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Klimaendringer tar ikke insektene
11. mai 2020
Av Morten Jødal, biolog
Studier de siste årene har fortalt at insektene er i tilbakegang. Vi har sett store tall (se her og her og her og her) og blitt fortalt at klimaendringer står bak. En ny meta-analyse viser langt mindre tall, og avviser klimaendringer som årsaksfaktor.
De nye studien som er publisert i Science har gått gjennom 166 langtidsstudier, fra 1 676 steder. Den bekrefter en nedgang både i antall og biomasse av landlevende (terrestre) insekter, men gir langt lavere tall. Og den forteller dessuten at insekter knyttet til ferskvann er i framgang.
For de terrestre insektene er nedgangen 9 prosent per tiår, som er 1/6 av hva de siste alarmerende oppslagene har indikert. Det er like fullt svært store tall. For de vannlevende artene er økningen på 11 prosent per tiår. Begge trendene er tydeligst i Nord-Amerika og Europa, hvorfra det også finnes best tall. Studien sier at det ikke finnes gode tall som kan slå fast at nedgangen eller oppgangen finner sted i alle miljøer, og i alle geografiske områder. Den slår i stedet fast at det er stor variasjon selv på geografisk meget nærliggende områder, hvilket i klartekst indikerer: Insektnedgangen kan ikke knyttes til klimaendringer.
Det er først og fremst i Nord-Amerika er nedgangen av terrestre insekter er sterkest, men vi ser det også i noen regioner i Europa. Tar vi bort dataene for Nord-Amerika, er det fremdeles en nedgang, men den blir mindre.
Årsaken til at ferskvannsinsekter klarer seg bedre, er sannsynligvis at ferskvannslokaliteter utvikles i en positiv retning (her og her og her), men studien slår også fast at 1) det kan skyldes global oppvarming, samt 2) en økt tilgang på næringssalter.
I Europa har nedgangen i terrestre insekter forsterket seg siden 2005, mens det ikke har skjedd i Nord-Amerika.
Studien så på tall for både vernede og ikke vernede lokaliteter, og konkluderte med at færre insekter går tapt på vernede steder. Det gir en sterk indikasjon: Det er arealendringer som ligger bak nedgangen i både insektantall og insektbiomasse. GIS-data, hvor de så på insekter i naturområder, landbruksområder og urbaniserte arealer, bekrefter at nedgangen kan knyttes til urbanisering og tap av livsområder (habitat), muligens også til bruk av kjemikalier i landbruket.
Konklusjoner
Det kan trekkes to viktige konklusjoner fra denne studien. For det første er tapene av terrestre insekter omtrent 1/6 av hva som har framkommet de 2-3 siste årene. Og for det andre er det arealbruk som er problemet, og ikke klimaendringer. I den grad klimaendringene slår inn, resulterer de i flere vannlevende insekter.
Det grønne skiftet, med en overgang til fornybar energi, er meget arealkrevende. Vindmøller, biodrivstoff og solceller i stor skala tar alle enormt med plass. Det er tilsvarende urbaniseringsfaktorer som har redusert biomangfoldet over hele kloden de siste årene, også insekter. Det grønne skiftet er altså en trussel mot både dyr og planter. Med i denne trusselen er også økologisk produsert mat, som i snitt gir halv avkastning i forhold til det konvensjonelle. Skulle politikere få til en slik overgang, krever det enormt store jordbruksarealer, og vil representere en trussel mot insekter på en skala vi aldri tidligere har sett.
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