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1. "Global warming"
Glaciersare melting,sealevelsare rising,forestsare dryingupandflora andfauna are strugglingtokeepup.It isincre asingly
clearthat humanshave causedmost of the warmingof the lastcentury,throughthe emissionof gasesthatretainheat,to
improve ourmodernlife.We call greenhouse gasesandtheirlevelsare increasing,now andinthe last 65,000 years.The
greenhouse effectisthe heatingthatoccurs whencertaingasesinthe earth'satmosphere retainheat.These gasesletinlightbut
keepthe heatlike the glasswallsof agreenhouse.The worldaverage temperature andthe concentrationsof carbondioxide (one
of the maingreenhouse gases) have fluctuatedinacycle of hundredsof thousandsof yearsbecause the positionof the Earth has
variedwithrespecttothe sun.As a result,differentagesof ice occurred.The rapidincrease ingreenhousegasesisaproblem
because the climate ischangingsofastthat some livingthingscannotadapt. Inthe same way,a new and more unpredictable
climate imposesunique challengesforall typesof life.Historically,the Earth'sclimate hasoscillatedbetweentemperatureslike
those we knowtodayand temperaturessocoldthatlarge ice caps coveredmostof NorthAmericaandEurope.Duringthe past
year, the "global average temperature"of terrestrial andoceanicsurfaceswas0.9degreescentigrade above the 20thcentury
average,reaching13.9 degreescentigrade.Inaddition,tenof the twelvemonthsof 2015 registeredrecordtemperatures.Most
of global warminghasoccurredinthe last 35 years,coincidingwiththe increase of greenhouse gasemissionsbyhumans,as
notedbyNASA.
Image representingwarming
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