- Most of the deadliest heat waves to date have been dry heat waves. But as our climate warms
a possibly even deadlier heat is on the rise. - It doesn't matter how breezy it is, it doesn't matter how
much shade you're under. It doesn't matter how much
water you're drinking. - These are extreme humid
heat waves, often referred to as wet-bulb events. And these are, in my opinion, one of the scariest byproducts
of climate change. They've been relatively rare historically, but a new study shows that
by two degrees Celsius of global warming, many of the most populated
places on Earth are likely to experience them. And the only way to protect ourselves from
these dangerous wet-bulb temperatures is to cool our environment. But what happens if that's not possible? - The time of year that always has the highest
stress on the grid is always just the hottest day of the year because so many people are using AC and so then the AC is liable to go out. - What happens if there's
another extreme weather event? If you have a tropical cyclone that comes in, wipes out power? - Stick around as we break down why these
temperatures are so deadly and how we can prepare for
a world that's so warm, our bodies literally can't handle it. Let's start by talking
about dry versus humid heat. Dry heat waves are usually driven by large high pressure systems that trap hot air near the surface. These systems push air downward, and as the air compresses, it heats up in a process
called adiabatic heating. If the high stays stuck in
place, the heat builds day after day with no clouds
or wind to carry it away. And that's exactly what happened during the 2003 European heat wave and the 2021 Pacific Northwest heat dome. Now let's take a look at humid heat. - As temperatures rise, we can hold a lot more
moisture in the atmosphere. And so this means that if
a given location has air temperatures going up with
ongoing climate change, it's likely that if they
have a moisture source, humidity's also going to increase. - We just saw how dangerous this can be in 2015 when one of the most extreme humid
heat events on record struck Karachi, Pakistan. Temperatures up to 45 degrees Celsius combined
with oppressive humidity, power outages and water shortages made conditions even worse. At least 1200 people died in just 10 days most from heat stroke and dehydration. Humans primarily cool down by sweating, but when the air is humid,
sweat can't evaporate as easily, so we don't cool off as well. This is where wet-bulb comes into play. wet-bulb temperature combines heat and humidity into a single number, which helps us understand
when conditions become dangerous or even lethal. - You can imagine taking a
normal thermometer. If you take that thermometer and you cover
the bulb in a little sock that is then placed into
a container of water, so it's constantly wetted. Evaporation's going to take
place off of that little sock and it's gonna have a net cooling effect. - The wet sock at the end of the wet-bulb thermometer
functions similarly to human skin. Water evaporates off the wet
sock while sweat evaporates off our wet skin. In both cases, evaporation carries away heat into the surrounding environment. - But the more humid the ambient
air is, the more difficult and less efficient that
evaporation is to take place. And so that makes any cooling
through evaporative cooling, less efficient at high
temperatures and high humidity. - Which is why humid heat feels so muggy and uncomfortable for us and
why it can be so dangerous. There have been a number of
attempts to better understand how humid heat affects the
human body, in particular where our physical limits are, but it's not easy to identify
dangerous wet-bulb thresholds because well, they're dangerous. - So obviously you can't put
someone in a heat chamber and truly cook them. That would be unethical. But what you can do is increase
temperature and humidity and measure someone's core temperature and see what's the point
at which their core temperature starts to increase. And that's the limit
of compensability. - The human body generally does a good job of regulating its core body
temperature through sweat. But once we cross the limit of livability or compensability, as scientists call it, our core body temperature starts
to increase uncontrollably. And this wet-bulb temperature
range is actually a lot lower than we previously believed. - So this paper is really trying to summarize the most state-of-the-art estimations of these thresholds. And so what we see is
that there is a range. So uncompensable wet-bulb temperatures range from about 19 to 32 degrees Celsius. - And you might think the
lower end of this range, 19 degrees Celsius sounds really low. But it's important to understand that a 19 degree wet-bulb
does not equal 19 degrees on a regular thermometer. So 19 degrees Celsius wet-bulb
is actually more like 46 degrees Celsius with low humidity or 32 degrees Celsius
with higher humidity. And the reason there's a range is because this threshold depends on a number of variables including activity level, exact air temperature, and
humidity levels and age. - Older adults thermo
regulatory responses are worse, they sweat less efficiently,
they also have higher risks of comorbidities, so
things like cardiovascular and respiratory diseases. - So according to their study,
where on earth are we likely to cross these thresholds? Well, at two degrees
Celsius of global warming, which could come in as
little as two decades for older adults. It's about a third of Earth's land area, but that only tells part of the story. - It's 35% of the land area, but it's also many of our
most populous places on earth. Most of India, most of the
populated area of China. This is most of the
eastern portion of the U.S. - And if we let global
warming get really out of hand or if climate sensitivity
is just on the higher end of our projections at four degrees Celsius above pre-industrial levels, over 60% of Earth's landmass
could see these dangerous wet-bulb temperatures. Heat is the deadliest weather
disaster in the U.S. in many parts of the world, and it's projected to get a lot deadlier. During the 2003 European heatwave, up to 3,400 people died in Paris
alone. At two degrees Celsius, which is again only a couple decades away, scientists found that Paris
will see deadly heat waves like this once every few years
rather than once a century. And though this heat wave in 2003 was among the deadliest in recent
history, it didn't get close to the dangerous wet-bulb
thresholds we've been discussing in this episode. But the 2015 heat wave in
Karachi did it passed the uncompensable wet-bulb
threshold for older adults for something like eight
to 10% of the time. But at two degrees Celsius
of warming, we can see that the uncompensable
threshold is crossed for younger adults as well. And at four degrees, models show that the same event would
cross the uncompensable threshold for older adults for about 90% of the heat waves duration. And the thing to remember
about these critical wet-bulb threshold is that once you
cross one, the only way to bring your internal temperature down is by cooling yourself or your environment. - It doesn't matter how breezy it is, it doesn't matter how
much shade you're under, it doesn't matter how much
water you're drinking. The only way you can protect
yourself from these conditions is by cooling your environment. And so that is why air
conditioning is really the major adaptation measure and
protection measure that we have. - And although AC is one
of the most important tools for surviving extreme heat,
it's far from perfect. First of all, it's expensive. AC is energy intensive, and as our climate gets warmer,
many people won't be able to afford to stay cool. And due to its financial inaccessibility, many people in places most vulnerable to deadly heat don't have access to AC. Second, air conditioning
doesn't eliminate heat, it just moves it. Cooling the indoors means
transferring the heat outside, which warms the surrounding air. And in cities, this added heat can worsen
the urban heat island effect. Now, let's imagine that everyone could
afford air conditioning. It still wouldn't automatically
solve the problem. Our power grids in the U.S. and globally weren't designed for everyone to crank up their units at once. During heat waves, widespread outages become
more likely leaving the most vulnerable at even greater risk. - If AC units were our only way
of protecting people as soon as the power system fails, whether that's from the grid being overloaded, or if we have another weather driven sort of infrastructure damage that's going to put people
immediately at risk. - And these compounding
hazards like a heat wave after a hurricane are a growing concern as we head towards unprecedented levels of warming for humans. And as weather across the
board just gets more extreme, but there's one more catch. The more we rely on ac, the more we could be fueling the base problem of global warming. - If you tried to just build
out air conditioning to deal with heat risk, how much
would that contribute to carbon emissions across the world? And how much would that positively feed back on global temperature making the temperature even higher? - Right now, air conditioning
accounts for about 3% of global greenhouse gas emissions. And according to the International
Energy Agency, the number of AC units worldwide is
expected to nearly triple by 2050 leading to a massive
rise in energy demand. So what do we do about this paradox? Well, I think it's a powerful
argument for transitioning as quickly as possible to clean energy. The only way to meet the growing need for AC without accelerating
climate change is to power our grids with renewables. And of course, there's a lot we can and should do beyond
just air conditioning. We can rethink the design of
our cities by installing white or green roofs and planting trees. We can also build more cooling centers, upgrade our electrical
grids to be more resilient and prioritize protecting
the most vulnerable during heat waves. The truth is that we are headed
into uncharted territory, but it's also true that we
still have time to choose how bad it gets. So do you live in an area that's already experiencing
dangerously hot and humid conditions? What strategies have worked
for you to handle the heat? Let us know in the comments and we'll see you next time on Weathered. Oh, and before you go, we also wanted to let you know about
something special EGREENEWS and edisasterx is also on tiktok and you can find us also on the web.
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