Australia's scientists have found that tropical cyclones are less frequent in the world due to climate change.
The team led by Savin Chand from Federation University discovered tropical cyclones were 13 per cent less frequent than in the pre-industrial period.
Dr Chand said that we have found that cyclone numbers are going down around the world.
The authors said that their study looked at the frequency of tropical cyclones, not their intensity, which they said was increasing due to climate change.
As the atmosphere warms, tropical cyclones forming have more fuel for their severity, Dr Chand said.
Even though cyclones will get fewer, they will get more intense. The authors had to find a way to go back in time to reconstruct a history of tropical cyclones around the world back to the 1850s.
Before the satellite era, the only way to know if a cyclone had occurred out to sea was if a plane or a ship had the misfortune to run into it.
Dr Chand said how often these things have been happening historically has been very controversial because of the short period of data.
The new weather data sets and sophisticated computer reconstructions of past weather have allowed scientists to look back in time with greater accuracy than before.
Dr Chand said that there has been a lot of progress in what we call reanalysis.
It uses a model that assimilates available observations and then goes even further. We use all this data to detect past tropical cyclones. Tropical cyclone numbers in the Australian region have declined by about 11 per cent since 1900, according to the scientists.
Kevin Walsh, a study co-author at the University of Melbourne, said tropical cyclone numbers had been decreasing quite a bit in the South Pacific region over the past few decades.
This decrease is associated with the likely impact of anthropogenic warming, Professor Walsh said.
The decline in Australia had increased since the 1950s as global warming accelerated, according to the researchers.
They said it was a trend that was mirrored in ocean basins around the world.
There was one exception.
Tropical cyclones have become more frequent in the North Atlantic since the 1960s, according to the study.
The basin may be recovering from a decline in tropical cyclone numbers due to human-related aerosol emissions in the late 20th century, according to Dr Chand.
The number of annual storms is lower than in pre-industrial times. Less frequent but more intense.
The finding was not a surprise for climate scientists.
As the climate has warmed over the 20th century, scientists have suggested that changes in underlying atmospheric conditions like humidity and wind shear have created an environment that is more hostile to tropical cyclone formation worldwide.
Professor Walsh said that the results needed to be interpreted in perspective as the study counted all tropical cyclones, severe or otherwise.
He said the really intense ones are the ones that cause most of the damage.
It means that you can have a situation where the total numbers are decreasing but the total damage actually increases, because there are pretty good theoretical reasons to believe that in the future the numbers of really intense storms will increase rather than decrease.