Publish at August 20 2018 Updated June 26 2025
"Greenhouse gas" means that certain gases block thermal radiation.
Diluted in the atmosphere, these gases prevent heat (thermal radiation) from escaping into space. Without this effect, we'd freeze as soon as the sun went down.But too much of this effect would turn our planet into an unbearable steam room. At present, we're on course for a radical temperature rise induced by an increase in the greenhouse effect.
So much for the situation. But while these gases block thermal radiation, they don't block it at all frequencies. There is a transmission window in the infrared, between 8 and 13 microns, in which these gases are transparent and through which thermal radiation can escape, at these specific frequencies.
This phenomenon has been observed for centuries in many countries when water froze at night, even though the air temperature was well above freezing. This phenomenon has been dubbed "night-sky cooling", with frost appearing on plants and ice forming on thin bodies of water even when the temperature is 4 or 5°.But cooling by radiation is insufficient during the day to counteract the sun's caloric input, which covers almost all other frequencies. So the phenomenon remains limited to clear-sky nights.
Currently, 17% of the world's energy consumption is used for cooling, and is responsible for 8% of greenhouse gas emissions (air conditioning of homes and offices, food cold chain, server cooling, etc.). This proportion is rising steadily, especially in developing countries where air-conditioning technologies are now economically accessible, boosting productivity and improving quality of life.
Aaswath Raman, a researcher at Stanford University, wondered how this cooling window could be used to improve air-conditioning systems. The need for improvement was obvious to him, because as the atmosphere warms up, the use of air-conditioning becomes a necessity, and itself a source of warming.The need for improvement was obvious to him, because as the atmosphere warms, the use of air-conditioning becomes a necessity, and itself a source of warming, both in terms of the energy it consumes and the heat it gives off.
He and his team have developed a reflective surface that transforms and re-emits a high proportion of thermal radiation at frequencies that are not blocked by greenhouse gases.As a result, the surface exposed to the sun becomes between 4 and 5°C cooler than the ambient temperature.
The space above the atmosphere is at -270°C, and this is where the thermal radiation is diffused. The coating is made up of different layers of silicon and hafnium oxides, silver, titanium and silicon, in thicknesses determined by nanophotonics research. All this in a film with a total thickness of less than two microns (0.0018 mm), 50 times thinner than a human hair! The technology is currently being commercialized by SkyCool Systems.
The applications are numerous, opening the door to a veritable energy revolution.cooling systems in general, but also the cooling of solar panels, the passive cooling of premises and, last but not least, the production of energy from the temperature difference between space and earth.
How many training programs and jobs will this create? Considering all those who are hot, probably a lot!
In his "Foundation" trilogy, Isaac Asimov describes the "Kan Sector", located at the South Pole of Trantor, the Empire's capital planet. This sector was dedicated to evacuating the heat produced by the planet's 40 billion inhabitants. It's a safe bet that we won't make it to that population level, but we can be sure that evacuating the heat we produce will be an interesting challenge for our civilization.
References
How we can turn the cold of outer space into a renewable resource - Aaswath Raman - Ted Conference 2018
https://www.ted.com/talks/aaswath_raman_how_we_can_turn_the_cold_of_outer_space_into_a_renewable_resource
SkyCool Systems - http://skycoolsystems.com/
Trantor - Wikipedia - https://fr.wikipedia.org/wiki/Trantor
The case for optimism on climate change - Al Gore - Ted 2016
https://www.ted.com/talks/al_gore_the_case_for_optimism_on_climate_change#t-1492168
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