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Do you ever think of what could cause the next big extinction? How about a super massive tropical storm that sweeps over continents? Hey, it could happen! Check out this SciShow Dose to see how a hypercane would be possible.

Hosted by: Hank Green
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Hurricane Isabel: Hurricane Floyd:
[SciShow intro plays]

Hank: Imagine a storm so big it reaches up into the stratosphere, so wide it could cover all of North America, and so catastrophic it could wipe out almost all life on Earth. I’m not talking about Hollywood’s next big disaster blockbuster, although they might want to take notes here, I’m talking about a hypercane!

One scientist hypothesized that this theoretical, super-buff kind of storm contributed to one of Earth’s mass extinction events. But could it have happened, and what would it take for it to happen again? To understand what a hypercane theoretically is, let’s talk about tropical cyclones, rotating thunderstorms that form over warm ocean water, with wind speeds of 119 kilometers per hour or more. We call them hurricanes, typhoons, and just plain cyclones, depending on where the storm occurs.

And these storms are already pretty huge: at least 15 kilometers high and around 200 kilometers across. But a hypothetical hypercane could kick up wind speeds to around 800 kilometers per hour, extend all the way up into the stratosphere, and span the North American continent. Which sounds... kind of terrifying.

But how would a tropical cyclone theoretically even get that big? A normal hurricane needs a region of warm ocean water to form, one that’s 26. 6 degrees Celsius for at least 50 meters below the surface. Plus, lots of wind.

The wind blows over the ocean, water evaporates, rises, cools, and condenses into a clump of thunderstormy cumulonimbus clouds. Y’know, the water cycle. All this warm, moist air that’s rising creates a region of lower pressure near the ocean’s surface, so more surrounding air swirls in.

As this mass of stormclouds grows, the winds get more intense, and it spins faster, counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere, because of the way the Earth rotates on its axis. Faster wind speeds means more evaporation and rising warm air, which causes even lower air pressure in the center of the storm. This eventually forms a calm, clear region that we call the eye of the hurricane.

So, as long as the winds keep blowing and there’s enough warm, evaporating ocean water, the tropical storm keeps growing and spinning faster. But since hurricanes get their energy from the difference in temperature between the ocean and the atmosphere, there’s a limit to how big they can grow, and how strong the winds can get. MIT climatologist Kerry Emanuel was looking into this limit when he realized that, hey: if you bump the ocean temperature, things could probably get intense.

To form a hypercane, we’d need the oceans to reach a temperature of almost 50 degrees Celsius, around 14 degrees hotter than it’s ever been recorded. And how could that happen...? Well, he suggests either an asteroid impact or a crazy undersea volcanic eruption. We’ve already got a hypercane, we’re also adding one of those things to the mix.

Super-warm water would mean that evaporation kicks up, wind speed increases, pressure in the hurricane’s eye falls even more, and the storm becomes a monster. A high-wind monster that would wreak havoc on our world, not only during the storm, but afterwards. In fact, this hypercane theory was presented as a possible explanation for mass extinction events, maybe even the extinction of the non-avian dinosaurs around 66 million years ago.

Emanuel hypothesizes that while a volcanic eruption or an asteroid impact could have catastrophic effects nearby, they wouldn’t throw enough stuff, high enough into the atmosphere, for long enough periods of time to change global conditions. Enter the hypercane: either one huge storm or many smaller storms that could pump water vapor and volcanic ash into the middle stratosphere. This might’ve shrouded the planet in darkness to cause a global freeze.

Or maybe it could’ve interfered with the Earth's protective ozone layer, exposing everything alive on the planet to lots of biologically dangerous UV radiation from the sun. So hypercanes sound terrifying but let’s remember that it’s a theoretical model and the study’s author admits that they haven’t found evidence of one ever occurring. And the theory still needs more review by other scientists.

Not to mention, if a hypercane were to occur, we would already be in hot water, both literally and figuratively, and probably have lots of other catastrophic weather problems to worry about. So don’t despair! A hypercane is just one, very unlikely, hypothetical disaster, among all of the much more likely hypothetical disasters. You'll be fine!

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