Let's consider this oversimplified architecture (https://pbs.twimg.com/media/FkqxnK7WAAEk6Lc?format=png&name=...): R1 is serving Asia, R2 Europe, R3 USA.

R1, R2, R3 are connected, but suddenly R1 has trouble reaching R2 and R3.

How does a CA system (consistent and available) behave?

A CA system will corrupt data during a partition. R1 will continue to accept writes/updates that R2/R3 cannot see. Likewise R2/R3 will perform different updates to the same data that R1 cannot see. Thus R1 and R2 will see inconsistent state.