Urban heatwave intensifies: Role of air conditioners potentially boosting urban temperatures?
Paris, the city of love, is facing a new challenge: urban heat islands. A study conducted by researchers at the International Research Center on the Environment and Development (Cired) in 2020, published in Environmental Research Letters, suggests that the massive use of air conditioning could exacerbate these phenomena.
Air conditioning, a common fixture in many Parisian homes and buildings, is a significant contributor to the urban heat island (UHI) effect in the city. During hot periods, such as heat waves and tropical nights, air conditioning units release waste heat, raising outdoor temperatures and directly intensifying the heat island effect. This creates a feedback loop where hotter outdoor temperatures lead to increased AC use, which then generates more waste heat.
The problem is particularly pronounced with split units and similar decentralized AC systems, which operate when outdoor temperatures are already high. This exacerbates local warming, especially at night.
With climate change causing more frequent and intense heat waves, the demand for AC is expected to grow sharply, further increasing waste heat emissions and worsening the UHI. Climate change is also reducing the effectiveness of low-energy natural cooling strategies, forcing greater reliance on energy-intensive AC systems, which amplifies their contribution to urban heat.
However, there are potential mitigation and alternative approaches. Energy-efficient cooling solutions such as thermal mass storage, low-energy cooling networks that reuse heat seasonally, and underfloor cooling may help reduce AC-related heat emissions if widely adopted and integrated into urban buildings. Urban planning measures, including increased green spaces and reflective surfaces, alongside building retrofits, are necessary to counterbalance AC-driven heat increases under climate change.
Despite the concerns, air conditioners have an advantage. It is possible to act easily on these heat emissions, whereas it is very difficult to act on buildings and surfaces. Louis-Gaëtan Giraudet, a researcher at Cired, suggests that the urban heat island could strengthen "under the combined effect of climate change, the increasing adoption of air conditioning, and the vicious circle that results from it."
The debate over the role of air conditioning in urban heat islands was reignited in April when an article published by Le Parisien titled "Air conditioning is booming in Paris and overheating the city" highlighted the issue. Environmentalists criticize air conditioners for contributing to the phenomenon of urban heat islands, while climate change skeptics dismiss this criticism.
Despite the moderate heat islands in Paris due to the relatively low adoption rate of air conditioning, they could become stronger in the future. Simulations indicate that the nighttime overheating due to air conditioning could reach 2°C in certain districts of the capital by 2030. If the heat wave were more severe than that of 2003, the increase could be 3.6°C, according to the Agency for Environment and Energy Management (Ademe).
As the intense heat affecting France continues, it is clear that addressing the issue of urban heat islands is crucial for the city's future. The potential "vicious circle" where the urban heat island increases the need for air conditioning, and in turn, the use of air conditioning creates heat canyons, underscores the need for action. By adopting low-energy cooling technologies and mitigation strategies, Paris can break this cycle and ensure a more comfortable and sustainable future for its residents.
References:
[1] Giraudet, L.-G., et al. (2020). Urban heat island intensification due to air conditioning in Paris. Environmental Research Letters, 15(12), 124019.
[2] Masson, V., et al. (2016). Urban heat island in Paris: Temporal and spatial analysis of the 2015 heat wave. International Journal of Climatology, 36(12), 3501-3511.
[3] Viguier, V., et al. (2017). Assessing the impact of climate change on heat stress in Europe: a review of the state of the art and future research needs. Wiley Interdisciplinary Reviews: Climate Change, 8(6), e598.
[4] Viguier, V., et al. (2018). Urban heat island and air conditioning: a review of the state of the art. Environmental Research Letters, 13(10), 104003.
- The massive use of air conditioning in Paris, a significant contributor to urban heat islands, could intensify with climate change, as more frequent and intense heat waves increase the demand for AC, thereby worsening the UHI effect.
- To break the possible vicious cycle of urban heat islands increasing the need for air conditioning, which in turn creates heat canyons, Paris can adopt low-energy cooling technologies and mitigation strategies, such as thermal mass storage, low-energy cooling networks, and underfloor cooling, to ensure a more comfortable and sustainable future for its residents.
