What if Oceans rise more than four feet by 2100?

IF ocean levels rise by four feet, all coastal regions will be devastated, and some low-lying regions eg Bandgladesh, will be underwater, causing mass refugee-dom. Let's hope it doesn't happen. Let's hope that the biggest poluters on the panet - America and China - mend their ways and cut down on CO2 emissions. Otherwise both countries face a bleak future.

then the earth is sink under the water and no one survive on it

If the house that you build, is on stilts that are more than 4 feet high, then you won't have to worry about a 4 foot rise in the sea level. But id you do buy now, you will still have 93 years to enjoy the property.

I guess you are right that people living along the coastal areas would be disadvantaged by this situation.