[JAKARTA] Average wave size will increase in many parts of the southern hemisphere over the twenty-first century, but decrease in the north, according to an international study on the impact of climate change on oceanic activity.

The study, published in Nature Climate Change last month (13 January), predicts a wave height increase of between 20 and 30 centimetres in an area covering at least seven per cent of the surface of the world's oceans. This is due to the poleward intensification of the westerly winds in the southern hemisphere, resulting from climate change.

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Fisheries, coral reefs and seaweed farmers are all likely to be affected

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Antarctica, Australia, Indonesia and Papua New Guinea are the four places that scientists think will chiefly be affected.

But the scientists also predict a drop in wave height across a quarter of the area of the world's oceans, particularly in the northern hemisphere, with potentially far-reaching impacts.

"The decreased wave height in the northern oceans is good news for the fishing industry there because the sea will be calmer," says Nobuhito Mori, associate professor at Kyoto University, Japan, and the study's co-author.

But the opposite may happen for fisheries in the South, as bigger waves may make conditions more difficult, Mori says. He warns that the seaweed industry may also be affected, as higher waves are disruptive for seaweed and prevent the plants from settling.

He also tells SciDev.Net that higher waves in the South could affect coral reefs and bring changes to coastal morphology, "as coastal sediment is influenced by wave height".

John Pariwono, a marine scientist based at Indonesia's Bogor Agricultural Institute, agrees that increased wave height could affect reefs.

"Higher waves could decrease the intensity of sunlight for coral reefs, which is not good for them," he says.

Pariwono believes that if wave height does increase as predicted, it will harm fisheries in the South, with traditional fishermen the group most likely to be affected.

Coastal communities in Indonesia and Papua New Guinea are among the poorest in the world and depend heavily on the ocean for their survival. A US Department of State report estimates that coastal fisheries in Indonesia have grown by 40 per cent in the last ten years and that fisheries generate some 20 per cent of the country's economy.

"They should change the way they use marine resources to survive," Pariwono says. "In the future, they could turn more to aquaculture," he adds.

When asked about specific wave height predictions for other countries, such as Thailand and the Philippines, Mori explains that the narrow seas in these areas have much larger natural variability and microclimates, so that it is currently more difficult to make projections. "Our study had a global focus and is therefore unable to determine the wave height of specific and narrow ocean areas. However, we are planning to make this our next project," Mori says.