Since the good old Industrial Revolution, with subsequent global warming, sea levels have been rising.Through the 20th century, they were rising at about one to two millimetres per year.But like everything else, they're now going up faster.Since the 1990s, global average sea levels have been rising about three millimetres per year.In fact, since the Industrial Revolution, global average sea level has risen by about 20 centimetres, about that much.In the last topic, I talked about how the polar ice caps and glaciers are melting.And this extra water is now contributing about 2/3 of the rise in sea level.The rest is coming from the fact that warmer water is actually less dense than cooler water.It simply takes up more space.And remember, I said that about 90% of the extra heat in Earth system is going into the oceans.So together, sea level is rising from two sources,warmer, less dense water, plus the extra water going in from the melting ice.But sea level is not actually going up at the same rate everywhere.The sea is not as flat as the water in a bathtub.In fact, it's quite bumpy.To illustrate this, take a look at this map of Australia and at the relative sea level rises in different parts of the coastline.What you can see is in the southern and eastern parts of the country, sea level is going up at about the global average or in some cases a little bit less.But over in the west and especially up in the north,sea level is rising at nearly nine millimetres a year.In the next topic, I want to put these changes of recent times in a much longer term context so that we can see just how special the last couple of hundred years has really been.