Sea level rise for an address: what the tide gauge projections say

The IPCC projects sea level on most of the Australian coast to rise by about 0.2 m by 2050 and by roughly 0.4 m to 0.8 m by 2100 compared with the 1995-2014 average, depending on how emissions track. Those figures are published for individual tide gauges, not for addresses, so the useful question for a property is which gauge is nearest and what was published for it.

The short version

• The IPCC's sixth assessment (AR6) publishes sea level projections at 72 named Australian tide gauges.
• Each projection is a change in sea level relative to the 1995-2014 average, not a height in metres AHD.
• By 2050 the three main scenarios sit close together. By 2100 they spread apart.
• The figure for the nearest gauge is an indication for that stretch of coast. It is not a water level on your block.
• The number that controls building is the sea level allowance in your council or state coastal hazard rules.

Where do sea level rise projections for Australia come from?

The IPCC AR6 projections were released with the 2021 report and published as open data (Garner et al. 2021). Each record gives a gauge, an emissions scenario, a year and a percentile. The figures are relative sea level, which means they include slow rise or sinking of the land at the gauge as well as the change in the ocean.

AR6 uses shared socioeconomic pathways, shortened to SSP, to describe possible futures. Three cover the range most readers need:

• SSP1-2.6: low emissions, strong cuts from now.
• SSP2-4.5: intermediate emissions, roughly current policy.
• SSP5-8.5: high emissions.

How much will sea level rise by 2050 and 2100?

As an example, these are the published figures at the Gold Coast Seaway gauge. The first number is the median. The range beneath it is the 17th to 83rd percentile, which the IPCC calls the likely range.

Scenario	By 2050	By 2100
SSP1-2.6, low emissions	0.18 m (0.13 to 0.25 m)	0.42 m (0.28 to 0.62 m)
SSP2-4.5, intermediate	0.20 m (0.14 to 0.27 m)	0.54 m (0.40 to 0.77 m)
SSP5-8.5, high emissions	0.23 m (0.18 to 0.30 m)	0.78 m (0.60 to 1.06 m)

Two points stand out. Over the life of a 30-year loan the choice of scenario makes little difference, a few centimetres. Over the life of a house built today it matters a great deal, and the high end of the high-emissions range passes one metre.

Can I add sea level rise to a flood level for my property?

No. A projected rise at a gauge cannot be added to a modelled flood level to give a future flood level at an address. Storm tide, waves, rainfall runoff from the catchment and the shape of the land all sit between the two, and each needs its own study. Many recent council flood studies already include a future climate event that allows for sea level rise. Where they do, that modelled event is the better number to read.

What sea level rise allowance does my council use?

Each state sets a planning benchmark, and councils apply it through coastal hazard overlays. Queensland's State Planning Policy uses an allowance of 0.8 m by 2100. Other states and councils use their own figures and dates. Where a coastal hazard overlay applies to a lot, it appears in the planning scheme, and that allowance is the one a building application is assessed against, not the IPCC median.

How far away is the nearest tide gauge?

Most coastal cities and regional towns have a gauge within 20 km. Parts of the coast are sparse: Warrnambool's nearest gauge is Portland, about 76 km away, and Batemans Bay's is Jervis Bay, about 81 km away. The further the gauge, the more the figure describes the region rather than the local coast. Some stretches, such as Lakes Entrance and the east coast of Tasmania, have no gauge within 100 km.

Where to find the figure for your address

The Flood Model Report includes a Sea Level Rise Indication page for addresses within 10 km of the coast or a tidal river and within 100 km of a tide gauge. It names the nearest gauge and its distance, and shows the AR6 figures for 2050 and 2100 under the three scenarios above with their likely ranges. Inland addresses do not get the page, because a tide gauge says nothing useful about them.

What to check before you buy or build on the coast

1. Find the nearest tide gauge and its projected rise for 2050 and 2100.
2. Check whether the council flood study includes a future climate event, and read that event's depth at the lot.
3. Look up the coastal hazard overlay and the sea level allowance your council applies.
4. If you are setting a floor level, ask your engineer or surveyor which allowance and which datum they are designing to.

Common questions

How much will sea level rise in Australia by 2100?

Around 0.4 m under low emissions, around 0.5 m under intermediate emissions and around 0.8 m under high emissions at most Australian gauges, relative to the 1995-2014 average. The likely range at the high end reaches about one metre.

Is the IPCC projection the same as my council's sea level rise allowance?

No. The IPCC publishes a range of projections. A council or state picks one planning allowance from that evidence, and only the planning allowance is used to assess development.

Does sea level rise mean my property will flood?

Not on its own. Whether a property floods depends on its height, storm tide, rainfall and drainage. A higher sea level raises the starting point for storm tide and slows drainage near the coast, which is why flood studies model future climate events separately.

About this article. Published by LayeredGeo and written from the published research cited in the Sources section above. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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