(CNN)Before the era of satellites, it was next to impossible to know whether a hurricane occurred out in the open ocean unless a ship was unlucky enough to run into it. And scientists for decades have been trying to piece together a historical record to better understand how the climate crisis is changing these storms.
Hurricane numbers are decreasing in every ocean basin except for one, study finds
But researchers said Monday they have constructed a clearer picture than ever, and found that the frequency of the planet's most devastating storms has decreased over the past century.
The study, published in the journal Nature Climate Change, found that the annual number of global hurricanes, typhoons and tropical storms — or tropical cyclones, more generally — declined by roughly 13% as the planet warmed during the 20th century.
Scientists found that trend in most of the world's oceans — except for the North Atlantic, where the number of storms increased.
The lead researcher on the study told CNN that while his team found a drop in frequency, that doesn't mean storms are becoming less of a threat. In fact, said Savin Chand, a senior lecturer at the Federation University in Australia, while there may be fewer tropical cyclones in the future, it is likely they will be more intense.
"Cyclones are no doubt one of the costliest natural disasters everywhere," Chand told CNN. "What's happening with global warming is that these underlying conditions are getting more unfavorable for cyclones to form in the first place. But even though cyclones are getting fewer, those that do form are now feeding more energy from the warming atmosphere, so that's why they're getting more intense."
Tropical cyclones need a special set of conditions in order to develop from a cluster of thunderstorms into enormous, swirling heat engines. Over the years, scientists have become increasingly confident that human-caused climate change is making those conditions more uncommon — but when they do form, warmer air and ocean temperatures are making them more potent.
Figuring out how the climate crisis is changing tropical cyclones has been a challenge due to limited historical data. Suzana Camargo, co-author of the study and professor at Columbia University, said the goal was to put all the existing evidence together to try to "breach the uncertainty — or make it a little smaller."
"People have been doing different attempts to try to figure out what happened with other datasets, using different methodologies, so I see this paper as another piece of the puzzle," Camargo told CNN. "We do not have data in the past, and we cannot go back and be there now, so this paper is trying to recreate in a different way that has been done so far what has happened in the relation to number of tropical cyclones."
Adding to that uncertainty is a field of developing research on the impact of air pollution. Unlike greenhouse gases like carbon dioxide or methane, this pollution reflects sunlight back to space, which has a cooling effect. While there are natural sources of this air pollution, much of it in the early to mid-20th century came from sources like industrial smokestacks and car exhaust.
"When you just look at the North Atlantic, the study is very consistent with my [previous research]," Hiro Murakami, co-author of the study and a scientist at the National Oceanic and Atmospheric Administration, told CNN.
Murakami's study published in May found that over the past four decades, a decrease in air pollution over North America and Europe resulted in an increase in the number of hurricanes in the North Atlantic. On the other side of the world, researchers detected a decrease in the number of typhoons in the western North Pacific, sparked by an increase in aerosol pollution in China and India.
Kevin Reed, a climate and hurricane scientist at Stony Brook University, said it's important to understand the differences between frequency changes versus storm characteristics. In April, Reed published a study that found climate change supercharged the rainfall in hurricanes during the record-breaking 2020 season.
"It's always important to look back to the past and use that to better understand how these events might change in the future, but also to acknowledge that it's not just the frequency of the events that matter," Reed, who was not involved with Monday's study, told CNN. "It is also their intensities, other characteristics, likelihood of landfall, and a lot of aspects like that, which the broader scientific community is exploring."
Scientists say that as the planet rapidly warms, extreme weather events will become more disastrous and possibly harder to predict. Chand told CNN that research into tropical cyclones is so important because they can lead to such devastation.
"The climate is changing, and humans are the major cause and contributors toward that change," Chand said. "So understanding all extremes in the context of climate change is very important, and tropical cyclones are one of those extremes that has very severe implications on society."