Historical Warmth in Scandinavia

Clues hidden deep in the trunks of ancient trees have revealed that last summer was the northern hemisphere's hottest in 2,000 years. 

Or at least that's what the BBC says, relaying along information provided by Ulf Büntgen, professor of environmental systems analysis at the University of Cambridge and co-author of the study. Researchers say that temperatures last June, July and August were nearly 4C warmer than the coldest summer two millennia ago. If that's not a typo, so what? Wouldn't even a normal summer, whatever that is, obviously be significantly warmer than the coldest summer two millennia ago?

A different study, using similar proxy indicators, has produced a very different result. Printed in the on-line Science Advances, this is the abstract of a study conducted of the faunal diversity from Nygrotta, a former entrance of the Storsteinhola cave system in Kjøpsvik, municipality of Narvik, northern Norway.

Abstract

 Paleo-archives are essential for our understanding of species responses to climate warming, yet such archives are extremely rare in the Arctic. Here, we combine morphological analyses and bulk-bone metabarcoding to investigate a unique chronology of bone deposits sealed in the high-latitude Storsteinhola cave system (68°50′ N 16°22′ E) in Norway. This deposit dates to a period of climate warming from the end of the Late Glacial [~13 thousand calibrated years before the present (ka cal B.P.)] to the Holocene thermal maximum (~5.6 ka cal B.P.). Paleogenetic analyses allow us to exploit the 1000s of morphologically unidentifiable bone fragments resulting in a high-resolution sequence with 40 different taxa, including species not previously found here. Our record reveals borealization in both the marine and terrestrial environments above the Arctic Circle as a naturally recurring phenomenon in past periods of warming, providing fundamental insights into the ecosystem-wide responses that are ongoing today.

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What they're saying is that bones of animals found in caves at nearly the same latitude as Prudhoe Bay, Alaska, dated from 9600 to 9005 years before the present,were animals that are no longer found that far north, such as species of grouse and cats because it was much warmer than today with intermittent cooling. It would appear that the Holocene thermal maximum of that era was dramatically warmer than the present, indicating that at least the northern hemisphere was also very much warmer than it is today.

This work was financially supported by The Research Council of Norway and Fonds de Recherche du Québec – Nature et Technologie (FRQNT) provided a doctoral fellowship to A.B.