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The Double Stress · The Climate Translation

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I've spent my entire life living in the American South, and if you grow up here, there's
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a phrase you hear over and over again, especially during the summer.
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It's not the heat, it's the humidity, and honestly, there's a lot of truth in that.
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I remember standing outside during Mississippi summers when the air felt thick enough to cut
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with a knife.
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Even in the shade, sweat wouldn't evaporate.
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You'd walk to your car and already feel exhausted and soaked.
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The atmosphere felt heavy and oppressive.
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But over the years, I've experienced another kind of heat.
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The kind where the ground cracks open, lawns turn brown, and trees begin dropping leaves
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in the middle of the summer.
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The air feels dry and dusty, and somehow, even without the humidity, it still fills relentless.
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Today we're going to talk about what scientists call a heat drought event.
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Why a hotter atmosphere is becoming a thirstier atmosphere.
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How drying landscapes can actually intensify heatwaves, and why researchers are increasingly
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concerned about what happens when multiple climate stresses start interacting instead
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of occurring alone.
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Welcome to the podcast, I'm Dr. Mac, and this is The Climate Translation.
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When we talk about dangerous heat, most people naturally focus on the temperature of the
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air.
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You can ask, how hot is it outside, or how high is the heat index?
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How long is this heatwave going to last?
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But there's another part of this system we often overlook, and that's the ground itself.
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The landscape around us doesn't just passively sit there under the sun.
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Under normal conditions, it is constantly helping to regulate temperature through the
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movement of water.
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To understand this, think about what happens when you step out of a swimming pool on a hot
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day.
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At first, you might feel cooler than the air around you.
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That's because the water on your skin is evaporating, and evaporation requires energy.
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As the water changes from liquid to vapor, it pulls and absorbs heat from your skin,
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and then carries some of that energy away.
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That process is one of the main ways the human body cools itself.
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The Earth's surface works in a surprisingly similar way.
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When soils contain moisture, and plants have access to that water, part of the sun's
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energy goes into evaporation instead of directly heating the air.
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Water evaporates from the soil, and plants pull water through their roots, and then release
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it through tiny openings in their leaves, in a process called transpiration.
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Together, scientists often combine these processes into one term, evapotranspiration.
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Indeed, fields and forests, grasslands and wetlands are constantly moving water into the atmosphere,
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and just like the sweat cooling your skin, that evapotranspiration removes heat energy from
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the Earth's surface.
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It's one of the reasons a healthy green field can feel noticeably cooler than the dry
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parking lot next to it.
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Some of the sun's energy is being used to move water instead of simply raising the
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temperature, but drought changes that balance.
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As soils dry out, less water is available to evaporate, and plants begin to conserve
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moisture.
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Many partially close those tiny openings on their leaves to reduce water loss, and in
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severe drought, many trees and plants begin shedding their leaves all together to protect
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themselves.
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And once that happens, one of the landscape's natural cooling systems starts to shut down.
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Now, instead of solar energy going into evaporation or transpiration, more of it goes directly
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into heating the ground and the air above it.
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This is where the atmosphere and the land begin to interact in ways you may not expect.
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For many years, we used to think of heat waves and droughts as separate events.
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A region might experience a drought, or it might experience extreme heat, but now scientists
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are finding that these events often reinforce each other in vicious cycles.
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The heat dries the soil faster.
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Now dry soils reduce evaporation, and that reduced evaporation allows temperatures
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to climb even higher, and it starts over again, becoming a feedback loop.
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This is where newer research is also raising concerns.
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Studies over the last few years suggest that, in many regions, extreme heat itself may
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now be helping create or intensify drought conditions.
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In other words, the atmosphere is becoming so warm that it's pulling moisture out of
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soils and vegetation faster than those systems can recover.
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You can almost think of the atmosphere as becoming thirstier.
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A warmer atmosphere has a greater capacity to hold water vapor, which means when conditions
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are dry, that atmosphere demands more moisture from the landscape below, sucking a dry.
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And if the rainfall doesn't replenish that moisture quickly enough, the cooling system
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weakens further.
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And when that happens, the heat doesn't just continue, it intensifies.
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You can probably see why a compound heat drought event worries people so much.
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The danger isn't just the heat, and it isn't just the drought, it's that interaction
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between them.
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Because once the land dries out and the atmosphere begins heating more efficiently, the system
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begins to feed upon itself and rapidly get out of control.
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It's where we move from simple weather into feedback loops.
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If you remember from previous episodes, we talked about the fact that a feedback loop happens
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when a change in the system creates conditions that reinforce even more of the same change.
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I often explain this using the example of a car engine.
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An engine produces enormous amounts of heat while it runs.
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Under normal conditions, coolant moves the heat away and helps to regulate the system
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and keep it in balance.
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But if the coolant level drops too low, the engine rapidly starts to overheat.
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That heat builds very quickly and builds upon itself.
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The landscape can work in a similar way.
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Water is like the Earth's cooling system.
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When moisture is available, energy can be redirected into things like evaporation
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and transpiration.
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But during drought, that cooling pathway weakens, and the system loses an ability to regulate
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heat.
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Now, the process can happen almost anywhere, but certain atmospheric patterns make it worse.
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In my recent episode, The Atmospheric Highway, we talked about how the jet stream can
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sometimes become more wavy or slow moving.
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And when large ridges of high pressure stall over a region, the air beneath them tends
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to sink.
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Sinking air suppresses cloud formation and reduces rainfall.
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And with fewer clouds, more sunlight reaches the surface, day after day.
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The sunlight keeps heating the ground.
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At the same time, the lack of rainfall prevents moisture from being replenished.
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Now the atmosphere is heating a landscape that is already struggling to cool itself.
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This is one reason compound events can become dangerous so quickly.
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The stress builds across multiple systems at once.
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Agriculture is affected because crops lose moisture faster, and then the reservoir
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and rivers decline because evaporation rates increase.
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Electrical demand rises as people rely more heavily on air conditioning.
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And wildfire risk can increase dramatically because vegetation becomes dry, hot, and
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more flammable.
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This is one of the reasons why scientists are paying increasing attention, not just to
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individual extremes, but those overlapping extremes.
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Because when the impacts multiply, for instance a hot day in a dry season, the heat and drought
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reinforce each other at the same time, and the entire system starts operating on what
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you might call double stress.
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Now up to this point, we've mostly been talking about local and regional feedback loops.
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The heat dries the soil, the soils reduce evaporation, and that a reduced evaporation
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allows temperatures to climb higher.
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But systems don't operate in isolation.
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Large-scale climate patterns can add additional stress to the atmosphere and the landscape
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at the same time.
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And one of the most important patterns scientists are watching right now is the developing El
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Nino in the Pacific Ocean at the time of this broadcast.
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If you've listened to previous episodes of this podcast, you may remember that El Nino
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is a natural occurring climate pattern that develops when unusually warm water spreads
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across parts of the central and eastern tropical Pacific Ocean.
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That warming changes how heat and moisture move to the atmosphere.
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And because the atmosphere is connected globally, those changes shift rainfall patterns, storm
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tracks, and most importantly drought risk and heat extremes in many parts of the world.
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Now, some regions do become wetter during El Nino years.
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Others become hotter and drier, but occasionally the Pacific warming becomes especially intense.
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That's what scientists refer to as a super El Nino.
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A super El Nino is not a separate phenomenon.
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It's basically just an unusually powerful El Nino event where the sea surface temperatures
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in parts of the Pacific rise far above the average.
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These stronger events allow enormous amounts of heat stored in the ocean to interact directly
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with the atmosphere.
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And that's important because the ocean is the planet's largest heat reservoir.
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In a normal year, much of that heat stays stored in the upper layers of the ocean, but
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during a super El Nino event, more of that energy can influence weather patterns around
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the globe.
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Historically, super El Nino years have been associated with major shifts in rainfall and drought
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patterns.
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Parts of Australia and Southeast Asia often become drier, while portions of central and
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South America experience more rain.
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Some regions see increased wildfire activity as vegetation dries out under persistent heat
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and other see flooding events.
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Right now, scientists are increasingly monitoring the possibility that a very strong El Nino, a
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super El Nino, may be developing once again for the summer of 2026.
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But now these events are unfolding in a world that's already warmer than it was during
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many previous El Nino years.
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Ocean temperatures globally are already elevated, and the atmosphere contains a lot of heat
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energy.
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That means natural climate patterns are now unfolding in an atmosphere and an ocean system
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already carrying additional heat.
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Right now, one of the reasons scientists are paying close attention to the current situation.
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It's because strong El Nino events can reshape rainfall and heat patterns across large
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parts of the United States, and combinations between the two matter.
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Historically, strong El Nino years tend to shift the jet stream farther south during parts
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of the cooler season, which can bring wetter conditions to portions of the Southern United
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States, while leaving others high and dry, such as the northern regions.
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But in summer months, the picture becomes even more complicated.
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What scientists are increasingly monitoring is how a strong El Nino may interact with
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already unusually warm ocean temperatures and dry landscapes that are entering a warm
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season with varying levels of drought stress.
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Parts of the Western United States are already dealing with long-term water stress and
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elevated wildfire risk.
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And now they could be particularly vulnerable to periods of prolonged heat and rapid
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drying.
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At the same time, portions of the southeast and Gulf coast can experience oppressive humidity
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and dangerous heat stress as warmer Gulf waters continue feeding moisture into the atmosphere.
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And in the plains and agricultural regions, the timing of rainfall has become critical.
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A few missed weeks during periods of extreme heat can place enormous stress on crops and
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reservoirs very quickly.
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Now, it doesn't mean that a super El Nino is going to guarantee a disaster in any one region.
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The atmosphere is way too complex for that.
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But it does mean that forecasters are increasingly watching for overlapping stresses, especially
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in a super El Nino situation.
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Modern societies are built around the assumption that most environmental stresses happen
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separately.
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A region might deal with a drought or a heat wave or many wildfire conditions.
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But as we've discussed, increasingly, we're finding that these stresses overlap and
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then reinforce one another.
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And when that happens, the impacts can grow very quickly.
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If we think about agriculture for a moment again, a crop can survive a short period of
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heat if enough soil moisture is available.
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And many crops can survive short dry spells if temperatures remain moderate.
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But when you combine those two things together, when extreme heat and drought arrive together,
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that stress multiplies.
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Soils lose moisture faster, plants close those tiny openings, growth slows, and crops
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can shift from growing to simply trying to survive to dying.
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Thus timing becomes critical.
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A few missed weeks of rainfall during periods of intense heat can dramatically affect the
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yields of crops, especially during key parts of the growing season.
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It's a reason scientists are increasingly monitoring something we call flash drought.
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Typically, droughts were thought of as slow moving disasters that develop gradually
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over months, maybe even years.
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But a flash drought can develop more rapidly.
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Under persistent heat and dry atmospheric conditions, soils can lose moisture surprisingly
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fast.
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Vegetation becomes stressed, streams decline, and agricultural impacts can begin appearing
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within weeks instead of seasons.
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In other words, the atmosphere can sometimes pull the moisture out of the land faster than
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the system can recover.
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And we're already seeing that in parts of the United States, such as the West and even
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Florida and South Georgia, where we had massive wildfires due to drought this spring.
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And agriculture is only one part of the story.
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Water systems can come under stress as reservoirs decline while evaporation rates increase.
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Electrical systems can face higher demand as more people rely on air conditioning during
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prolonged heat waves.
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Wildfire risk can increase as vegetation becomes hotter, drier, and more vulnerable to
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ignition.
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And ecosystems that normally buffer heat and moisture stress can begin losing resilience
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at the same time.
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This is why climate scientists are increasingly studying interactions instead of isolated
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events.
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Because the atmosphere is not a collection of separate systems that all operate independently.
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Heat affects water, water affects vegetation, vegetation affects evaporation, evaporation
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affects temperature.
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And large-scale climate patterns, like El Niño, influence all of these all at once.
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One of the most important educational shifts happening in climate science right now is the
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growing recognition that climate change is not just altering temperatures.
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It's altering how energy and water move through the entire Earth system.
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And when you stop and think of the atmosphere that way, you can notice how connected these
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processes really are.
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A heat wave is no longer just a number on a thermometer.
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It's about soil moisture, vegetation stress, reservoir levels, and wildfire conditions.
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And yes, humidity.
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Natural variability still plays a major role in our weather patterns, but the growing
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likelihood of multiple stresses arriving at the same time and reinforcing one another
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as they do raises new challenges for both human systems and infrastructure that was largely
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built around more stable conditions.
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That's why, as we watched the possibility of a super El Niño forming in 2026, it's
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more important than ever to pay attention to the signals we are seeing across our living
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planet.
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Because the better we understand these connected systems, the better prepared we are to respond
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proactively instead of reactively.
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Growing up, I used to think of humid heat and dry heat as completely different experiences.
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But the more we study the climate system, the more we realize they're connected by the
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same underlying physics of heat, water and energy moving through the atmosphere and across
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the land.
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What is important is not just the individual extremes, but what happens when multiple
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stresses begin overlapping at the same time.
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A hotter atmosphere can intensify drought and dry landscapes can intensify heat.
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And large-scale patterns can sometimes add additional stress to systems that are already
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struggling.
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As we begin another summer here in the northern hemisphere and face the likelihood of a more
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intense El Niño, I think it's important to pay attention to the weather patterns we're
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seeing around us and how they may be changing over time.
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Because the atmosphere is not isolated, it's a connected system and the more we understand
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those connections, the better prepared we are for the changes ahead.
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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
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a differing opinion, I want to hear from you.
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I can use your viewpoints and future episodes.
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You can reach me at the climate translation at gmail.com.
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I'll see you next time.