New figures have revealed that sea levels along the coast of Western Australia are rising at a rate double that of the world average.

Statistics from Australia's National Tidal Centre show levels have increased by 8.6mm a year off the coast of the state capital Perth.

That compares to a global average of just over 3mm.

Scientists have said that man-made climate change has played a significant role in the rise.

Climatologists have said that a combination of natural variability and man-made pollution have caused sea levels to rise around the world.

link [news.bbc.co.uk]

Now I might be being stupid here (and probably am knowing me ) but how do they measure sea level with that amount of precision? It's not exactly a level surface is it? And I doubt there's a mean sea level you can get from the peaks and troughs of waves. It's an ever changing chaotic surface surely?

So if anyone knows, how do they measure sea level rises (or falls) with such precision?

Australia is listing!!