We know that increasing atmospheric levels of CO2 will result in higher temperatures (the mechanism is well understood, and the IPCC models have done a good job of predicting that over the past couple decades), we also know rising temperatures will result in rising sea levels (again, we have empirically observed this happening at rates consistent with our understanding of the mechanism). From there it's just math to figure out how much coastal land will be inundated over the coming century (which is just one of many implications of climate change).
You are suggesting various ways in which that might not happen, with no evidence supporting them, from the perspective of someone who doesn't have much of an understanding of climate science. Do you think it is more likely that you have outsmarted 97% of climate scientists, or that the experts are more likely to know what they're talking about than you are?