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Clouds – The Biggest Uncertainty in Climate Science · Talking Science

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Look up at a cloud today and I mean you just
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see peaceful scenery right like a painted backdrop
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drifting lazily by. Yeah exactly. It's just part
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of the sky to most of us. But the thing is you
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are actually looking at. arguably the single
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greatest threat to the accuracy of modern climate
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science. It really is this ultimate paradox.
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I mean, the thing we associate most with a calm,
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lazy afternoon is actually this hyperactive,
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just incredibly complex engine of thermodynamics.
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Right. And we take this massive churning machine
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and we just dismiss it. Which is why today we're
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taking a deep dive into an excerpt perfectly
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titled, Look Out the Window on Almost Any Day
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and Theirs. And our mission for this deep dive
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is to shortcut you, the listener, to being completely
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well informed about the hidden physics of clouds.
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We want to take them from being just background
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scenery into, well, the single most fascinating
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puzzle in earth science right now. Exactly. OK,
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let's unpack this, because before we can understand
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how they are literally breaking the world's most
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advanced climate models, we have to shift our
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focus to what a cloud actually is at a fundamental
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level. We need to talk about the invisible ingredients.
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Right. And the primary ingredient is already
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all around you. Like the air you are breathing
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right now holds water, not as liquid drops, obviously,
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but as an invisible gas, water vapor. And the
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main rule governing this is that temperature
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dictates capacity. So warmer air has the energy
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to hold a lot of this invisible vapor, but cooler
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air holds significantly less. Which brings us
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to the saturation point, right? Yes, exactly.
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When air cools down. its capacity to hold that
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water vapor just shrinks. And eventually it hits
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this specific temperature threshold where it's
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completely full. Like it cannot hold a single
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other molecule of gaseous water. That's the saturation
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point. Right. And because that excess vapor has
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to go somewhere, it undergoes a phase change.
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It condenses out of that invisible gas state
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and becomes liquid water droplets. Or, you know,
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if it's cold enough, ice crystals. So this makes
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intuitive sense. I mean, it's the classic cold
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glass of lemonade on a sweltering summer day.
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Oh, yeah. Perfect analogy. Right, because the
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ice cold glass chills the warm summer air immediately
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surrounding it. That localized pocket of air
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drops past its saturation point, its capacity
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shrinks, and the excess water vapor just... Well,
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it condenses into sweat on the side of the glass.
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It does, but, and this is key, the lemonade glass
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provides a crucial element there. It provides
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a surface. Okay, surface. Yeah, because out in
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the open sky, water vapor is remarkably stubborn.
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Even when the air is super saturated and desperately
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needs to unload excess water, the vapor actually
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struggles to condense on its own. Really? Yeah,
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it requires a physical scaffold to cling to.
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Otherwise, it often just remains a gas. Wait,
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so in the sky, pure water vapor is just floating
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there, refusing to turn into a cloud unless it
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can grab onto a speck of dust. I mean, if the
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sky is mostly empty space, where is it finding
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a surface? Well, that's the thing. The atmosphere
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is actually brimming with microscopic solid surfaces.
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We call them condensation nuclei. And we are
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talking about ultrafine sea salt whipped up from
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the crests of ocean waves or microscopic soil
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particles blown from dry deserts. Wow. Even ash
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and soot from forest fires. Trillions upon trillions
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of these invisible specks are constantly suspended
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in the air up there. But wait, if the atmosphere
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is completely loaded with trillions of these
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condensation nuclei at all times and water vapors
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everywhere, why aren't we just surrounded by
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a permanent global fog down here? Like, why isn't
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the entire planet just one giant cloud? Because
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the presence of the dust scaffolds isn't enough
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on its own, the air temperature still has to
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drop low enough to force the vapor out of its
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gaseous state. Oh, okay. Down here at ground
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level, the air is usually warm enough to easily
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hold onto its vapor. To get a cloud, you need
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a mechanism to drastically cool a massive volume
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of air. Which brings us to the giant refrigerator
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in the sky. Or, well, rather, the lack of one.
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Because if there's no massive cold object chilling
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the air like our lemonade glass, how does the
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sky drop below that saturation point in the first
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place? Right. It happens through this thermodynamic
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phenomenon called adiabatic cooling. Adiabatic
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cooling. Okay, explain that. So adiabatic simply
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describes a change in temperature that happens
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without any heat being exchanged with the surrounding
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environment. Wait, what? Yeah, there's no cold
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front swooping in to chill the air, and it's
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not touching a freezing surface. Cooling without
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touching anything cold. I mean, that sounds like
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a physical contradiction. It does, but think
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of a parcel of air as a giant invisible balloon.
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As that balloon rises higher into the atmosphere,
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the ambient atmospheric pressure around it drops.
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Because the air is thinner up there. Exactly.
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There is simply less air above it pushing down,
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and because the outside pressure drops, the balloon
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naturally expands outward. But expanding takes
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physical effort, right? Like, it has to swish
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against the air around it. That is the absolute
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key. Pushing against the surrounding atmosphere
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requires work. The air parcel has to spend its
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own internal thermal energy to push its boundaries
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outward. Oh, I see. By expending that internal
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heat energy to expand, the balloon's overall
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temperature plummets. It cools itself purely
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through the mechanics of its own expansion. The
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perfect everyday analogy for this, I think, is
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a bicycle tire. Like, when you let the air rapidly
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out of a highly pressurized bike tire and put
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your finger near the metal valve, that rushing
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air feels freezing cold. Yes, that's exactly
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the same physics. And it isn't because the tire
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was stored in a freezer. It's because the air
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is expanding rapidly as it hits the lower pressure
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of the outside room. It is literally burning
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its internal energy to expand, and it drops in
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temperature as a direct result. Precisely. Now
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just scale that bicycle tire effect up to a massive
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column of rising air. It rises, the ambient pressure
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drops, it expands, and it cools. Here's where
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it gets really interesting. Because this cooling
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is driven by consistent physical laws, it creates
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visual boundaries we can actually see in the
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sky, right? We can. As that massive air bubble
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rises and cools, it eventually hits the exact
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altitude where its temperature drops past that
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magical saturation point. And you can see this
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invisible threshold drawn across the sky. You're
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referring to the flat bases of clouds. Yes. Like
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when you look at a field of fluffy clouds and
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the bottoms are completely flat, like someone
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just sliced them off at a laser level. Yeah,
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it's striking when you really notice it. That
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flat base isn't a coincidence, is it? It is the
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visual evidence of the exact altitude. where
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the expanding air finally got cold enough for
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the water vapor to grab onto the dust scaffolds.
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It really is a literal line of atmospheric physics
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made visible. That's so wild. Below that flat
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line, the air is expanding and cooling, sure,
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but it's still warm enough to hold its vapor.
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But the millisecond it crosses that altitude
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line, the temperature drops below the threshold,
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condensation occurs instantly, droplets form,
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and a visible cloud appears. So the expansion
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cools the air and that forms the cloud. And this
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is the next logical step. What initiates the
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rising? What pushes the air up to expand in the
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first place? And how does the way it's pushed
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alter the physical shape of the cloud we see?
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Well, the mechanism of the upward push dictates
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pretty much everything about the cloud's architecture.
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Take the sun, for instance. It heats the Earth's
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surface. Unevenly. Unevenly. Yeah. So a dark,
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plowed agricultural field absorbs way more heat
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than, say, a lush green forest sitting right
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next to it. Ah, okay. So the air directly above
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that plowed field gets much hotter than the surrounding
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air. Right. And that heat creates localized,
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highly buoyant pockets of air that just shoot
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upward, almost like an invisible hot air balloon.
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When air is pushed up vigorously in these tight,
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localized columns, it builds vertically. And
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this creates cumulus clouds, which actually comes
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from the Latin word for a heap or pile. The classic
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fluffy ones. Exactly. These are your classic
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cotton wool clouds with those flat bases we just
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talked about and puffy bubbling tops that reflect
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that really forceful upper boiling of the air.
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But what happens when that upward push isn't
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a tight localized column? Like what if an entire
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region of the sky is being lifted slowly? Then
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you get a completely different structure. This
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often happens when two massive weather fronts
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collide, forcing a huge, broad wedge of warm
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air to slowly slide up and over a denser, colder
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air mass. Okay, so a much gentler lift. Very
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gentle. Because the rising is gentle, widespread,
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and stable over hundreds of miles, the resulting
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cloud spreads out in a massive, continuous layer.
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Which are? These are stratus clouds. Stratus
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is Latin for spreading out. That's your typical
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overcast day, just a featureless gray blanket
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covering the entire sky. The source material
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also mentions terrain as a trigger. Or a graphic
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lifting, it called it. Oh, yeah. That occurs
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when a fast -moving wind hits a massive physical
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barrier, like a mountain rain. Right, because
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the air can't just go through the rock. Exactly.
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The entire mass is forced violently up and over
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the peaks. And this forced lifting can create
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those really dramatic lens -shaped clouds that
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hover over mountains or trigger massive precipitation
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on the windward side of the range. And if the
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upward push is just unimaginably powerful, regardless
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of what triggered it, it just keeps building
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upward, right? Oh, it... builds up to incredible
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freezing heights. A vigorous cumulus cloud can
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just keep feeding on hot, moist air, expanding
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and rising violently until it becomes a cumulonimbus,
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the classic thunderhead. Those look so intimidating.
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They are. These monstrous clouds can reach all
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the way to the upper boundary of the troposphere.
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Which means it gets so cold that it completely
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changes the composition from water droplets to
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ice crystals. And that explains cirrus clouds
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too, right? It does. Cirrus clouds form so incredibly
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high up that it's far below freezing. And fierce
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upper -level jet stream winds stretch those ice
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crystals into wispy hair -like curls. Actually,
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cirrus is literally Latin for a curl of hair.
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I love that. So the physical state of the water
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and the sheer force of the wind at those extreme
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altitudes completely change the visual texture.
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Exactly. Every single cloud shape you see is
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basically just a physical. record of how the
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air was lifted and how cold it got. That makes
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me think about fog. If a cloud shape is just
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a record of atmospheric physics and fog forms
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when the ground loses heat overnight, chilling
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the air right above it until it condenses, does
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that mean when you're walking through a thick
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morning fog and you feel that mist on your face,
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are you literally just wandering around inside
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a ground -level stratus cloud? You are. In every
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meaningful physical sense, fog is a cloud on
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the ground. That is wild to think about. It's
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true. The mechanics of vapor, the dust scaffolds,
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reaching that saturation threshold, it's all
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completely identical. The only real difference
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is the lifting mechanism. Right, because there
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isn't one. Exactly. Instead of the air rising
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to reach cold temperatures, the cold temperatures
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came down to meet the air at the surface. So
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you were experiencing the inside of a cloud without
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ever leaving the pavement. It's almost unsettling
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when you realize we live our daily lives wandering
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through the exact same physical mechanisms that
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dictate the sky. But, and this brings us to the
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real crux of the issue, we've decoded how clouds
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form and why they take these different shapes.
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It's lovely descriptive science. But why does
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this basic recipe make clouds the ultimate headache
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for climate scientists? Ah, well, it's because
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clouds play a massive, dual, and heavily contradictory
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role in the Earth's energy budget. The energy
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budget. Yeah, the energy budget is essentially
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the delicate balance between the solar radiation
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coming in from the sun and the infrared heat
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radiating back out from the Earth into space.
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And clouds are interfering with both directions
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of that traffic. Drastically so. On one hand,
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clouds act like giant mirrors. Think about those
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low, thick stratus clouds we talked about. The
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big gray blankets. Right. But from space... They
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are incredibly bright white. They reflect a massive
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percentage of incoming sunlight straight back
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out into the void before it can ever reach the
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surface to warm the planet. So this reflection
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provides a huge net cooling effect on the globe.
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Exactly. Okay, that part seems straightforward.
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More mirrors equal a cooler planet. If only it
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stopped there right. But on the other hand...
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Clouds also act like blankets. Blankets? Yeah.
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High, thin clouds like those wispy ice crystal
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cirrus clouds. They're too transparent to reflect
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much incoming sunlight. The visible solar energy
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just passes right through them. But they are
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highly effective at absorbing the invisible infrared
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heat that the warmed Earth is trying to radiate
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back out into space. Wait, I have to push back
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here. Cirrus clouds are made of ice. How can
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a cloud made of literal ice act as a warming
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blanket? It's a great question, but it isn't
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about the physical temperature of the ice itself.
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It's about the molecular structure trapping radiation.
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Oh, I see. Because they are so high up, they
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absorb the outgoing heat from the Earth, but
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they are too cold to effectively radiate that
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heat away into space. Instead, they trap it and
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re -radiate a portion of it back down to the
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surface. So they act exactly like a greenhouse
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gas. Exactly. This creates a net warming effect.
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This is maddening. So clouds aren't just a simple
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thermostat doll we can turn up or down. They
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are constantly fighting themselves, some cooling,
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some warming, all at the exact same time across
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the globe. Yes. Complexity only deepens when
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you realize humans are actively altering this
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thermodynamic tug of war. By accident, presumably.
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Entirely by accident. Let me guess. This loops
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back to the condensation nuclei, the invisible
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dust scaffolds. It does. Human industrial activity
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are factories, power plants, massive diesel engines.
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It pumps billions of fine aerosol particles into
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the atmosphere every single day. Oh, wow. So
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we are essentially... injecting the sky with
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a massive surplus of artificial condensation
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nuclei. Precisely. We're giving the water vapor
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more scaffolds to grab onto. Yeah. But wait,
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if the overall amount of water vapor in a specific
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air mass stays the same and we just add a ton
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more dust. Doesn't that just mean the same amount
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of water gets divided among a whole lot more
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seeds? That is the exact mechanism. You nailed
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it. The resulting cloud is composed of significantly
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more droplets, but each individual droplet is
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much, much smaller than it would be in pristine
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air. Okay, but why does the size of the droplet
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matter to the climate? It's the same amount of
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water. Surface area. A cloud made of millions
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of tiny droplets has vastly more surface area
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than a cloud made of a few large droplets. And
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that increased surface area makes the cloud significantly
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brighter and more opaque. It becomes a much more
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effective mirror, scattering that incoming sunlight
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way more aggressively. So our pollution is accidentally
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creating super mirrors. That's staggering. It
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really is. And you can see the undeniable visual
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proof of this from satellites. Really? Like you
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can just see it? Oh, yeah. When you look at satellite
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imagery of the oceans, you can often spot what
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meteorologists call ship tracks. Ship tracks?
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Yeah. These are long, brilliantly white streaks
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cutting through otherwise dull, gray marine clouds.
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And they perfectly trace the commercial shipping
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lanes. So the exhaust from the ships is making
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the clouds brighter. Exactly. The diesel exhaust.
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from massive cargo ships acts as this localized
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injection of condensation nuclei, instantly brightening
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the clouds directly above their path. Okay, let's
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pull all of this together because my head is
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spinning a bit. Every single cloud is doing something
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completely different based on its height, its
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thickness, whether it's made of ice or water,
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and whether a cargo ship just happened to sail
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underneath it. Right. How on earth do climate
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scientists program that chaos into a computer
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to predict global warming? It pushes the absolute
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limits of computational physics. I mean, to understand
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the challenge, you have to look at how global
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climate models actually operate. Okay. They essentially
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wrap a digital 3D grid around the entire Earth,
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and supercomputers then calculate how heat, wind,
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and moisture transfer from one good cell to the
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next. Like breaking the atmosphere down into
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a giant Rubik's Cube. A Rubik's Cube where the
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individual blocks are massive, yes, because the
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Earth is huge. A single grid cell in a global
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climate model might be tens of kilometers wide
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and tens of kilometers tall. Oh, I see the problem
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immediately. A single cumulus cloud might only
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be one or two kilometers wide. It's way too small
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for the grid. Far too small. It sounds absurd
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given modern technology, but even our most advanced
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supercomputers do not have remotely enough processing
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power to simulate the fluid dynamics of every
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individual cloud on the planet. It's just too
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much data. The scale is computationally impossible.
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We simply cannot simulate the microscopic physics
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of water vapor condensing on dust across the
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entire globe simultaneously. It sounds like trying
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to describe... every single individual pixel
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of a massive 4K movie. But you're only allowed
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to use a giant broad paintbrush. Yeah. You physically
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cannot paint the fine details. That is an excellent
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analogy. So since they can't paint the individual
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clouds pixel by pixel, scientists have to rely
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on what are called parameterizations. Parameterizations.
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Okay, let's define that. How does a parameterization
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act as the giant paintbrush? Well, a parameterization
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is essentially a simplified mathematical rule.
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So instead of asking the computer to build a
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cloud droplet by droplet, the scientists write
17:34
a rule that says, look at the average temperature
17:37
and humidity of this massive 50 kilometer grid
17:40
cell. And based on those broad conditions, approximate
17:43
how many clouds would probably be there and estimate
17:46
their net effect on the sunlight. So they're
17:48
incredibly sophisticated, educated guesses. They
17:50
are heavily researched approximations based on
17:53
vast amounts of real -world data, yes, but they
17:55
are still approximations. And because different
17:58
scientific teams around the world construct these
18:00
mathematical rules slightly differently, their
18:03
climate models produce slightly different predictions
18:05
about how clouds will behave as the Earth continues
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to warm. Because if the Earth warms, the atmosphere
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changes, which means cloud formations will inevitably
18:14
change too. Yes, and this creates a massive feedback
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loop. Will a warmer world create more low thick
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clouds that act as mirrors and dampen the warming?
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Or will it create more high thin clouds that
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act as blankets and amplify the warming? It's
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terrifying not to know for sure. This phenomenon,
18:34
known as cloud feedback, is the single largest
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source of uncertainty in climate science today.
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So what does this all mean? When we read a headline
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saying global temperatures might rise anywhere
18:43
from 2 to 4 degrees over the next century, a
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huge portion of that gap exists simply because
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we can't perfectly predict what the clouds are
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going to do. Exactly. It is a primary driving
18:53
factor behind that margin of error. And this
18:56
highlights a really vital aspect of scientific
18:58
honesty. How so? Well, the foundational physics
19:01
of greenhouse gases trapping heat. That is settled
19:05
certainty. It has been understood as basic physics
19:07
for over a century. The honest, actively researched
19:11
uncertainty lies entirely in the hyper -complex,
19:15
chaotic reaction of the clouds to that initial
19:17
warming. Right, but uncertainty isn't an excuse
19:20
to throw our hands up and just stop trying. Oh,
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far from it. The global scientific community
19:25
is actively attacking this puzzle from every
19:28
conceivable angle right now. What are they doing?
19:30
We deploy fleets of satellites to continuously
19:33
measure cloud albedo or reflexes. It is genuinely
19:58
incredible. I mean, we started this deep dive
20:01
by just looking at a lazy, puffy white shape
20:03
in the sky. And we followed the invisible water
20:06
vapor as it desperately seeks out microscopic
20:08
specks of sea salt. We watched it cool down by
20:11
expanding in a drop of pressure, shaping the
20:14
skies based on the terrain below, and ultimately
20:16
holding the entire future of our climate models
20:19
in its delicate balance of mirrors and blankets.
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It forces you to realize that nothing in our
20:23
atmosphere is truly passive. Every fluffy shape
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you see up there is a visual readout of invisible,
20:29
incredibly powerful thermodynamic forces. It
20:32
really is. to you listening to this deep dive
20:35
right now, the next time you look out the window
20:37
at a flat -bottomed cumulus cloud or you feel
20:40
the mist of a morning fog bank against your face,
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remember that you aren't just looking at the
20:45
weather. You are watching the invisible, hyperactive
20:48
mechanics of the planet's entire energy budget
20:50
happening in real time. It completely transforms
20:53
a mundane commute into a front row seat to the
20:56
most beautiful confounding puzzle in earth science.
20:58
It does. And I want to leave you with a final
21:01
provocative thought to mull over. We talked about
21:03
how human diesel exhaust is already unintentionally
21:06
creating bright ship tracks over the oceans,
21:08
forcing clouds to reflect more sunlight away.
21:11
Well, if we were already accidentally building
21:13
super mirrors, what would happen if we tried
21:16
to use this exact same dust seeding physics on
21:18
purpose? Could we intentionally deploy a fleet
21:21
of ships to spray microscopic sea salt into the
21:24
marine clouds to artificially brighten them,
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deliberately trying to cool down the Earth? The
21:29
physics says it would work, but the global consequences
21:31
of hacking the sky's thermostat? Well, that's
21:34
a whole other puzzle for another day. Thank you
21:35
so much for joining us on this deep dive.