Tropical cyclones have become more destructive

Two severe tropical cyclones over northern Australia. Analysis of satellite records from 1979 to 2017 has found a clear rise in the most destructive storms, in keeping with climate predictions about global heating. Photograph: Nasa Earth Observatory/EPA

From The Guardian:

Tropical cyclones have become more intense around the globe in the past four decades, with more destructive storms forming more often, according to a study that further confirms the theory that warming oceans would drive more dangerous cyclones.

Analysis of satellite records from 1979 to 2017 found a clear rise in the most destructive cyclones – also known as hurricanes or typhoons – that deliver sustained winds in excess of about 185km/h.

Experts told Guardian Australia the finding was in line with climate model predictions and the knowledge that increasing ocean temperatures gave tropical storms more energy.  Dr Hamish Ramsay, a senior research scientist at CSIRO who studies cyclones, said: “This study confirms what the climate models have been predicting for some time – that the proportion of the most intense storms will increase as the climate warms.”

While climate scientists have long predicted that global heating would deliver stronger cyclones, a trend that was statistically significant has been challenging to identify in part due to the natural swings in the world’s climate masking changes.

Published in the leading journal the Proceedings of the National Academy of Sciences, the study was carried out by scientists at the US government’s National Oceanic and Atmospheric Administration.

The scientists did not try to find a cause for the increase in more dangerous cyclones, but said the trends were consistent with understanding of physics and modelling, and the finding “increases confidence that [tropical cyclones] have become substantially stronger, and that there is a likely human fingerprint on this increase”.

The probability of a cyclone reaching wind speeds greater than 185km/h had risen by about 15% over the 39 years studied.

“[The study] suggests that the climate change signal in the data is potentially already emerging and this is something that climate scientists have been saying for some time,” Ramsay said. “We maybe at a point now where we are starting to evidence from observational data that supports what the models have been telling us.”

Ramsay said as well as increasing the wind speeds in cyclones, warming oceans would also likely see cyclones delivering more rainfall. There was still uncertainty as to whether the numbers of all categories of cyclones would rise or fall under climate change.

Previous research has found that when cyclones form, they are tending to move more slowly, while delivering more rain.

Dr Greg Holland, a senior scientist emeritus at the National Center for Atmospheric Research in Colorado, has studied cyclones for about 40 years.  The Melbourne-based scientist said while there were legitimate arguments over the finer details of trends and intensity in relation to tropical cyclones: “The work all points in the same direction – the proportion of the most intense cyclones is going up.”

He said: “There is nobody saying the trend will go the other way. The physics has been well set out for 30 or 40 years. If you get a warmer ocean then the intensities of cyclones goes up. That’s a 5% or 10% increase in maximum winds for every 1C of warming in the ocean. The world is warming and its because we have put more greenhouse gases into the atmosphere.

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