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Ice Fall · The Climate Translation

• 0:00
  If you spend any time in the Great Plains during the spring, you learn pretty quickly
• 0:13
  to respect severe thunderstorms.
• 0:17
  Back in my 20s and 30s, I spent many Mays traveling across the area, studying and chasing
• 0:23
  thunderstorms.
• 0:25
  Like many meteorologists, I was fascinated by tornadoes, but one of the most memorable
• 0:31
  moments of my career didn't involve a tornado at all.
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  I was riding in a university research van while we tracked a severe thunderstorm.
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  We thought we were in a relatively safe position.
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  Then the rain suddenly stopped.
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  The sky turned an unsettling shade of green, and we began to hear the clink and clunk
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  of hail.
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  Or anyone could react, a softball sized hail stone came crashing through the window of
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  the van.
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  Fortunately, no one was injured.
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  But staring at that chunk of ice on the floorboard, I remember thinking about how remarkable
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  it was that a thunderstorm could suspend something that large and the air long enough
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  for it to grow.
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  How does a storm create a piece of ice the size of a softball?
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  And what happens to that process when the atmosphere itself begins to change?
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  Today, we're going to explore the science of hail, how these destructive ice stones form
• 1:31
  inside thunderstorms, and what new research is revealing about how a warming climate
• 1:37
  may be changing where and when some of the world's most severe hail storms occur.
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  Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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  To understand why scientists are interested and how climate change may affect hail, we
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  first need to understand how hail forms in the first place.
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  It all starts inside a thunderstorm.
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  Now most people think of hail as frozen rain, and while that's not exactly entirely wrong,
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  it doesn't really explain how you end up with a piece of ice the size of a golf ball,
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  a baseball, or in rare cases, a softball.
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  For that we need to talk about what's happening inside the storm itself.
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  I often tell my students you can think of the severe thunderstorm like a giant atmospheric
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  elevator or maybe an escalator.
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  On a hot summer day the sun heats the ground, and the air near the surface becomes warm
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  and humid, and because warm air is less dense than cooler air, it wants to rise.
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  If the atmosphere is unstable enough, that rising motion can become quite powerful.
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  Meteorologists call the fuel for this process Convective Available Potential Energy,
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  or CAPE.
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  You don't have to remember the acronym, just think of CAPE as the amount of fuel available
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  to launch air upward through the atmosphere.
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  The more heat and moisture available near the surface, the larger that fuel tank can become,
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  and when that fuel tank gets large enough, and the conditions are just right, air can
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  shoot upwards at remarkable speeds.
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  In some severe thunderstorms, those updrafts can exceed 100 miles an hour.
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  Now let's go back to that hail stone.
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  Even a tiny raindrop or some kind of particle of matter being carried upward in one of these
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  powerful updrafts.
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  As it rises higher into the storm, temperatures eventually drop below freezing.
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  That raindrop or the seed begins to freeze.
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  At that point gravity begins to pull it back towards the ground.
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  But the updraft, it has other ideas.
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  Instead of falling all the way back to the earth, that tiny ice pellet gets caught in
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  an atmospheric elevator or escalator that begins to push it upward again.
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  As it moves through the storm, it collides with supercooled water droplets, liquid water
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  that exists even though the temperature is below freezing.
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  Those droplets freeze onto the surface of the hail stone.
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  And layer by layer, trip after trip, the hail stone grows larger and larger as it continually
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  falls and then is pushed upward again.
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  If you've ever seen a large hail stone... cut it in half, it'll look a little bit like
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  the cross-section of a tree.
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  You'll see rings and layers that form during repeated journeys up and down through different
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  parts of the storm.
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  And this is where the physics becomes surprisingly simple.
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  The stronger the updraft, the larger the hail stone can become.
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  A small hail stone can be supported by a relatively modest updraft.
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  A baseball-sized hail stone would require a larger one.
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  And that softball-sized stone that came through the window of our research van all those
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  years ago? That required an extraordinarily powerful thunderstorm, capable of keeping
• 5:24
  a chunk of ice suspended long enough to grow that large before gravity finally won.
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  In many ways, hail is a balancing act between two competing forces, gravity trying to pull
• 5:39
  the ice downward and the storm trying to push it back up.
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  As long as the storm keeps winning, the hail stone keeps growing.
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  But what happens when the environment that those stones form in begins to change?
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  Human-induced climate change is not only affecting temperatures on the ground, it's also changing
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  the dynamics of the upper layers of our atmosphere and the potential energy that's available
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  with thunderstorms form.
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  And that means it can influence the physics of the hail equation in surprising ways.
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  Now at this point you might think the connection between climate change and hail would be
• 6:20
  straight forward.
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  After all, hail is made of ice.
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  So if the atmosphere is getting warmer, shouldn't hail become less common?
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  For years, many people assumed that might be the case.
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  But the reality turns out to be more complicated.
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  That's because hail exists and what we might call a meteorological goldilocks zone.
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  The conditions need to be just right.
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  Look back to that escalator or elevator we talked about a few moments ago that's going
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  up and down.
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  A hail stone needs a powerful updraft to lift it high into the storm and keep it suspended
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  long enough to grow.
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  A warmer atmosphere can help with that.
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  Warmer air can hold more water vapor and more water vapor means more fuel for thunderstorms.
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  More fuel means stronger updrafts.
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  At first glance, that sounds like good news for hail.
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  But of course there's another side to the equation.
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  Remember that hail stones only exist because part of the storm is below freezing.
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  As the atmosphere warms, the altitude in which temperatures reach freezing, begins to move
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  higher into the sky.
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  Meteorologists call this the freezing level.
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  You can think of it as kind of like the storm's ice maker.
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  And a warmer climate that ice maker is being pushed farther upward.
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  Now our hail stone faces a new problem.
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  Once it leaves the storm, it has a much longer journey through warmer air before it reaches
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  the ground.
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  Small hail stones may melt completely before they ever get there.
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  Others may shrink significantly during their descent.
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  So now we have two competing forces.
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  A warmer atmosphere can create stronger thunderstorms that are capable of growing larger hail stones.
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  But that same warmer atmosphere can make it harder for hail to survive the trip back
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  to the surface.
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  One process favors larger hail, the other favors more melting.
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  And for decades, scientists weren't entirely sure which effect would dominate.
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  That's one reason hail historically, it's been one of the most difficult, severe weather
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  hazards to project in a changing climate.
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  The atmosphere is essentially pulling the system in two different directions at the
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  same time.
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  But thanks to improvements in computing power, satellite observations, and high-resolution
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  climate modeling, researchers are beginning to finally untangle that puzzle.
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  And what they're finding suggests that the answer may not be that hail disappears.
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  Instead, the environment favorable for hail may just be shifting.
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  And in some places, it may be shifting dramatically.
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  If a warmer climate strengthens some parts of the hail-making process, while weakening
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  others, what does this mean for the overall picture going forward?
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  The answer that researchers are starting to find is not exactly what people expected.
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  A recent study published in Nature suggests that hail is not simply becoming more common
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  or less common everywhere.
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  Instead, the environment that favors severe hail appears to be shifting.
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  To understand what that means, imagine that hail has a preferred neighborhood.
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  Well, maybe not a physical neighborhood, but a region of the atmosphere where all
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  the ingredients happen to line up just right.
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  You need enough warmth and moisture near the surface to generate those strong updrafts,
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  that CAPE or fuel we talked about earlier.
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  You need cold enough temperatures higher in the atmosphere to support ice formation,
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  our ice maker.
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  You need enough wind shear that separates warm updrafts from cooler downdrafts and
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  generates some rotation to organize the thunderstorm.
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  And you need all of those ingredients to exist at the same time.
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  Historically, some of the best neighborhoods for hail have existed in places like the Great
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  Plains of the United States, parts of Argentina, South Africa, Europe, and portions of Australia.
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  That's why some of these regions develop reputations as hail hotspots.
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  But new research is suggesting that those neighborhoods are changing.
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  As temperatures continue to rise, many regions, closer to the subtropics, are projected to
• 11:03
  see conditions less favorable for frequent hail formation.
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  At the same time, areas farther poleward, may begin experiencing more of the atmospheric
• 11:14
  ingredients that support severe hail.
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  In other words, that sweet spot appears to be moving north.
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  It hasn't been a rapid movement yet, but it's been enough that scientists are beginning
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  to see a constant signal emerge across multiple regions.
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  The researchers are also finding something that's equally important.
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  The changes aren't just geographical, they also may be seasonal.
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  In some regions, the timing of hail favorable conditions may be shifting within the year.
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  That means agricultural areas that have traditionally experienced the highest hail risk during
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  one part of the growing season could see it arrive earlier or later than expected.
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  That matters because timing is important, especially in agriculture.
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  A hail storm striking a wheat field a few weeks before harvest can have a different consequence
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  than the same storm, striking shortly after planting.
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  Now it's important to remember, this is not a forecast for every individual thunderstorm.
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  I'm just talking about probabilities here.
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  As I've mentioned many times, the atmosphere is incredibly complex.
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  Regions that have experienced hail for years are still going to experience it.
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  But local weather patterns may begin to change.
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  What this research is suggesting is that the background environment supporting the hail
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  may be slowly reorganizing itself.
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  So what does this mean for you?
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  I think the most important lesson is that weather risk isn't just about intensity, it's
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  also about location.
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  In the Great Plains, where severe weather is common, hail is simply part of the environment,
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  Farmers, insurance companies, and builders expect it.
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  Nobody likes it, but nobody's surprised by it either.
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  People understand that living in this part of the country means accepting a certain amount
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  of hail risk as part of everyday life.
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  The challenge highlighted by this research is that the geography of the risk may be changing.
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  If hail-favored environments begin shifting poleward, some communities can find themselves
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  dealing with a hazard that historically wasn't a major concern.
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  Our infrastructure is often designed around whether we expect, not exactly the weather
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  we may experience decades from now.
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  Think about something as simple as a roof.
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  Building codes in different regions account for different risks.
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  Some places prioritize snow loads, others prioritize hurricane force winds.
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  That same principle applies to hail.
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  Communities that rarely experience damaging hail in the past may not have invested heavily
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  in hail-resistant materials or forecasting programs or mitigation strategies.
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  And of course, insurance works the same way.
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  Insurance companies depend heavily on historical records to estimate future risk.
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  We discussed this in a previous episode.
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  But one of the reoccurring things we've explored is that climate change can make the future
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  look different from the past.
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  When that happens, the historical record becomes a less reliable guide.
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  We've seen this conversation emerge around flooding, hurricanes, droughts, and wildfires.
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  This research suggests that hail may be another example of that broader pattern.
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  And there's another interesting challenge.
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  Many of the technologies we are building to help combat future climate, such as solar
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  panels, upgraded electrical substations, new transmission lines, wind turbines, and
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  electric vehicles, even more densely packed cities clad in glass.
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  All of them exist in an atmosphere, which means they're all exposed to whatever weather
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  the atmosphere decides to deliver.
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  Historically engineers design infrastructure for the risks they know.
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  If you're building in Minnesota, you think about snow and ice.
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  If you're building in Florida, you think about hurricanes.
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  If you build in the Great Plains, you think about tornadoes, wind, and hail.
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  But what happens when the geography of risk begins to shift?
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  Imagine investing millions of dollars in a solar installation in a region that is rarely
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  experienced severe hail.
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  The panels may be engineered to withstand the weather that location has historically experienced.
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  The insurance models may be based on decades of local observations.
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  The maintenance plans may assume that destructive hail is a relatively rare event.
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  Then, over time, the atmosphere changes, and the probability of severe hail begins increasing.
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  Suddenly, the assumptions used to design that system may no longer match the environment
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  in which it operates.
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  The same challenge applies to electrical infrastructure, vehicles, homes, buildings, and countless
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  other systems that were built using yesterday's climate statistics.
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  And that's one of the broader lessons emerging from climate science.
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  We are changing not only the physics of the atmosphere, but also the probabilities and
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  risks concerning where certain hazards are most likely to occur and when they are most
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  likely to occur.
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  For communities that have long dealt with hail, adaptation is already part of life.
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  Building materials, insurance practices, warning systems, and personal experience all help
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  reduce vulnerability.
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  But for regions where severe hail has historically been uncommon, the learning curve may be much
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  steeper.
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  A hail storm depends on a very specific balance of ingredients.
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  It needs heat, it needs moisture, it needs instability.
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  It needs freezing temperatures high above the ground, and it needs all of those ingredients
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  to come together exactly in the right place and exactly the right time.
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  Climate change isn't eliminating these variables, but it is changing them.
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  As a meteorologist, that's when I find so fascinating about this.
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  The softball-sized hail storm that shattered the window of my research fan all those years
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  ago left an indelible impression on me.
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  It taught me that no matter how knowledgeable or experienced you are, the atmosphere can
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  throw you curveballs.
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  That massive stone was a product of a very specific set of atmosphere conditions.
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  I thought I was witnessing a rare, localized spectacle of nature's raw power, a Great
• 18:09
  Plains anomaly.
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  But the question scientists are now asking is how similar conditions may change in the
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  decades ahead.
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  While that doesn't mean such events will become more common, it does mean if you live in
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  an area that rarely experiences hail, you may have to keep an eye on the sky more often
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  in the future.
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  I'm Dr. Mac, and this has been the Climate Translation.
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  If you have a question about the climate you've been too afraid to ask, or if you have
• 18:38
  a differing opinion, I want to hear from you.
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  I can use your viewpoints in future episodes.
• 18:44
  You can reach me at theclimatetranslation at gmail.com.
• 18:49
  I'll see you next time.