World’s oceans are becoming stormier, researchers discover | World news | The Guardian

The world’s oceans have become more stormy during the past three decades, according to the largest and most detailed study of its kind.

The findings add to concerns that as the world gets hotter, extreme events such as storms and floods could become more frequent and more devastating in their impact.

Slight increases in average wave height and wind speed were recorded in oceans across the globe, with the strongest effects in the Southern Ocean. The study relied on data from 31 satellites and more than 80 ocean buoys collected between 1985 and 2018, with about 4 billion observations.

Extreme winds in the Southern Ocean have increased by 1.5 metres per second, or 8%, over the past 30 years, while the highest waves have increased in height by 30 centimetres, or 5%. The strongest winds increased in the equatorial Pacific and Atlantic and the North Atlantic by about 0.6 metres per second.

Prof Ian Young, the first author of the work from the University of Melbourne, said: “Although increases of 5 and 8% might not seem like much, if sustained into the future such changes to our climate will have major impacts.”

Young said that increases in wave height could lead to more serious flooding and coastal erosion, and put offshore structures such as wind farms at risk of damage.

The researchers said the observations were in line with predictions by climate models and from historical records that suggested that as the world got hotter, weather and storms became more extreme, although the relationship was complex and not fully understood.

“The role climate change plays in wind speed and hence wave height is still not clear,” said Young.

Others said that the role of global warming in the latest observations was yet to be established. “It’s a bit difficult to extrapolate these finding to the wider picture,” said Dr Paulo Ceppi, of the Grantham Institute at Imperial College London. “During 30-year periods you can still have pretty significant natural variations in winds.”

Ceppi said that the observed changes in the Southern Ocean were likely to be driven by the hole in the ozone layer, in the Antarctic stratosphere, to a greater extent than global warming – although this could also be contributing.

The study, published in the journal Science, updates previous work from the same team published nearly a decade ago. A major challenge in compiling long-running data series, they said, is accounting for significant changes in technology and data processing over the time period. For the earliest part of the time period the coverage was not as extensive and the measurements were less accurate. The scientists needed to rule out the possibility that they were simply seeing more violent storms because there are now more satellites to spot them, for instance.

The findings also suggest that conditions in the Southern Ocean are becoming more treacherous for ships. According to Young, more intense storms circling the Southern Ocean can also generate larger ocean swells that propagate across the Indian, Pacific and South Atlantic. “Increasing wave conditions in the Southern Ocean impact regions across the globe,” he said.

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