A pyrocumulonimbus cloud, a looming thunderstorm generated by an intensely hot wildfire, has been observed with radar in France for the first time. These deadly “fire clouds” of rising hot air, smoke and moisture, which accelerate blazes with strong winds and soaring embers, are expected to become more common in Europe as wildfires there get bigger.  

“You have this tilted column that is sucking air and then propagating embers in front, and it also creates lightning. That’s another way of lighting up fuels in front of the fire, so these cells are unstoppable,” says at the University of Corsica, France. “You cannot stop a thunderstorm, and neither can you stop a firestorm, a strong pyrocumulonimbus.”

Alongside huge blazes in Spain, France has been suffering a wildfire in the Gironde region, which President Emmanuel Macron has called the country’s most severe crisis since the second world war. The fire has burned more than 420 square kilometres since last week, coming within 15 kilometres of the city of Bordeaux and forcing around 220,000 people to evacuate. It generated a pyrocumulonimbus cloud on 24 July and another on 25 July, according to regional officials. Embers and lightning ignited new fires around the original inferno.

“We faced another firestorm, the same incredible, unprecedented, unknown phenomenon as the one we saw on Friday, when we realised we were entering a new dimension,” Gironde prefect Sophie Brocas told journalists.

It is a miracle this pyrocumulonimbus-fuelled fire hasn’t claimed any casualties, Filippi says.

Sometimes the “fire-breathing dragon of clouds”, pyrocumulonimbus are typically generated by massive wildfires in the forests of North America, Siberia and Australia. They’ve spurred on infamous fires like the that killed 173 people in Australia in 2009 and the conflagration that in 2016. Canada’s record-breaking wildfires in 2023 142 of these storms.

In Europe, however, there have been only a handful of confirmed pyrocumulonimbus in Spain and Portugal, including one during Portugal’s devastating Pedrógão Grande fire in 2017, which destroyed hundreds of homes and killed 66 people. But that appears to be changing.

“You have to have two things happening at the same time: an extreme heat source and an unstable atmosphere that interacts with the fire,” says at the European Centre for Medium-Range Weather Forecasts. “If… the heat from the fire increases, like it’s projected to increase from our studies, then yes, you should see more of these events.”

This firestorm begins to take shape when temperatures as high as 800°C send a plume of smoke into the sky. As the hot air rises and cools, water vapour condenses onto the ash to form pyrocumulus clouds, like the fluffy white clouds you might see on a summer day, only brown or grey.  

If the plume is hot enough and the atmosphere is unstable enough, the cloud can keep rising to reach the upper troposphere at 10,000 metres, the cruising altitude of a passenger plane. It sometimes reaches the stratosphere, as much smoke as a moderate volcano. It becomes a pyrocumulonimbus when the static electricity from colliding ice particles sparks thunder and lightning.

Although rain from the cloud often evaporates in the hot air, this kind of thunderstorm nonetheless creates its own weather system. The cloud’s updraft pulls in air, fanning the flames with winds reaching 160 kilometres per hour and accelerating the fire’s spread by up to five times, according to Filippi.

Meanwhile, strong downdrafts create erratic gusts that carry embers off to start new fires. Dozens of lightning strikes can blazes as far as 100 kilometres ahead of the main fire. It can also create fire tornadoes of twisting flames. As the winds, embers and lightning strengthen and expand the wildfire, it releases more heat and smoke, a feedback loop that can amplify the rising cloud for many hours.

Both wind shear higher in the atmosphere and erratic gusts at the ground can take the fire in unpredictable directions, making it nearly impossible to contain its acceleration or plan targeted evacuations.

“The fire front is constantly shifting. We cannot fight it directly. It’s a David-versus-Goliath scenario,” Eric Brocardi of the National Firefighters Federation of France local media about the Gironde fire on 2 August.  

Wildfire plumes have expanded in height since 2003 in the western US, creating more pyrocumulonimbus clouds, an increase that’s projected to continue.

Pyrocumulonimbus will have more chances to occur in Europe as well, as the fastest-warming continent experiences more extreme heat, such as the record-breaking heatwave in June, and wildfires. could also contribute, such as when a wet spring last year boosted vegetation growth on the Iberian peninsula, only for record summer heat to dry it out. This led to Europe’s worst-ever wildfires, including a in Spain.

“We need to adapt, so get prepared,” Filippi says. “Burn-proof and reduce the amount of fuel around your house.”

Europe suffered unprecedented wildfires and heatwaves in 2025, impacts that are expected to worsen on the world’s fastest-warming continent.

Last year was the hottest year on record in the UK, Iceland and Norway and one of the three hottest years in Europe as a whole, according to an annual report by the European Centre for Medium-Range Weather Forecasts (ECMWF). More than 95 per cent of the continent experienced above-average annual temperatures. Scandinavia, Finland and north-western Russia saw their worst-ever heatwave, 21 days of simmering temperatures that reached 30°C (86°F) even at the Arctic circle.

This extreme heat probably stunted animal and plant growth while encouraging the spread of invasive species and pests, showing how the climate crisis is contributing to a crash in biodiversity, at the World Meteorological Organization said at a press conference.

“This region would [typically] see zero to two days of strong heat stress, and we are speaking about 21, so this had a major impact on ecosystem health,” she said. “Since 1980, Europe has been warming twice as fast as the global average, [and] heatwaves are becoming more frequent and severe.”

Climate warming set the stage for record wildfires in Portugal and Spain in August, the extremely hot, dry, windy conditions there at least 40 times more likely. More than 10,000 square kilometres burned, and at least three people were killed. Fires approached Madrid, and authorities had to shut down parts of the Camino de Santiago pilgrimage route. Smoke drifted as far as the UK.

Across Europe, wildfires emitted 47 million tonnes of carbon, a record amount. Spain, the UK, the Netherlands, Germany and Cyprus all topped their previous fire-emissions records.

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Soil conditions were the driest in 33 years of observations, with more than a third of Europe suffering extreme agricultural drought, especially the UK, Turkey and Ukraine. While parched soils probably encouraged wildfires in many countries, it was increasing fluctuations in the weather that supercharged the blazes in Portugal and Spain, according to at ECMWF. An extremely wet spring that boosted vegetation growth was followed by record summer heat, which dried out those plants and shrubs, creating a tinderbox.

“If you have a very high fuel load in addition to the wildfire weather, so hot, dry winds in particular, that’s when we get these catastrophic conditions where wildfires spread very quickly,” Burgess said at the briefing. “National parks need… firebreaks around them to make sure if there is a fire, it doesn’t spread.”

The ocean around Europe was also abnormally hot, breaking the record for annual sea surface temperature for the fourth year in a row. A record 86 per cent of these seas suffered strong, severe or extreme marine heatwaves. The most extreme hotspots occurred west of Ireland, south of Iceland and south-east of Spain.

For the past three years, heatwaves have struck 100 per cent of the Mediterranean Sea, which is warming up faster than the global average. Waters in Italy and Spain reached 30°C, warmer than a typical swimming pool, raising the risk of fish death, as well as the spread of bacteria and algae. Past marine heatwaves in the Mediterranean have killed off huge amounts of coral, seagrass beds and shellfish.

To limit future damage, Europe needs to lead the way on slowing climate change, of the European Commission said at the briefing. In 2025, solar power generated a record 12.5 per cent of the continent’s electricity, with a total 46 per cent coming from renewables.

European countries are also among those taking part in the first in Colombia this week, which was organised after the COP30 climate summit in Brazil failed to agree on a roadmap to end oil, gas and coal emissions.

At the same time, Europe should adapt to future climate risks, such as multi-year megadroughts similar to the one already gripping the western US, according to officials.

“We need to address these risks,” Chrenek said. “The cost of inaction is significantly higher than the cost of tackling negative impacts.”

Atmospheric carbon dioxide levels jumped by a record amount in 2024 to push concentrations to their highest point since measurements began, the UN’s World Meteorological Organization (WMO) has reported.

Between 2023 and 2024, the global average concentration of CO2 surged by 3.5 parts per million (ppm) to reach 423.9 ppm, the WMO has said. This is the largest increase since modern measurements started in 1957 and is well in excess of the 2022 to 2023 increase of 2.3 ppm.

It marks the latest in a trend of accelerating annual increases, with growth rates tripling since the 1960s. The last time Earth experienced a comparable concentration of CO2 was 3 million to 5 million years ago.

Excess CO2 in the atmosphere will have a warming effect on the planet for centuries to come, the WMO warns. “The heat trapped by CO2 and other greenhouse gases is turbocharging our climate and leading to more extreme weather,” at the WMO said in a statement.

Ongoing emissions from fossil fuels, alongside a surge in emissions from wildfires and a slump in the carbon uptake by the world’s lands and oceans, were the key drivers of last year’s record surge, according to the WMO.

Researchers expected a slump in the uptake of carbon by oceans, forests and other ecosystems in 2024 due to the recent El Niño weather pattern, which pushed up global temperatures and dulled carbon absorption by driving heat, fires and drought in key regions like the Amazon. The amount of tropical forest lost in 2024 was double that of 2023, scientists noted earlier this year. “It is normal for some tropical lands to be drier and store less carbon during warm El Niño years such as 2024,” says at the University of Reading, UK.

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But there is concern that this dip in carbon uptake by the planet – particularly by the land – is part of a longer-term trend that could mean climate change is weakening the planet’s ability to soak up excess carbon.

“There has been some suggestions that the land sink was particularly low in 2023 and 2024, even for El Niño years, and that there has been a worrying reduction over time, particularly in the northern hemisphere outside the tropics,” says r, a climate scientist at the Breakthrough Institute. “In short, there are worrying signs that the land sink in particular is declining, but it’s too early to know with confidence without another few years of data.”

In the meantime, it is more urgent than ever for humanity to curb ongoing fossil fuel emissions, says at the University of Leeds, UK. “The biggest reason for the ongoing increase [in CO2 concentrations] is fossil fuel emissions being at a persistent all-time high and not yet coming down.”

A battery made of iron and salt could provide emergency power – without the threat of fire – near one of California’s oldest redwood forests.

The 200-kilowatt battery will be paired with solar panels at the Alliance Redwoods Conference Grounds in Sonoma County, California. This facility is in a high wildfire risk zone in a redwood forest, and it’s only 16 kilometres from the Armstrong Redwoods State Natural Reserve, home to some of the state’s tallest and oldest trees. During extreme weather and wildfires, firefighters and evacuees rely on the conference site, but it’s also vulnerable to electricity grid outages.

“The way we looked at the technology is, how could we make a safe, abundant, low-cost energy storage system,” says at Inlyte Energy in California. “And that led us to very large cells with a very cheap and abundant active material, iron and salt.”

The battery project could deliver up to two weeks of emergency backup power once it becomes operational in 2027. That could keep the lights on in the conference grounds and also supply energy to a firefighting water pump station nearby, without putting the iconic redwoods at risk.

That is because these easily-sourced battery materials – powdered iron and salt contained in a ceramic tube – are also non-flammable. “We can put these batteries and battery cells quite close together without any sort of fire and explosion risk, which is a main issue with packing tons of lithium-ion batteries close together,” says Kaun.

The lithium-ion batteries in smartphones or electric cars sometimes catch fire, and this risk can be magnified when many batteries are clustered together in large energy storage plants. In January 2025, for example, a fire at the world’s largest battery storage facility in California destroyed 300 megawatts of energy storage. By comparison, Inlyte’s iron-salt batteries could store energy with much lower risk. The iron-salt battery project received just over $4 million in from the US Department of Energy to improve energy resilience in the wildfire-prone region near the redwood forest.

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“These non-flammable batteries seem like a smart choice for project developers looking to put energy storage systems in any remote or arid places or near forests subject to periodic drought,” says at San José State University in California. “Energy technologies and infrastructure have a long history of starting wildfires, and non-flammable batteries offer a way to avoid some of that risk.”