Extreme weather: What is it and how is it connected to climate change?
Is climate change causing droughts, heatwaves, wildfires and floods?
(2 months later)
People around the globe are experiencing more intense heatwaves, deadly floods and wildfires as a result of climate change.
Extreme weather is becoming more frequent and more intense in many places because of climate change.
Unless global emissions are cut, this cycle will continue.
Scientists say this will continue whilst humans keep releasing planet-warming greenhouse gases.
A really simple guide to climate change
Here are four ways climate change is linked to extreme weather.
How do we know climate change is caused by humans?
Dozens of bushfires as heat grips Australia's east
Here are four ways climate change is changing the weather.
1. Hotter, longer heatwaves
1. Hotter, longer heatwaves
To understand the impact of small changes to average temperatures, think of them as a bell curve with extreme cold and hot at either end, and the bulk of temperatures in the middle.
Even a small increase to average temperatures makes a big difference.
A small shift in the centre means more of the curve touches the extremes - and so heatwaves become more frequent and extreme.
This is because the whole distribution of daily temperatures shifts to warmer levels, making hotter days more likely and more extreme.
Temperatures in the UK topped 40C for the first time on record, in July last year, leading to transport disruption and water shortage.
Scientists use computer simulations to judge whether extreme weather events have been made more likely by warming caused by humans.
The Met Office estimates the extreme heat is ten times more likely now because of climate change. And things could worsen.
For example, a record-breaking heatwave across Spain, Portugal and northwest Africa in April was made at least 100 times more likely by climate change, according to the World Weather Attribution network (WWA).
"In a few decades this might actually be a quite a cool summer," says Professor Friederike Otto, a climate scientist at Imperial College London.
Temperatures which topped 40C in the UK for the first time on record in July 2022 would have been "extremely unlikely" without climate change, the WWA says.
The Met Office has also pointed out that heatwaves are not just hotter: They're also lasting longer. Warm spells have more than doubled in length in the past 50 years.
Why is it so hot in the UK?
Why is it so hot in the UK?
Is the UK getting hotter?
Is the UK getting hotter?
Heatwaves can be made longer and more intense by another weather phenomenon - a heat dome.
Heatwaves are also becoming longer and more intense - including in the UK.
In an area of high pressure, hot air is pushed down and trapped in place, causing temperatures to soar over an entire continent.
This can happen through "heat domes" - an area of high pressure where hot air is pushed down and trapped in place, causing temperatures to soar over large areas.
When a storm distorts the jet stream, which is made of currents of fast-flowing air, it is a bit like yanking a skipping rope at one end and seeing the ripples move along it.
One theory suggests higher temperatures in the Arctic - which has warmed more than four times faster than the global average - are causing strong winds called the jet stream to slow and increasing the likelihood of heat domes.
These waves cause everything to slow drastically and weather systems can become stuck over the same areas for days on end.
India and Pakistan faced successive heatwaves, with Jacobabad, in Pakistan, registering 49C at one point in May.
In the same month, Onslow in Western Australia hit 50.7C, the joint-highest temperature ever reliably recorded in the Southern Hemisphere.
One theory suggests higher temperatures in the Arctic are causing the jet stream to slow, increasing the likelihood of heat domes.
The Arctic is also warming more than four times faster than the global average in recent decades. In June 2020, average temperatures in Siberia were up to 10°C above normal, reaching a new record of 38°C in the Arctic circle. This triggered devastating wildfires and sea ice loss.
The World Weather Attribution network (WWA), a collaboration between international climate scientist, concluded this was "almost impossible" without climate change.
Scientists warn 2023 could be even warmer, as a climate phenomenon called La Niña - which has been suppressing global temperatures - has come to an end.
Life at 50 degrees
Life at 50 degrees
How do El Niño and La Niña change the weather?
2. Longer droughts
2. More persistent droughts
Linking climate change and individual droughts can be difficult. The availability of water is not just down to temperature and rainfall.
Making a direct link between climate change and individual drought events is challenging. A number of factors influence water availability, not just temperature and precipitation.
But longer and more intense heatwaves can worsen droughts by drying out soils. The air above then warms up faster, leading to more intense heat.
But as heatwaves become more intense and longer, droughts are likely to worsen.
Demand for water from humans and farming in hot weather puts even more stress on the water supply.
Less rain falls between heatwaves, so ground moisture and water supplies run dry more quickly. This means the ground takes less time to heat up, warming the air above and leading to more intense heat.
In parts of East Africa, an ongoing drought has left more than 20 million people at risk of being dangerously short of food. Climate change made this drought more than 100 times more likely, according to the WWA.
Drought in Somalia - the country has suffered three failed rainy seasons in a row
Drought in Somalia - the country has suffered five failed rainy seasons in a row
Demand for water from humans and farming puts even more stress on water supply, adding to shortages.
3. More fuel for wildfires
3. More fuel for wildfires
Wildfires can be sparked by direct human involvement - but natural factors can also play a huge part.
Wildfires happen naturally in many parts of the world. It's difficult to know if climate change has caused a wildfire because other factors like changes to land use can be involved.
The cycle of extreme and long-lasting heat caused by climate change draws more and more moisture out of the ground and vegetation.
Some regions - such as the western US - have seen an increase in the area burnt by wildfires, but global wildfire trends are complex.
These tinder-dry conditions provide fuel for fires, which can spread at an incredible speed.
However, scientists say climate change is making the weather conditions needed for wildfires more likely.
Earlier this year the Chilean government put three regions on high alert for forest fires amid weeks of high temperatures.
Extreme and long-lasting heat draws more and more moisture out of the ground and vegetation.
Dozens of people have died and been evacuated in Chile as wildfires burn across the country
Dozens of people died and were evacuated in Chile as wildfires burned across the country
In Australia, New South Wales is experiencing its worst fires since the 2019/20 "Black Summer" - as strong winds and scorching temperatures drive the fires' rapid spread.
These tinder-dry conditions provide fuel for fires, which can spread at an incredible speed, particularly if winds are strong.
Last summer, France, Spain, Portugal, Greece, Croatia and Albania experienced severe wildfires - with thousands of residents evacuated and several hundreds reported to have died.
Alberta in Canada has seen "unprecedented" wildfires, forcing nearly 30,000 people to leave their homes. This follows severe wildfires in Chile and Australia earlier in 2023.
More than 10,000 residents and tourists were evacuated in France during the 2022 wildfires
Scientists expect wildfires to become more frequent and intense in future due to the combined effects of land use and climate change.
In 2021, Canada experienced heatwaves that led to fires which developed so rapidly and explosively that they created their own weather system, forming pyrocumulonimbus clouds. These colossal clouds then produced lightning, igniting more fires.
Compared with the 1970s, fires larger than 10,000 acres (40 sq km) are now seven times more common in western America, according to Climate Central, an independent organisation of scientists and journalists.
Then and now: The burning issue of wildfires
Then and now: The burning issue of wildfires
How do wildfires start?
How do wildfires start?
4. More extreme rainfall events
4. More extreme rain
In the usual weather cycle, hot weather creates moisture and water vapour in the air, which turns into droplets to create rain.
The warmer it becomes, the more moisture the atmosphere can hold.
The warmer it becomes, however, the more vapour there is in the atmosphere. This results in more droplets and heavier rainfall, sometimes in a shorter space of time and over a smaller area.
This results in more droplets and heavier rainfall, sometimes in a shorter space of time and over a smaller area.
In 2022 floods hit Spain and also parts of eastern Australia. In a period of just six days Brisbane saw almost 80% of its annual rainfall, while Sydney recorded more than its average annual rainfall in little over three months.
In 2022, Pakistan experienced its wettest July and August on record, triggering devastating floods affecting more than 33 million people. It is "likely" that climate change played a role, according to the WWA, but natural weather patterns like the monsoon may have been involved too.
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How do El Niño and La Niña change the weather?
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Extreme rainfall and flooding has also hit other regions, including West Africa between May and October 2022, and New Zealand in February 2023.
Watch: Record-breaking floods hit Spain’s east coast
Scientists cannot say for certain that they were caused by climate change, but the floods are consistent with the changes they expect in a warming world.
Watch: Record-breaking floods hit Spain’s east coast
A really simple guide to climate change
These rainfall events are connected to the effects of climate change elsewhere, according to Peter Gleick, a water specialist from the US National Academy of Sciences.
How do we know climate change is caused by humans?
"When areas of drought grow, like in Siberia and western US, that water falls elsewhere, in a smaller area, worsening flooding," he said.
The weather across the globe will always be highly variable - but climate change is making those variations more extreme.
And the challenge now is not only limiting the further impact people have on the atmosphere but also adapting to and tackling the extremes we are already facing.
