I don't understand why not. That's the literal definition of a commons in the political economy sense -- a public resource everyone can take from freely. (As opposed to a public resource that is managed via licenses, auctions, limits, etc.) On what basis would you not call them a commons, in political economy?

The entire point of the "tragedy of the commons" is the tragedy of overfishing, the tragedy of CO2 levels, because nobody is in charge of managing it.