LIving underground with Skywells seems like a good idea to me to beat the heat of summers and the ice of winters

 A skywell as I understand it is an ancient Chinese idea to beat the heat. Moisture in some areas comes down the skywell into the main living quarters or business quarters and helps aerate the air and make it cooler.

However, building underground has to only be done in certain places where you aren't near rivers or lakes that could flood you out. For example, digging into the base of a mountain with an airwell towards the back of where you dig might be useful.

I think if you are going to build an underground house where there is a water issue part of the year you almost have to think like a submarine where you have the conning tower above where water might go but also hatches to prevent flooding of your underground home. So, where you build underground and how you build underground is very important.

However, when you are about 10 feet or more underground the temperature tends to stay around 60 degrees Fahrenheit some places. 

For example, I have gone into Lava tubes around Mt. Shasta where it is well over 100 degrees outside and there is ice inside those lava tubes. In fact, at Jot Dean Ice Cave I have gone into this place with 100 degree temperatures and slid down and ice waterfall with rocks embeded in the ice to another level further down. (Jot Dean Ice Cave is off of Highway 89 to the west of McCloud. However, if you go there your cell phone isn't going to work so you need forest service maps or a satellite phone of some sort to navigate out that far from civilization.

So, the point I'm trying to make here is one way to beat the heat is to live far enough underground to where it stays much cooler than the surface of the earth. After all, dogs and bears and squirrels including Go downs on the prairies of the plains often live underground especially to bear their young to prepare them for the outside world later on.

So, living underground a lot is what many mammals do and how they survived 65 million years ago when all the bigger dinosaurs went extinct from lack of food or froze to death from exposure when an asteroid from the asteroid belt hit earth and turned it into a nuclear winter for a few years and all the bigger dinosaurs not living in the ocean died out then.

Humans who don't find useful ways to adapt to the heat (beyond air conditioners) might die out too over time during this century if they don't also move underground where it is cooler most days of summers especially.

I think many "Survivors" of the increasing heat will find ways to move partially or completely underground during the days and come out at night when it is cooler to work and go to school then worldwide.

When I was young I experimented a little with this by digging straight down about 14 feet or more on my father's land in the desert (Yucca Valley, California area) and I found that below about 2 or 3 feet deep there is was a type of sandstone which was fairly safe to hollow out an area in. However, it might be important if you dig down to use wood supports as well as plywood and cement to prevent what you dig from caving in on you. So, a lot of engineering is involved in living underground like this. But, it's definitely a lot cooler than at the surface. During the nights you could turn on a fan to change the air and turn off the fan during the day to stay cool underground during the heat of the day. So, by coming out to work at night or go to school at night you stay cool even without an air conditioner in this way worldwide.

I think more and more cultures will have to do this or they are going to have to move somewhere else where it isn't as hot to survive. Only the richest of people who can afford Air conditioning are going to be able to stay in the hottest parts of the world in summers from now on unless they move underground.

I heard about one guy from somewhere else going hiking in 115 degrees in Death Valley with the temperature still rising to around 120 or more. They found his body later that day.

If you aren't used to dry heat and come from a humid place you have no useful reference points regarding your survival regarding evaporation and the amount of water you have to drink to stay alive in a dry desert. Also, if you are not familiar with how deserts are you might be in danger too from things like Cholla Cactus and what they do to sandals if you step on a piece of cholla cactus. I likely still have cholla Quills in parts of my feet and legs from when my father and I built his retirement home in the desert from 1968 until 1980 when my father and mother retired there on the upper desert above Yucca Valley in the high deserts of California.