In Ulaanbaatar, Mongolia, winters are a matter of life and death. The city is 1,300 metres above sea level in a valley on the Tuul River, and temperatures can plunge below −35 °C. The average yearly temperature is around −0.8 °C, and the city nudges out Astana in Kazakhstan and Reykjavik, Iceland, to rank as the coldest capital in the world.

Around one million of Ulaanbaatar’s 1.6 million inhabitants reside in around 200,000 yurts — circular family tents, known locally as gers. The city “was only planned for a population of 600,000” when the country was part of the Soviet bloc in the 1970s, says Unurbat Erdenemunkh, co-founder and chief science officer of local science start-up company URECA.

Now, during the winter months, huddled around furnaces inside the gers, locals burn coal, wood, tyres and even plastics for heating. Steel chimneys spew smoke and ash, which becomes trapped in the valley. This has resulted in one of the world’s gravest air-pollution crises, posing severe health risks.

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Air-quality indices were above levels categorized as hazardous most days from December 2025 through to February, according to values recorded by the US Embassy in Ulaanbaatar. In the deepest winter, concentrations of PM2.5 particulates in the air reached 687 micrograms per cubic metre, 27 times higher than the World Health Organization’s recommended limit of 25 micrograms per cubic metre.

The ger itself is a structure with a history dating back at least 2,500 years, and the United Nations cultural organization UNESCO recognizes gers and the craft of making them as part of the world’s intangible cultural heritage. When ethnic Mongol soldiers conquered medieval China and eastern Europe in the thirteenth century, they probably slept in gers similar to the ones seen today.

According to URECA, the coal burnt in household furnaces is responsible for 70–80% of the city’s smog. Although those who burn it are contributing to climate change, many are themselves climate-displaced, having previously engaged in rural herding, a practice that one-third of Mongolians still depend on for their livelihoods.

“Catastrophic weather events in Mongolia are occurring with greater frequency,” says Erdenemunkh. He adds that zud — a Mongolian phenomenon in which the ground freezes so completely that grazing animals starve to death — has “forced huge numbers of people to migrate to Ulaanbaatar”.

Many of the residents of the ger districts were forced to abandon their traditional lifestyle as nomadic herders, mostly owing to disastrous climatic events, including drought; others were motivated by economic reasons, such as the hope of finding better work and education opportunities.

A series of images showing physicist Unurbat standing outside a yurt with hands in his pockets and a close-up of him near the open door of the yurt., image

A will to fight climate change and give back to fellow Mongolians spurred Erdenemunkh, a former experimental physicist, to return home after a career in medical research in Massachusetts and the Netherlands. “I specialized in proton therapy for cancer treatment, but after working in labs for almost seven years, I wanted to do something good for my home city,” he says. In 2022, he co-founded URECA — which stands for Universal Renewable Energy Certificate Accreditor — together with fellow Mongolian and investor Orchlon Enkhtsetseg, after completing a master’s in environmental economics at the Catholic University of Leuven (KU Leuven) in Belgium.

URECA’s focus is on developing climate solutions for Central Asia. Closest to home is their flagship project, Coal-to-Solar (C2S), a pilot programme involving 80 Ulaanbaatar families who live in gers, which are concentrated in the hills surrounding the city. The company pays for the installation of solar panels, an electric heater, batteries and a URECA smart meter for monitoring the system’s performance. “It took a lot of trust for these families to take part in this project. We’ve replaced the burning of coal for heating with clean, renewable energy and shown that low-income families can be champions for climate action,” explains Erdenemunkh.

C2S is a hybrid system, backed up by grid electricity. A combination of heat storage, using bricks inside the ger’s heater, and energy storage using batteries, can cover up to six hours without the grid, which is prone to outages.

Unurbat Erdenemunkh checks one of the control panels of the C2S renewable-energy system.

A series of images showing physicist Unurbat sitting on the bench in a yurt, checking the control panel of the solar panel installed outside the yurt and a close-up of batteries in a closet inside the yurt., image

The lead-acid batteries installed by URECA last for three years.

Erdenemunkh, who has two young children with his wife Onon Bayasgalan, URECA’s chief sustainability officer, knows the dangers of air p

A breath of fresh air: solving Ulaanbaatar's pollution issues — in photos