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Comment by mschuster91 | Hacker News Reader

> The good thing about green energy is that one there is a sufficient amount of it, it can also be used for extensive air conditioning.

The heat doesn't vanish with AC, at least not unless you use a very expensive deep-underground well as a heatsink instead of the open air.

Even if everyone has AC indoor - the air outdoor will still be too hot and, most likely, humid, with all the expelled heat from the ACs added on top of that. Animals won't stand a chance, especially wild ones, and humans that absolutely have to work outside (e.g. policemen, firefighters, EMS) will be just as impacted.

We have to face the reality: large parts of the globe, impacting billions of people, will be unable to support human and a lot of animal and plant life during the summer months if climate change continues at the current pace in a short enough time that most people reading this text will eventually witness this.

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There's much more air outside than inside, so 15C colder inside does not mean that the entire city gets 15C hotter outside. And in a heat event, most people are inside, not outside. 1C hotter outside to make it livable for 99% of humans sounds fine. And this is only about cities, anything living outside cities will be fully unaffected.

For the people that have to work outside: air conditioning in the vehicle, frequent breaks in air conditioned areas, and I wonder if we could get proper air conditioned clothing at some point (currently vests with fans embedded are quite frequent in Japan, but that's the best there is as of today).

But I agree with the last paragraph. Air conditioning is the only countermeasure we have but in the end the fact remains that many cities will eventually become incompatible with human life in summer.

In a dense residential community, when 70% of the units are running ACs and a minority are not, it's going to get substantially hotter than 1C for the ones that are not. It will be upward of 5C hotter in the non-AC units in my experience when the wind is minimal. The 1C you came up with does not apply in the close proximity of the dense urban air conditioning.

Reflective clothing using PDRC materials will be a lot more feasible than personal air conditioning. The latter would require a powered spacesuit anyway which makes it awkward to work. See https://youtu.be/NVAcSgLZues although it's not about clothing, but the idea is the same.

> Reflective clothing using PDRC materials will be a lot more feasible than personal air conditioning.

Doesn't change the fact that when the wet-bulb temperature (i.e. a combination of the air temperature and humidity) does not allow for evaporative cooling (aka sweating) to work any more. No matter what, you cannot survive such conditions for a prolonged amount of time, as your body will slowly cook itself.

You can survive heat on its own in dry air (that's how people have thrived across MENA deserts, or how people survive saunas), you can survive extensive moisture (that's how people and plants have thrived in the rainforests). But you physically cannot survive in a wet-bulb temperature of > 35 °C for prolonged times.

Tell this to the politicians that make jokes about not putting AC units on schools. This happened on Spain a few days ago.

There's PDRC, but we can't mass produce the "photonic metamaterials" that make it good.

https://en.wikipedia.org/wiki/Passive_daytime_radiative_cool...

It ought to be great. Takes no energy, sends heat through the infrared window back out into space where it came from.

I researched the topic and produced a short video on it: https://youtu.be/NVAcSgLZues

Purdue University produced a barium sulfate nanocomposite paint that has 98% reflectance in the desired band using a 150μm layer, cooling surfaces by 4.5C.

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