Oppsummering: Ny informasjon tyder på at nedsmeltingen av isbeer i Alpene begynte tidligere enn begynnelsen av den industrielle revolusjon. Under den lille istid (1300 -1870) nådde isbreene sitt høyeste nivå. Deretter begynte nedsmelting som et resultat av naturlige klimaendringer, upåvirket av menneskelige aktiviteter. Det har tidliger vært antatt at store sotutslipp fra industriene etter 1860-årenen var ansvarlig for økte bresmelting. Men mellom 1850 og 1875-årene var ikke atmosfærens inhold av sotpartikler høyere enn det som ville være normalt. Det var først etter disse årene at sotpartikler begynte å overstige naturlige nivåer. Studiet tar ikke stilling til om menneskeskapte aktiviteter bidrar til klimaendringer, som kan ha påvirket bresmeltingen.
Kilde: Global Warming Policy Foundation (GWPF): Swiss Info 21.10.2018
New Study Reveals Alpine Glaciers Started Melting Much Earlier Than Thought (Swiss info, 21 October 2018)
New reserch by a Swiss institute has thrown doubt on the widespread assumption that the melting of Alpine glaciers began with the onset of industrialisation in the middle of the 19th century.
To date, writes Swiss public broadcaster SRF, many researchers have assumed that glacial retreat began around 1860 with the increased volumes of soot and smoke belched out by the new factories of the industrial age.
However, researchers from the Paul Scherrer Institute have found that a deeper analysis of soot levels within the ice itself throws this assumption into doubt.
Working with (among others) the Fiescherhorn glacier between cantons Bern and Valais, the scientists managed to trace soot particles in the ice right back to 1740; a veritable “history book” of what would have been in the atmosphere at the time, said researcher Michael Sigl.
Interestingly, they found that industrial soot most likely does not account for the melting of glaciers between 1850 and 1875, since it was only after that year that levels of soot in the air exceeded natural atmospheric levels for Central Europe.
Thus, according to the researchers, the so-called Little Ice Age (c. 1300-1870), during which Alpine glaciers reached their peak volume, likely came to an end as a result of natural climatic variations rather than being precipitated by human interference.
Indeed, as Sigl said in a separate interview in the Le Matin Dimanche newspaper on Sunday, “in 1875, some 80% of the glaciers’ retreat had already occurred”.
He nevertheless stressed that the study did not provide any grand refutation of the idea that human actions contribute to global warming; rather, he said, “the question is to know from when human activities began to take effect on the climate” – a question that remains open.