Forbes magazine briefly described a green swan event as
“a climate event that is unexpected and rare, with far-reaching impacts.”
https://www.forbes.com/sites/servicenow/2021/06/18/sustainable-finance-surviving-the-green-swan/
This concept is obviously related to Nassim Nicholas Taleb’s renowned book The Black Swan: The Impact Of The Highly Improbable.
However, if that description leaves you wishing to know more, the BIS has devoted an entire book to the issue of how Central Banks can mitigate the impact of climate change on the financial system; The green swan Central banking and financial stability in the age of climate change.