As regular readers will know, there is a mantra "Change is Normal" when it comes to our planet and its many systems. One such concern among the global warming community is that sea levels will rise as a result of a warming trend.
As just about all geologists will attest, global sea levels change through time. This statement was best put into the scientific mainstream by Peter Vail. He produced a global sea level change chart which is reproduced here (source):
Why these changes? Have ice sheets been growing and receding through time? Yes, but temperature change is far from being the main reason behind global sea level changes. And we also know that any description of a global sea level change will have its exceptions at any one time. As good examples, the Strait of Hormuz is sinking rapidly today while the Baltic is rising rapidly. I use the word "rapidly" in a geological time concept. As solid as the Earth's crust appears to be, we know that it is constantly moving up and down and around, and it is this activity that is the prime cause for global as well as local sea level changes. Ice Ages are rare phenomena in the geological time span covered by the chart (600 million years) so cannot and should not be invoked as reasons why we may be facing rising sea levels in the future. Better to look to plate tectonic motions if you want to predict whether or not London, New York and Shanghai will all disappear in the geological future!