Where to store environmental variables

According to this article I should create files like PRODUCTION or STAGING with lists of hosts that belong to these environments.

But how can I specify variables for these environments? For example variable ERROR_REPORTING.

Is there any way to create something similar to /group_vars ? For example /environment_vars ?

In my case (many ways to do this), everything in the production inventory is part of the production group, so group_vars/production works for me.