It was so cold that frost formed inside trees in the middle of summer. Traces of this have been found in Russia, among other places. It is very rare for trees to freeze internally during the summer.

The long, harsh Fimbul winter is not a myth

How would this freezing leave a "trace"?

  • $\begingroup$ the trace is probably no/narrow growth rings in the trees for this period 535-537,there is information from other areas of the world that the sun was as dim as the moon during parts of this period.link only in norwegian no.wikipedia.org/wiki/Fimbulvinter $\endgroup$ Commented Sep 7, 2020 at 4:40
  • $\begingroup$ here is an other source smithsonianmag.com/science-nature/… $\endgroup$ Commented Sep 7, 2020 at 13:07
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    $\begingroup$ @trondhansen There is the Exploding tree phenomenon, but this WP article gives no modern scientific sources. $\endgroup$ Commented Sep 7, 2020 at 16:42

1 Answer 1


Frost leaves a record by damaging the cell structure, creating a "frost ring". Hadd et al discuss data on frost rings in N. American trees.

There is specific discussion of the Fimbul event (in AD 536) in this paper by Helama et al. 2019 (unfortunately with a pay wall). There is also discussion that there may have been a similar event in 1627 BC.

If the data is good enough, it may be possible to get an estimate of the time of year at which the damage occurred by looking at the structure of the damaged cells and seeing how it fits with what is known about the annual cycle of cell growth. This requires more detailed analysis than the widely used approach of measuring ring thickness to estimate annual mean (or growing season mean) temperature.

There is more recent information on ultra-cold summers in the Northern hemisphere, the "year without winter".

  • $\begingroup$ But, the damage occurs in the newly growing outer layers and only later becomes internal. Is this what they mean? $\endgroup$ Commented Oct 19, 2020 at 0:18

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