It's interesting to see a nearly linear trend as far back as the data goes (1880). Do you know of any sources to see how that trend might've looked going even further back in time?
Well, 1880 is right after the industrial revolution. Unluckily we only started keeping good records after we kicked changes into a higher gear. This page has one graph that goes back further [1] (and a bunch of other interesting graphs).
On geological scales we are at or near a high point [2] after the previous ice age
Have an industrial revolution -> get rich enough to care about science -> realize we should track the environment -> start to take measurements and writing them down.
The only other path that leads to environmental tracking is if some order of monks developed an obscure interest in it in pre-industrial times.
> The global mean water level in the ocean rose by 0.14 inches (3.6 millimeters) per year from 2006–2015, which was 2.5 times the average rate of 0.06 inches (1.4 millimeters) per year throughout most of the twentieth century.
On geological scales we are at or near a high point [2] after the previous ice age
1: https://research.csiro.au/slrwavescoast/sea-level/sea-level-...
2: https://www.e-education.psu.edu/earth107/node/1506