ARCTIC SEA ICE DECLINE EXAGGERATED

Any day now the Arctic sea-ice will cease melting and start to refreeze as the brief boreal summer draws to a close. It’s been a cool and stormy summer in those parts and this year’s sea-ice minimum will be one of the highest of the past decade at around 4.73 million sq km which is greater than in 2020, 2019, 2018, 2017, 2016, 2015, 2012, 2011, 2008 and 2007.

Putting the Arctic sea-ice variability into a longer perspective few realise that during the early 20th century the Arctic experienced a period of remarkable warming which is not well understood. Aizawa et al reporting in Geophysical Research Letters use what they call a “state-of-the-art” climate model that appears to successfully reproduce the warming event using internal climate variability and the influences of the Sun and volcanoes, in doing so it casts light on the balance of the effects on the region today.

Looking on the longer term Helama et al in Climate Dynamics 2021 note that Holocene climate variability is punctuated by episodic climatic events such as the Little Ice Age (LIA) predating the industrial-era warming. Their dates and causes are controversial. Even more crucially they add, it is uncertain whether earlier events represent climatic regimes similar to the LIA. So they analyse a new 7500-year long palaeoclimate record tailored to detect LIA-like climatic regimes from northern European tree-ring data.

As well as the actual 17th Century LIA, they found many 100–800 year periods with cold temperatures combined with clear sky conditions from 540 CE, 1670 BCE, 3240 BCE and 5450 BCE onwards. In total these LIA-like regimes covered 20% of the study period. They notes that the ongoing decline in Arctic sea-ice extent is mirrored in their data which shows reversal of LIA-like conditions since the late nineteenth century.

So in a real sense the Arctic sea-ice extent is an emblem of climate change and the various forces contributing to it. Today, as the well-defined ice edge that stretches along most of the Russian side of the Arctic Ocean starts to freeze, the only certain thing is the oncoming cold and dark.

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