Cooling Subways and Trains in a Warming World
▼ Summary
– Jonathan Paul recorded London’s highest Tube temperature at 42°C (107.6°F), using a smartphone thermometer to measure extreme underground heat.
– The Tube’s clay surroundings have absorbed heat from trains for over a century, and adding air conditioning risks worsening tunnel temperatures by releasing warm air.
– Paul proposes using London’s abundant groundwater at 10°C as a refrigerant to remove excess heat from stations, testing this in a chalk quarry near Reading.
– Rising global temperatures due to climate change make cooling public transport critical, with heat issues reported in Japan, Morocco, and India where train temperatures hit 47°C.
– Paul has observed commuters fainting from heat on overground trains, and historical records show summer travel discomfort has persisted for nearly a century.
The challenge of keeping subway systems and trains cool is intensifying as global temperatures rise, creating uncomfortable and potentially unsafe conditions for millions of daily commuters. Researcher Jonathan Paul once recorded a staggering 42 degrees Celsius (107.6 Fahrenheit) inside a London Tube station, a level of heat that would typically drive people indoors for air-conditioned relief. Underground, however, there is no escape from the stifling environment of tunnels and trains.
London’s Tube network is embedded within dense clay, a material that has been steadily absorbing heat from train operations for over a century in some lines. Installing conventional air conditioning on trains presents a serious drawback: it would expel warm air from the carriages directly into the tunnels, further raising temperatures in the confined spaces. This creates a difficult cycle where cooling one area inadvertently heats another.
Paul, a researcher at Royal Holloway, University of London, is developing an innovative approach that targets the tunnels themselves. He explains that water can absorb enormous quantities of heat and notes that groundwater is readily available beneath London at temperatures around 10 degrees Celsius. His proposed system would use this cool groundwater to draw excess heat away from stations. To test the concept, his team is conducting experiments deep inside a chalk quarry west of London, near the town of Reading.
Trains are essentially metal tubes filled with passengers, making them inherently difficult to cool effectively. As climate change leads to hotter summers, maintaining safe and comfortable conditions on public transportation has become a pressing worldwide concern. Recent heat waves have led to complaints about inadequate train cooling in countries like Japan and Morocco, while a 2023 study documented carriage temperatures in India reaching as high as 47 degrees Celsius.
Paul has observed the direct impact of overheating on commuters using above-ground rail services. He reports, “I’ve seen four people faint this summer,” highlighting the urgent need for workable solutions.
Air-conditioned trains have been around for nearly a century. A newspaper article from 1933 celebrated their arrival by noting, “Until now, every one has dreaded a railway journey in summer.” If only the authors could have foreseen today’s reality, where intense heat waves often make rail travel so unpleasant that many people choose to avoid it entirely.
Paul and his colleagues are confident their groundwater cooling method can make a difference. To see the experimental setup, one must descend 20 meters by ladder into the chalk quarry near Reading. There, multiple chambers of different sizes have been carved out of the chalk and separated by doors. “We’re trying to simulate real-life conditions in the Tube,” Paul says, though he admits the quarry environment is considerably more bleak, very dark and quite dingy.
(Source: Wired)
