I took a vacation to Maine recently where the temperatures were quite pleasant. In fact, the evenings were cool enough that I routinely wore a quarter-zip over my shirt in the evenings. Unfortunately, all vacations come to an end and I returned to Kansas City in the middle of a stretch of oppressive heat – with daily heat advisories and heat index values that repeatedly exceeded 100 degrees. And to confirm that I was not alone in my suffering, the National Oceanic and Atmospheric Administration (NOAA) recently announced that the meteorological summer (June through August) in the continental United States was the hottest ever recorded based on records going back to 1895. [1]
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| Source: Google Gemini AI |
The thing is, it's not just Kansas City or just the USA. Heat has been a news story for much of the year in places all over the globe. Europe has been sweltering all summer and the number of “excess deaths” is estimated to be 35,000 and growing. Great Britain had their hottest summer ever, sparking widespread droughts and numerous wildfires.
Climate scientists have been warning for years that the world was warming to dangerous levels. In fact, if you examine the past 150 years for which we have reasonably reliable temperature records, the ten hottest years for average global surface temperatures have all occurred in the past 11 years. 2026 isn’t on track to be the hottest year ever but it is likely to place in the top four which would mean that the four hottest years ever recorded will all have happened in the past four years.
All of this talk about heatwaves made me think about the potential effects on life in our cities, particularly if things continue to get worse. This post is the second in a series of posts that examine scenarios that could easily be disruptive to our cities and our societies. As I noted in my previous post, incorporating plausible but disruptive scenarios into city planning efforts has become a bit of a trend. The goal of this practice is to keep long-range plans relevant even when unexpected things happen. And while global warming isn’t exactly unexpected, I don’t think many of us are planning on severe heat becoming a standard part of our lives.
Measuring Heat
If heat does become a major concern, one change that is likely to take place is that we will start talking about heat more precisely. Most of us are currently satisfied with temperatures taken by a dry-bulb thermometer – the standard reading shown by the weather app on your phone, the temperature read-out on your car’s dashboard, or what the TV weatherperson typically reports. While useful, the dry-bulb temperature is not a very precise measurement of what the temperature feels like to human beings (and most mammals).
A wet-bulb measurement – basically a standard thermometer wrapped in a wet towel – is more helpful because it accounts for the impact of humidity. In dry air, our bodies naturally keep us cool by sweating which evaporates into the air. This evaporative cooling works great unless the air is already saturated with water vapor (i.e. high humidity) in which case our sweat doesn’t evaporate and we overheat.
A similar but somewhat more sophisticated measure is the Heat Index which has been popularized in the U.S. by NOAA. The Heat Index is based on dry-bulb temperature plus humidity, combined using a complex formula. So for example, a temperature of 90 degrees and relative humidity of 40 percent yields a Heat Index of 91. Increase the relative humidity to 60 percent and the Heat Index reading goes up to 100; increase it to 80 percent and the Heat Index is 113. In theory, the Heat Index tells you what a given combination of heat and humidity “feels like.”
What the Heat Index doesn’t take into account are the effects of direct sunlight and wind (the Heat Index assumes you are in the shade and the wind is light). To get those factors involved, you need what is known as the wet-bulb globe temperature (WBGT) which measures the true physiological impact of working or exercising in sunlight. Consequently, WBGT is commonly used by the military, OSHA and athletic organizations to prevent heat related illnesses.
The WBGT includes the impact of sunshine hitting your skin or clothing (mitigated by the percent of cloud cover) and the impact of wind which can enhance the cooling effect of sweat evaporation. Even the sun angle (latitude and month of the year) is taken into account. For example, a temperature of 95 degrees in Kansas City in September with 60 percent humidity, a wind speed of 12 mph, and 40 percent cloud cover would result in a Heat Index value of 113 and a WBGT of 88. Generally speaking, health risks for moderate outdoor activity become relevant at a WBGT of 85 or so, become severe risks with a WBGT of 90, and a WBGT of 95 is considered the borderline limit of human survivability.
Obviously, different people react to heat differently, so all of these numbers need to be used with some caution. The elderly or people with significant health conditions are more vulnerable, but even healthy people are susceptible to heat-induced illness if extreme heat levels are reached.
The “What If” Future of Extreme Heat
It is possible that people are like the proverbial frog in a pot of hot water. If the temperature increases slowly over time, we (and the frog) might not take any serious action until at some point we are cooked. However, if the temperature jumps dramatically in a short period of time, we might be spurred to take substantive steps to lessen further increases or perhaps even roll temperature increases back (although it's not entirely clear if that is possible). Of course, it would probably be best for mankind if the clear trend over the past several decades prompted us to take action now. Many initial steps have been taken by countries all over the world to stem the increase in greenhouse gases in the atmosphere, but the steps have been half-hearted in most cases and the results have been disappointing.
Despite the dire warnings of climate scientists, I suspect that many people have adapted so easily to our warming planet that the predictions of something catastrophic happening seem overblown. The incremental changes we have seen so far are one thing, but scientists are concerned that climate “tipping points” will be much harder to handle. In climate science, a tipping point is a critical threshold that, when crossed, leads to large, accelerating and often irreversible changes to the climate system.
For example, permafrost – land which is almost always frozen – accounts for roughly 24 percent of all the land mass in the Northern Hemisphere. This frozen dirt, rock and ice contains approximately half of all the organic carbon stored within the planet’s soil. For thousands of years, this organic matter has stayed safely frozen. However, rising amounts of greenhouse gases are causing the planet to warm up (particularly in arctic areas) which is causing the permafrost to melt, which in turn causes the organic matter to decay causing methane and carbon dioxide to be released into the atmosphere. Higher levels of greenhouse gases (methane and carbon dioxide) cause even more global warming, leading to even more permafrost melting, leading to more methane and carbon dioxide being released – and on and on. [2] Unfortunately, this is just one of several potential climate tipping points that could cause rapid weather changes.
I don’t want to debate climate science here, but I included this brief explanation of what could happen simply to underscore that a relatively rapid increase in summer temperatures throughout the midwest (and much of the world) is at least plausible. And for the purposes of my “what if” series, plausible is all I need. Again, if we are serious about planning for the future we can’t just assume the linear extension of past trends. Disruptive things will happen and planning for the most plausible disruptive things seems like a reasonable thing to do.
In some ways, the harbingers of extreme heat are already showing up. Phoenix has long been known for its hot summers, but recent weather trends are making even “dry heat” unbearable. Over the past 20 years, the number of days where the high temperature exceeded 110 degrees has rocketed upward. For the first 10 years of that 20-year period (2006-2015) the city averaged just under 19 days per year with highs at or over 110 degrees. For the second ten years, the average essentially doubled to 36 days per year. And it isn’t hot just in Arizona – as of mid-August, all but six U.S. states had recorded temperatures over 100 degrees, several as early as mid-March (the exceptions were Maine, New Hampshire, Vermont, Rhode Island, Kentucky and Indiana). Fifteen states had temps over 110.
Given this backdrop, my “what if” scenario involves midwestern cities (particularly in the southern and central portions of the country) routinely experiencing Phoenix-like temperatures and Miami-like humidity. For example, in Kansas City in July a temperature of 103 degrees with a relative humidity of 45 percent, a wind of 12 mph, and a sky cover of 33 percent would yield a Heat Index of 122 and a WBGT of 92. This is hot enough to make even moderate outdoor activities life threatening.
Furthermore, my scenario includes days like this not just once a year, but 10 to 15 times per year – often enough that it can’t be written off as a fluke. Even routine summer days might have Heat Index values well over 100 degrees. This scenario might seem ridiculous to some, but I think if things go badly it is within the realm of possibility within the next 10 years, and perhaps even sooner.
The Ramifications of Extreme Heat
Generally speaking, one of the most obvious side-effects of extreme heat is that bodies of water, vegetation and the soil will experience a higher rate of evaporation. This process will exacerbate the drought conditions that are already affecting much of the U.S. This is likely to lead to water usage restrictions for communities that rely upon wells and rivers for their water supply. Kansas City, for example, pulls about 80 percent of its raw water from the Missouri River and abnormally low flows would create significant problems. Fortunately, there are six upstream dams operated by the Corps of Engineers that keep the river flow within a fairly predictable range. Of course, that is what people used to think about the Colorado River with the reservoirs of Lake Mead and Lake Powell (and 8 smaller reservoirs).
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| Source: University of Nebraska |
Increased drought conditions are likely to reduce crop and livestock yields which will put a damper on the economy of most midwestern cities. Drought will also elevate wildfire risks throughout the area, particularly in the exurban fringe. The resulting price hikes for food and insurance will place added stress on low- and moderate-income families.
Perhaps surprisingly, extreme temperatures are likely to not only increase drought conditions but also increase the chances of flooding. Dry soils that have been baked by high temperatures do not absorb rainfall as well as you might expect and so there tends to be more stormwater runoff than normal, particularly during big storms. In addition, warmer air can hold more water vapor than cooler air so when a cold front does cause a thunderstorm, the volume of water that falls as precipitation can be greater than normal. Consequently, the probability tables that lie behind the rainfall predictions that yield designations such as a “100-year storm” or the “100-year floodplain” are changing in a bad way. What used to be a 100-year rainfall is now a 50- or 60-year rainfall in many locations.
Also surprisingly, extreme summer temperatures do not necessarily mean that winters will suddenly become balmy. Generally speaking, average winter temps are expected to be warmer, cold extremes less frequent, and some precipitation may fall as rain when snow would normally be expected. Still, there will be cold snaps, heavy snows, and extended periods of freezing weather. It turns out that global warming doesn’t really make winter go away, it just makes it shorter and less predictable.
Impact on Cities and Society
Perhaps the most significant impact of extreme temperatures will be on the behavior of urban residents. Some outdoor activities that we currently take for granted, such as construction work or sports, may need to be modified or cancelled. Keep in mind that my “what if” scenario results in numerous days where the heat level is life-threatening even for healthy people. Extreme heat already causes roughly 1,700 deaths in the U.S. according to official death certificates, and some estimates go as high as 9,000 deaths where heat is a contributing factor. [3] If healthy construction workers die laying asphalt on a hot day or tennis players collapse during a high school match, the public outcry and potential liability will cause organizations to quickly change course, particularly if those outcomes are repeated multiple times across the country.
Outdoor activities may be divided into split shifts – perhaps 6 AM to Noon, and 5 PM to 9 PM – with the intervening time used for indoor activities or unpaid time off. Essentially, modern culture might resurrect the old Spanish siesta. I also expect that clothing designers will invent new types of hot-weather clothes that include active cooling technology. If skiers or ice fishermen can wear electrically heated socks or mittens, why can’t the bullet-resistant vests worn by police officers include a micro-sized air conditioner that circulates cool air around the torso. In any case, organizations will have to re-think their scheduling decisions and potentially invest in a new category of personal protective equipment.
The second impact is that people will spend more time indoors. Enclosed malls may make a comeback simply because they offer safer and more comfortable shopping than outdoor commercial districts. Businesses offering indoor golf simulators may take business away from actual golf courses. Pickleball may continue to take participants away from tennis since it can more easily be played on indoor courts. And on and on. All of this assumes, of course, that virtually all indoor spaces are air conditioned. That is already the case in many cities, but the increased load caused by extremely hot weather will stress many current HVAC setups as well as the electrical grid. Personal utility bills will rise which again will be a particular hardship for low-income households.
The third impact is that cars parked in surface parking lots for extended periods of time will become kilns on wheels. Parking lot light poles may be replaced with shade structures, perhaps containing solar panels. Car owners may install solar-powered cooling devices to keep their interiors from being destroyed by the heat. Whatever the solution, it will bring additional costs to many people who rely upon cars for daily transportation. I also suspect that it will continue the trend of reductions in the amount of parking that land owners provide. The result will be that new buildings will start popping up in old parking lots which will improve property tax revenues without requiring cities to build much additional infrastructure. It may also cause a shift away from personal cars to transportation services such as Uber, Lyft or Waymo, and perhaps even a slight bump in mass transit ridership.
The fourth impact will be that urban infrastructure will fail more frequently. Asphalt roads, for example, become so pliable in extreme heat that normal traffic creates ruts and cracks in the roadway. Overhead electrical lines start to sag. Drying soils can contract or shift in ways that damage semi-rigid underground utilities such as water lines or gas lines. Many cities already have their hands full with aging infrastructure that they can’t maintain; adding a new source of potential failure simply makes a bad problem worse.
The fifth impact is that insulation and energy efficiency requirements for buildings will become even more stringent than they already are, thus increasing the cost of construction. Building owners will want to reduce utility costs. Electric utilities will want to reduce peak demand so that outages are minimized. Environmentalists will decry the increase in greenhouse gases that will accompany spiking electrical demand. All of this will push building code writers to make new buildings and major renovations as energy efficient as possible. The downside, of course, is that solving the housing affordability problem will become more difficult as gains in energy efficiency make housing construction more complicated and expensive.
In addition, expect backup power systems to become far more common since being without power during a heatwave may become both more frequent and more devastating to building occupants. Battery-based backup systems will be particularly popular because they will allow “peak shaving” to reduce energy bills (buying electricity and storing it in the battery when prices are cheap and using power from the battery instead of the grid when prices are high).
The sixth impact is that many cities will want to re-think (and rebuild) their stormwater systems. Although rain storms may become less frequent, they are also likely to be more intense which will overwhelm municipal stormwater infrastructure. Buildings that are currently near the floodplain but safely outside may end up well inside the flood-prone area and experience damage on a regular basis. Consequently, cities may end up acquiring flood-prone properties, building new stormwater detention basins, expanding culvert and drainageway sizes, and looking for creative ways to handle stormwater that overflows the underground system. Again, more costs passed on to local taxpayers.
Finally, extreme heat may eventually change the southward migration patterns that have been in effect for decades in this country. The households trading the long and frigid winters of northern cities for the mild winters of the deep south have historically been willing to put up with one or two hot summer months, but if those months become brutally hot then the pattern might start to reverse or at least slow down. The extreme heat in Phoenix and the desert southwest was mentioned above, but other southern cities have been nearly as bad. Many cities set records in 2026 for the number of days over 100 degrees [4], but here are the top four:
Avg Number of Days Over 100℉
100℉ Days In 2026
Dallas 20 52
Austin 29 48
Oklahoma City 13 45
Tulsa 11 35
Really cold weather can be as uncomfortable and dangerous as really hot weather, but the coldest temperatures happen at night when most people are sleeping while the hottest temperatures happen during the afternoon when people like to be outside doing things. I don’t expect a large swing in migration patterns, but a noticeable shift is possible.
Unfortunately, the effects of extreme temperatures in cities tends to be magnified by what is known as the urban heat island effect – the tendency for city centers to be significantly warmer than surrounding rural areas. On a hot summer day, New York City is estimated to be roughly 7 degrees warmer, a by-product of dark materials with a lot of mass – such as brick, concrete and asphalt – that absorb heat energy from the sun and retain it for hours. Most city centers have so much mass that they are not only hotter during the day but they stay hotter overnight as the heat is slowly released.
Is any of this catastrophic? No, but it is not trivial either. Many of my previous posts have talked about the rapidity of change in our world and the difficulty that people have dealing with that change. We like predictability and the comfortable nostalgia of “the way things were.” Extreme heat would be one more thing that pushes us out of our comfort zone, changes our behaviors, and costs us money.
Extreme Heat Adaptations
Hot weather has been around for all of recorded history, of course, which means that humans have constantly looked for ways to adapt to hot weather. Even the current global warming trends don’t mean that every city gets hotter every year. Weather is the product of a vast array of factors and we are not particularly good at precisely predicting weather patterns more than a few days or weeks in advance, let alone years into the future. My “what if” scenario assumes a rapid and sustained rise in summer temperatures which is plausible but its likelihood is difficult to predict. What is troubling is that we have become so dependent on technological solutions such as air conditioning that we have ignored lessons from the past and from other cultures. Cities may be at greater risk than we perceive because we have become complacent about the potential impact of weather on our lives. Fortunately, there are things that can be done to make cities somewhat more resilient to heatwaves should that become a regular summer event.
To begin with, if we are going to rely upon air conditioning to make life bearable it will probably make economic sense for clusters of buildings to share some type of district air conditioning system for base load cooling needs. Smaller scale units can be used to fine-tune cooling for specific spaces but large units are likely to be more energy efficient – an important consideration given that electrical demand from air conditioners places a great deal of stress on the grid. In addition, waste heat from air conditioners can raise urban temperatures by up to two degrees at certain times of the day, so inefficient systems can make things better for individual buildings but much worse overall.
A second way to combat hot weather and the urban heat island effect is to use building materials that are white or very light colored. It is already fairly common, for example, for office buildings and warehouses to be re-roofed with a bright white surface. A high quality white roof coating can reflect 80 percent of the sun’s rays back toward space and reduce air conditioning costs by as much as 20 percent. [5] Similar treatments have been tried with street surfaces, although with less success.
Oddly enough, buildings with reflective glass walls are less useful. While they can reduce the air conditioning load of the host building, they tend to reflect the heat onto neighboring property rather than back into space. Thus, the problem is simply shifted rather than improved. One famous example is the 38-story office building at 20 Fenchurch Street in London (also known as the walkie-talkie building because of its distinctive shape). As construction was nearing completion in 2013, it was discovered that the building’s reflective glass and curvilinear shape were acting as a concave mirror that created areas of intense heat on portions of the adjacent street. Parts of a parked car actually melted. Eventually, sun shading fins were added to the building to eliminate the problem.
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| Cross-sections of 20 Fenchurch Street, London |
Another approach is to expand urban tree planting programs to take advantage of the cooling effects of evapotranspiration. Trees pull water up through their roots and release it as water vapor through their leaves. As the water evaporates, it cools the surrounding air. In addition, trees provide shade which reduces direct solar heat gain. Most midwestern cities already have a fairly extensive tree canopy except in densely developed areas such as the central business district. Planing trees in downtown areas can be expensive and disruptive so the focus should be on areas that are pedestrian corridors or gathering spaces such as plazas or transit stops.
Unfortunately, evapotranspiration only works when the soil has adequate moisture. An extended heatwave can leave trees without the needed moisture which means that they need to be watered which in turn can exacerbate water shortage issues. Greywater systems, which reuse water from fixtures such as showers, bathroom sinks and washing machines, might become more common for irrigation purposes.
Finally, cities may want to build numerous, small reservoirs throughout the urban area to reduce the flooding associated with torrential rains, provide some cooling relief in the form of evaporation, and provide a source for landscape watering that doesn’t rely on municipal water systems. This approach is commonly used for golf courses but could be applied much more broadly.
The Bottom Line
My conclusion is that a rapid increase in extreme heat would not be a disaster, but it would be ugly, particularly for low- and moderate-income households who would be hard pressed to absorb the increased costs without cuts to their lifestyle. Stretches of weather so hot that normal summer activities get cancelled and economic output drops might be the thing that finally gets the majority of Americans to support serious initiatives to combat global warming. Of course by that time we might be in a “too little, too late” type of situation.
On the other hand, my “what it” scenario might never happen. The weather on our planet is affected by so many interconnected systems that it is possible that the effects of increasing greenhouse gases will be offset by some other factor. That possibility raises the very legitimate question of how many changes should be made and how much money should be spent to protect against something that might never occur? Money spent to lessen the impact of hypothetical problem A means less money to spend on existing problem B. Exactly how bad does problem A have to be to divert money away from existing issues? That is a thorny question that politicians will have a difficult time answering unless there is a groundswell of public support one way or the other.
At the very least, we could plan for what actions should be taken first if things start to go south weatherwise. In my opinion, the seriousness of climate change on the scale of “Fictional - Annoying - Critical” is moving past Annoying and rapidly closing in on Critical. I personally would support additional actions to accelerate the shift away from fossil fuels since I think that could be done with relatively little impact on our economy or lifestyle, particularly if we diverted money away from triumphal arches, gilded ballrooms and pointless wars in the middle east. As John Kenneth Galbraith once said: “Politics is not the art of the possible. It consists in choosing between the disastrous and the unpalatable.“
Notes:
Ignacio Calderon and Doyle Rice; “Hottest Summer Ever? US breaks longstanding record”; September 2026; USA Today; https://www.usatoday.com/story/news/weather/2026/09/10/summer-2026-heat-record/91673943007/
Alina Bykova; “Permafrost Thaw in a Warming World”; October 2020; The Arctic Institute; https://www.thearcticinstitute.org/permafrost-thaw-warming-world-arctic-institute-permafrost-series-fall-winter-2020/
Alejandra Borunda; “He died of ‘natural causes.’ But his mother says she knows what killed him: heat”; September 2026; NPR; https://www.npr.org/2026/09/02/nx-s1-5887544/heat-deaths-undercount
Julia Musto; “These US cities set records over the summer with more 100-degree days than ever before”; September 2026; Independent; https://www.independent.co.uk/news/world/americas/us-cities-heat-temperature-el-nino-climate-change-b3053632.html
“Why Are White Roofs Becoming More Popular?”; August 2022; Perma-Tech Roofing Supply; https://permatechroofing.com/blog/why-are-white-roofs-becoming-more-popular
