Air carrier First Officer reported a GPWS terrain alert on a night visual approach to SAV. The Captain corrected the glide path and landed when the crew determined the altimeter was improperly set.

Narrative

Approach controller to SAV gave altimeter setting of 30.30. We requested the RNAV 01 to SAV. As pilot monitoring I noticed 4 red on the PAPI at about 800'. I announced to the captain 'We're low; the PAPI is four red.' He responded 'we are on the glide path. If we were in the clouds you wouldn't say that.' I responded 'we are not in the clouds; we are too low. Look at the PAPI and the runway.' The captain said 'we are perfectly fine' and continued. As I opened my mouth to call for go-around the EGPWS (Enhanced Ground Proximity Warning System) caution 'too low terrain' alert sounded. The captain added power; disconnected auto pilot; and corrected to the PAPI and continued to land. Upon landing I asked the tower for the altimeter setting; they responded with 30.03. Several issues are present. The incorrect altimeter setting given by the approach controller; or heard by flight crew. The captains over reliance on the GPS glide path in visual conditions; and his non-chalant response to my call outs of an issue. I should have been more assertive and aggressive with what I saw. We should have elected to go-around after the EGPWS caution alert; and I should have called go-around immediately upon noticing the PAPI was 4 red.