Large data centres in cities risk suburban heating

Cities have long been known to trap heat, creating pockets of warmth that are noticeably hotter than the surrounding countryside. This happens because concrete and asphalt soak up the sun's energy and release it slowly, while the lack of soil and plants means less cooling evaporation occurs. Now, a new layer of heat is being added to this urban mix, one that comes from the massive servers powering the artificial intelligence revolution. These facilities, known as data centres, consume vast amounts of electricity to keep their computers running and cool. While the energy they use is essential for modern life, the heat generated as a byproduct of that energy use is being released directly into the atmosphere, day and night. As these facilities grow from small server rooms into gigawatt-scale campuses, scientists are asking a critical question: are we inadvertently turning our cities into even hotter places, especially during dangerous heatwaves?

A team of researchers led by Andrew Pitman at the University of New South Wales set out to answer this question by looking at Sydney, Australia. They focused on the city's rapid expansion of data centres, which includes dozens of existing sites, many under construction, and several massive projects in the planning stages. To understand the impact, the team used a sophisticated computer model of the atmosphere that simulates weather patterns at a very fine scale, zooming in to one-kilometre squares across the city. They ran simulations of ten separate heatwave events, comparing the weather as it is now against a scenario where all the current, under-construction, and planned data centres were switched on at full capacity. This allowed them to isolate the specific effect of the waste heat from these facilities on the local air temperature.

The results revealed a clear and significant warming effect, particularly in the western part of the city where the largest data centres are located. When all these facilities operate together, the average air temperature during a heatwave rises by between 0.5 and 1.0 degrees Celsius across a large area. In the immediate vicinity of the biggest sites, the warming is even more intense, with average temperatures climbing by more than 1.5 degrees. The model showed that this extra heat affects both the hottest part of the day and the coolest part of the night, but the impact on nighttime temperatures is particularly striking. Near the largest data centre, the minimum temperature—the lowest point the air reaches before sunrise—could rise by up to 3.5 degrees Celsius. This means that on a hot summer night, the air might not cool down as much as it normally would, leaving the environment and the people living nearby with less relief.

The scale of the problem depends heavily on how the data centres are cooled and how large they are. The researchers found that smaller facilities have a negligible effect, but the new generation of massive data centres, some planned to be over 1,000 megawatts, changes the local climate. The method of cooling also matters. Many data centres use water to absorb heat, which turns into vapour and carries the energy away. While this prevents the immediate release of hot air, the researchers noted that in a city like Sydney, which faces water shortages, relying on this method is risky. If water cooling were banned and all the heat had to be released directly into the air as sensible heat, the area affected by warming would expand significantly, reaching further into northern Sydney and exposing more people to higher temperatures.

The human cost of this warming is measurable. Based on current population data, the researchers estimated that in their most extreme scenario, where all planned large data centres are built, nearly 255,000 people in Sydney could be exposed to heatwaves that are at least 0.3 degrees Celsius hotter than they would be otherwise. More than 78,000 of those people could face heatwaves that are at least 0.5 degrees hotter. This is not just a matter of comfort; higher temperatures during heatwaves are linked to increased mortality, economic losses, and health risks. The study highlights that the heat from these facilities is additive to the existing urban heat island effect and the broader trend of global warming, creating a compounding risk for city dwellers.

The researchers suggest that the solution may lie in where these facilities are built. Placing large data centres outside of city limits could prevent them from intensifying the heat within urban areas. This approach could also offer benefits to regional towns, as connecting these remote facilities to cities via high-speed networks would improve digital connectivity for those communities. If data centres must remain in cities, the study advises against clustering them together in technology precincts, as the combined heat from multiple sites creates a much stronger local warming effect than scattered, smaller facilities. Furthermore, the reliance on backup diesel or gas generators, which would release even more heat and pollution during power outages, presents another layer of risk that planners need to consider.

Ultimately, this work brings a previously overlooked factor into the conversation about urban planning and climate resilience. While the energy these data centres consume drives scientific and medical breakthroughs, the physical heat they release is reshaping the local environment. The study suggests that as the demand for artificial intelligence grows, so too does the need to manage the thermal footprint of the infrastructure that supports it. By understanding these dynamics, city planners and policymakers can make more informed decisions about where to locate these essential facilities, ensuring that the pursuit of technological advancement does not come at the cost of making cities dangerously hot.