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Global warming

see Global warming/temp forproposed change inlayoutthis entry

Global warmingan increase over time ofaverage temperatureEarth's atmosphereoceans. Itgenerally useddescribetemperature rise overpast century or so, andeffectshumans ontemperature. The more neutral term climate changeusually useddescribe previous natural variations. The term may be useddescribe theories explaining such an increase orcrisis that many advocates say will arise if no one does anythingprevent such an increase from occurring.

Since 1990,prospect thatearth's atmosphere might heat up too much -- becausecarbon dioxideother "greenhouse gases" -- has beenhotly debated topic.

Tablecontents
1 Temperature records
2 Scientific opinion
3 The greenhouse gas theory
4 The solar variation theory
5 Global warming controversy
6 Historical temperature record
7 Evidence forcurrent warming period
8 Evidence againstcurrent warming period
9 Climate models
10 Potential Effects
11 The Intergovernmental Panel on Climate Change
12 The Kyoto Protocol
13 External links
14 Educational
15 Scientific
16 United Nations
17 Environmentalist
18 Conservative-affiliated
19 Industry-sponsored
20 Independent (or receives too little supportconstitute "sponsorship")
21 Other
22 See also

Temperature records

Depending on what data one choosesemphasize, different conclusionspossible (see historical temperature record).

MBH98 Warming Graph

Northern Hemisphere temperature variations.

All quantitative reconstructions show temperatures as having been roughly stable forlast 1,000 years but sharply rising inlast century (see Temperature record ofpast 1000 years). These records, combinedattribution analysis, indicate that itlikely thisduehuman activity (see anthropogenic climate change). Environmentalists have been quickbelieve thisgenerally urge quickradical actionsaveenvironment (see Kyoto ProtocolUNFCCC).

Qualitative historical evidence show warmingcooling,theresome evidence that these correlatesunspotsother aspectssolar activity;example, some historians argue thatMedieval Warm Period enabledcolonizationGreenland. Recent research suggests that episodeswarmingcooling such asMedieval Warm Period orLittle Ice Age may have been regional not global.

The difference betweeninterpretations ofhistorical record affects howmost recent warming trendviewed:quantitative records showrecent warming trend, andcurrent warmth, as unusual; fromqualitative record, many "skeptics" believe thatrecent trendnot unusual,reject callsactions such asKyoto Protocol (see global warming controversy, Maunder Minimum, Little Ice Age, Sargasso Sea proxy).

The current conflict resultsprofessionalpersonal disagreements as well as pressuring political forces. Presently thisparticularly visible in various interpretationstopics such as the UNFCCC Kyoto Protocol (see global warming controversy).

The above paragraphs might giveimpression that belief incoursepast climate change correlates stronglyadvocacyfuture actions: thisnot necessarily so. Itpossible, perhaps common,studypast recordgive no counsel onfuture.

Intwentieth century, both marineland-based thermometers have recorded suchwarming from1880sabout 1940, followed bylesser cooling from 19401975,another periodwarming from 1975present [1]. See Historical temperature recordmore discussion;anthropogenic climate changeattribution ofchange.

Scientific opinion

The climate system varies both through natural, "internal" processes as well asresponsevariations"external forcing" from both humannon-human causes, including changessolar activityvolcanic emissions as well as greenhouse gases.

A survey by Dennis BrayHans von Storch1996 showedtendencyscientiststhis fieldagree that it"certain that, without changehuman behavior, global warming will definitely occur sometime infuture" - withsurvey showing these scientists giving this statement an average score2.6 onscale from 17, where 1 indicated complete agreement7 indicated complete disagreement.

See scientific opinionglobal warmingfurther discussionthis opinion surveyscientists.

The greenhouse gas theory

The hypothesis that increases or decreasesgreenhouse gas concentration would leadhigher or lower global mean temperature was first postulated inlate 19th century by Swedish chemist1903 Nobel Laureate Svante Arrhenius, largely as an attemptexplain ice ages. Attime his peers largely rejected his theory.

The theory that human greenhouse gas emissions have contributed towarming ofEarth's atmosphere in20th century has gained both adherentsopponents inscientific community withinpast 25 years. Climate researcher Stephen Schneider, who thought in1970s that aerosols might leadglobal cooling, has becomestrong proponent ofglobal warming hypothesis. Atmospheric physicist Richard LindzenHarvard astronomer Sallie Baliunas opposetheory. The IPCC endorsedtheory, as didUnited States National AcademySciences.

Automobile exhausts, coal-burning power plants, factory smokestacks,other waste vents ofindustrial age now pump six billion tonscarbon dioxideother greenhouse gases intoearth's atmosphere each year. Theycalled greenhouse gases becausetrap radiant energy fromsun that would otherwise be re-radiated back into space. (The fact thatnatural greenhouse effect occurswell-knownis not at issue indebate over global warming. Without it, temperatures would drop by approximately 30°C,oceans would freezelife as we knowwould be impossible.) What climatologistsconcerned about, rather,that increased levelsgreenhouse gases inatmosphere might cause more heatbe trapped. Concentrationsgreenhouse gases inatmospherecurrently at approximately 25% above pre-industrial values. Thisconsiderably higher than at any time duringlast 420,000 years,periodwhich reliable data exists, from ice cores. From less direct geological evidence itbelieved that values this high were last attained 40 million years ago.

The solar variation theory

Various theories have been proposedlink terrestrial temperature variationssolar variations. The meteorological community has respondedskepticism,part because theoriesthis nature have comegone overcourse of20th century. The theories have usually been onethree types:

Although often correlationspresented andmechanismspeculative. Manythese effects have fared badly over time,inpaper "Solar activityterrestrial climate: an analysissome purported correlations" (J. Atmos.Solar-Terr. Phy., 2003 p801-812) Peter Laut demonstrates problemssome ofmost popular, notably those by Svensmarkby Lassen (below).

In 1991, Knud Lassen ofDanish Meteorological InstituteCopenhagenhis colleague Eigil Friis-Christensen foundstrong correlation betweenlength ofsolar cycletemperature changes throughoutnorthern hemisphere. Initially,used sunspottemperature measurements from 18611989, but later found that climate records dating back four centuries supported their findings. This relationship appearedaccountnearly 80 per cent ofmeasured temperature changes over this period (see graph). Sallie Baliunas, an astronomer atHarvard-Smithsonian CenterAstrophysics, has been amongsupporters oftheory that changes insun "can accountmajor climate changes on Earth forpast 300 years, including part ofrecent surgeglobal warming." [1]

On May 6, 2000, however, New Scientist magazine reported that Lassenastrophysicist Peter Thejll had updated Lassen's 1991 researchfound that whilesolar cycle still accountsabout halftemperature rise since 1900,failsexplainrise0.4 °C since 1980. "The curves diverge after 1980," Thejll said, "and it'sstartlingly large deviation. Something elseacting onclimate. ... It hasfingerprints ofgreenhouse effect."[1]

Later that same year, Peter Stottother researchers atHadley Centre inUnited Kingdom publishedpaperwhichreported onmost comprehensive model simulationsdate ofclimate of20th century. Their study looked at both natural forcing agents (solar variationsvolcanic emissions) as well as anthropogenic forcing (greenhouse gasessulphate aerosols). Like LassenThejll,found thatnatural factors accountedgradual warmingabout 1960 followed byreturnlate 19th-century temperatures, consistent withgradual changesolar forcing throughout20th centuryvolcanic activity duringpast few decades. These factors alone, however, could not account forwarmingrecent decades. Similarly, anthropogenic forcing alone was insufficientexplain1910-1945 warming, but was necessarysimulatewarming since 1976. Stott's team found that combining allthese factors enabled themclosely simulate global temperature changes throughout20th century. They predicted that continued greenhouse gas emissions would cause additional future temperature increases "atrate similarthat observedrecent decades."[1] A graphical representation ofrelationship between naturalanthropogenic factors contributingclimate change appears"Climate Change 2001: The Scientific Basis,"report byIntergovernmental Panel on Climate Change (IPCC). [1]

Global warming controversy

A separate article on socio-political issues surroundingtheoryglobal warming

Historical temperature record

Overpast 20,000 yearsdominant temperature signal has beenend oflast ice age, approximately 12,000 years ago.[1] Since thentemperature has been quite stable, thoughvarious fluctuations, e.g. Medieval Warm Period or Little Ice Age.

Evidence forcurrent warming period

According toIPCC, Earth has seensignificant increaseaverage global surface temperature overlast 150 years.

The main evidenceglobal warming comes from thermometer measurements from land stationsships [1], which independently show muchsame warming since 1860. The data from these stations, particularly those located outside ofUnited States, show an average surface temperature increase0.40.8 Celsius degrees during20th century. Most ofwarming occurred during two periods: 1910194519762000. (Source: Intergovernmental Panel on Climate Change,IPCC).

See anthropogenic global warmingdiscussionattribution ofchanges.

Secondary evidence comes from observed variations insnow coverice extent, global average sea level, precipitation, cloud cover, El Niñoextreme weather events during20th century.

For example, satellite data shows10% decreasesnow cover sincelate 1960s, andNorthern Hemisphere springsummer sea-ice extent has decreased by about 10%15% since1950sthere has beenwidespread retreatmountain glaciersnon-polar regions throughout20th century. (Source: IPCC).

Evidenceglobal warmingunevencertain places, especiallynorth shoreAlaska, showing dramatic rises temperature far aboveaverage forglobe aswhole [1].

Evidence againstcurrent warming period

Weather balloonssatellites measuringtemperature ofatmosphere aboveearth's surface since 1979 showwarming trend introposhere0.074 °C / decade upAugust 2003 [1]; see satellite temperature measurementsdetails. A National AcademySciences panel that reviewedapparent discrepancy concluded that "the warming trendglobal-mean surface temperature observations duringpast 20 yearsundoubtedly realis substantially greater thanaverage ratewarming duringtwentieth century. The disparity between surfaceupper air trendsno way invalidatesconclusion that surface temperature has been rising."class="external">[1

The satellite datacontroversialincorporatenumbercorrections for, amongst other effects, orbital drift ofsatellites [1]. Other analyses ofsame data produce different (higher) trends.

Climate models

Climate simulations (vague) do not unambiguously attributewarming that occurred from 19101945either variationsolar radiation (internalnatural forcing) oranthropogenic forcing (see climate change). The models (which sort?)usedestimaterelative importance ofvarious factors mentioned above. Most models show that warming occurring from 19752000 needs anthropogenic greenhouse gas emissionsbe explained. This conclusion depends onaccuracy ofmodels usedoncorrect estimation ofexternal factors. The majorityscientists agree that important climate featuresincorrectly accountedbyclimate models but don't think that better models would changeconclusion. (Source: IPCC)

Critics point out that thereflaws inmodelsexternal factors not taken into consideration that could changeconclusion above (whichthese?). Some critics (who?) say thatclimate simulationsunablefitwater vapor feedback,handle clouds. Critics also point out thatsun may haveshareresponsibility forobserved global warming greater than now thought bymajority ofscientific community. Some indirect solar effects may be very important andnot accountedbymodels. So,argue,shareglobal warming caused by anthropogenic greenhouse gases may be lower than thought. (Source: The Skeptical Environmentalist)

See also: climate models

Potential Effects

Many public policy organizationsgovernment officialsconcerned thatcurrent warming haspotentialharm toenvironmentagriculture.

This ismatterconsiderable controversy,environmentalist groups typically emphasizingpossible dangersgroups closeindustry questioningclimate modelsconsequencesglobal warming -funding scientistsdo so.

Duepotential effects on human healtheconomy due toimpact onenvironment, global warming iscausegreat concern. Some important environmental changes have been observedlinkedglobal warming.

The examplessecondary evidence cited above (lessened snow cover, rising sea levels, weather changes)examplesconsequencesglobal warming that may influence not only human activities but alsoecosystems. Increasing global temperature means that ecosystems may change; some species may be forced outtheir habitats (possiblyextinction) becausechanging conditions, while others may spread. Few ofterrestrial ecoregions on Earth could expectbe unaffected.

Another causegreat concernsea level rise. Sea levelsrising 12 centimetres (around half an inch) per decade,some small countries inPacific Oceanexpressing concerns that if this risesea level continues,soon will be entirely under water. Global warming causessea levelrise mainly because sea water expands aswarms, but some scientistsconcerned that infuture,polar ice capsglaciers may melt. Asconsequence,sea level could rise several metres. Atmoment, scientistsnot expecting any major ice melting innext 100 years. (Sources: IPCC fordata andmass media forgeneral perception that climate changeimportant.) Some researchers have foundnegative correlation between sea level riseaverage global temperature; water evaporates more quickly thanexpands. (Source: ScienceEnvironmental Policy Project)

Asclimate gets hotter, evaporation will increase. This will cause heavier rainfallmore erosion. Many people think thatcould resultmore extreme weather as global warming progresses.

Global warming can also have other, less obvious effects. The North Atlantic drift,instance,driven by temperature changes. It seems as though itdiminishing asclimate grows warmer,this means that areas like ScandinaviaBritain thatwarmed bydrift might facecolder climatespite ofgeneral global warming. Itnow feared that Global Warming may be abletriggertypeabrupt massive temperature shifts which bracketedYounger Dryas period.

However, global warming can also have positive effects, since higher temperatureshigher CO2 concentrations improveecosystems' productivity. Satellite data shows thatproductivity ofNorthern Hemisphere has increased since 1982. Onother hand, an increase intotal amountbiomass producednot necessarily all good, since biodiversity can still decrease even thoughsmall numberspeciesflourishing. Similarly, fromhuman economic viewpoint, an increasetotal biomass butdecreasecrop harvests would benet disadvantage. In addition, IPCC models predict that higher CO2 concentrations would only spur growthflora up topoint, becausemany regionslimiting factorswater or nutrients, not temperature or CO2; after that, though greenhouse effectswarming would continue there would be no compensatory increasegrowth.

The Intergovernmental Panel on Climate Change

Since itsuch an important issue, governments need predictionsfuture trendsglobal change socan take political decisionsavoid undesired impacts. Global warmingbeing studied byIntergovernmental Panel on Climate Change (IPCC).

The Kyoto Protocol

The Kyoto Protocol toUNFCCC proposes binding greenhouse gas limitsdeveloped countries.

External links

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