Why the French are painting their windows with chalk to beat the heat

 

by Sophie Hardach

 

A simple, low-tech remedy may help cool homes. Here's the science behind the trend.

As record-breaking heat sweeps over France, some shops are running out of a simple, cheap and unexpected product – crushed chalk.

Known as Blanc de Meudon, or Meudon whiting, it is normally used to make paints or as a cleaning product. But faced with punishing temperatures, there are reports that ingenious people have been using the chalky material as a home remedy against the heat, covering windows in schools and private homes.

Mixed with water, then painted on glass, the result is a milky, whitish coating that lets in some light but reflects the heat. And a growing body of research suggests that there may be some solid science behind the DIY cooling hack.

 With heatwaves growing ever more frequent and intense due to rising global temperatures – and posing a particular danger to populations in cities – could a simple lick of white paint help people cope better when it hots up?

 

Radiative cooling

White paint – on walls and roofs, usually – is widely known to have a cooling effect. Generally speaking, white surfaces reflect sunlight and heat, while dark surfaces absorb it. This principle can be used to cool buildings and cities. Commercially available white paint on a surface can reduce temperatures on the other side by at least 1.7C (3F) compared to the ambient temperature at noon.

Paints specially developed to maximise cooling, such as ultra-white paint, have been shown to reduce the indoor temperature by several degrees by not only reflecting sunlight but also shedding heat through a process know as "radiative cooling".

One study of ultra-white paint found it could reflect up to 98.1% of sunlight, while a previous formulation reflected 95.5% of sunlight. Another study showed that combining it with a layer of ultra-black paint underneath could lower daytime temperatures by up to 7.6C (14F).

 One of the reasons why chalk might be effective, however, lies in the properties of its main component, calcium carbonate, which is not only highly reflective but also resistant to solar radiation. This property has led some researchers to use nanoparticles of calcium carbonate in new kinds of "super cool" paint.

 

"These kinds of particles are widely used in radiative cooling paint, also in our super cool paint," says Jiashuo Wang, a student at the University of New South Wales in Sydney, Australia, who is part of a team working on cooling paint.

Chalk has also been used as a coating for fabric that keeps the wearer cool. Particles of calcium carbonate – the main ingredient in chalk – are good at reflecting ultraviolet and near-infrared light (the portion of sunlight that transmits heat).

In addition, chalk is considered to be relatively benign in terms of its health and environmental impact – though there may be some risks to respiratory health from indoor chalk use, and inhaling particles.

Blanc de Meudon, or Meudon whiting, is helping the French stay cool this summer (Credit: Getty Images)

White windows and 'le cool roofing'

According to French media reports, demand for Blanc de Meudon is leading to stock shortages around the country as people struggle against temperatures of more than 40C (104F).

 

Blanc de Meudon is traditionally used to whiten shop windows during renovations or by gardeners in their greenhouses. But after the chalk-paint trick circulated on social media, demand for the product soared, French newspapers report.

"We'd known about the idea for a while, we talked about it during the last heatwave but forgot to buy any," Ouest France quotes a shopper called Philippe. "Now it's too late! It's sold out everywhere!"

Some French schools have also used the chalk paint on their windows, though an official warned that it's "not a miracle solution" and that properly insulated roofs are needed instead.

People have also whitened the windows of their apartments.

The chalk, as well as white paint more generally, is cheap. And unlike air conditioning, which worsens the overall heat effect and emissions problem by consuming energy and releasing heat outside, paint only uses energy when it's produced.

 

More like this:

• The white roofs cooling Indian slums

• The simple ways cities can adapt to heatwaves

• How to exercise safely in hot weather 

White-painted cool roofs – also known as "le cool roofing" in France – are also getting more attention there as a sustainable, low-tech way of combating extreme heat. The idea taps into a long tradition in many southern parts of Europe, such as Greece, of painting houses white to ward off the heat. 

One study suggests that cool roofs – roofs painted white or with reflective coating – could have cooled London "by about 0.8C (1.4F) on average during a heatwave, preventing the heat-related deaths of an estimated 249 people". (Read about how women in India are using white paint to cool their homes.) 

 

For those interested in another home remedy, there is an alternative: yoghurt. An experiment by researchers in the UK found that the indoor temperature of a house with yoghurt-painted windows was on average 0.6C (1.08F) cooler. They found that a thin film of the dairy product could lead to rooms being up to 3.5C (6.3F) cooler when it was "hot and sunny". While a smelly solution at first, the odour apparently disappears quickly as the yoghurt paint dries.

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Snow and ice on Swiss glaciers melting at alarming rate amid heatwave, expert says

 

Swiss glaciers are set to lose an enormous amount of ice and snow due to the heatwave battering Europe. Photograph: freeartist/Alamy

 Accumulation on Switzerland’s glaciers from last winter expected to all be gone by Monday amid ‘enormous’ melt rates across Alps

 Agence France-Presse

 

Swiss glaciers are set to lose an enormous amount of ice due to the heatwave battering Europe, according to the head of Glacier Monitoring in Switzerland (Glamos).

The snow and ice accumulated last winter by Switzerland’s glaciers is expected to have all melted away by Monday, marking the alarming second-earliest arrival on record of the tipping point known as glacier loss day.

All further melting between now and October will see the size of glaciers in the Swiss Alps shrink.

In data going back to 2000, the only time that the tipping point arrived even earlier was in 2022, when it came on 26 June. The grim scenario is driven by the current heatwave, as well as the one in May – both coming on the back of another winter with poor snowfall.

“We’re just seeing enormous ablation, ice melt rates and snow melt rates all over the Alps,” Glamos network chief Matthias Huss told AFP on Friday, as multiple Swiss weather stations registered new all-time records.

 

“We are three months too early compared to a healthy state.”

This century, the tipping point, on average, has been reached in mid-August – already bad news for the nation’s glaciers, which are shrinking at a staggering rate.

Much of the water that flows into the Rhine and the Rhone – two of Europe’s major rivers – comes from the Alpine glaciers.

Huss said he had just returned from the Rhone Glacier and that in the 10 days since his previous visit “there was one metre of ice melted in the vertical direction – one metre of melting within just the last 10 days”.

 

“It’s very impressive to see, and this is just the effect of the heatwave.”

“The more days that are added that are very high temperatures, not even mattering whether it’s 35C or 40C, this is just very bad for the glaciers.”

Huss said the “very bad state of the glaciers at the moment” was down to a “combination of bad circumstances”, including less snowfall and the arrival of dust from the Sahara desert in March.

He said 2026 was “surprisingly similar” to 2022, which for glaciers was “by far the most extreme year ever recorded in the Alps, with melt rates shattering everything we had seen before”.

He said this year had seen 25% less snow replenishing the surface of the glaciers compared with the 2010-20 figures. Meanwhile May was warm, causing the snowpack to disappear earlier.

Glaciers in the Swiss Alps began to retreat about 170 years ago, initially modestly, but in recent decades melting has accelerated significantly as the climate warms.

The volume of Swiss glaciers shrank by 38% between 2000 and 2024. Huss said Switzerland had already lost 1,200 glaciers in the past 50 years, and now only 1,300 were left.

“Those lost were small glaciers, but they were still relevant in peripheral regions of the Alps,” the glaciologist said.

“If warming continues as it did over the last decades, by 2100 we will only be left with some little remnants of ice.”

France restricts public drinking as Europe swelters under a ‘heat-dome driven furnace’ for the second time in two months

 

A woman on the Trocadero square near the Eiffel Tower as temperatures rise in Paris during a second heatwave affecting a large part of France, on June 20, 2026. Sarah Meyssonnier/Reuters

Homem mergulha em fonte perto da Torre Eiffel, em Paris, na França, em meio a onda de calor histórica no país europeu, en 22 de junho de 2026. — Foto: Abdul Saboor/ Reuters 

 

Franceses às margens do Canal Saint-Martin, em Paris, onde o banho foi liberado — Foto: REUTERS/Alice Sacco

 

by  Laura Paddison 

 

Europe is sweltering under its second heat dome in two months, with temperatures spiking above 104 degrees Fahrenheit, bringing dangerous conditions across swaths of the planet’s fastest-warming continent. France banned public alcohol consumption, Spain closed a World Cup fan zone and the UK is bracing for an annihilation of its all-time June temperature record.

Heat alerts were posted Monday by 26 countries, from Ireland to Greece, as soaring temperatures deliver one of Western Europe’s worst June heat waves on record.

The punishing temperatures are the result of a heat dome parked over the continent for the second time in two months. Heat domes are persistent high-pressure systems which act like a lid on a pot, trapping hot air and pushing it downward. The heat waves also come as a strengthening El Niño takes shape in the tropical Pacific. This natural climate pattern is known to increase the frequency and severity of heat extremes worldwide.

Scientists say these kinds of heat waves are becoming more severe and more frequent as humans continue to burn fossil fuels and heat the planet. 

 Extreme heat can quickly become dangerous and even deadly, especially on a continent where very few people have air conditioning. Only about 20% of European homes have AC, compared to around 90% in the United States. 

 

In France, the blistering heat has been unrelenting. More than half of its 96 regions were under red heat wave alerts Sunday, the most severe level. Temperatures reached above 104 degrees Fahrenheit in some parts of the country.

The heat was so intense Sunday, the government banned public alcohol drinking at Fête de la musique, an annual music festival which takes place across the country and brings millions onto the streets. The ban applied to regions under red heat wave alerts.

“For ‌all ⁠events organized by the state and its agencies, instructions have been given not to offer alcohol,” the Prime Minister’s office said in a statement. 

 Monday is set to be even hotter, with temperatures rising to more than 107 degrees Fahrenheit in some places. The government has ordered the closure of more than 800 schools, according to a report in the Associated Press.

 

Monday could be France’s hottest day on record for any month, and there is little chance of respite; temperatures are expected to reach “a very high plateau” until at least Thursday, Météo-France said. On Monday, at least four locations in France set all-time high temperature records for any month of the year, while other locations broke June records.

“This heatwave will be quite comparable in severity to the one in August 2003. It is expected to surpass it in terms of maximum intensity,” Météo France said Monday, referring to a deadly 16-day heat wave that killed nearly 15,000 people.

Other parts of Europe are also set to endure unprecedented heat. In the United Kingdom, temperatures are forecast to reach at least 102.2 degrees Fahrenheit Wednesday, according to the country’s Met Office, which would smash the UK’s all-time heat record for June of 96.08 degrees Fahrenheit, last recorded in 1976. Humidity levels will be high, making the heat even more oppressive.

The Met Office issued a rare “Red Extreme Heat Warning” for Wednesday and Thursday. 

 The country will also endure tropical nights, where temperatures don’t dip below 68 degrees Fahrenheit. Nighttime heat is particularly pernicious as it gives people little chance to rest and recover. 

 

Scientists have sounded the alarm on the extent of the UK’s heat wave. It means two consecutive months “in which the UK temperature records have been annihilated by well over 2 degrees Celsius (3.6 Fahrenheit),” said Liz Bentley, chief executive at the Royal Meteorological Society.

“This is not just a heatwave, it is a heat-dome driven furnace that will grip most of southern UK and push temperatures into truly exceptional territory,” said Akshay Deoras, a meteorologist at the University of Reading. 

 

Termômetro em Rennes, no oeste da França, em 22 de junho de 2026. — Foto: Jeremias González/ AP

Parts of Spain are sweltering under triple digit temperatures and tropical nights. On the Almería coast in southeastern Spain, nighttime temperatures Sunday into Monday didn’t drop below 86 degrees Fahrenheit, according to the country’s weather service AEMET.

In Madrid, a fan zone set up with big screens for people to watch the World Cup was closed Sunday due to the heat, according to Reuters.

Monday is set to be extremely hot again, AEMET posted on X, adding “the danger is significant in much of the country.” 

A woman seen reading in the Ciutadella Park sheltered from the sun in a comfortable area in Barcelona, Spain, on June 2. SOPA Images/LightRocket/Getty Images

 

Heat is often called a silent killer. It lacks the visible destruction of a hurricane, flood or wildfire, yet it’s the deadliest type of extreme weather. Extreme temperatures, especially when combined with high humidity, make sweating and other mechanisms people rely on to cool down become less effective.

Heat and humidity are increasingly reaching levels the human body struggles to cope with. Extreme temperatures have killed more than 200,000 people over the past four years, according to the World Health Organization. 

 Scientists warn these types of extreme heat waves will only become more common as the planet heats up. “Human-driven climate change has provided the springboard for this event, loading the atmosphere with extra heat and making extreme temperatures far more intense than they would have been in the past,” Deoras said. 

 Andrew Freedman contributed to this report.

Tensions are rising between states that rely on the Colorado River. A prolonged drought means the nation’s largest reservoirs are dwindling, and litigation over access to water could lie ahead.

 

(Nina Riggio | The New York Times) The Upper Colorado River in Grand Canyon National Park in Colorado on May 16, 2026. About 40 million people and 5.5 million acres of cropland depend on the Colorado for drinking water and irrigation.

 

 By  Scott Dance | The New York Times

 

Boulder, Colo. • Water in the Colorado River is dwindling to levels that haven’t been seen in decades, and the seven states whose residents and farmers depend on the river can’t agree on a fair way to divide up what’s left.

Negotiations are going nowhere despite more than six months of ongoing talks, plus cajoling by the Trump administration, which twice gathered governors in hopes of a breakthrough that never came. States are already sniping at aspects of a water-use plan the federal Bureau of Reclamation is set to unveil this summer and impose later this year, and they’re threatening to sue each other over water deliveries, raising the prospects of prolonged legal battles just as Western states face demands to sharply reduce water use.

The river’s system of reservoirs and canals was designed for the climate and population of a century ago. It has strained to adapt to a declining water supply and enormous growth in communities in the river basin, despite improvements in efficiency that mean even booming cities are using less water than in the past. Water rights that may date back to the arrival of European settlers also complicate matters. And a year of extreme drought is making it even harder to decide how much each state can draw from the Colorado.

 

It is not for lack of effort.

“We have invested time, effort and money in trying to facilitate a multistate agreement,” Scott Cameron, the acting commissioner of the Bureau of Reclamation, said in an interview this month, moments after signing a deal that could one day augment the basin’s supply using desalinated water from a plant in Carlsbad, California.

But a day later, Cameron told a conference of water experts in Boulder, Colorado, that states have repeatedly rejected proposals for compromise. He said he doesn’t expect any state to be pleased with the measures the federal government is expected to take to delay or prevent reservoirs from dropping to critical lows in the short term.

“I think we’ve succeeded in making everyone unhappy, and maybe making everyone mad,” he said.

 About 40 million people and 5.5 million acres of cropland depend on the Colorado for drinking water and irrigation, but its flow has gradually diminished over the past two decades as the climate becomes warmer and more arid across the West. Now the arcane system of water rights governing the river entitles each state and Mexico to far more water than is actually available. The rules prioritize the longest-established uses of water, in many cases dating to the 1850s and 1860s.

 

But the states have been unable to agree upon water cuts that would reflect the new reality.

In the river’s lower basin — which includes growing urban areas in California, Arizona and Nevada, vast agricultural operations and the nation’s largest reservoir, Lake Mead — communities have agreed to significant reductions in recent years. A new proposal that the states are asking the federal government to consider would curtail use even more, but the lower basin states and tribal nations have asked upstream communities in New Mexico, Utah, Colorado and Wyoming to cut back, too.

 

But any time winter snowpack in the river’s headwaters is meager, the upper basin is forced to use less water, so those states have resisted committing to permanent annual water use cuts. While a 1922 compact divides the United States’ share of the river’s flow equally between the two basins, the less-populated upper basin consumes significantly less water each year than the lower basin.

The stalemate between the basins has deepened as the stakes rise. An existing water-use plan expired this winter, and the states missed key deadlines to agree on a new one, which must be in place by October to avoid chaos and confusion in water deliveries.

(Chet Strange | The New York Times) The shrinking Dillon Reservoir in Frisco, Colo., on May 18, 2026. The reservoir will remain closed this year because of low water levels after a worryingly dry winter. 

A mild winter and extreme spring heat left winter snowpack so depleted that Lake Powell, the nation’s second-largest reservoir, which straddles the upper and lower basins, risked falling below levels critical for hydropower until federal officials began emergency actions to shift water around and keep dams generating electricity.

So far, Trump administration officials have resisted imposing any plan unilaterally, though Cameron said the bureau had “not been passive.” It has offered $454 million for water conservation projects across the basin, using money left over from the Inflation Reduction Act, which was passed under President Joe Biden and included $4 billion for drought response in the West. Cameron said less than $100 million is left to help pay for more water savings.

“We have floated, three times, solutions that we thought represented something that the seven states could agree on,” Cameron said. “Turns out we were wrong.”

 

With the states unable to agree, the federal government is set to put new guidelines in place. Cameron said he expects Interior Secretary Doug Burgum, whose department includes the Reclamation Bureau, to release a plan in July to govern use of the river for the next decade. Before that plan becomes final, it would need approval from a White House that has so far not gotten very involved in Western water issues.

A draft plan released in January included a range of options, some of which would make significant cuts across the lower basin, where the federal government’s control of reservoirs gives it more power to cut off flows. The alternatives would force water shortages, mostly in the lower basin, based upon reservoir conditions. They include varying levels of cutbacks that would leave some risks of unplanned emergency water shortages in the lower basin.

Arizona is especially vulnerable because of its heavy reliance on the reservoirs and its relatively junior water rights.

The federal plan would include room for tweaks and negotiations every two years, Cameron said. But state officials from across the region said that could make things worse.

The biggest problem is that reopening the whole plan every two years would undermine any certainty over water supplies, which is a key goal of the talks, said Becky Mitchell, Colorado’s top water negotiator.

 

“The constant renegotiation every two years is difficult to fathom,” Mitchell said, adding she believed it could create even more tension between the states. John Entsminger, Nevada’s negotiator, agreed it was “not a good plan.”

But Cameron said it was the best option given how difficult it has been to craft a longer-term deal.

As the talks stall, the threat of litigation is looming larger, even though negotiators have said they are hoping to avoid court battles that would undoubtedly be lengthy, expensive and unpredictable. Sen. Mike Lee, R-Utah, warned Wednesday on Capitol Hill that he would seek to block federal drought relief funds from any states that sue over Colorado River water.

In Arizona and Colorado, state officials have been readying lawyers and setting aside public funds for a legal fight over water. Earlier this year, television ads paid for by a coalition of Arizona water users warned that the state is “being targeted” with crippling cuts. Officials in both states said litigation was a real possibility.

In public comments submitted in response to the federal proposal, the states have hinted at contradictory legal interpretations of the 1922 compact, offering dueling arguments that both suggest that the Trump administration was at risk of violating that document. In dispute is whether the compact requires upper basin states to deliver a set amount of water downstream, regardless of conditions, or if the compact simply bars those upstream states from using more than they are officially allotted.

 

Arizona officials said the federal plan would “improperly prioritize maintaining Lake Powell elevations at the expense of required downstream releases,” and thus reduce the flows the state says it’s owed. Colorado said the plan “fails to impose adequate shortages in the Lower Basin to protect the system” and could unlawfully draw from upper basin reservoirs to stabilize Lake Powell and Lake Mead.

Focusing on legal arguments could keep the states from reaching a compromise, Mitchell said. But Arizona’s top water official, Tom Buschatzke, said litigation was “still very much in play.” State lawmakers tripled the size of a fund for river-related litigation when it included $6 million for that purpose in a budget sent Thursday for approval by Gov. Katie Hobbs, a Democrat who has stressed Arizona’s need to protect its water supply.

Because the 1922 agreement is only about 1,700 words long, Entsminger suggested that the states might never agree on what exactly each of them is entitled to — and that was all the more reason for them to find common ground without resorting to litigation.

“The only way you’re ever going to have any certainty on that is probably the Supreme Court action,” Entsminger said. “The way you avoid that is a seven-state agreement.”

This article originally appeared in The New York Times.