Hurricane Melissa, recognized as one of the most formidable Atlantic storms on record, has prompted the U.S. National Hurricane Center to warn of “extremely dangerous and life-threatening” conditions in Jamaica.
While climate change is not believed to directly increase the overall frequency of hurricanes, typhoons, and cyclones worldwide, its influence on storm intensity is a growing concern.
Warmer ocean temperatures, combined with a warmer atmosphere – both consequences of climate change – create conditions that can intensify these weather events.
This intensification can manifest as higher wind speeds, increased rainfall, and an elevated risk of coastal flooding.
Hurricanes are powerful storms that originate in warm, tropical ocean waters.
Known as cyclones or typhoons in other regions, these storms are collectively referred to as “tropical cyclones.”
Tropical cyclones are characterized by high-velocity winds, torrential rainfall, and storm surges – short-term increases in sea levels – often resulting in widespread damage and flooding.
Hurricanes are categorized based on their peak sustained wind speeds.
Major hurricanes are classified as Category 3 or higher, reaching wind speeds of at least 111 mph (178 km/h).
Hurricanes, typhoons, and cyclones typically begin as atmospheric disturbances, such as tropical waves, which are areas of low pressure where thunderstorms and cloud formations develop.
As warm, moist air rises from the ocean’s surface, winds begin to rotate, a process influenced by the Earth’s rotation on winds in tropical regions away from the equator.
For a hurricane to develop and sustain its rotation, the sea surface generally needs to be at least 27°C to provide sufficient energy, and wind patterns need to remain relatively consistent with height.
When these factors align, a powerful hurricane can emerge, although the specific dynamics of individual storms are complex.
Globally, the overall frequency of tropical cyclones has not increased over the past century; in fact, the number may have decreased, though long-term data remains limited in some regions.
However, the UN’s climate body, the IPCC, states that it is “likely” that a larger proportion of tropical cyclones globally have reached Category 3 or higher over the last four decades, indicating a trend toward more intense storms.
The IPCC expresses “medium confidence” that there has been an increase in the average and peak rainfall rates associated with tropical cyclones.
The frequency and magnitude of “rapid intensification events” in the Atlantic have also likely increased. This refers to instances where maximum wind speeds increase dramatically in a short period, posing significant risks.
Additionally, there appears to be a slowdown in the speed at which tropical cyclones move across the Earth’s surface, typically resulting in greater rainfall accumulation in affected areas. For example, in 2017, Hurricane Harvey “stalled” over Houston, releasing 100cm of rain in three days.
In certain regions, the average location where tropical cyclones reach their peak intensity has shifted poleward, such as in the western North Pacific, potentially exposing new communities to these hazards.
Furthermore, evidence suggests that the increased intensity of US hurricanes has led to greater damage.
Determining the precise influence of climate change on individual tropical cyclones can be difficult due to the complexity of these systems.
However, rising temperatures are known to affect these storms in several ways.
First, warmer ocean waters provide storms with more energy, potentially leading to higher wind speeds.
According to a recent study, the maximum wind speeds of hurricanes between 2019 and 2023 were estimated to be boosted by an average of 19 mph (30 km/h) as a result of human-driven ocean warming.
Second, a warmer atmosphere can hold more moisture, resulting in more intense rainfall.
One estimate suggests that climate change made the extreme rainfall from Hurricane Harvey in 2017 approximately three times more likely, according to one estimate.
Finally, rising sea levels, primarily due to a combination of melting glaciers and ice sheets, and the thermal expansion of water, cause storm surges to occur on top of already elevated sea levels, exacerbating coastal flooding. Local factors can also contribute to this effect.
For instance, it is estimated that flood heights from Hurricane Katrina in 2005 – one of America’s deadliest storms – were 15-60% higher than they would have been under the climate conditions of 1900.
Overall, the IPCC concludes with “high confidence” that human activities have contributed to increases in precipitation associated with tropical cyclones, and with “medium confidence” that they have contributed to a higher probability of more intense tropical cyclones.
According to the IPCC, the number of tropical cyclones globally is unlikely to increase.
However, as global temperatures rise, it is “very likely” that these storms will exhibit higher rates of rainfall and reach greater peak wind speeds. This suggests that a larger proportion of tropical cyclones will reach the most intense categories, four and five.
The more global temperatures rise, the more pronounced these changes are likely to become.
The IPCC projects that the proportion of tropical cyclones reaching Category 4 and 5 could increase by approximately 10% if global temperature rises are limited to 1.5°C, rising to 13% at 2°C and 20% at 4°C, although there remains uncertainty in these specific figures.
Storm surges of 13 feet (3.9m) above ground level and destructive waves are expected as the storm hits Jamaica.
Ahead of the landfall of the world’s strongest storm of the year in Jamaica, people describe frantic preparations.
Melissa’s 185 mph winds at landfall means it could eclipse all storms the island has experienced before.
Ian and Trudi Ferguson have been told to barricade themselves into their hotel bathroom.
The powerful storm is set to be the world’s strongest of the year.