Is LA's Marine Layer — AKA May Gray, June Gloom — Going To Burn Off Someday And Never Ever Come Back?

Los Angeles's summer marine layer — aka June Gloom, aka May gray —is one of the most unique aspects of living along the coast. It keeps things cool through the morning and burns off in the afternoon to reveal gorgeous blue skies.

But what will happen to the marine layer as the climate changes?

Carole Ann Wright from Culver City sent LAist a question about the future of our beloved coastal cloudiness:

Here's what we know.

What It Is

At its most basic, our summer marine layer is those low lying grey clouds over L.A. that are particularly prevalent between May and September.

At a little less basic, the clouds are much bigger than a dreary day at the beach. They're just the edge of a giant atmospheric system called a stratocumulus cloud deck that stretches hundreds of miles out into the Pacific.

They form as high pressure systems push warm, dry air downward, until it crashes into the cool, moist air above the ocean, creating this thin layer of clouds that live within something called the marine boundary layer. You've probably seen how thin they are if you've flown out of LAX. Even if it's a grey day at the beach, it's not long after takeoff until you burst through their tops and have to close your window because it's too sunny.

They're particularly prevalent off the west coast of continents between a latitude of 30 degrees south and 30 degrees north. And, I can't overstate this, they're mightily important for keeping things cool, reflecting energy from the sun away from the earth.

What Happens In 50 Years?

I asked some climate scientists.

"We don't know what's going to happen to the marine layer," said Park Williams, Research professor at Lamont Doherty Earth Observatory of Columbia University

"We don't necessarily know yet at this point," said Daniel Swain, climate scientist at the UCLA Institute of the Environment and Sustainability.

"No, there is no evidence that that will happen," said Tapio Schneider, Professor of Environmental Science and Engineering at Caltech.

Note — they're not necessarily saying we're in the clear.

While there's always uncertainty in climate modeling (no one model will ever be 100% accurate), it's particularly difficult to predict the impact of global climate change on clouds, especially on marine layer clouds, especially in an area as small as L.A.

But There's Also Urban Sprawl And The Heat Island Effect

Park Williams and his colleagues dug into cloud observation from airports across Southern California, dating back to 1948.

They compared the height and frequency of marine layer cover in those spots, to changes in temperature and the growth of urban sprawl.

They found decreases in marine layer cover.

In all of Southern California, the biggest decreases were found near L.A.-area airports. The average decrease was 23%. The largest decrease was in Van Nuys — 46%.

"We saw the biggest decrease ... at the sites that have urbanized the most, and these sites tended to be in the greater L.A. area," wrote Williams in an email.

In their research about the marine layer, they posit that much of the decrease in stratocumulus clouds is a result of increased temperature due, at least in part, to the urban heat island effect, which has become more pronounced as L.A.'s developed.

Trees and vegetation have been replaced by asphalt, concrete and houses, which retain and give off more heat than the bare earth.

If you've ever stood on concrete on a sunny day and felt the heat coming off of it, you've experienced this effect.

"In many places clouds have been rising in height and eventually getting squeezed out altogether," Williams said. "Land heats up, then it heats up the warm air, or the air above it. And as that air warms, the clouds fall apart because the liquid water droplets begin evaporating away."

A decrease in local marine layer is concerning, because it's essential for cooling our environment and providing plants with much needed moisture.

If the pattern continues there's a chance that we'll see desertification of our coastal systems. And a need for more air conditioners.

The Catastrophic Scenario

What if we zoomed out from L.A. and SoCal, and used modeling to theorize what could happen to the Earth's marine clouds if we cranked greenhouse gas emissions to 11?

Schneider and his colleagues did just that sort of modeling and published their findings in a paper earlier this year. The outcomes (which are highly theoretical) were ... not good.

"I don't hope and don't think that this would actually be happening," said Schneider. But if it did, "it would be a global calamity."

They saw stratocumulus clouds start to break up when the concentration of CO2 in the atmosphere reached 1,300 parts per million. A number that we're adding to all of the time - in part - by burning fossil fuels. Current concentrations are at about 400 PPM.

"We're talking about future concentrations that are three times, at least, of what we currently have. So, this is not something that we would be reaching within the century," said Schneider.

Under an aggressive emissions scenario, however, we could theoretically hit that concentration in roughly 100 years, he said.

"The net effect will be global, whether it happens in a few years or a few decades, because if you replace these stratus decks with just ... scattered cumulus clouds, you would warm earth globally by about eight degrees centigrade, so 14 degrees Fahrenheit," Schneider said.

What that could mean for our micro climates here in SoCal is unclear, but "global calamity" does seem to suggest it wouldn't be good.

And keep in mind, there's always the possibility that the breakup of the clouds could happen at lower — or higher — concentrations of CO2. So, that's either a little bit of good news or possibly even worse news. We'll have a clearer idea as time goes on, we gather more data and modeling improves.

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