How rising sea levels will affect our coastal cities and towns

By Thomas Mortlock, UNSW Sydney

Sea-level rise – along with increasing temperatures – is one of the clearest signals of man-made global warming. Yet exactly how rising water levels affect the coast is often misunderstood.

A new coastal hazard assessment for Victoria’s Port Phillip Bay has again thrown the spotlight on the impact of sea-level rise on coastal communities in Australia. Should we be worried? Or is the reality more nuanced?

While there are still many uncertainties, even a small change in sea level can have big impacts. We should be doing all we can to limit sea-level rise to protect our coastal cities and towns. And because sea levels will continue to rise for centuries after we cut emissions to net zero, planning decisions for coastal areas must factor this in.

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Why are sea levels rising?

Global sea levels are rising for two main reasons: the oceans are getting warmer, and land-based ice sheets and glaciers are melting.

As ocean water warms, it expands. Because the ocean basins are finite (like a bathtub), this results in a rise in water levels.

Since the 1970s, thermal expansion of the oceans has accounted for roughly half of measured global sea-level rise. The other half is due to land-based ice melt from ice sheets and glaciers. Together, these make up what is known as “eustatic” sea level.

The rate of sea-level rise experienced at the coast also depends on whether the land is moving up or down. “Relative” or “isostatic” sea level is the sum of “eustatic” sea level plus local vertical land movement.

Australia is rising by about 0.3-0.4 millimetres a year due to glacial isostatic adjustment. This is the result of the land continuing to move upward following the loss of ice on land during previous glaciations. The land subsided under the weight of this ice and is now rebounding as the ice is gone. This slow rebound of the land provides a small offset to eustatic sea levels around Australia.

Read Full Story https://theconversation.com/how-rising-sea-levels-will-affect-our-coastal-cities-and-towns-221121