Correct. Sea ice is already in the water.
Land based ice is the more scary one, since there is quite a bit of it. 30 × 10 6 km3 on Antarctica, enough ro raise SL for at least 250 feet, some figures estimate up to 500. (64 x 10 6 km3)
Of course that's not going to happen that quickly, but only a fraction of both the bigh chunks, Greenland and Antarctica will do a lot of hurt.
As for how much the human contribution is, that is a question that will never be completely answered, but it is being worked on. For the first several thousands of years after the Ice age, man did almost nothing, but has been gaining in the last 1000 years or so, and impressively in the last 200, stunningly in the last decades.
The contribution of CO2 can be calculated, however the effect of the increase is more of a challenge.
It's all sad really, - you have 2 camps, - the corporates and the environmentalists, both use dirty tricks, and there are scientists in both camps, although I suspect that most of them are just trying to do their jobs