Extreme heat is a challenge for all species on the Earth.  We know that we're buying into a hotter planet now more than ever thanks to a greater breadth and depth of knowledge on how humans are impacting the global climate.  What's more, we understand that the story of a warmer planet is far more intricate than tracking a slow up-tick in degrees.  As the planet warms, how heat is distributed is changing.  And how this distribution changes impacts more than just the temperature, but how the Earth's systems behave.

Heat generally behaves like other fluid systems on the Earth.  Similar to water and air, heat is always trying to reach an equilibrium, moving from hotter regions to colder regions, from high pressure areas to low pressure areas.  When the systems this heat hitches a ride on start to change, it in turn has an effect on said heat.  In terms of extreme heat, we're looking at when these effects lead to higher than average temperatures.

One of those effects is what we'd like to cover here: the heat dome.  This year (2021), we've been hearing that our recent heat waves have been intensified thanks to these phenomena, so we wanted to take a look at what heat domes are and why they occur.  And we can start by taking a look a very recent example to boot, so let's dive in!

The 2021 Western North America Heat Wave

In late June to early July of 2021, the western edge of North America experienced a heat wave that set numerous record temperature highs in the northwestern Unites States and most of Canada from west to east.  Canada even experienced its highest temperature ever recorded for the country at 121.3 F (49.6 C), far higher than the average the region is known for.  So, where did all of this heat come from?

Well, from a combination of things really.
Starting with the gradual impact, global climate change has been warming the oceans for some time.  The western Pacific ocean, in particular, is warming at a considerable rate where surface winds and currents push that heat to the east.  So we have a warmer-than-normal Pacific ocean surface temperature, but this doesn't really add up to a heat wave.  That's where 2 other weather events come into play as catalysts.

​In mid-to-late June of 2021, there were 2 meteorological events happening in different parts of the globe.  In China, there were torrential rains hitting the country that resulted in a higher-than-average atmospheric temperature.  This heat was sucked into the jet stream, or a system of atmospheric air currents, which started moving that heat to the east over the Pacific ocean.  As it traveled, this created a patch of the atmosphere with unusually high pressure.
The 2021 Western North America Heat Dome traveled all the way to the eastern reaches of Canada before dissipating, lasting about 2 weeks!
At the same time, the southwestern United States was experiencing a drought that led to high surface temperatures in the region.  In effect, the southwestern US was experiencing their own heat wave lacking any cooling effect from the weather.  This heat pushed northward toward the Pacific northwest.

When these phenomena met, a heat dome was formed.
The heat dome that hit North America in 2021 is recorded as a "1000 year event made 150 times more likely by global climate change"

Convection & Efficient Heat Transfer

That isn't to say that these meteorological events meeting played a magic trick either.  A heat dome is born of trapped heat.  Thanks to the growing warmth of the ocean surface temperature, tropical storms were unable to dissipate the high-pressure zone generated from the heat transferred by the jet stream.  And thanks to the heat from the southwestern US drought, we saw the formation of the "bottom" of a high pressure container.  Having a high-pressure surface covered by a high-pressure "lid" traps circulating air until it is disrupted by a source of cool air.  In the case of the heat wave above, there were 2 spots where cool air was introduced: the Hudson Bay and the Atlantic ocean.  The former dropped the intensity of the heat dome as the westerly winds moved it eastward, but it didn't dissipate until the eastern part of the dome reached the Atlantic ocean in mid-July.

Okay, so we have a lot of trapped heat in a dome, why does this result in such an intense wave of extreme heat?
To help understand that, we don't need to look much farther than our own kitchens!  Or in lieu of having this appliance, having watched a cooking show at some point.  This same phenomenon is employed by one of humanity's own inventions: the convection oven!

In a standard conventional oven, the contents of the oven are cooked by simply being enveloped in heat being generated by the oven.  The heat moves around by gravitating toward cooler regions of the oven, usually by rising from where the heat is generated and subsequently falling when it rises enough to reach a cooler portion of the oven.  This works pretty well, but it isn't the most efficient way to put the heat to work.
Enter the convection oven which introduces an unlikely ally to the mix: a fan.  One would think this would interfere with the heat being generated from the oven, but the contrary is true.  Similar to the jet stream in our heat wave example, this circulating air is now carrying the warm air.  Since the oven is creating a vacuum from outside elements, this added wind simply adds more force behind the circulating heat, both increasing the speed at which the contents are cooked and, in turn, reducing the net energy required to do the same work as a conventional oven.

In the case of the western North America heat wave, the heat dome is the oven, and all of us inside it are being cooked.  At least it's being efficient!  Similar to how an oven creates a vacuum from outside elements, the high-pressure containerization of the heat dome creates a cavity for the heat to circulate without drastic cooling.  Heat domes are essentially the Earth's mobile convection oven in action.
Heat domes sustain themselves using convection, the same principle used in convection ovens to heat food faster and more efficiently, only we're in the oven with heat domes!

Extreme Heat & Humanity

One of the key takeaways from the recent heat dome is how much extreme heat impacts humanity.  Not just on a physical level, but in dimensions unique to our species on the human-dominated planet.

Where I'm from, around Chicago, IL in the United States, we experience a wide range of temperature fluctuation.  In a sense, this area of the midwestern United States is particularly well-equipped to handle relative extremes in both the hot and cold directions.  In my lifetime, I've experienced effective temperatures as low as -40 F (-40 C, and yes, this is the point at which Fahrenheit and Celsius reach parity) and as high as 110 F (43.3 C).  Residents here have felt the biting cold and the sweltering heat.

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By U. S. National Weather Service/National Ocean Service - Link

Phenomena like the heat dome, though, impact more than just areas familiar with extreme heat.  Hyperthermia, or heat stroke, isn't something everyone is used to being aware of, but is a very real health risk for humans.  Our bodies are equipped to handle some heat dissipation, but not at the level extreme heat thrusts upon us.  When our bodies fail to dissipate heat, we react in ways ranging from swelling to rashes to cramping to losing consciousness.  In the world of modern medicine extending our lives, being on medications that worsen our heat dissipation makes these risks even higher.  And our bodies have a certain "sweet-spot" for heat dissipation, too, making the elderly and young children much more susceptible to heat.  Being sick or overweight also reduces the body's ability to dissipate heat, further increasing risk of heat-related illness and death.  Further, the temperature compounds with the level of humidity in an area, or the level of moisture in the air.  Human bodies don't dissipate heat as well in high-moisture environments, effectively raising the temperature we feel as humans.  Take today for example, where my area has a high of 88 F (31.1 C) with a relative humidity of 70%, which compounds to an effective temperature of 100 F (37.7 C).  That base temperature is already one that the NOAA encourages caution in, but taking humidity into consideration makes it straddle between extreme caution and danger.  This is in September, well after the warmest, most humid times of the year for my area.
The prolonged conditions in recent heat waves has been enough to cripple human-built infrastructure causing railroads to warp, roads to shatter, and power lines to sag
In addition to the physical reality of prolonged exposure to extreme heat, humans also have a few other dimensions to consider, one of them being the infrastructure we've built and rely on.  A lot, and I mean a LOT, of human infrastructure in the northern hemisphere is not built with extreme heat in mind.  From cabling to roads to transport, all of these buckle under the pressure of extreme heat.  We saw this with the above heat wave where reports of deformed railroad tracks, sagging power lines, and the shattering of concrete roads and sidewalks due to thermal expansion were widespread.  Under these days of prolonged exposure to extreme heat, it shows that human infrastructure begins to crumble rather quickly, something that is abundantly clear now, but needs attention much sooner rather than later.

In a similar light, when our infrastructure fails, we also see our social dimension begin to deteriorate as well.  Humans are able to act within our society thanks to a lot of this infrastructure, and when it's down for the count or destabilized, our ability to live and work is diminished or otherwise endangered.  During this heat wave, a lot of businesses closed down due to this infrastructure being down, and those that forced people to work in the extreme conditions were faced with walkouts and strikes.  Turns out people don't want to risk their lives on their employer's behalf.
The main point here is that humans and extreme heat aren't particularly compatible.  In the world we fashioned for ourselves, it makes sense we never really planned for the things we're not really built to handle.  But extreme heat and phenomena like the heat dome are present concerns, ones we've bought into higher likelihoods of happening, and are now things we must be aware of.  We need to consider these dimensions of heat and humanity now more than ever before.  

The reality of this is that humanity has already bought into making these kinds of phenomena more common.  The heat dome western North America experienced is recorded as a "1000 year event made 150 times more likely due to global climate change."  Moderate storms on the other side of the planet coupled with warmer surface temperatures on both land and sea are now triggers for events like these.  The silver lining here is that we know what they feel like now, we know they're happening more frequently and phenomena like heat waves, warming ocean temperature, and the jet stream can interact to form compounding events.  We can see where we need to invest in making the world humanity has built capable of withstanding these events.  We also know we're a driving cause in how these occur and know we can act now to mitigate the likelihood of these events for the generations that follow.  We just need to commit to that action and do it now.
~ And, as always, don't forget to keep wondering ~
Sources
2021 Western North America Heat Wave
https://en.wikipedia.org/wiki/2021_Western_North_America_heat_wave​

Conventional vs Convection Ovens
https://www.thespruceeats.com/convection-oven-cooking-tips-1805817​

Heat Domes and Heat Waves
https://oceanservice.noaa.gov/facts/heat-dome.htm
​https://en.wikipedia.org/wiki/Heat_wave​
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