made greenhouse gas (GHG) emissions. [88]

Related climatic issues[засварлах | edit source]

Үндсэн өгүүлэл: Ocean acidification, global dimming, ба 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.[89] 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,[90] 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][91] 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.[92]

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.

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References[засварлах | edit source]

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