Of course Fort Denison is a local observation point. Of course it is not an adequate measure of the global changes.
Try satellite data of sea level if you want to make a valid point.
The globe has tides due to the gravitational pull of the moon and the sun. Naturally, because our globe is round, most of the effect from gravity is concentrated in the tropical zones. Therefore the tides rise higher around the equator than it does at a median latitude such as Sydney.
Sea level rise would therefore also be greatest at the tropic zones while regions in the median zones may show no change in sea level.
