A minor news item from the weekend.

On Sunday a passenger flight from Houston to Phoenix turned around midway and landed safely at Houston. There were no mechanical issues. All passengers and crew were healthy. No storms were encountered. What happened was that the pilots and their airline were aware of laws that forbid planes to land when the temperature exceeds 120 degrees. At that point certain instruments on older planes may lose precision and smaller planes are subject to additional danger from the waves of heat radiating up from the ground.

It's likely that the plane could have proceeded without incident and the turnaround could be described as an abundance of caution. But the incident highlights the fact that Phoenix Sky Harbor Airport recorded a record high of 117 F in the shade on Sunday, with ground temps on the black asphalt runway easily over 120. For the overseas folks, 117 F is 47 C. It is, in the scientific sense, balls hot. It's almost too hot to imagine. Having spent a fair amount of time in southern Arizona, I subscribe to the easy to mock "It's a dry heat!" theory. Compared to sweltering Midwestern and Southern humidity, I find that 100 F in the dry desert does not feel as hot – as long as you're in the shade. 110 F in the shade might be bearable, even if still hot. In the sun you'd be dead in a couple of hours.

The question the current Southwestern heat wave raises is one that is one it might be useful to start thinking about more: At what point is it just going to get too hot to live in some parts of the world? Calm down, I'm not talking about right now. In the long term – thirty or forty years down the road – the continuation of current warming trends could push it to the limit of what we can reasonably inhabit. Some serious research has suggested that at some point between 2050 and 2100, for example, parts of the Middle East and Africa may simply be too hot for humans to survive in. Granted it is arguable that humans can survive in any environment given all the advantages of technology, but with caveats. One is that infrastructure degrades at a certain point – roads buckle, rails bend, and transformers explode. Another is that if the ability to live in an environment depends entirely on limitless availability of water, electricity, and air conditioning in the middle of deserts, such an environment is "habitable" only in a limited sense. We assume those things, which far from guarantees that they will always be there. The combination of water scarcity and sheer heat eventually have to reach a breaking point. It's not going to happen tomorrow, but we can't hold back nature forever.

Long-time readers know my Crazy Old Man theory that the mass migration of population and economic resources to the Sun Belt is a temporary phenomenon. There simply is no long-term logic, for example, to having 10 million people live in the Phoenix-Tucson urban area with water sufficient to sustain maybe a quarter that many. Add in (slowly) rising temperatures, longer summers, and explosive population growth and it's clear that the current trends cannot continue indefinitely. The United States industrialized and populated itself from the Northeast and Midwest because, despite the crappy winters, they were actually survivable during the summer before the widespread availability of cheap power and they have ample water resources for transportation, agriculture, and urban use. We probably won't be alive to see the waves of migration reverse and move back in that direction, but it will happen eventually. The funny thing about unsustainable behavior is that it can't go on forever.