Additive backup and restore?

I am designing a database for a web application. In the near future I will
require past data for Audit, Security and Analysis purpose. But storing all
that data will increase the database size. What are some well known
approaches to archiving data for later use without increasing the database
size?

One approach I am thinking of is compressed additive backup and restore
i.e. copy the rows of the tables that will be required later and store them
in a compressed form, and then delete those rows from the table. And when
the data is required then restore them from the backup files in an additive
way.

Is there an easy way to achieve this, say via pg_dump?