Jul
07
2010

Questions in the Clouds
A recent article in Scientific American described a study in which a few scientists interviewed 14 of their colleagues specializing in climate change to make predictions about three possible future scenarios: low, medium, and high degrees of global warming. The climate scientists were also asked to predict when Earth's climate might reach a tipping point and change so drastically that humans find it difficult to survive. As part of their response, they drew attention to factors that added caveats to their predictions. One of the biggest questions: what will the clouds do?

Low-level clouds are tricksy: Studies show that these low-level clouds, called stratocumulus, cause climate researchers to squeeze their stress balls.
Low-level clouds are tricksy: Studies show that these low-level clouds, called stratocumulus, cause climate researchers to squeeze their stress balls.Courtesy Benutzer:LivingShadow, Wikimedia Commons

As the climate changes, the atmosphere's behavior changes, too--making predictions difficult. Clouds are interesting characters because they both reflect sunlight and absorb it. Different types of clouds both reflect and absorb in different proportions, but their behavior also changes with the temperature, making them difficult to model. CMMAP is one organization working to improve cloud representations in models of Earth's climate. (And their website is loaded with great information about clouds!)

Since scientists began modeling climate change, there have been many ideas about how clouds will impact global warming. But they faced difficulties because many of the same questions asked about clouds in the 1950s remain unanswered today. Some researchers thought that low-level clouds would reflect more sunlight on warm days, thereby slowing global warming in its tracks.

Cumulonimbus: Vertical growth ain't no joke.
Cumulonimbus: Vertical growth ain't no joke.Courtesy Simon Eugster, Wikimedia Commons

Cloudy Answers
But research at NASA has shown that in general, low-level clouds reflect more sunlight on cold days and less sunlight on warm days. Further, as the oceans warm, low-level clouds dissipate. This had led scientists to predict that warming would initiate a positive-feedback cycle, whereby as the climate warmed, low-level clouds would dissipate and spur on further warming.

However, the low-level clouds are thought to be balanced out by clouds with vertical growth, which may expand and reflect more sun on warm days. Researchers think that these vertical clouds could mitigate some or all of the effects of clouds' behavior on global warming. Of course, it's important to keep in mind that scientists are still only beginning to unravel the mysteries of clouds and further research will be essential to create accurate models of their behavior.

Noctilucent: "Why you gotta be all up in my grill with your carbon, yo?"
Noctilucent: "Why you gotta be all up in my grill with your carbon, yo?"Courtesy Hrald, Wikimedia Commons

Signs from Above
Another type of cloud is important in climate change discussions as an indicator of global warming rather than an influence on climate: noctilucent clouds. These clouds occur higher in the atmosphere than any other. They used to be visible only from latitudes near the poles, but began appearing closer to the equator in recent years. Because noctilucent clouds can only form in very cold temperatures, their presence at lower latitudes indicates cooler temperatures high in the atmosphere than before. Researchers think that these cooler temperatures are caused by global warming--that phenomenon creates warmer temperatures near the surface by reflecting heat emitted by the surface back toward the surface. Before global warming, this heat would have escaped to higher areas of the atmosphere to warm them, making the formation of noctilucent clouds impossible at lower latitudes.

Of course, global warming isn't the only way we impact clouds…

Contrails: Not only do they give off greenhouse gases, jets mess with the clouds. Jerks.
Contrails: Not only do they give off greenhouse gases, jets mess with the clouds. Jerks.Courtesy NASA, Wikimedia Commons

Jets and Clouds
As if natural clouds weren't enough of a question mark, jets throw a monkey wrench in climate models, too. The contrails they leave behind can create pseudo clouds that alter temperatures by lowering daytime highs and decreasing nighttime lows because of the ways they reflect and absorb radiation. Jets also punch holes in natural clouds and cause immediate impacts on the weather.

And just 'cause I can't get enough, here's more cloud info.

Your Comments, Thoughts, Questions, Ideas

cory pansini's picture
cory pansini says:

do clouds really come from water?

posted on Thu, 08/26/2010 - 3:57pm
Shana's picture
Shana says:

"Aircraft condensation trails criss-crossing the sky may be warming the planet on a normal day more than the carbon dioxide emitted by all planes since the Wright Brothers' first flight in 1903, a study said on Tuesday."

posted on Fri, 04/08/2011 - 12:11pm

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