Summary of Key Points
High temperatures have led to a surge in demand for air conditioning, but air conditioners come with drawbacks such as high energy consumption, high costs, and exacerbation of the urban heat island effect. Research indicates that passive cooling materials (such as radiative cooling coatings and gel films) could be a viable alternative. These materials require almost no energy to cool buildings by reflecting heat into space. Some have already been shown to reduce surface temperatures by 5-7°C, but their widespread adoption depends on policy support.
Air Conditioning: A Lifesaver or a Source of Trouble?
While air conditioners appear to solve the problem of high temperatures, they pose several significant issues:
1. Overload on Power Grids: When many people turn on their air conditioners at the same time during hot periods, the demand for electricity surges, potentially leading to power outages, which can be particularly dangerous for vulnerable groups like the elderly.
2. Vicious Cycle of Heat: Split-air conditioners release heat indoors directly into the outside, causing the city temperature to rise. This leads to more people turning on their air conditioners, creating a cycle that makes cities even hotter.
3. Unaffordable for Many: Air conditioners themselves are not expensive, but the electricity costs can be prohibitive for low-income families. For example, in countries like India and Mexico, 100 million households may still be unable to afford air conditioning by 2040, leaving them particularly vulnerable to the effects of high temperatures.
Global Cooling Demand: An Explosive Increase in Electricity Use and Emissions
Currently, cooling buildings accounts for 10% of global electricity consumption. As the number of hot days increases in intensity and duration, this figure is expected to soar:
- By 2050, the electricity used for cooling buildings is projected to increase by 210% (more than tripling) compared to 2024.
- The greenhouse gas emissions from air conditioners could also triple. The more air conditioners are used, the warmer the Earth becomes, leading to an even more severe problem of high temperatures and a vicious cycle.
Passive Cooling: The Power-Free “Natural Air Conditioner”
Scientists have discovered a power-free method of cooling based on passive radiative cooling. The principle is simple: the atmosphere has a “window” (infrared waves with wavelengths of 8-13 micrometers) through which heat can be directly released into space. Passive cooling materials reflect this heat, effectively removing it from buildings.
Examples of such materials include:
- Coatings containing nano-silicon oxide, which can reflect 97% of solar radiation and reduce surface temperatures by 5.26°C when applied.
- Plastic films with absorbent gels that absorb water vapor at night and release heat during the day, with the hydrophobic top layer directing the heat into space, reducing temperatures by up to 7°C under direct sunlight.
Effectiveness of New Materials
The effectiveness of these new materials is already comparable to that of air conditioners:
- Some coatings and films can reduce indoor temperatures by 5-7°C, providing significant relief from heat.
- Automatic blinds and window shades are already being used in offices to reduce the need for air conditioning.
- However, most of these new materials are still in the prototype or testing phase, with further experimentation required, especially for those that combine radiative cooling and evaporation mechanisms.
Why Haven’t They Become More Widespread?
The lack of widespread adoption of these technologies is mainly due to two factors:
1. Lack of Policy Support: There are no mandatory requirements for the use of passive cooling materials in new buildings, so developers have no incentive to adopt them.
2. A Comprehensive Approach is Needed: Simply using cooling materials is not enough; additional measures such as outdoor cooling strategies (like greenery and permeable pavements) are also required to address the urban heat island effect.
Experts emphasize that a combination of policy initiatives and technological advancements is necessary to make passive cooling solutions accessible and affordable for everyone.
In summary, passive cooling materials represent a sustainable solution to high temperatures. However, their practical application depends on the joint efforts of policymakers and the market to bring these technologies from the laboratory to everyday use.
(Note: Data and examples are drawn from authoritative research cited in the article, such as Nature Reviews.)