{"id":475,"date":"2017-09-20T20:46:58","date_gmt":"2017-09-20T20:46:58","guid":{"rendered":"http:\/\/80.85.86.254\/sjor\/?p=475"},"modified":"2024-02-20T13:29:44","modified_gmt":"2024-02-20T13:29:44","slug":"3-3-grodurhusaahrif-og-loftslagsbreytingar","status":"publish","type":"post","link":"https:\/\/himinnoghaf.is\/mengunsjavar\/index.php\/2017\/09\/20\/3-3-grodurhusaahrif-og-loftslagsbreytingar\/","title":{"rendered":"3.3 Gr\u00f3\u00f0urh\u00fasa\u00e1hrif og loftslagsbreytingar"},"content":{"rendered":"

J\u00f6r\u00f0inni og lofthj\u00fap jar\u00f0ar m\u00e1 l\u00edkja vi\u00f0 gr\u00f3\u00f0urh\u00fas. Lofthj\u00fapurinn er \u00fe\u00e1 eins og gleri\u00f0 \u00ed gr\u00f3\u00f0urh\u00fasinu. Hann hleypir grei\u00f0lega \u00ed gegnum sig \u00fatfj\u00f3lubl\u00e1rri og s\u00fdnilegri s\u00f3largeislun (stuttbylgjugeislun) en heldur inni hluta varmageislunarinnar (langbylgjugeislun) sem berst fr\u00e1 yfirbor\u00f0i jar\u00f0ar. \u00deannig dregur lofthj\u00fapurinn \u00far varmatapi fr\u00e1 j\u00f6r\u00f0inni. \u00deessi \u00e1hrif lofthj\u00fapsins \u00e1 hitastig og loftslag \u00e1 j\u00f6r\u00f0inni eru nefnd gr\u00f3\u00f0urh\u00fasa\u00e1hrif. \u00c1n gr\u00f3\u00f0urh\u00fasa\u00e1hrifa v\u00e6ri me\u00f0alhitastig \u00e1 j\u00f6r\u00f0inni \u00ed kringum -18\u00b0C \u00ed sta\u00f0 +15\u00b0C, eins og \u00fea\u00f0 er n\u00fa. Gr\u00f3\u00f0urh\u00fasa\u00e1hrifin eru \u00feannig forsenda fyrir l\u00edfi \u00e1 j\u00f6r\u00f0inni eins og vi\u00f0 \u00feekkjum \u00fea\u00f0.<\/p>\n

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Mynd 3.3. Gr\u00f3\u00f0urh\u00fasa\u00e1hrifin \u00fatsk\u00fdr\u00f0.<\/p><\/div>\n

Mynd 3.3 s\u00fdnir hvernig s\u00f3largeislun berst inn \u00ed lofthj\u00fapinn, en s\u00f3largeislunin er a\u00f0 st\u00e6rstum hluta orkur\u00edk stuttbylgjugeislun. Hluti \u00feeirrar s\u00f3largeislunar sem berst inn \u00ed lofthj\u00fapinn, endurkastast fr\u00e1 lofthj\u00fapnum og fr\u00e1 yfirbor\u00f0i jar\u00f0ar og n\u00fdtist \u00fev\u00ed ekki til a\u00f0 hita j\u00f6r\u00f0ina. Lj\u00f3sir fletir eins og j\u00f6klar, snj\u00f3r og sk\u00fd endurkasta h\u00e6rra hlutfalli geislunarinnar en d\u00f6kkir fletir. Megni\u00f0 af s\u00f3largeisluninni n\u00e6r ni\u00f0ur a\u00f0 yfirbor\u00f0i jar\u00f0ar, sem gleypir \u00ed sig geislunina og hitnar vi\u00f0 \u00fea\u00f0. Hitinn streymir svo aftur \u00fat fr\u00e1 yfirbor\u00f0i jar\u00f0ar \u00ed formi varmageisla (langbylgjugeislun). Gr\u00f3\u00f0urh\u00fasalofttegundir \u00ed lofthj\u00fapnum gleypa hluta varmageislunarinnar og endursenda hana \u00ed allar \u00e1ttir. Vi\u00f0 \u00fea\u00f0 berst hluti varmageislunarinnar aftur a\u00f0 yfirbor\u00f0i jar\u00f0ar, sem lei\u00f0ir til \u00feess a\u00f0 yfirbor\u00f0i\u00f0 og ne\u00f0ri l\u00f6g lofthj\u00fapsins hitna enn frekar. Gr\u00f3\u00f0urh\u00fasalofttegundirnar koma \u00feannig \u00ed veg fyrir a\u00f0 hluti varmageislunarinnar glatist \u00fat \u00ed geim og valda \u00fev\u00ed a\u00f0 me\u00f0alhitastig vi\u00f0 yfirbor\u00f0 jar\u00f0ar er h\u00e6rra en ef gr\u00f3\u00f0urh\u00fasa\u00e1hrifanna nyti ekki vi\u00f0.<\/p>\n

K\u00f6fnunarefni (N2<\/sub>) og s\u00farefni (O2<\/sub>) sem mynda samanlagt 99% lofthj\u00fapsins gleypa ekki varmageislun fr\u00e1 j\u00f6r\u00f0u. \u00dea\u00f0 gera hins vegar lofttegundir sem er a\u00f0 finna \u00ed litlu magni \u00ed andr\u00famsloftinu, einkum vatnsgufa\u00a0(H2<\/sub>O), kold\u00edox\u00ed\u00f0 (CO2<\/sub>), metan (CH4<\/sub>), \u00f3son (O3<\/sub>), gla\u00f0loft (N2<\/sub>O) og \u00fdmsar lofttegundir sem innihalda fl\u00faor (brennisteinshexafl\u00faor\u00ed\u00f0 (SF6<\/sub>), k\u00f6fnunarefnistr\u00edfl\u00faor\u00ed\u00f0 (NF3<\/sub>) og \u00fdmis hal\u00f3genkolefni (HFC, PFC, CFC, hal\u00f3n)). \u00deessar lofttegundir eru kalla\u00f0ar gr\u00f3\u00f0urh\u00fasalofttegundir<\/strong> vegna gr\u00f3\u00f0urh\u00fasa\u00e1hrifanna sem \u00fe\u00e6r valda. \u00de\u00e6r eiga \u00fea\u00f0 sameiginlegt a\u00f0 hafa langan l\u00edft\u00edma \u00ed andr\u00famsloftinu, e\u00f0a dvelja \u00fear me\u00f0 \u00f6\u00f0rum or\u00f0um lengi ef \u00fe\u00e6r komast \u00feanga\u00f0 \u00e1 anna\u00f0 bor\u00f0. \u00dea\u00f0 skiptir ekki m\u00e1li hvar \u00feessar lofttegundir sleppa \u00fat \u00ed andr\u00famslofti\u00f0, \u00fe\u00e6r dreifast um allt og \u00e1hrifin koma alls sta\u00f0ar fram.<\/p>\n

Magn kold\u00edox\u00ed\u00f0s og hitastig jar\u00f0ar hafa sveiflast \u00ed takt \u00ed gegnum t\u00ed\u00f0ina (mynd 3.4).<\/p>\n

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Mynd 3.4. Magn kold\u00edox\u00ed\u00f0s \u00ed andr\u00famslofti og hitastigsbreytingar s\u00ed\u00f0ustu 400.000 \u00e1r.<\/p><\/div>\n

\u00c1 jar\u00f0s\u00f6gulegum t\u00edma hafa \u00fdmsir \u00fe\u00e6ttir haft \u00e1hrif \u00e1 loftslag jar\u00f0ar s.s. magn gr\u00f3\u00f0urh\u00fasalofttegunda \u00ed andr\u00famslofti, breytingar \u00e1 sporbaug jar\u00f0ar, breytingar \u00e1 s\u00f3larinngeislun og eldgos. \u00de\u00e6r hr\u00f6\u00f0u breytingar sem eiga s\u00e9r sta\u00f0 \u00e1 loftslagi jar\u00f0ar um \u00feessar mundir m\u00e1 hins vegar rekja til aukins magns gr\u00f3\u00f0urh\u00fasalofttegunda \u2013 s\u00e9rstaklega kold\u00edox\u00ed\u00f0s \u2013 \u00ed andr\u00famsloftinu.<\/p>\n

Myndband 3.1 s\u00fdnir styrk kold\u00edox\u00ed\u00f0s \u00ed andr\u00famslofti s\u00ed\u00f0ustu 800.000 \u00e1r. \u00cd upphafi myndbandsins er s\u00fdnt hvernig styrkur kold\u00edox\u00ed\u00f0s hefur aukist jafnt og \u00fe\u00e9tt s\u00ed\u00f0an 1980. S\u00ed\u00f0an er fari\u00f0 me\u00f0 okkur aftur \u00ed t\u00edmann. S\u00ed\u00f0ustu 800.000 \u00e1rin og fram til 1860 sveifla\u00f0ist styrkur kold\u00edox\u00ed\u00f0s fr\u00e1 um 185 ppm \u00e1 \u00edsaldarskei\u00f0um upp \u00ed um 300 ppm \u00e1 hl\u00fdskei\u00f0um. Eins og sj\u00e1 m\u00e1 f\u00f3r styrkur kold\u00edox\u00ed\u00f0s ekki upp fyrir 300 ppm fyrr en vi\u00f0 mannf\u00f3lki\u00f0 f\u00f3rum a\u00f0 brenna jar\u00f0eldsneyti (kolum, ol\u00edu og jar\u00f0gasi) \u00ed st\u00f3rum st\u00edl. Fornar loftb\u00f3lur fastar \u00ed \u00eds gera okkur kleift a\u00f0 fara aftur \u00ed t\u00edmann \u00e1 \u00feennan h\u00e1tt og sj\u00e1 hvernig andr\u00famsloft jar\u00f0ar \u2013 og \u00fear me\u00f0 loftslagi\u00f0 \u2013 leit \u00fat \u00e1 fors\u00f6gulegum t\u00edma.<\/p>\n