Although it's difficult to prove what the future will bring (note the future tense used by Opaline), anyone can do an experiment to investigate the likelihood of sea levels rising.
Fill a glass with water to about 10 mm from the rim of the glass. Put the glass in a warm room. Then add a big chunk of ice. Keep adding more ice. The water level in the glass will rise and fall over the rim of the glass as you add more ice and the ice melts. This is similar to what will happen to the ocean as the land ice melts.
For more proof, look to the past. In the past (millions of years ago) when land ice melted the sea levels rose and land went under water. (When ice formed the sea levels went down.) There is really nowhere else for most of the melted ice to go. Some will possibly find its way into aquifers and some will go into the atmosphere (but fall again as rain or snow). Most will end up in the oceans.
In regard to floods even now, before seas have risen a huge amount, what is considered dangerous to a nation like Bangladesh, with most of the country a flood plain and not very much above sea level and a fairly high population density and nowhere else for its people to go - might not be considered dangerous by a person who lives in a mansion on a mountain top. Climate change by itself will be bad enough for a country like Bangladesh - with more intense monsoons and intermittent drought. Rising sea levels will make it worse. It has in the past had catastrophic floods (not the normal small scale flooding Seden33 was describing) - from storm surges, extra heavy monsoons and extra heavy localised rain.
According to Wikipedia - in 1987 50% of the country was flooded. In 1988 60% was flooded. In 1998 75% was flooded. In 2004 about the same, and these are 50 to 100 year floods - less than a decade apart. http://en.wikipedia.org/wiki/Floods_in_Bangladesh
