These self-cooling walls could replace air conditioning

Air Conditioning is not a particularly eco-friendly technology. Yes, it cools down the room you're sitting in, but the energy used (around 200bn kilowatt hours of power per year in the US alone) contributes to global warming.  As the planet gets incrementally hotter, the effect will be depressingly self-perpetuating: hotter air will result in more AC usage, which will create more heat, ad infinitum.

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