Why Hurricane Melissa is a wake-up call on how a warming climate can intensify natural disasters

With sustained winds estimated at 295 kilometres per hour, Melissa is ranked as the third-strongest Atlantic hurricane since reliable record-keeping began in the early 1900s. It holds this position alongside the infamous "Labour Day" hurricane of 1935. Melissa was not only a storm of intense winds but also of great size, with its hurricane-force winds extending over 70 kilometres from its centre. This vast area of impact subjected a large swath of the Caribbean to its destructive forces, resulting in 83 deaths and $6 billion in damages. The mighty Melissa demonstrates how a warming climate can intensify natural disasters.

To gauge a hurricane's true strength, scientists use a specific measure. They look at the minimum atmospheric pressure at sea level within the storm's core. Atmospheric pressure is the weight of the air above us. A lower pressure reading indicates a more powerful and intense storm system. Normal air pressure at sea level is approximately 1013 millibars.

In contrast, the most intense Atlantic hurricane ever recorded, Hurricane Wilma in 2005, had a central pressure of 882 millibars. The second most intense was Hurricane Gilbert in 1988, with a pressure of 888 millibars. Hurricane Melissa, with a minimum pressure of 892 millibars, ranks third, confirming its status as a historic and extreme weather event.

The Atlantic hurricane season is a predictable period from June to November. On average, this season produces about fourteen 'named storms', which are low-pressure systems with wind speeds of more than 63 kilometres per hour. Of these, seven develop into hurricanes and three reach major hurricane status every year. Only rarely does one evolve into a super hurricane, such as Melissa. Therefore, the initial formation of a storm like Melissa was not entirely unexpected.

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Melissa's beginnings were first observed as a weather disturbance near West Africa in mid-October. This system travelled across the Atlantic, developing into a tropical storm by October 21. For its first few days, Melissa was a relatively disorganised and meandering storm, posing little immediate threat.

However, the situation changed dramatically in the next few hours. The storm moved into a region of the Caribbean where the sea surface temperatures were unusually high, about 1.5 degrees Celsius above the normal range for that time of year. Warm ocean water acts as the primary fuel for a hurricane. It provides the heat and moisture that the storm needs to intensify. As warm, moist air rises from the ocean surface, it cools, and the water vapour condenses into clouds and rain. This process releases latent heat, a stored form of energy. This released energy powers the storm's engine, causing winds to spin faster and the entire system to grow more organised and ferocious.

Melissa's transformation was both sudden and terrifying. What had been a moderate storm began a period of rapid intensification on October 25. In just 18 hours, its maximum sustained winds increased from 115 km per hour to 225 km per hour. In less than 48 hours, those winds had peaked at a devastating 295 km per hour. It was at this peak intensity that Hurricane Melissa, now a Category 5 storm, made landfall near New Hope, Jamaica, on October 28. Hurricanes are categoried as one to five, based on sustained wind speed, with category five being the strongest.

The Caribbean is no stranger to hurricanes. However, storms of this exceptional strength are rare. The impact was severe, causing widespread damage. Critical infrastructure, like telecommunications, roads, hospitals and water systems, was disrupted. Huge and extensive damage to infrastructure caused an added hurdle for both immediate emergency response and long-term recovery efforts.

A hurricane weakens when it is cut off from its warm water energy source. After ravaging Jamaica, Melissa moved on and made a second landfall near Chivirico, Cuba. By this time, interaction with land had weakened it to a Category 3 hurricane. It continued to lose strength as it moved further, becoming a Category 2 storm as it passed northeast of Bermuda. The remnants eventually moved into the North Atlantic, dissipating southeast of Iceland on November 4.

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The influence of climate change on tropical cyclones is a complex area of study, as their impacts are driven by a combination of extreme winds and heavy rainfall. However, recent advances in computer-based modeling and simulations are allowing researchers to quantify this connection with increasing confidence. To understand Melissa's place in a changing climate, scientists used sophisticated computer models. These are complex programs that simulate weather systems. One such tool, the Imperial College Storm Model (IRIS), is explicitly designed to simulate tropical cyclone wind hazards globally. It helps assess the risk of ongoing storms and analyse the impact of climate change.

Researchers used this model to investigate the strong winds of Hurricane Melissa by analysing storms that make landfall in the same region. They then ran simulations to see how such storms would behave in a world 1.3°C cooler, which is the difference between today's global average temperature and the pre-industrial average. The results were striking. The model showed that climate change has made storms with Melissa's wind intensity about five times more frequent than they were in the past. In today's climate, such an event can be expected, on average, once every 1,700 years. In a cooler world, it would have been a much rarer event, occurring only once every 8,100 years. Furthermore, the model indicated that the maximum wind speeds of similar storms are now about seven per cent more intense, owing to the warmer climate. This is significant because even small increases in wind speed lead to an exponential increase in potential damage.

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The influence of climate change extended beyond wind. The same scientific analysis found that the extreme rainfall associated with Hurricane Melissa, particularly the five days of pounding rain over Jamaica, was about 30 per cent more intense and twice as likely to occur because of today's altered climate. A comprehensive study by the World Weather Attribution consortium, a group of international researchers, concluded that climate change directly increased Melissa's maximum wind speeds by seven per cent and its extreme rainfall by 16 per cent.

Hurricane Melissa serves as a solemn reminder of the new reality in a warming world. The scientific evidence is crystal clear; the elevated ocean temperatures driven by global warming are providing more fuel for stronger, wetter storms. The increased frequency and intensity of such events underline the urgent need for a concerted international effort to reduce carbon emissions and arrest the pace of global warming.