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Big waves predicted to drop along Australia's east coast

Surf's down Surf's up will be a cry of the past along Australia's east coast, according to new research that reveals the impact of climate change on ocean wave height.

The paper, published today in Nature Climate Change , shows an increase in greenhouse gas emissions will reduce the number of large waves along the central east coast of Australia.

Lead researcher Dr Andrew Dowdy, from the Centre for Australian Weather and Climate Research , says a moderate increase in the level of greenhouse gas emissions could cause 25 per cent fewer days with storm waves in this region.

Higher increases in greenhouse gas emission levels could mean about 40 per cent fewer storm waves by 2070 to 2100, he adds.

"If you like to surf large waves, you may have to be better at picking your days for going out in the future, as there is likely to be fewer large waves in this region," says Dowdy.

The Bureau of Meteorology researcher and colleagues used data from five buoys in deep ocean located from six to 12 kilometres off the coast between Coffs Harbour and Eden in New South Wales.

The buoys move with the surface of the water so can observe wave height. Dowdy says they used wave observations from 1992 to 2010 and discovered a strong relationship between large waves and storm conditions high in the atmosphere about five kilometres above the surface.

They then looked for these same atmospheric conditions in climate simulation produced by 18 different global models to measure the impact of increasing emissions between 1950 and 2100.

Climate impact is clear

"When you look over 150 years you can really see the climate signal clearly," says Dowdy.

"Some changes are likely to have already started happening, but towards the end of this century we are expecting about 40 per cent fewer storm wave events under a high emissions scenario."

He says the main effect of increasing greenhouse gas emissions is likely to be on waves of four metres and higher with "little or no change on waves lower than four metres".

Dowdy says greenhouse gas emissions can impact on wave height because emissions have a direct impact on temperatures.

It is the temperature gradient throughout the world that cause winds and drive the circulation of the atmosphere, leading to the formation of the storms that can cause large ocean waves.

Dowdy says while storm waves may become rarer in the future, "it is possible the storms that do occur [in the future] could become more intense".

He says while the reduction in "storminess" could potentially bring positive impacts in terms of coastal erosion and inundation, it is hard to quantify that because of the counter effects of rising sea levels.

The decrease in storms could also affect coastal water supplies as these storm events are associated with a significant amount of the inflow to reservoirs along the central eastern seaboard of Australia.