Why is the weather becoming more extreme?

LONDON - A deadly hurricane that left a trail of destruction across the Caribbean from Haiti to the Bahamas was made four times more likely because of climate change driven by burning fossil fuels, according to a rapid estimate by scientists.

Hurricane Melissa hit Jamaica with winds of up to 185 mph (298 kph) on Tuesday, making it the strongest ever hurricane to directly hit the island’s shores. It also struck Cuba and the Bahamas and caused heavy rains in Haiti, where around 25 people were killed.

U.S. forecaster AccuWeather said Melissa was the Caribbean's third-most intense recorded hurricane, as well as its slowest-moving, which made it particularly destructive.

Scientists at Imperial College London, who released the rapid assessment, said a hurricane like Melissa at landfall was about four times more likely in the 2025 climate compared to a pre-industrial baseline.

"This event was unlikely without climate change," they wrote.

Even a small increase of 0.5 C degrees Celsius (0.9 degrees Fahrenheit) can cause significant changes in the weather, according to the Intergovernmental Panel on Climate Change (IPCC).

The warmer atmosphere causes more moisture to be absorbed in the air, resulting in both hotter, drier conditions and heavier rainfall, Sonia Seneviratne, a lead author of an IPCC assessment report, told Context.

So how does climate change affect different weather events?

Heatwaves

Heat trapped in the atmosphere by greenhouse gases from burning fossil fuels is raising temperatures to levels unfamiliar to many parts of the world.

In June, tens of millions of Americans sweltered as the heat index exceeded 40 C (104 F). In early July, Europe was gripped by a heatwave that meteorologists said was "exceptional" because it struck so early in the year.

Precipitation

For every degree of warming, extreme daily rainfall can increase by up to 7%, according to the World Meteorological Organization.

In Pakistan, intense monsoon rainfall from June to August left hundreds dead and destroyed farmland and infrastructure.

A rapid analysis by World Weather Attribution (WWA) found that climate change had increased rainfall intensity by at least 15%.

Heavy rains and flooding that killed 16 people in March in Argentina were partly fuelled by climate change, scientists said.

A WWA analysis found that extreme heat before the floods caused a warmer, more humid mass of air that clashed with a cold front from Patagonia, causing torrential rains south of Buenos Aires.

Floods

Between 2000 and 2020, the number of major floods worldwide more than doubled, from 1,389 to 3,254, while the incidence of storms grew from 1,457 to 2,034, according to a United Nations report.

Flooding is caused by increased rainfall from water stored in the atmosphere and rising sea levels. The latter happens as sea ice melts and ocean water expands, Seneviratne said.

In July, around 130 people, including children and counsellors at a summer camp, were swept to their deaths during flash floods in central Texas.

Climate Central, a U.S.-based advocacy group, said the floods were fuelled by an intense, moisture-heavy storm, which is made more likely and powerful in a warmer climate.

Storms

Tropical cyclones, like typhoons and hurricanes, are unlikely to occur more frequently because of climate change, but the proportion of extreme ones is rising, according to the IPCC.

Large amounts of water held in the atmosphere and the energy created by warmer air temperatures make storms more intense.

U.S. government scientists forecast an above-normal 2025 hurricane season, with warmer sea-surface temperatures a major contributor. Last year's Atlantic hurricane season was one of the costliest on record with five major hurricanes.

Drought

Higher temperatures draw more moisture from the land and dry out the soil, which cannot absorb water when it does rain. Instead, it runs off into rivers, increasing the risk of floods following droughts.

Droughts also increase temperatures as air above the ground warms more quickly.

Wildfires

Intense heat and dry land and soil create perfect conditions for wildfires to spread.

Climate change and land-use changes are expected to increase the occurrence of extreme wildfires by 14% by 2030 and 50% by the end of the century, according to a report by the U.N. Environment Programme and non-profit GRID-Arendal.

The destruction of key ecosystems that help to absorb carbon, like peatland and rainforest, will make it harder to slow rising temperatures.

This story was updated on October 30 to add details about Hurricane Melissa.

(Reporting by Beatrice Tridimas; Editing by Clar Ni Chonghaile.)