Nassim Nicholas Taleb popularized the concept of a Black Swan event in his 2007 book, The Black Swan: The Impact of the Highly Improbable. Taleb laid out three requirements: the event must be unknown and unpredictable, it must cause a massive impact and people then try to rationalize that it really was predictable after all.
Now that the BIS has guzzled the green global warming Kool-Aid, it suggests that a 'Green Swan' event is unpredictable as to when it will occur, but is absolutely certain that it will occur.
Many central banks already contribute to the effort by monitoring climate-related risks through stress tests, incorporating environmental, social and governance criteria in pension funds, or working with banks on disclosing carbon-intensive exposure to assess potential financial-stability risks. [Bank of France Governor] Villeroy says that's simply not enough however.