Why is a number of notifications showing up on one of my calendars? MacOS has just (last couple of days) started placing a red circle with a white number on the Calendar (version 8.0 (2034.9)) icon, as if there are calendar notifications sitting around, waiting to be read. It's just like the mail notification that tells you how many unread emails you have, or the App Center notification that tells you how many unapplied updates you have.

When I open up the calendar, I likewise see that number next to one of my Google calendars.

But in reality there are no notifications that need dismissal. That calendar hasn't even had any events this week. The context menu offers no clues, nor do I see anything in the Preferences that illuminates this new behavior. The Notification Center has nothing from the Calendar.

What on earth is causing this? How do I get rid of this Red Bubble of Disinformation?
I discovered the cause once I arrived at work: the notifications, which came from an airline, were sitting on my desktop computer, waiting to be approved. For some reason, they didn't pop up on my laptop while I was at home. (possibly different OS version: 10.11.6 vs. 10.10.5)

It still isn't disappearing from my laptop, but hopefully if I wait it out a while Apple's Calendar will get around to noticing.