Cyclones are among the earth’s most powerful storms. Like forest fires and lightning strikes, they are natural — yet their effects are becoming more destructive thanks to climate change.
In a new study published by researchers at ETH Zurich in Switzerland, the world’s cyclones can be expected to wreak more havoc in new ways if global warming follows a future climate scenario called SSP5-8.5.
This is both due to the cyclones’ intensity and their occurring in places where they didn’t occur before.
Climate change has many moving parts. To make sense of its impact on various sectors and ecosystems, experts often use the shared socioeconomic pathways (SSPs). Each SSP describes a world affected in a particular way by climate change. SSP3 describes a politically fragmented world in which environmental protection is not a priority. The SSP5 world is rapidly burning fossil fuels and depleting a great amount of resources.
SSP5-8.5 is the SSP5 pathway plus a radiative forcing — the amount of extra energy being added to the planet’s surface — of 8.5 W/m2. Currently this figure is 2.7 W/m2 over the value in 1750. (A radiative forcing of 2.6 W/m2 is required to keep global warming by 2100 under 2º C, as suggested by the Paris Agreement.)
“Based on the data, SSP5 is already gaining momentum,” said Chahan Kropf, a scientist specialising in weather and climate risk studies at ETH Zürich and a coauthor of both studies. “But we still need broader agreement on that.”
A follow-up study published by the same team plus two more researchers also reported that roughly half of the world’s mangroves will be at high to severe risk by 2100. Coastal ecosystems protect inland areas from storms, reduce soil erosion, and store carbon. Mangroves in particular can also store four- to five-times more carbon per unit area than terrestrial forests.
The two studies show the effects of climate change on tropical cyclones could have far-reaching and multifaceted consequences around the world, not just in the tropics.
Cyclones in an SSP5-8.5 world
In the first study, the researchers used the CLIMADA (CLIMate ADAptation) open-source risk modelling platform to check how specific ecoregions around the world responded to shifts in tropical cyclone patterns between 1980-2017 and to projected shifts for 2015-2050. They assumed that the world would be in the SSP5-8.5 scenario in the latter period.
For the analysis, the researchers used the STORM-B and STORM-C datasets, which are based on synthetic probabilistic cyclone tracks, and the Holland model to simulate wind fields.
First they classified each terrestrial ecoregion in the following way: resilient (historically oft-exposed to cyclones and able to recover quickly); dependent (regularly disturbed by cyclones that also shape the area’s ecosystem dynamics); and vulnerable (rarely disturbed by cyclones and recovering slowly when exposed to one).
They also grouped the cyclones into three categories based on the intensity of wind speed: low, medium, and high.
For each ecoregion, the researchers estimated the average time between cyclones. Finally, they were able to determine the ecosystem risk under climate change by the projected shifts in these return periods and the corresponding ability — or lack thereof — of ecosystems to recover.
According to Philip Ward, climate researcher at the Institute for Environmental Studies at Vrije Universiteit Amsterdam, “The authors used state-of-the-art data and models to provide valuable insights.” He wasn’t involved in the study.
Modelling mangroves
In the second study, the team used a probabilistic spatially explicit risk index — a number that simultaneously measures the odds of an event and its expected spatial distribution — to assess how mangroves worldwide will be affected by changes in tropical cyclone frequency and sea-level rise by 2100.
For this, the researchers used a tropical cyclone model based on the most up-to-date climate model data and used it to simulate three scenarios: SSP2-4.5, SSP3-7.0, and SSP5-8.5.
Each of these scenarios quantified three kinds of risk. (i) ‘Hazard’ modelled the wind speeds and frequencies of tropical cyclones. (ii) Vulnerability modelled the capacity of mangroves to adapt to sea-level rise. (iii) Exposure modelled the how much the areas covered with mangroves overlapped with areas of higher hazard.
To this end, the team grouped tropical cyclone wind speeds into three ranges: 33-49 m/s, 50-70 m/s, and more than 70 m/s. Similarly, they grouped sea-level rise into low (0-4 mm/year), medium (4-7 mm/year), and high (>7 mm/year) ranges.
Mangroves were considered to be at risk if the frequency of intense cyclones doubled or if they were newly exposed to such storms. The team also considered ecosystem services to be at risk — including mangroves’ ability to sequester carbon, protect coasts, and improve fish stock — based on rankings from previous studies.
New places, new perils
The models found that of the world’s 844 ecoregions, 290 are already affected by tropical cyclones. The models revealed 200 more can be considered vulnerable and 26 to be resilient.
However, in the resilient ecoregions, the models showed that the time available to recover between storms could drop from 19 years in the 1980-2017 period to 12 years in the 2015-2050 period for high-intensity storms.
The bulk of these shifts are expected to occur in East Asia, Central America, and the Caribbean because these places are abundant in resilient or dependent ecoregions. The models also found that Madagascar and parts of Oceania are increasingly at risk.
Some areas including the Philippines could experience cyclone frequencies that exceed anything experienced so far in recorded history.
In the SSP5-8.5 scenario, up to 56% of mangrove areas worldwide could be at high to severe risk by 2100. Southeast Asia is expected to be the most affected, with 52-78% of its mangrove areas at such risk.
But the models also showed that even in the less destructive SSP3-7.0 scenario, 97-98% of mangroves that protect people and property in Southeast Asia could be at high to severe risk.
The researchers also warned that some of the affected ecosystems could shift into entirely different states from which they may not recover.
The models also concluded that tropical cyclone belts could shift away from the equator, bringing new cyclone activity to higher-latitude regions and exposing ecosystems there to threats to which they have not adapted.
According to Kropf, whether the world ends up in the SSP5-8.5 scenario hinges on how long it banks on fossil fuels and how committed countries remain to the Paris Agreement.
In the meantime, the authors suggest including long-term recovery time in risk assessments in addition to damage caused by cyclones and risk-sensitive conservation planning, including decision-making processes that explicitly consider shifting disturbance regimes.
“We’re underestimating the scale of what’s coming,” Kropf said. “The changing cyclone patterns could have enormous consequences.”
Madhurima Pattanayak is a freelance science writer and journalist based in Kolkata.
Published – May 22, 2025 05:30 am IST