You have climate change, then you have global warming, and then you have sea level rise. One is not necessarily a subset of the other (starting from the left.)
It’s almost impossible to say there is no such thing as climate change. You see how dynamic the atmosphere is and micro-changes caused by cultural factors (humans) are so prevalent people often mistake them for global change. Examples of micro-changes are increased flooding with increased built-up in a given area, increased average temperature due to removal of foliage and exposed soil (again just in that given area,) poor air quality.
Is there really a global warming? Geologists know average temperatures happen in several cycles, from thousands of years, to tens of thousands. It’s hard to measure the greenhouse effect because you have to factor out the effects of the biggest greenhouse gas of all: water. Measuring the effects of CO2, methane, etc. takes a lot of creativity.
Sea floor rising? Again recorded geologically but many of these episodes are in cycles millions of years long. But you have the sheer math of the effects of polar ice melt. But maybe a scientist who does the actual research in this could enlighten us some more.
Your questions regarding saving low-lying cities are in the realm of engineering, not climatology.