Why is the weather becoming more extreme?

• Climate change causing more extreme weather
• Scientists warn storms, floods, heatwaves could get worse
• Extreme events cost billions of dollars in damages 

LONDON - Hundreds of people, and possibly even thousands, may have been killed after Cyclone Chido devastated France’s poorest overseas territory, the Indian Ocean archipelago of Mayotte, over the weekend.

The cyclone was the strongest storm to strike Mayotte in more than 90 years with winds of more than 200 kph (124 mph) tearing up makeshift houses and leaving streets covered in mud and rubble and residents without water or power.

Scientists say human-induced climate change is making extreme weather events like heatwaves, floods and storms more frequent and deadly and this trend will continue if the world keeps burning fossil fuels.

Poorer nations often say they are bearing the brunt of the environmental crisis despite historically emitting far less planet-heating CO2 than richer countries.

This latest disaster follows a record-breaking storm season in the Pacific Ocean, with six typhoons hitting the Philippines in 30 days, according to World Weather Attribution (WWA), a global team of scientists that examines the role played by climate change in extreme weather.

The likelihood of compounding events like this series of typhoons, or hurricanes Helene and Milton that hit the United States back-to-back in late September and October, will increase with global warming, according to WWA.

Scientists say halving planet-heating greenhouse gas emissions by 2030 is crucial to stop temperatures rising by more than 1.5 degrees Celsius (2.7 Fahrenheit), which would unleash more extreme weather and heat.

But the world is well off target and so extreme weather is expected to become more regular and intense.

So how exactly does climate change make the weather worse?

How does climate change affect weather events? 

Even small increases of 0.5C degrees in global warming can cause significant changes in the weather, according to the Intergovernmental Panel on Climate Change (IPCC).

Global warming happens when greenhouse gases from burning fossil fuels are released into the atmosphere where they trap heat, causing the temperature of the air and seas to rise.  

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

Different weather extremes are affected in various ways. 

Heatwaves

The heat trapped in the atmosphere because of greenhouse gases is making temperatures hotter than they would have been without global warming.  

Temperatures of 40C and 50C are already becoming more frequent across the world, with the last two summers breaking heat records and causing tens of thousands of deaths.

Precipitation 

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

Unprecedented rainfall that caused at least 24 deaths in the United Arab Emirates and Oman in April was found to be up to 40% more intense than if it had occurred without the current 1.2C global warming above pre-industrial levels.

Floods

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

Flooding is caused by increased rainfall from water stored in the atmosphere and rising sea levels. The latter happens when global warming melts ice and warms oceans, causing the water to expand, according to Seneviratne. 

In October, the deadliest flooding to hit Spain for three decades was made twice as likely and 7% heavier by climate change, according to WWA.

Meteorologists think the warming of the Mediterranean, which increases water evaporation, plays a key role in making torrential rains, like those that hit Spain's Valencia, more severe.

Cyclones, hurricanes and typhoons 

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 the warmer temperatures in the air will make the storms more intense. 

After an analysis of Hurricane Helene, which killed more than 200 people across six states, WWA said it found that climate change is enhancing conditions conducive to the most powerful hurricanes, with more intense rainfall totals and wind speeds.

The WWA also found that the liklihood of three major typhoons making landfall in the Philippines was 25% higher because of the burning of fossil fuels.

Drought

Higher temperatures draw more moisture from the land and dry out the soil. Dry soil cannot absorb rainwater, meaning that it runs off into rivers, increasing the risk of drought, and later floods. 

Droughts can also increase temperatures as the air above the ground warms up more quickly, leading to more intense heat, said Seneviratne. 

Wildfires 

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

A combination of climate change and land-use change 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.

How much is extreme weather costing global economies?  

Extreme weather and climate-related events caused nearly 12,000 disasters between 1970 and 2021, costing $4.3 trillion in economic losses, according to the most recent update of The World Meteorological Organization's Atlas of Mortality and Economic Losses from Weather, Climate and Water-related hazards. 

A study published by Nature found that annual gross domestic product could decrease by up to 10% if the world warms by 3C, owing to the economic losses incurred from climate-related events. 

U.S. President Joe Biden has said it will cost billions of dollars to deal with the aftermath of Hurricane Helene while Hurricane Milton could result in a $60 billion loss for the global insurance industry, according to analysts at RBC Capital.

In early September, Typhoon Yagi caused over $3 billion worth of damages in northern Vietnam, devastating export-oriented industrial hubs, destroying factories and facilities, flooding farmland and damaging homes.

Individual households also face long-term economic losses from extreme events through rising home insurance premiums or costs associated with lost work days in order to prepare for, or clean up from, disasters.

Can we predict extreme weather? 

Advances in technology, including artificial intelligence, and greater data availability have improved weather forecasts.

Heavy rainfall was predicted several days in advance of September's floods in Europe, allowing authorities to empty reservoirs, build flood defence walls and warn people of the imminent danger, according to WWA analysis.  

It said the death toll was lower compared to the 1997 and 2002 floods, pointing to the effectiveness of investments made in forecasting, early warning systems, and preventative actions such as evacuations.

In 2022, U.N. Secretary-General António Guterres launched the Early Warnings for All initiative to ensure that everyone is protected from hazardous weather, water, or climate events through early warning systems by the end of 2027.

This story was updated on Dec. 16 to add details about the Cyclone Chido

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