I recently read Ferguson's The Vikings and was struck by the notion that the legend of Fimbulwinter has its origin in Procopius's "year [when] the sun shone like the moon", and that the legend of Ragnarök likewise in stories of the depopulation of the Mediterranean basin by the Plague of Justinian. It's not a theory I've seen elsewhere and I'd like to know what support is available for it.
Unfortunately for me, given that I have very little Swedish, the only source I've been able to find for this very interesting notion is a 2007 paper called "Fimbulvinteren, Ragnarök, och Klimatkrisen år 536-537 e. kr." (Bo Gräslund, Saga och Sed). Which I can't read.
Does anyone know of an English translation of this paper, or if this theory has been properly discussed otherwise in an English-language publication? Can anyone speak to it from their own scholarship?
Or do I need to just finally buckle down and learn Swedish?
This is a very exciting topic! I don't know Swedish, but Graslund wrote an English article on this a few years later: 'Twilight of the gods? The ‘dust veil event’ of AD 536 in critical perspective', Antiquity, 86 (2012), pp.428-443. This should hopefully do the job!
The cloud was a fairly well-recorded phenomenon and was discussed in many sources beyond Procopius; a summary can be found in A. Arjava, 'The Mystery Cloud of 536 CE in the Mediterranean Sources', Dumbarton Oaks Papers, 59 (2005). This paper however argues that it wasn't a particularly devastating event (at least, no worse than any other famine or natural disasters of the time), mostly because these sources were far more concerned about the plague that followed a few years later. Scandinavia is beyond my area of expertise though, so you will have to make do with Graslund's article. Interestingly, it is cited in two even newer articles concerning the cloud's impact in Sweden and Estonia, which might be useful for you as well.
More generally, the cloud and the plague have a wide range of literature dedicated to them. For an older view of 536 (possibly less useful because of more recent studies on this), see J. Gunn (ed.), The Years without Summer: Tracing A.D. 536 and Its Aftermath (2000). On the plague, see L. Little (ed.), Plague and the End of Antiquity: The Pandemic of 541–750 (2006). To tie this together, take a look at M. McCormick et al., 'Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence', Journal of Interdisciplinary History, 43 (2012) for an overview of how the environment might have impacted on the Roman world. There is also another very exciting development from February year - the postulation of a 'late antique little ice age' that started in 536! Conveniently, this article is open access and can be found here.
I hope this is helpful!