The spectacular sky in Edvard Munch’s iconic set of paintings and pastels, “The Scream” (1893–1910), may have less to do with the tortured figure’s psychological state — or a volcanic eruption, as some have hypothesized — and more to do with the clouds the artist saw over Oslo one day at sunset. In a research paper presented this week at the general assembly of the European Geosciences Union in Vienna, three meteorologists argue that Munch’s wavy red, yellow, and blue skies are in fact a representation of a rare nacreous or “mother-of-pearl” cloud formation.

The study, titled “Screaming Clouds,” was carried out by Norwegian meteorologists Øyvind Nordli and Svein M. Fikke and the late Icelandic meteorologist Jón Egill Kristjánsson, and published in last month’s issue of the journal Weather.

“If we take Edvard Munch’s words literally and compare them with the sharp colors and distinct and undulating shape of the sky in ‘The Scream,’ it is our opinion that they fit well with the appearance of mother-of-pearl clouds,” they write, citing a poem Munch wrote in his diary around 1890–92 that mentions “flaming clouds as blood” above Oslo. “Such clouds appear in the stratosphere only at high latitudes and have been known in the Nordic countries since the second half of the 19th century.”

The scientists not only explain the meteorological phenomena that cause mother-of-pearl clouds’ unique “brilliance of colors and strong intensity,” but also recap the entire early history of such formations’ appearances in Norway based on the logbooks of the Christiania Observatory and amateur meteorologists. Records show instances of mother-of-pearl clouds in 1890, 1891, and 1892, the year that Munch created “Despair,” which many consider the precursor to his masterpiece.

The authors also make a point of refuting the theory articulated by US astronomers Donald W. Olson, Marilynn S. Olson, and Russell L. Doescher in 2004, suggesting that Munch’s gripping skies captured the effects of the cataclysmic 1883 eruption of the Indonesian volcano Krakatoa. They point out that Munch’s poem and contemporaneous writings by his friend and fellow artist Christian Skredsvig suggest that the red sky phenomenon Munch struggled to paint was a one-time occurrence, whereas red sunrises and sunsets in the eruption’s aftermath were more or less daily occurrences in much of the world. Furthermore, they note that the “global haze” generated by the sulphuric gases thrown up by Krakatoa would explain the sky’s color, but not its wavy pattern.

“From this discussion we find very strong indications that Edvard Munch was overwhelmed by an event of mother-of-pearl clouds in Oslo, at some time before 1892,” the scientists conclude. “It is the interpretation of the authors that by painting ‘Despair,’ Edvard Munch broke a mental barrier for himself. He painted the flaring sky, ‘red as blood,’ and his own unrest.”

Though “The Scream” is not the subject of quite as many more-or-less rigorous theories as Leonardo da Vinci’s “Mona Lisa,” there have been plenty over the years, from the slaughterhouse theory to the Peruvian mummy theory. At least one, the bird shit theory, has been definitively disproven.

Read the full “Screaming Clouds” paper here.