Tides themselves are drastic fluctuations in sea level around the world.
Some places, like Hawaii, only have a 2-3 feet between high and low tides.
Where some places in the Northeast USA or Canada have tides that can fluctuate almost 20 feet between high and low.
The decades old tide gauges (some centuries old) average out those tide swings and can see when the absolute highs are slightly higher from years/decades past.
I witnessed storm surge inside Redondo King harbor back in the 83 El Nino (over 36 years ago now), that I doubt has been seen since. Huge surf during the highest tides of the year coincided, and surge was coming up over the walkways way inside King Harbor where the restaurants were inside the inner basin. I don't think thats EVER happened since. But with all the talk of AGW causing increased sea level rise, you'd think we'd see that situation more common than ever by now. Sea levels have only risen a couple inches at best since then. Not the feet or multiple feet predicted back in the late 80's/early 90's we're supposed to be living with now.
Yet here we are again, getting rehashed predictions of 3 feet of sea level rise in ours and our kids lifetimes (2030, 2050, 2100?).
Where is it, and when did it start? If it hasn't started yet, when? Over night in 2099?
Again, I resubmit my bet on it? (tried this almost 20 years ago now, and would've made a killing if anyone took me up on it).
According to predictions back as recent as the 90's we were supposed to see 3 feet of sea level rise by 2020. Many low lying coastal areas would be under water by now. Memories conveniently fade and are forgiven on those claims, because the emotion and political motivation of AGW wins out over facts and actual outcomes.