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U moet hierdie land besoek voordat dit letterlik in die see sak

U moet hierdie land besoek voordat dit letterlik in die see sak


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Klimaatsverandering het die afgelope paar jaar baie chaos veroorsaak esdoringstroop en koffie tekorte aan vegetariese grizzlybere aan veranderinge in Brittanje se geliefde fish and chips sowel as sy posisie in die wynmaakbedryf.

Die skrikwekkendste is dat klimaatsverandering ook baie skade berokken het aan die huise van miljoene mense, wat dit in sommige gevalle heeltemal laat verdwyn het. Danksy stygende seevlakke het hele eilande in die see verdwyn. Tot dusver was die meeste van hulle onbewoon, maar die paar wat nie ontruimings en hartseer tot gevolg gehad het nie.

Baie pragtige eilande loop tans die risiko om deur klimaatsverandering vernietig te word. Een daarvan is die opvallend pragtige Suid -Asiatiese land van die Maledive, geleë in die Indiese Oseaan, suidwes van Indië en Sri Lanka. Onbekend as 'n toeristebestemming tot in die sewentigerjare, het sy toerismebedryf sedertdien vinnig gegroei, met die aantal oorde tussen 1972 en 2007 van twee tot 92. Elke jaar besoek meer as 'n miljoen mense die eilandnasie, bekend vir sy natuurlike skoonheid: 'n kristalhelder blou oseaan, skoon lug en sandstrande. Dit is een van die beste plekke ter wêreld om te gaan duik, en dit is na berig word die gewildste wittebroodbestemming.

Dit bestaan ​​uit 26 atolle en het die laagste hoogte van enige land ter wêreld, met 'n gemiddelde natuurlike grondvlak van ongeveer 4 voet en 11 sentimeter bo seespieël. Meer as 80 persent van die land bestaan ​​uit koraal -eilande wat minder as een meter bo seespieël meet, en sodoende die land 'n uiters risiko loop om te dompel.

Volgens die omgewingspaneel van die Verenigde Nasies sou die Maledive as die seevlak teen die huidige tempo bly styg, teen 2100 onbewoonbaar wees. As die seevlak nog vinniger styg, kan die dag gouer kom. In 'n poging om dit te bekamp, ​​het die regering 'n plan opgestel wat al sy kweekhuisgasvrystellings teen 2020 sal uitskakel of vergoed. Klimaatsverandering is egter 'n wêreldwye kwessie, en seevlakke is ook afhanklik van die deelname van ander lande in inisiatiewe vir klimaatsverandering. Gewasse oor die hele wêreld loop die gevaar om geraak te word (terwyl 'n paar ander daarby baat kan vind). As u meer wil weet oor die uitwerking van klimaatsverandering op verskillende streke, Lees meer oor wat dit beteken vir appels, tamaties en 15 ander kosse.


Watter stede sak eerste in die see? Miskien nie diegene wat u verwag nie

B etter wetenskaplike begrip van aardverwarming maak die bespreking oor die geopolitieke gevolge daarvan steeds dringender. Eenvoudig gestel, daar gaan wenners en verloorders wees: warmer plekke en kouer plekke natter plekke en droër plekke en ja, plekke wat onder die see verdwyn. Maar die werklikheid is 'n bietjie ingewikkelder. Veral die seevlak veral op of af? Die antwoord lyk duidelik as u in ag neem dat Antarktika die afgelope 25 jaar 3 biljoen ton ys verloor het.

Maar om te verstaan ​​wat aan die gang is, moet ons eers besef dat die aarde nie solied is nie. Dit het ongeveer 4,5 miljard jaar gelede begin lewe as 'n bol warm vloeistof en ons planeet het sedertdien afgekoel. Reg in die middel van die aarde is 'n soliede kern van metaal gemaak van yster en nikkel teen 'n temperatuur van ongeveer 5.000C. Maar hierdie kern word omring deur 'n oseaan van gesmelte metaal van ongeveer 2 000 km dik, weer meestal yster en nikkel. Rondom hierdie is 'n rotslaag wat die mantel genoem word, tussen 500C en 900C, en by hierdie rooiwarm temperature gedra die rots hom oor 'n kort tydperk (sekondes, ure en dae) soos 'n vaste stof, maar soos 'n vloeistof oor langer tyd. tydperke (maande tot jare) - sodat die rots vloei, alhoewel dit nie gesmelt is nie. Bo -op die vloeistofmantel dryf die kors, wat soos die vel van die aarde is. Dit is 'n relatief dun laag koel rots wat tussen 30 en 100 km dik is en al die berge, woude, riviere, seë, vastelande bevat - ons wêreld.

Aangesien die kors op die vloeistofmantel dryf, as u sy gewig verhoog deur byvoorbeeld kilometers ys bo -op te bou, sak dit verder in die mantel. Dit is wat gebeur het met die landmassas van Antarktika en Groenland, wat albei bedek is in 2km tot 3km dik ys. As aardverwarming al die ys laat smelt, dan styg die seevlak van die oseane met meer as 50 meter, wat al die kusstede ter wêreld dompel en honderde miljoene mense dakloos maak. Dit lyk voor die hand liggend. Wat minder duidelik is, is hoe dit kan ontvou.

As die hele ys wat Antarktika bedek, smelt, sal die vrystelling van sy gewig die gesteentes daaronder vernietig, wat, omdat dit op die mantel dryf, sal stamp. Dit word post-glacial rebound genoem. Die posisie met Groenland is soortgelyk: die kors daaronder word swaar gemaak deur die 3 miljoen biljoen liter water wat in die ys gehou word, en as die ys alles smelt, sal dele van die Noord -Amerikaanse tektoniese landmassa opstaan. As die gevolglike toename in die hoogte van die vasteland groter is as die seevlakstyging, kan groot oorstromings vermy word. Om uit te vind watter scenario meer waarskynlik is, is uiters belangrik vir toekomstige geslagte, want een van hierdie resultate sal begin afspeel as aardverwarming toeneem.

Wat ons weet is dit: die wêreld se gemiddelde seevlak het sedert die begin van die 20ste eeu met 20 cm gestyg. Sommige daarvan is te danke aan die water wat termies uitbrei namate die oseane warmer word - aangesien warmer vloeistowwe meer volume inneem (dit is hoe vloeibare termometers werk). Sommige van die styging in seevlak was te wyte aan die ysplate van Groenland en Antarktika wat gesmelt het, en sommige as gevolg van die smelt van ander gletsers. Die stygende seevlakke is wêreldwyd: dit raak almal met 'n kuslyn, van klein eilande in die Stille Oseaan wat heeltemal onder water sou wees tot 'n groot land soos Bangladesh, waarna 'n styging van een meter in seevlak in byna 'n vyfde van die land sou lei onder water en 30 miljoen mense verplaas. Alhoewel stygende seevlakke almal beïnvloed, beïnvloed die post-glaciale rebound slegs die kuste wat verband hou met dele van die aardkors wat die Groenland- en Antarktiese ysplate afweer.

Dit is moeilik om die belangrikheid van hierdie kwessie te oorskat, en ons het meer data en wetenskaplike kennis van hierdie vloeibare prosesse nodig. 'N Beperkte aantal gespesialiseerde satelliete, soos CryoSat, GRACE en ICESat-2-wat pas deur Nasa gelanseer is-word gebruik om ysdikte te monitor en modelle van post-glacial rebound te ontwikkel. Wat die wetenskap voorspel, is dat as die ys eers in die noordelike halfrond smelt, Groenland hoër kan styg as die gemiddelde seevlak, net soos dele van Noord -Amerika, en dus kan die seevlak aanvanklik daal. As die teenoorgestelde gebeur, en die ys van die Antarktika smelt voor die Groenlandse ys, dan is dit die suidelike tektoniese plate wat eers opspring en die hele oostelike kus van Noord -Amerika eers onder water gaan. Die groot onbekendes is hoe vinnig die ys op elke plek gaan, en hoe vinnig die post-glaciale rebound sal wees.

Ons moet hierdie prosesse vinnig beter verstaan, want as ons dit nie doen nie, kan dit te laat wees om katastrofe te voorkom. Hierdie kwessies oorheers nie nuusagenda nie, maar dit moet. Onlangs bedank die Franse minister van omgewingsake, met verwysing na die gebrek aan vordering en dringendheid van die president oor kwessies oor klimaatsverandering. Hierdeur het hy die kommer van die hele wetenskaplike gemeenskap uitgespreek oor wêreldleiers - ons het 'n stapsgewys verandering in die regering nodig. Maar daar is 'n punt: nie alle regerings voel dringend daaroor nie. En waarom? Miskien is dit omdat, soos die kwessie van post-glacial rebound toon, daar wenners en verloorders sal wees van aardverwarming. Lande soos Rusland sal byvoorbeeld minder geraak word deur styging in seevlak, en kan baat vind by 'n meer gematigde klimaat. Daarteenoor ly die VSA moontlik nie net aan nuwe droogtesones nie, maar die laagliggende oostelike kus word bedreig deur die versnelde verlies van ys in Antarktika. Namate die 21ste eeu voortduur en die ys steeds smelt, sal dit duideliker word watter lande 'n groter aansporing het om klimaatsverandering te versag, en die gevolglike geopolitiek kan die verdeeldheid en konflik dryf.


Watter stede sak eerste in die see? Miskien nie diegene wat u verwag nie

B etter wetenskaplike begrip van aardverwarming maak die bespreking oor die geopolitieke gevolge daarvan steeds dringender. Eenvoudig gestel, daar gaan wenners en verloorders wees: warmer plekke en kouer plekke natter plekke en droër plekke en ja, plekke wat onder die see verdwyn. Maar die werklikheid is 'n bietjie ingewikkelder. Veral die seevlak veral op of af? Die antwoord lyk duidelik as u in ag neem dat Antarktika die afgelope 25 jaar 3 biljoen ton ys verloor het.

Maar om te verstaan ​​wat aan die gang is, moet ons eers besef dat die aarde nie solied is nie. Dit het ongeveer 4,5 miljard jaar gelede begin lewe as 'n bol warm vloeistof en ons planeet het sedertdien afgekoel. Reg in die middel van die aarde is 'n soliede kern van metaal gemaak van yster en nikkel teen 'n temperatuur van ongeveer 5.000C. Maar hierdie kern word omring deur 'n oseaan van gesmelte metaal van ongeveer 2 000 km dik, weer meestal yster en nikkel. Rondom dit is 'n rotslaag wat die mantel genoem word, tussen 500C en 900C, en by hierdie rooiwarm temperature gedra die rots hom oor 'n kort tyd (sekondes, ure en dae) soos 'n vaste stof, maar oor langer tyd soos 'n vloeistof. tydperke (maande tot jare) - sodat die rots vloei, alhoewel dit nie gesmelt is nie. Bo -op die vloeistofmantel dryf die kors, wat soos die vel van die aarde is. Dit is 'n relatief dun laag koel rots wat tussen 30 en 100 km dik is en al die berge, woude, riviere, seë, vastelande bevat - ons wêreld.

Aangesien die kors op die vloeistofmantel dryf, as u sy gewig verhoog deur byvoorbeeld kilometers ys bo -op te bou, sak dit verder in die mantel. Dit is wat gebeur het met die landmassas van Antarktika en Groenland, wat albei bedek is in 2km tot 3km dik ys. As aardverwarming al die ys laat smelt, dan styg die seevlak van die oseane met meer as 50 meter, wat al die kusstede ter wêreld dompel en honderde miljoene mense dakloos maak. Dit lyk voor die hand liggend. Wat minder duidelik is, is hoe dit kan ontvou.

As die hele ys wat Antarktika bedek, smelt, sal die vrystelling van sy gewig die gesteentes daaronder vernietig, wat, omdat dit op die mantel dryf, sal opduik. Dit word post-glacial rebound genoem. Die posisie met Groenland is soortgelyk: die kors daaronder word swaar gemaak deur die 3 miljoen biljoen liter water wat in die ys gehou word, en as die ys alles smelt, sal dele van die Noord -Amerikaanse tektoniese landmassa opstaan. As die gevolglike toename in die hoogte van die vasteland groter is as die seespieël, kan groot oorstromings vermy word. Om uit te vind watter scenario meer waarskynlik is, is uiters belangrik vir toekomstige geslagte, want een van hierdie resultate sal begin afspeel as aardverwarming toeneem.

Wat ons weet is dit: die wêreld se gemiddelde seevlak het sedert die begin van die 20ste eeu met 20 cm gestyg. Sommige daarvan is te danke aan die water wat termies uitbrei namate die oseane warmer word - aangesien warmer vloeistowwe meer volume inneem (dit is hoe vloeibare termometers werk). Sommige van die styging in seevlak was te wyte aan die ysplate van Groenland en Antarktika wat gesmelt het, en sommige as gevolg van die smelt van ander gletsers. Die stygende seevlakke is wêreldwyd: dit raak almal met 'n kuslyn, van klein eilande in die Stille Oseaan wat heeltemal ondergedompel sou word tot 'n groot land soos Bangladesh, waarna 'n styging van een meter in seevlak tot byna 'n vyfde van die land sou lei onder water en 30 miljoen mense verplaas. Alhoewel stygende seevlakke almal beïnvloed, beïnvloed die post-glaciale rebound slegs die kuste wat verband hou met dele van die aardkors wat die Groenland- en Antarktiese ysplate afweer.

Dit is moeilik om die belangrikheid van hierdie kwessie te oorskat, en ons het meer data en wetenskaplike begrip van hierdie vloeibare prosesse nodig. 'N Beperkte aantal gespesialiseerde satelliete, soos CryoSat, GRACE en ICESat-2-wat pas deur Nasa gelanseer is-word gebruik om ysdikte te monitor en modelle van post-glacial rebound te ontwikkel. Wat die wetenskap voorspel, is dat as die ys eers in die noordelike halfrond smelt, Groenland hoër kan styg as die gemiddelde seevlak, net soos dele van Noord -Amerika, en dus kan die seevlak aanvanklik daal. As die teenoorgestelde gebeur, en die ys van die Antarktika smelt voor die Groenlandse ys, dan is dit die suidelike tektoniese plate wat eers opspring en die hele oostelike kus van Noord -Amerika eers onder water gaan. Die groot onbekendes is hoe vinnig die ys op elke plek gaan, en hoe vinnig die post-glaciale rebound sal wees.

Ons moet hierdie prosesse vinnig beter verstaan, want as ons dit nie doen nie, kan dit te laat wees om katastrofe te voorkom. Hierdie kwessies oorheers nie nuusagenda nie, maar dit moet. Onlangs bedank die Franse minister van omgewingsake, met verwysing na die gebrek aan vordering en dringendheid van die president oor kwessies oor klimaatsverandering. Hierdeur het hy die kommer van die hele wetenskaplike gemeenskap uitgespreek oor wêreldleiers - ons het 'n stapsgewys verandering in die regering nodig. Maar daar is 'n punt: nie alle regerings voel dringend daaroor nie. En waarom? Miskien is dit omdat, soos die kwessie van post-glacial rebound toon, daar wenners en verloorders sal wees van aardverwarming. Lande soos Rusland sal byvoorbeeld minder geraak word deur styging in seevlak en kan baat by 'n meer gematigde klimaat. Daarteenoor ly die VSA moontlik nie net aan nuwe droogtesones nie, maar die laagliggende oostelike kus word bedreig deur die versnelde verlies van ys in Antarktika. Namate die 21ste eeu voortduur en die ys steeds smelt, sal dit duideliker word watter lande 'n groter aansporing het om klimaatsverandering te versag, en die gevolglike geopolitiek het die moontlikheid om verdeeldheid en konflik te dryf.


Watter stede sal eerste in die see sink? Miskien nie diegene wat u verwag nie

B etter wetenskaplike begrip van aardverwarming maak die bespreking oor die geopolitieke gevolge daarvan steeds dringender. Eenvoudig gestel, daar gaan wenners en verloorders wees: warmer plekke en kouer plekke natter plekke en droër plekke en ja, plekke wat onder die see verdwyn. Maar die werklikheid is 'n bietjie ingewikkelder. Veral die seevlakke veral op of af? Die antwoord lyk duidelik as u in ag neem dat Antarktika die afgelope 25 jaar 3 biljoen ton ys verloor het.

Maar om te verstaan ​​wat aan die gang is, moet ons eers besef dat die aarde nie solied is nie. Dit het ongeveer 4,5 miljard jaar gelede begin lewe as 'n bol warm vloeistof en ons planeet het sedertdien afgekoel. Reg in die middel van die aarde is 'n soliede kern van metaal gemaak van yster en nikkel teen 'n temperatuur van ongeveer 5.000C. Maar hierdie kern word omring deur 'n oseaan van gesmelte metaal van ongeveer 2 000 km dik, weer meestal yster en nikkel. Rondom dit is 'n rotslaag wat die mantel genoem word, tussen 500C en 900C, en by hierdie rooiwarm temperature gedra die rots hom oor 'n kort tyd (sekondes, ure en dae) soos 'n vaste stof, maar oor langer tyd soos 'n vloeistof. tydperke (maande tot jare) - sodat die rots vloei, alhoewel dit nie gesmelt is nie. Bo -op die vloeistofmantel dryf die kors, wat soos die vel van die aarde is. Dit is 'n relatief dun laag koel rots wat tussen 30 en 100 km dik is en al die berge, woude, riviere, seë, vastelande bevat - ons wêreld.

Aangesien die kors op die vloeistofmantel dryf, as u die gewig verhoog deur byvoorbeeld kilometers ys bo -op te bou, sak dit verder in die mantel. Dit is wat gebeur het met die landmassas van Antarktika en Groenland, wat albei bedek is in 2km tot 3km dik ys. As aardverwarming al die ys laat smelt, dan styg die seevlak van die oseane met meer as 50 meter, wat al die kusstede ter wêreld dompel en honderde miljoene mense dakloos maak. Dit lyk voor die hand liggend. Wat minder duidelik is, is hoe dit kan ontvou.

As die hele ys wat Antarktika bedek, smelt, sal die vrystelling van sy gewig die gesteentes daaronder vernietig, wat, omdat dit op die mantel dryf, sal stamp. Dit word post-glacial rebound genoem. Die posisie met Groenland is soortgelyk: die kors daaronder word swaar gemaak deur die 3 miljoen biljoen liter water wat in die ys gehou word, en as die ys alles smelt, sal dele van die Noord -Amerikaanse tektoniese landmassa opstaan. As die gevolglike toename in die hoogte van die vasteland groter is as die seespieël, kan groot oorstromings vermy word. Om uit te vind watter scenario meer waarskynlik is, is uiters belangrik vir toekomstige geslagte, want een van hierdie resultate sal begin afspeel as aardverwarming toeneem.

Wat ons weet is dit: die wêreldwye gemiddelde seevlak het sedert die begin van die 20ste eeu met 20 cm gestyg. Sommige daarvan is te danke aan die water wat termies uitbrei namate die oseane warmer word - aangesien warmer vloeistowwe meer volume inneem (dit is hoe vloeibare termometers werk). Sommige van die styging in seevlak was te wyte aan die ysplate van Groenland en Antarktika wat gesmelt het, en sommige as gevolg van die smelt van ander gletsers. Die stygende seevlakke is wêreldwyd: dit raak almal met 'n kuslyn, van klein eilande in die Stille Oseaan wat heeltemal ondergedompel sou word tot 'n groot land soos Bangladesh, waarna 'n styging van een meter in seevlak tot byna 'n vyfde van die land sou lei onder water en 30 miljoen mense verplaas. Alhoewel stygende seevlakke almal raak, beïnvloed die post-gletseropkoms slegs die kusstreekse wat verband hou met dele van die aardkors wat deur die Groenland- en Antarktiese ysplate verswak is.

Dit is moeilik om die belangrikheid van hierdie kwessie te oorskat, en ons het meer data en wetenskaplike kennis van hierdie vloeibare prosesse nodig. 'N Beperkte aantal gespesialiseerde satelliete, soos CryoSat, GRACE en ICESat-2-wat pas deur Nasa gelanseer is-word gebruik om ysdikte te monitor en modelle van post-glacial rebound te ontwikkel. Wat die wetenskap voorspel, is dat as die ys eers in die noordelike halfrond smelt, Groenland hoër kan styg as die gemiddelde seevlak, net soos dele van Noord -Amerika, en dus kan die seevlak aanvanklik daal. As die teenoorgestelde gebeur, en die ys van die Antarktika smelt voor die Groenlandse ys, dan is dit die suidelike tektoniese plate wat eers opspring en die hele oostelike kus van Noord -Amerika eers onder water gaan. Die groot onbekendes is hoe vinnig die ys op elke plek gaan, en hoe vinnig die post-glaciale rebound sal wees.

Ons moet hierdie prosesse vinnig beter verstaan, want as ons dit nie doen nie, kan dit te laat wees om katastrofe te voorkom. Hierdie kwessies oorheers nie nuusagenda nie, maar dit moet. Onlangs bedank die Franse minister van omgewingsake, met verwysing na die gebrek aan vordering en dringendheid van die president oor kwessies oor klimaatsverandering. Hierdeur het hy die kommer van die hele wetenskaplike gemeenskap uitgespreek oor wêreldleiers - ons het 'n stapsgewys verandering in die regering nodig. Maar daar is 'n punt: nie alle regerings voel dringend daaroor nie. En waarom? Miskien is dit omdat, soos die kwessie van post-glacial rebound toon, daar wenners en verloorders sal wees van aardverwarming. Lande soos Rusland sal byvoorbeeld minder geraak word deur styging in seevlak en kan baat by 'n meer gematigde klimaat. Daarteenoor ly die VSA moontlik nie net aan nuwe droogtesones nie, maar die laagliggende oostelike kus word bedreig deur die versnelde verlies van ys in Antarktika. Namate die 21ste eeu voortduur en die ys steeds smelt, sal dit duideliker word watter lande 'n groter aansporing het om klimaatsverandering te versag, en die gevolglike geopolitiek het die moontlikheid om verdeeldheid en konflik te dryf.


Watter stede sal eerste in die see sink? Miskien nie diegene wat u verwag nie

B etter wetenskaplike begrip van aardverwarming maak die bespreking oor die geopolitieke gevolge daarvan steeds dringender. Eenvoudig gestel, daar gaan wenners en verloorders wees: warmer plekke en kouer plekke natter plekke en droër plekke en ja, plekke wat onder die see verdwyn. Maar die werklikheid is 'n bietjie ingewikkelder. Veral die seevlak veral op of af? Die antwoord lyk duidelik as u in ag neem dat Antarktika die afgelope 25 jaar 3 biljoen ton ys verloor het.

Maar om te verstaan ​​wat aan die gang is, moet ons eers besef dat die aarde nie solied is nie. Dit het ongeveer 4,5 miljard jaar gelede begin lewe as 'n bol warm vloeistof en ons planeet het sedertdien afgekoel. Reg in die middel van die aarde is 'n soliede kern van metaal gemaak van yster en nikkel teen 'n temperatuur van ongeveer 5.000C. Maar hierdie kern word omring deur 'n oseaan van gesmelte metaal van ongeveer 2 000 km dik, weer meestal yster en nikkel. Rondom hierdie is 'n rotslaag wat die mantel genoem word, tussen 500C en 900C, en by hierdie rooiwarm temperature gedra die rots hom oor 'n kort tydperk (sekondes, ure en dae) soos 'n vaste stof, maar soos 'n vloeistof oor langer tyd. tydperke (maande tot jare) - sodat die rots vloei, alhoewel dit nie gesmelt is nie. Bo -op die vloeistofmantel dryf die kors, wat soos die vel van die aarde is. Dit is 'n relatief dun laag koel rots wat tussen 30 en 100 km dik is en al die berge, woude, riviere, seë, vastelande bevat - ons wêreld.

Aangesien die kors op die vloeistofmantel dryf, as u sy gewig verhoog deur byvoorbeeld kilometers ys bo -op te bou, sak dit verder in die mantel. Dit is wat gebeur het met die landmassas van Antarktika en Groenland, wat albei bedek is in 2km tot 3km dik ys. As aardverwarming al die ys laat smelt, sal die seevlak van die oseane met meer as 50 meter styg, wat al die kusstede ter wêreld dompel en honderde miljoene mense dakloos maak. Dit lyk voor die hand liggend. Wat minder duidelik is, is hoe dit kan ontvou.

As die hele ys wat Antarktika bedek, smelt, sal die vrystelling van sy gewig die gesteentes daaronder vernietig, wat, omdat dit op die mantel dryf, sal stamp. Dit word post-glacial rebound genoem. Die posisie met Groenland is soortgelyk: die kors daaronder word swaar gemaak deur die 3 miljoen biljoen liter water wat in die ys gehou word, en as die ys alles smelt, sal dele van die Noord -Amerikaanse tektoniese landmassa opstaan. As die gevolglike toename in die hoogte van die vasteland groter is as die seespieël, kan groot oorstromings vermy word. Om uit te vind watter scenario meer waarskynlik is, is uiters belangrik vir toekomstige geslagte, want een van hierdie resultate sal begin afspeel as aardverwarming toeneem.

Wat ons weet is dit: die wêreld se gemiddelde seevlak het sedert die begin van die 20ste eeu met 20 cm gestyg. Sommige daarvan is te danke aan die water wat termies uitbrei namate die oseane warmer word - aangesien warmer vloeistowwe meer volume inneem (dit is hoe vloeibare termometers werk). Sommige van die styging in seevlak was te wyte aan die ysplate van Groenland en Antarktika wat gesmelt het, en sommige as gevolg van die smelt van ander gletsers. Die stygende seevlakke is wêreldwyd: dit raak almal met 'n kuslyn, van klein eilande in die Stille Oseaan wat heeltemal ondergedompel sou word tot 'n groot land soos Bangladesh, waarna 'n styging van een meter in seevlak tot byna 'n vyfde van die land sou lei onder water en 30 miljoen mense verplaas. Alhoewel stygende seevlakke almal raak, beïnvloed die post-gletseropkoms slegs die kusstreekse wat verband hou met dele van die aardkors wat deur die Groenland- en Antarktiese ysplate verswak is.

Dit is moeilik om die belangrikheid van hierdie kwessie te oorskat, en ons het meer data en wetenskaplike kennis van hierdie vloeibare prosesse nodig. 'N Beperkte aantal gespesialiseerde satelliete, soos CryoSat, GRACE en ICESat-2-wat pas deur Nasa gelanseer is-word gebruik om ysdikte te monitor en modelle van post-glacial rebound te ontwikkel. Wat die wetenskap voorspel, is dat as die ys eers in die noordelike halfrond smelt, Groenland hoër kan styg as die gemiddelde seevlak, net soos dele van Noord -Amerika, en dus kan die seevlak aanvanklik daal. As die teenoorgestelde gebeur, en die Antarktiese ys smelt voor die Groenlandse ys, dan is dit die suidelike tektoniese plate wat eerste sal opspring en die hele oostelike kus van Noord -Amerika eers onder water gaan. Die groot onbekendes is hoe vinnig die ys op elke plek gaan, en hoe vinnig die post-glaciale rebound sal wees.

Ons moet hierdie prosesse vinnig beter verstaan, want as ons dit nie doen nie, kan dit te laat wees om katastrofe te voorkom. Hierdie kwessies oorheers nie nuusagenda nie, maar dit moet. Onlangs bedank die Franse minister van omgewingsake, met verwysing na die gebrek aan vordering en dringendheid van die president oor kwessies oor klimaatsverandering. Hierdeur het hy die kommer van die hele wetenskaplike gemeenskap uitgespreek oor wêreldleiers - ons het 'n stapsgewys verandering in die regering nodig. Maar daar is 'n punt: nie alle regerings voel dringend daaroor nie. En waarom? Miskien is dit omdat, soos die kwessie van post-glacial rebound toon, daar wenners en verloorders sal wees van aardverwarming. Lande soos Rusland sal byvoorbeeld minder geraak word deur styging in seevlak, en kan baat vind by 'n meer gematigde klimaat. Daarteenoor ly die VSA moontlik nie net aan nuwe droogtesones nie, maar die laagliggende oostelike kus word bedreig deur die versnelde verlies van Antarktiese ys. Namate die 21ste eeu voortduur en die ys steeds smelt, sal dit duideliker word watter lande 'n groter aansporing het om klimaatsverandering te versag, en die gevolglike geopolitiek het die moontlikheid om verdeeldheid en konflik te dryf.


Watter stede sal eerste in die see sink? Miskien nie diegene wat u verwag nie

B etter wetenskaplike begrip van aardverwarming maak die bespreking oor die geopolitieke gevolge daarvan steeds dringender. Eenvoudig gestel, daar gaan wenners en verloorders wees: warmer plekke en kouer plekke natter plekke en droër plekke en ja, plekke wat onder die see verdwyn. Maar die werklikheid is 'n bietjie ingewikkelder. Veral die seevlak veral op of af? Die antwoord lyk duidelik as u in ag neem dat Antarktika die afgelope 25 jaar 3 biljoen ton ys verloor het.

Maar om te verstaan ​​wat aan die gang is, moet ons eers besef dat die aarde nie solied is nie. Dit het ongeveer 4,5 miljard jaar gelede begin lewe as 'n bol warm vloeistof en ons planeet het sedertdien afgekoel. Reg in die middel van die aarde is 'n soliede kern van metaal gemaak van yster en nikkel teen 'n temperatuur van ongeveer 5.000C. Maar hierdie kern word omring deur 'n oseaan van gesmelte metaal van ongeveer 2 000 km dik, weer meestal yster en nikkel. Rondom hierdie is 'n rotslaag wat die mantel genoem word, tussen 500C en 900C, en by hierdie rooiwarm temperature gedra die rots hom oor 'n kort tydperk (sekondes, ure en dae) soos 'n vaste stof, maar soos 'n vloeistof oor langer tyd. tydperke (maande tot jare) - sodat die rots vloei, alhoewel dit nie gesmelt is nie. Bo -op die vloeistofmantel dryf die kors, wat soos die vel van die aarde is. Dit is 'n relatief dun laag koel rots wat tussen 30 en 100 km dik is en al die berge, woude, riviere, seë, vastelande bevat - ons wêreld.

Aangesien die kors op die vloeistofmantel dryf, as u sy gewig verhoog deur byvoorbeeld kilometers ys bo -op te bou, sak dit verder in die mantel. Dit is wat gebeur het met die landmassas van Antarktika en Groenland, wat albei bedek is in 2km tot 3km dik ys. As aardverwarming al die ys laat smelt, sal die seevlak van die oseane met meer as 50 meter styg, wat al die kusstede ter wêreld dompel en honderde miljoene mense dakloos maak. Dit lyk voor die hand liggend. Wat minder duidelik is, is hoe dit kan ontvou.

As die hele ys wat Antarktika bedek, smelt, sal die vrystelling van sy gewig die gesteentes daaronder vernietig, wat, omdat dit op die mantel dryf, sal opduik. Dit word post-glacial rebound genoem. Die posisie met Groenland is soortgelyk: die kors daaronder word swaar gemaak deur die 3 miljoen biljoen liter water wat in die ys gehou word, en as die ys alles smelt, sal dele van die Noord -Amerikaanse tektoniese landmassa opstaan. As die gevolglike toename in die hoogte van die vasteland groter is as die seevlakstyging, kan groot oorstromings vermy word. Om uit te vind watter scenario meer waarskynlik is, is uiters belangrik vir toekomstige geslagte, want een van hierdie resultate sal begin afspeel as aardverwarming toeneem.

Wat ons weet is dit: die wêreld se gemiddelde seevlak het sedert die begin van die 20ste eeu met 20 cm gestyg. Sommige daarvan is te danke aan die water wat termies uitbrei namate die oseane warmer word - aangesien warmer vloeistowwe meer volume inneem (dit is hoe vloeibare termometers werk). Sommige van die styging in seevlak was te wyte aan die ysplate van Groenland en Antarktika wat gesmelt het, en sommige as gevolg van die smelt van ander gletsers. Die stygende seevlakke is wêreldwyd: dit raak almal met 'n kuslyn, van klein eilande in die Stille Oseaan wat heeltemal onder water sou wees tot 'n groot land soos Bangladesh, waarna 'n styging van een meter in seevlak in byna 'n vyfde van die land sou lei onder water en 30 miljoen mense verplaas. Alhoewel stygende seevlakke almal beïnvloed, beïnvloed die post-glaciale rebound slegs die kuste wat verband hou met dele van die aardkors wat die Groenland- en Antarktiese ysplate afweer.

Dit is moeilik om die belangrikheid van hierdie kwessie te oorskat, en ons het meer data en wetenskaplike begrip van hierdie vloeibare prosesse nodig. 'N Beperkte aantal gespesialiseerde satelliete, soos CryoSat, GRACE en ICESat-2-wat pas deur Nasa gelanseer is-word gebruik om ysdikte te monitor en modelle van post-glacial rebound te ontwikkel. Wat die wetenskap voorspel, is dat as die ys eers in die noordelike halfrond smelt, Groenland hoër kan styg as die gemiddelde seevlak, net soos dele van Noord -Amerika, en dus kan die seevlak aanvanklik daal. As die teenoorgestelde gebeur, en die ys van die Antarktika smelt voor die Groenlandse ys, dan is dit die suidelike tektoniese plate wat eers opspring en die hele oostelike kus van Noord -Amerika eers onder water gaan. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.


Which cities will sink into the sea first? Maybe not the ones you expect

B etter scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent. Put simply, there are going to be winners and losers: hotter places and colder places wetter places and drier places and, yes, places that disappear under the sea. But the reality is a bit more complicated. In particular, are sea levels going up or down? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.

Yet to understand what is going on we first have to recognise that the Earth isn’t solid. It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since. Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C. But this core is surrounded by an approximately 2,000km-thick ocean of molten metal, again mostly iron and nickel. Surrounding this is a layer of rock called the mantle that is between 500C to 900C, and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds, hours, and days) but like a liquid over longer time periods (months to years) – so the rock flows, even though it is not molten. On top of the fluid mantle floats the crust, which is like the skin of the Earth. It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains, forests, rivers, seas, continents – our world.

Since the crust is floating on the fluid mantle, if you increase its weight by, for instance, building up kilometres of ice on top of it, then it sinks further into the mantle. This is what has happened to the landmasses of Antarctica and Greenland, which are both covered in 2km to 3km of thick ice. If global warming were to cause all that ice to melt, then the sea level of the oceans would rise by more than 50 metres, submerging all the coastal cities of the world and making hundreds of millions of people homeless. This seems obvious. What is less obvious is how it might unfold.

If the whole ice sheet covering Antarctica melts, the release of its weight will destress the rocks below, which, because they float on the mantle, will bob up. This is called post-glacial rebound. The position with Greenland is similar: the crust below it is being weighed down by the 3 million trillion litres of water held in the ice sheet, and if that ice sheet all melts then parts of the North American tectonic landmass will rise up. If the resulting increase in the height of the continent is bigger than the sea level rise, then major flooding may be avoided. Working out which scenario is more likely is vitally important for future generations, because one of these results will start to play out if global warming intensifies.

What we know is this: the global mean sea level has risen 20cm since the beginning of the 20th century. Some of this has been owing to the water thermally expanding as the oceans have got hotter – since hotter liquids take up more volume (this is how liquid thermometers work). Some of the rise in sea level has been due to the Greenland and Antarctic ice sheets melting, and some due to other glaciers melting. The rising sea levels are global: they affect everyone with a coastline, from tiny Pacific islands that would be entirely submerged to a huge country such as Bangladesh, for which a one-metre rise in sea levels would result in nearly a fifth of the country being submerged and 30 million people being displaced. But while rising sea levels affect everyone, the post-glacial rebound affects only the coasts connected to parts of the Earth’s crust weighed down by the Greenland and Antarctic ice sheets.

It is hard to overestimate the importance of this issue, and we badly need more data and scientific understanding of these liquid processes. A limited number of specialised satellites, such as CryoSat, GRACE and ICESat-2 – just launched by Nasa – are being used to monitor ice thickness and to develop models of post-glacial rebound. What the science predicts is that if the ice melts first in the northern hemisphere, then Greenland may bounce up higher than the average sea level, as will parts of North America, and so sea levels there may initially go down. If the opposite happens, and the Antarctic ice melts before the Greenland ice sheet, then it is the southern tectonic plates that will bounce up first and the whole of North America’s eastern coast will go under water first. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.


Which cities will sink into the sea first? Maybe not the ones you expect

B etter scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent. Put simply, there are going to be winners and losers: hotter places and colder places wetter places and drier places and, yes, places that disappear under the sea. But the reality is a bit more complicated. In particular, are sea levels going up or down? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.

Yet to understand what is going on we first have to recognise that the Earth isn’t solid. It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since. Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C. But this core is surrounded by an approximately 2,000km-thick ocean of molten metal, again mostly iron and nickel. Surrounding this is a layer of rock called the mantle that is between 500C to 900C, and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds, hours, and days) but like a liquid over longer time periods (months to years) – so the rock flows, even though it is not molten. On top of the fluid mantle floats the crust, which is like the skin of the Earth. It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains, forests, rivers, seas, continents – our world.

Since the crust is floating on the fluid mantle, if you increase its weight by, for instance, building up kilometres of ice on top of it, then it sinks further into the mantle. This is what has happened to the landmasses of Antarctica and Greenland, which are both covered in 2km to 3km of thick ice. If global warming were to cause all that ice to melt, then the sea level of the oceans would rise by more than 50 metres, submerging all the coastal cities of the world and making hundreds of millions of people homeless. This seems obvious. What is less obvious is how it might unfold.

If the whole ice sheet covering Antarctica melts, the release of its weight will destress the rocks below, which, because they float on the mantle, will bob up. This is called post-glacial rebound. The position with Greenland is similar: the crust below it is being weighed down by the 3 million trillion litres of water held in the ice sheet, and if that ice sheet all melts then parts of the North American tectonic landmass will rise up. If the resulting increase in the height of the continent is bigger than the sea level rise, then major flooding may be avoided. Working out which scenario is more likely is vitally important for future generations, because one of these results will start to play out if global warming intensifies.

What we know is this: the global mean sea level has risen 20cm since the beginning of the 20th century. Some of this has been owing to the water thermally expanding as the oceans have got hotter – since hotter liquids take up more volume (this is how liquid thermometers work). Some of the rise in sea level has been due to the Greenland and Antarctic ice sheets melting, and some due to other glaciers melting. The rising sea levels are global: they affect everyone with a coastline, from tiny Pacific islands that would be entirely submerged to a huge country such as Bangladesh, for which a one-metre rise in sea levels would result in nearly a fifth of the country being submerged and 30 million people being displaced. But while rising sea levels affect everyone, the post-glacial rebound affects only the coasts connected to parts of the Earth’s crust weighed down by the Greenland and Antarctic ice sheets.

It is hard to overestimate the importance of this issue, and we badly need more data and scientific understanding of these liquid processes. A limited number of specialised satellites, such as CryoSat, GRACE and ICESat-2 – just launched by Nasa – are being used to monitor ice thickness and to develop models of post-glacial rebound. What the science predicts is that if the ice melts first in the northern hemisphere, then Greenland may bounce up higher than the average sea level, as will parts of North America, and so sea levels there may initially go down. If the opposite happens, and the Antarctic ice melts before the Greenland ice sheet, then it is the southern tectonic plates that will bounce up first and the whole of North America’s eastern coast will go under water first. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.


Which cities will sink into the sea first? Maybe not the ones you expect

B etter scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent. Put simply, there are going to be winners and losers: hotter places and colder places wetter places and drier places and, yes, places that disappear under the sea. But the reality is a bit more complicated. In particular, are sea levels going up or down? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.

Yet to understand what is going on we first have to recognise that the Earth isn’t solid. It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since. Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C. But this core is surrounded by an approximately 2,000km-thick ocean of molten metal, again mostly iron and nickel. Surrounding this is a layer of rock called the mantle that is between 500C to 900C, and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds, hours, and days) but like a liquid over longer time periods (months to years) – so the rock flows, even though it is not molten. On top of the fluid mantle floats the crust, which is like the skin of the Earth. It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains, forests, rivers, seas, continents – our world.

Since the crust is floating on the fluid mantle, if you increase its weight by, for instance, building up kilometres of ice on top of it, then it sinks further into the mantle. This is what has happened to the landmasses of Antarctica and Greenland, which are both covered in 2km to 3km of thick ice. If global warming were to cause all that ice to melt, then the sea level of the oceans would rise by more than 50 metres, submerging all the coastal cities of the world and making hundreds of millions of people homeless. This seems obvious. What is less obvious is how it might unfold.

If the whole ice sheet covering Antarctica melts, the release of its weight will destress the rocks below, which, because they float on the mantle, will bob up. This is called post-glacial rebound. The position with Greenland is similar: the crust below it is being weighed down by the 3 million trillion litres of water held in the ice sheet, and if that ice sheet all melts then parts of the North American tectonic landmass will rise up. If the resulting increase in the height of the continent is bigger than the sea level rise, then major flooding may be avoided. Working out which scenario is more likely is vitally important for future generations, because one of these results will start to play out if global warming intensifies.

What we know is this: the global mean sea level has risen 20cm since the beginning of the 20th century. Some of this has been owing to the water thermally expanding as the oceans have got hotter – since hotter liquids take up more volume (this is how liquid thermometers work). Some of the rise in sea level has been due to the Greenland and Antarctic ice sheets melting, and some due to other glaciers melting. The rising sea levels are global: they affect everyone with a coastline, from tiny Pacific islands that would be entirely submerged to a huge country such as Bangladesh, for which a one-metre rise in sea levels would result in nearly a fifth of the country being submerged and 30 million people being displaced. But while rising sea levels affect everyone, the post-glacial rebound affects only the coasts connected to parts of the Earth’s crust weighed down by the Greenland and Antarctic ice sheets.

It is hard to overestimate the importance of this issue, and we badly need more data and scientific understanding of these liquid processes. A limited number of specialised satellites, such as CryoSat, GRACE and ICESat-2 – just launched by Nasa – are being used to monitor ice thickness and to develop models of post-glacial rebound. What the science predicts is that if the ice melts first in the northern hemisphere, then Greenland may bounce up higher than the average sea level, as will parts of North America, and so sea levels there may initially go down. If the opposite happens, and the Antarctic ice melts before the Greenland ice sheet, then it is the southern tectonic plates that will bounce up first and the whole of North America’s eastern coast will go under water first. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.


Which cities will sink into the sea first? Maybe not the ones you expect

B etter scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent. Put simply, there are going to be winners and losers: hotter places and colder places wetter places and drier places and, yes, places that disappear under the sea. But the reality is a bit more complicated. In particular, are sea levels going up or down? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.

Yet to understand what is going on we first have to recognise that the Earth isn’t solid. It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since. Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C. But this core is surrounded by an approximately 2,000km-thick ocean of molten metal, again mostly iron and nickel. Surrounding this is a layer of rock called the mantle that is between 500C to 900C, and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds, hours, and days) but like a liquid over longer time periods (months to years) – so the rock flows, even though it is not molten. On top of the fluid mantle floats the crust, which is like the skin of the Earth. It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains, forests, rivers, seas, continents – our world.

Since the crust is floating on the fluid mantle, if you increase its weight by, for instance, building up kilometres of ice on top of it, then it sinks further into the mantle. This is what has happened to the landmasses of Antarctica and Greenland, which are both covered in 2km to 3km of thick ice. If global warming were to cause all that ice to melt, then the sea level of the oceans would rise by more than 50 metres, submerging all the coastal cities of the world and making hundreds of millions of people homeless. This seems obvious. What is less obvious is how it might unfold.

If the whole ice sheet covering Antarctica melts, the release of its weight will destress the rocks below, which, because they float on the mantle, will bob up. This is called post-glacial rebound. The position with Greenland is similar: the crust below it is being weighed down by the 3 million trillion litres of water held in the ice sheet, and if that ice sheet all melts then parts of the North American tectonic landmass will rise up. If the resulting increase in the height of the continent is bigger than the sea level rise, then major flooding may be avoided. Working out which scenario is more likely is vitally important for future generations, because one of these results will start to play out if global warming intensifies.

What we know is this: the global mean sea level has risen 20cm since the beginning of the 20th century. Some of this has been owing to the water thermally expanding as the oceans have got hotter – since hotter liquids take up more volume (this is how liquid thermometers work). Some of the rise in sea level has been due to the Greenland and Antarctic ice sheets melting, and some due to other glaciers melting. The rising sea levels are global: they affect everyone with a coastline, from tiny Pacific islands that would be entirely submerged to a huge country such as Bangladesh, for which a one-metre rise in sea levels would result in nearly a fifth of the country being submerged and 30 million people being displaced. But while rising sea levels affect everyone, the post-glacial rebound affects only the coasts connected to parts of the Earth’s crust weighed down by the Greenland and Antarctic ice sheets.

It is hard to overestimate the importance of this issue, and we badly need more data and scientific understanding of these liquid processes. A limited number of specialised satellites, such as CryoSat, GRACE and ICESat-2 – just launched by Nasa – are being used to monitor ice thickness and to develop models of post-glacial rebound. What the science predicts is that if the ice melts first in the northern hemisphere, then Greenland may bounce up higher than the average sea level, as will parts of North America, and so sea levels there may initially go down. If the opposite happens, and the Antarctic ice melts before the Greenland ice sheet, then it is the southern tectonic plates that will bounce up first and the whole of North America’s eastern coast will go under water first. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.


Which cities will sink into the sea first? Maybe not the ones you expect

B etter scientific understanding of global warming makes the discussion about its geopolitical consequences increasingly urgent. Put simply, there are going to be winners and losers: hotter places and colder places wetter places and drier places and, yes, places that disappear under the sea. But the reality is a bit more complicated. In particular, are sea levels going up or down? The answer seems clear when you consider that Antarctica has lost 3 trillion tonnes of ice in the last 25 years.

Yet to understand what is going on we first have to recognise that the Earth isn’t solid. It started life as a ball of hot liquid about 4.5bn years ago and our planet has been cooling ever since. Right at the centre of the Earth is a solid core of metal made of iron and nickel at a temperature of approximately 5,000C. But this core is surrounded by an approximately 2,000km-thick ocean of molten metal, again mostly iron and nickel. Surrounding this is a layer of rock called the mantle that is between 500C to 900C, and at these red-hot temperatures the rock behaves like a solid over short periods of time (seconds, hours, and days) but like a liquid over longer time periods (months to years) – so the rock flows, even though it is not molten. On top of the fluid mantle floats the crust, which is like the skin of the Earth. It is a relatively thin layer of cool rock that is between 30 to 100km thick and contains all the mountains, forests, rivers, seas, continents – our world.

Since the crust is floating on the fluid mantle, if you increase its weight by, for instance, building up kilometres of ice on top of it, then it sinks further into the mantle. This is what has happened to the landmasses of Antarctica and Greenland, which are both covered in 2km to 3km of thick ice. If global warming were to cause all that ice to melt, then the sea level of the oceans would rise by more than 50 metres, submerging all the coastal cities of the world and making hundreds of millions of people homeless. This seems obvious. What is less obvious is how it might unfold.

If the whole ice sheet covering Antarctica melts, the release of its weight will destress the rocks below, which, because they float on the mantle, will bob up. This is called post-glacial rebound. The position with Greenland is similar: the crust below it is being weighed down by the 3 million trillion litres of water held in the ice sheet, and if that ice sheet all melts then parts of the North American tectonic landmass will rise up. If the resulting increase in the height of the continent is bigger than the sea level rise, then major flooding may be avoided. Working out which scenario is more likely is vitally important for future generations, because one of these results will start to play out if global warming intensifies.

What we know is this: the global mean sea level has risen 20cm since the beginning of the 20th century. Some of this has been owing to the water thermally expanding as the oceans have got hotter – since hotter liquids take up more volume (this is how liquid thermometers work). Some of the rise in sea level has been due to the Greenland and Antarctic ice sheets melting, and some due to other glaciers melting. The rising sea levels are global: they affect everyone with a coastline, from tiny Pacific islands that would be entirely submerged to a huge country such as Bangladesh, for which a one-metre rise in sea levels would result in nearly a fifth of the country being submerged and 30 million people being displaced. But while rising sea levels affect everyone, the post-glacial rebound affects only the coasts connected to parts of the Earth’s crust weighed down by the Greenland and Antarctic ice sheets.

It is hard to overestimate the importance of this issue, and we badly need more data and scientific understanding of these liquid processes. A limited number of specialised satellites, such as CryoSat, GRACE and ICESat-2 – just launched by Nasa – are being used to monitor ice thickness and to develop models of post-glacial rebound. What the science predicts is that if the ice melts first in the northern hemisphere, then Greenland may bounce up higher than the average sea level, as will parts of North America, and so sea levels there may initially go down. If the opposite happens, and the Antarctic ice melts before the Greenland ice sheet, then it is the southern tectonic plates that will bounce up first and the whole of North America’s eastern coast will go under water first. The big unknowns are how quick the ice will go in each location, and how fast the post-glacial rebound will be.

We need to get a better understanding of these processes fast, because if we don’t it may be too late to avert catastrophe. These issues don’t dominate news agendas but they should. Recently the French environment minister resigned, citing the president’s lack of progress and urgency on climate change issues. In doing so, he voiced the concern of the whole scientific community about world leaders – we need a step change in governmental action. But there’s the rub: not all governments feel urgent about it. En waarom? Perhaps it’s because, as the issue of post-glacial rebound shows, there will be winners and losers from global warming. For instance, countries such as Russia will be less affected by sea level rises, and may benefit from a more temperate climate. In contrast, the US may not only suffer from new drought zones, but its low-lying eastern coast is threatened by the accelerating loss of Antarctic ice. As the 21st century continues and the ice continues to melt, it will become clearer which countries have a greater incentive to mitigate climate change, and the resulting geopolitics has the potential to drive division and conflict.