At the end of the last ice age the oceans rose rapidly, as much of the water trapped in the large ice sheets was returned to the sea. Over the course of the last century, ocean levels rose again as rising temperatures caused glaciers to melt and the water itself to expand.
In between the two, however, we haven't had a very clear picture of what has been happening. Various records exist from around the world, indicating where the ocean level was in the past. But these numbers are influenced by local changes and don't give a clear picture of any global changes, which can be key to understanding the oceans' response to climate change and predicting where the sea levels are likely to go in the future.
Now, an international team of researchers has taken these local records and built a global database that allows them to track ocean levels for the past 1,500 years or so. And the picture that results looks a lot like that of the temperature reconstructions: centuries of small variations, followed by a sudden rise over the last century. The authors estimate that the oceans haven't seen changes like this in more than 2,800 years.