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 - Around 100 people, including children and counsellors at a summer camp, were swept to their deaths during flash floods in central Texas last week as climate scientists warned that such extreme weather events were more likely in a warming world.

Climate Central, a U.S.-based advocacy group, said the atmosphere can hold more moisture in a warming climate, leading to heavier and more intense rainfall.

"Instead of uniform, widespread rain, we're seeing more localised, extreme downpours as storms tap into unusually high moisture levels," it said on its website analysing the Texas floods.

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). But the world is well off target, making extreme weather likelier.

Even a small increase of 0.5 C degrees 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. In early July, Europe was gripped by a heatwave that meteorologists said was "exceptional" because it struck so early in the year.

A March heatwave in central Asia was unusually intense, said World Weather Attribution (WWA), a global team of scientists who examine the role played by climate change in extreme weather. Climate change made it about 4 C hotter, it said.

Precipitation

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

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 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.

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

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 Tuesday July 8 at 16:06 GMT to add details about the Texas floods.

(Reporting by Beatrice Tridimas; Editing by Clar Ni Chonghaile and Ayla Jean Yackley.)