is an absolutely massive amount of temperature increase in geological perspective. Just saying. We'll need to go back far, far back to a time where we think the earth was that warm. From the top of head, probably into the Paleocene.

6C is a convenient number to quote, but establishing a figure on climate sensitivity has been and still is the holy grail of climate science, and it's not settled. I'm agnostic on what it will be. To me, the number matters more for establishing proper adaptation gaols, than that it acts as a stimulus for switching to a non-carbon society.

Right now, the IPCC projection of sea level rise until 2100 range from a few cms to 1 meter - a figure which has been corroborated by younger studies. However, current sea level rise will have to accelerate a lot to find itself in the higher end of that bracket. Even so, in the medium long term (decades to 1 century), the Netherlands has little to worry.