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Zubar da hankali a duniya wani zato ne, musamman a cikin shekarun 1970s, na sanyaya mai zuwa na Duniya wanda ya ƙare a cikin wani lokaci mai zurfi, saboda tasirin sanyaya na aerosols ko tilastawar orbital. Wasu rahotanni na manema labarai a cikin shekarun 1970 sun yi hasashe game da ci gaba da sanyaya; waɗannan ba su nuna ainihin wallafe-wallafen kimiyya na lokacin ba, wanda gabaɗaya ya fi damuwa da dumama daga ingantaccen tasirin greenhouse.[1]
A tsakiyar shekarun 1970s, iyakantaccen jerin zafin jiki da ake samu ya nuna cewa zafin jiki ya ragu na shekaru da yawa har zuwa lokacin. Yayin da jerin lokaci masu tsawo na inganci mafi girma suka kasance, ya zama bayyananne cewa zafin jiki na duniya ya nuna karuwa mai yawa gaba ɗaya.
A cikin shekarun 1970s, masana kimiyya sun kara fahimtar cewa kimantawa na yanayin zafi na duniya ya nuna sanyaya tun 1945, da kuma yiwuwar babban dumama saboda fitar da iskar gas. A cikin takardun kimiyya waɗanda suka yi la'akari da yanayin yanayi na karni na 21, ƙasa da kashi 10% sun karkata zuwa sanyaya na gaba, yayin da yawancin takardun suka yi hasashen dumama na gaba.[2] Jama'a ba su da masaniya game da tasirin carbon dioxide akan yanayi, amma Labaran Kimiyya a watan Mayu 1959 sun yi hasashen karuwar kashi 25% a cikin carbon dioxide na yanayi a cikin shekaru 150 daga 1850 zuwa 2000, tare da yanayin dumama. Ainihin karuwa a wannan lokacin ya kasance 29%. Paul R. Ehrlich ya ambaci dumamar duniya daga iskar gas a matsayin mai hanawa ga tasirin sanyaya na aerosols a shekarar 1968. A lokacin da ra'ayin sanyaya duniya ya kai ga manema labarai a tsakiyar shekarun 1970 yanayin zafi ya daina faduwa, kuma akwai damuwa a cikin al'ummar yanayin yanayi game da tasirin zafi na carbon dioxide.[3] A mayar da martani ga irin waɗannan rahotanni, Hukumar Kula da Yanayi ta Duniya ta ba da gargadi a watan Yunin 1976 cewa "wani gagarumin zafi na yanayi na duniya" mai yiwuwa ne.[4]
A halin yanzu, akwai wasu damuwa game da yiwuwar tasirin sanyaya na yanki na raguwa ko rufewar yaduwar thermohaline, wanda zai iya haifar da karuwar ruwa mai kyau da ke haɗuwa a cikin Arewacin Atlantic saboda narkewar glacial. Ana ganin yiwuwar wannan ya faru a matsayin ƙasa sosai, kuma IPCC ta lura, "ko da a cikin samfuran inda THC ke raunana, har yanzu akwai dumi a Turai. Misali, a cikin duk haɗin AOGCM inda tilasta radiative ke ƙaruwa, alamar canjin zafin jiki a arewa maso yammacin Turai tana da kyau.
Lokacin sanyaya yana sakewa ta hanyar tsarin yanayi na duniya na yanzu (1999 a kan) wanda ya haɗa da tasirin jiki na sulfate aerosols, kuma yanzu akwai yarjejeniya ta gaba ɗaya cewa tasirin aerosol shine babban dalilin sanyaya na tsakiyar karni na 20. A lokacin akwai hanyoyin jiki guda biyu waɗanda aka fi ci gaba da su akai-akai don haifar da sanyaya: aerosols da tilasta orbital.
Ayyukan ɗan adam - galibi a matsayin samfur na ƙonewar man fetur, wani ɓangare ta hanyar canje-canje na amfani da ƙasa - yana ƙara yawan ƙananan barbashi (aerosols) a cikin yanayi. Wadannan suna da tasiri kai tsaye: suna kara yawan albedo na duniya, don haka suna sanyaya duniya ta hanyar rage hasken rana da ya kai saman; da kuma sakamako na kai tsaye: sun shafi kaddarorin girgije ta hanyar aiki a matsayin ƙwayoyin girgije.[5] A farkon shekarun 1970 wasu sun yi hasashen cewa wannan tasirin sanyaya na iya mamaye tasirin dumama na sakin CO2: duba tattaunawar Rasool da Schneider (1971), a ƙasa. A sakamakon lura da sauyawa zuwa ƙone mai tsabta, wannan ba zai yiwu ba; aikin kimiyya na yanzu yana nuna cewa dumamar duniya ya fi dacewa. Kodayake raguwar zafin jiki da wannan tsarin ya hango yanzu an watsar da shi saboda mafi kyawun ka'idar da kuma yanayin zafi da aka lura, ana zaton aerosols sun ba da gudummawa ga yanayin sanyaya (wanda ya fi ƙarfin karuwar iskar gas) kuma sun ba da damar dimming na duniya.
Orbital tilasta yana nufin jinkirin, canje-canje na cyclical a cikin karkatawar axis na Duniya da kuma siffar ta. Wadannan sake zagayowar suna canza jimlar hasken rana da ke isa Duniya da karamin adadi kuma suna shafar lokaci da tsananin yanayi. Wannan hanyar ana zaton tana da alhakin lokacin sake zagayowar zamanin kankara, kuma fahimtar hanyar tana ƙaruwa cikin sauri a tsakiyar shekarun 1970.
Takardar Hays, Imbrie, da Shackleton "Variations in the Earth's Orbit: Pacemaker of the Ice Ages" sun cancanci tsinkayinsu tare da cewa "dole ne a cancanta hasashen ta hanyoyi biyu. Na farko, suna amfani ne kawai ga bangaren halitta na yanayin yanayi na gaba - kuma ba ga tasirin ɗan adam ba kamar waɗanda ke haifar da ƙone burbushin burbushin halittu. Na biyu, suna bayyana yanayin dogon lokaci ne kawai, saboda suna da alaƙa da bambance-bambance na orbital tare da lokutan shekaru 20,000 da tsayi. Ba a yi hasashen sauye-sauyen yanayi a mafi girma ba ... sakamakon ya nuna cewa yanayin dogon lokaci a cikin shekaru 20,000 masu zuwa yana zuwa ga babban glaciation na Arewacin Hemisphere da yanayin sanyi. "[6]
Ra'ayin cewa za'a iya hango yanayin shekarun kankara da ra'ayin cewa wani ya kasance saboda "ba da daɗewa ba" - watakila saboda yawancin wannan binciken ya faru ne daga masana kimiyyar ƙasa, waɗanda suka saba da ma'amala da ma'auni na dogon lokaci kuma suna amfani da "ba da sauri" don komawa ga lokutan dubban shekaru. Aikace-aikacen ƙa'idar Milankovitch ba ya ba da damar tsinkaya na farkon shekarun kankara "da sauri" (watau, ƙasa da ƙarni ɗaya ko biyu) tunda lokacin da ya fi sauri ya kai kimanin shekaru 20,000. [ana buƙatar ƙa'ida] An sami wasu hanyoyin kirkirar wannan, musamman wanda Nigel Calder ya goyi bayan shi a ƙarƙashin sunan "snowblitz", amma waɗannan ra'ayoyin ba su sami karɓa sosai ba.
Ya zama ruwan dare a ga ya tabbatar da cewa tsawon yawan zafin jiki na yanzu yana kama da tsawon saman interglacial da ya gabata (Sangamon / Eem), kuma daga wannan kammalawa cewa muna iya kusantar ƙarshen wannan lokacin dumi. Wannan kammalawa ba daidai ba ne. Da farko, saboda tsawon interglacials na baya ba na yau da kullun ba ne; duba adadi.[7] Petit et al. sun lura cewa "interglacials 5.5 da 9.3 sun bambanta da Holocene, amma suna kama da juna a tsawon lokaci, siffar da faɗin. A lokacin kowane ɗayan waɗannan abubuwan biyu, akwai lokacin dumi na 4 kyr wanda ya biyo bayan sanyaya mai sauri. "[8] Abu na biyu, bambance-bambance na gaba ba za su yi kama da na baya ba.
A cikin 1923, akwai damuwa game da sabon zamanin kankara kuma Kyaftin Donald Baxter MacMillan ya tashi zuwa Arctic wanda National Geographical Society ta tallafawa don neman shaidar ci gaba da kankara.
A cikin 1926, wani masanin taurari na Berlin yana hasashen sanyaya duniya amma cewa "tsufa" ne.
Damuwa cewa sabon zamanin kankara yana gabatowa an farfado da shi a cikin shekarun 1950. A lokacin Yakin Cold, Harry Wexler ya damu da cewa kashe bama-bamai na atom na iya hanzarta sabon zamanin kankara daga yanayin hunturu na nukiliya.
J. Murray Mitchell ya nuna tun farkon 1963 sanyaya da yawa tun daga 1940.[2] A wani taro kan canjin yanayi da aka gudanar a Boulder, Colorado a shekarar 1965, shaidar da ke tallafawa sake zagayowar Milankovitch ta haifar da hasashe kan yadda aka lissafa ƙananan canje-canje a hasken rana na iya haifar da shekarun kankara. A cikin 1966, Cesare Emiliani ya yi hasashen cewa "sabon ƙanƙara zai fara cikin 'yan dubban shekaru". A cikin littafinsa na 1968 The Population Bomb, Paul R. Ehrlich ya rubuta "An inganta tasirin greenhouse yanzu ta hanyar karuwar matakin carbon dioxide ... [wannan] ana magance shi da girgije mai ƙarancin matakin da aka samar da ƙura, ƙura, da sauran gurɓataccen abu. A halin yanzu ba za mu iya hango abin da sakamakon yanayi zai kasance na amfani da yanayi a matsayin zubar da shara ba.
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