By chance, I typed
gpg2 --search myemailaddress on the command line, and searched public keyservers for my email address (I'd actually just meant to search my local keyring, for which I should have used
gpg2 -k myemailaddress).
To my surprise, I discovered that there was a public key, created just a few days ago, which as far as I know I did not create. It wasn't on my local keyring, or on the keyrings of other computers on which I've ever used GPG.
I'm at a loss how this may have happened. Are there any applications that would "helpfully" create OpenPGP keys and publish them, without telling me or attaching them to my local keychain? Is there some scam for which this would be useful?