Like we could be edging closer and closer to a world with no clouds, which could contribute

a significant 8 degrees to the already predicted global temperature rise.

(looking up at the sky) “No come bacccckkkk!”

We all know climate change is already radically changing our world and will continue to do

so.

But an unexpected byproduct of high atmospheric carbon dioxide levels is a loss of clouds.

I know it sounds insane, but it may have happened before.

Around 56 million years ago, the geologic record indicates that the world was essentially

ice free.

In other words, it was SUPER hot, with an average annual temperature of around 30 degrees

celsius—a hot flash in the earth’s history we now refer to as the Paleocene-Eocene Thermal

Maximum.

In trying to figure out how the heck earth could have gotten that toasty, today’s scientists

estimate that it could be due to a loss of cloud cover—particularly stratocumulus clouds.

To help us unravel this theory, we spoke to journalist Nathalie Wolchover, who spent over

a year researching this topic.

Nathalie: The question of how stratocumulus clouds will change is kind of the most important

question in knowing how bad kind of global warming is going to be going forward.

Stratocumulus clouds are the most common cloud type and more of earth’s surface is covered

by them than any other kind of cloud.

They keep Earth and its oceans cool by shading all of us underneath them and bouncing sunlight

back into space, away from us.

A lot of them also produce a nice drizzle.

They’re dependent on convective instability, and they form a distinctive, relatively thin

layer because their growth upwards is limited by a zone of dry stable air above them, even

while they draw moisture from whatever’s underneath them.

Their structure is totally dependent on their ability to release and absorb heat and moisture

in a very particular way.

A way that cannot be disturbed.

Now, we do have very high-fidelity simulations and computer models that help us understand

the possible effects of climate change.

From sea ice melt to sea level rise to temperature changes, we can understand how fluctuating

factors like levels of atmospheric CO2 may affect the earth’s natural systems.

These kinds of models are run on supercomputers because they have so many intricate moving

parts that the calculations would just be impossible on any other kind of computer.

But cloud dynamics, like what’s happening inside stratocumulus clouds, actually take

place on too small a scale to be included in these larger models.

They’re also just so complex that they’re very difficult to predict, so they get left

out of big climate simulations that tell us a lot about what could happen to our world

as it warms.

A joint research team from CalTech and the Pacific Northwest National Laboratory tackled

this gap in our climate models.

They created a novel application of the same kind of simulations we use for larger climate

phenomena: a large-eddy simulation.

Applying this on a smaller scale allowed them to study cloud behavior in response to several

factors—one of them being atmospheric CO2 concentration.

And it turns out—as the CO2 levels rise, the stratocumulus clouds can’t achieve as

much longwave cooling, or the release of heat from the top of the cloud.

This disturbs the convection that keeps the cloud together, and they just break apart.

Nathalie Wolchever: So they found that this breakup of stratocumulus clouds could actually

add eight degrees Celsius of additional warming to the Earth's system in the future.

And a big question is at what point will that tipping point occur.

But based on some Simple simple assumptions this tipping point would occur when the CO2

in the atmosphere reaches twelve hundred parts per million.

And that's actually CO2 equivalent.

So that would include other greenhouse gases Kind of yeah.

So that level is three times the current level of CO2 in the atmosphere.

This work confirms that high historic CO2 levels may have caused the lack of cloud cover

that led to a sweltering PETM back in the day.

But it also presents the alarming prospect that rising atmospheric CO2 today not only

raises global temperatures, but could lead to loss of cloud cover.

This results in even hotter global temperatures than we’d previously anticipated—just

because our climate models didn’t include cloud dynamics.

Nathalie: And it's also important to remember that this tipping point is far enough away

that we can avoid it.

And that's been interesting to talk to these scientists and kind of understand that they

are more optimistic than you might expect because I mean maybe that's the nature of

the people who study climate change.

You have to be optimistic or you just wouldn't be able to stand dealing day in and day out

with this prospect.

This research makes an essential contribution to our understanding of atmospheric science

in an era of changing climate.

But this simulation only looked at one particular area of the globe that’s prone to cloud

loss, and we may not be able to extrapolate that behavior to the whole world, at least

not without further work on the subject.

It’s a crucial example of why continuing to understand how all these complex unknowns

work together is SO important, and needs to be supported.

So we can keep preparing for our new reality, and hopefully, if we detect these issues early

enough, take action that could keep them from happening in the first place.

Now that we have your attention, it’s Earth DayAnd let’s not forget about Earth Day,

. Ever wonder what would happen if the earth just get a liiiiittle bit hotter?

Found out in this episode and if you like climate science updates like these subscribe!

Thanks so much for watching and we’ll see you next time on Seeker.