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A very recent study by Swedish scientists appearing in the journal Climate of the Past examining bottom water temperature (BWT) off the coast of Western Sweden (Gullmar Fjord) going back 2500 years found that “the most recent warming of the 20th century does not stand out.”

Team of researchers led by Irina Polovodova Asteman, University of Gotheberg, produced a record of bottom water temperature off the coast of western Sweden and found 20th century warming “does not stand out.” Photo: ResearchGate, University of Gothenburg

The 2500-year winter temperature record was of reconstructed by using a fjord sediment archive from the NE Atlantic and through analysis of oxygen isotopes and other methods. The study was based on an approximately 8-meter long sediment core extracted from the Gullmar Fjord (Sweden).

They found that the Gullmar Fjord d18O record mainly reflects variability of the winter bottom water temperatures with a minor salinity influence.

The researchers also pointed out that a comparison with instrumental winter temperature observations from Central England and Stockholm shows that the fjord record picks up the contemporary warming of the 20th century, see following diagrams:

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Chart: Polovodova et al 2018

According to the scientists, the Gullmar Fjord record shows a substantial and long-term warming during the Roman Warm Period (~350 BCE – 450 CE) which was followed by variable bottom water temperatures during the Dark Ages (~450 – 850 CE).

The Viking Age/Medieval Climate Anomaly (~850 – 1350 CE) is also indicated by positive bottom water temperature anomalies, while the Little Ice Age (~1350 – 1850 CE) is characterized by a long-term cooling with distinct multidecadal variability.

The team of Swedish scientists, led by Irina Polovodova Asteman, Department of Marine Sciences, University of Gothenburg, Sweden, noted “the most recent warming of the 20th century does not stand out, but appears to be comparable to both the Roman Warm Period and the MCA (Medieval Climate Anomaly).”