Clouds and Aerosols

Clouds and aerosols are two of the most important, but least understood, aspects of climate change. How much do you know about them?

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1. SPECKS APPEAL

What are aerosols?

Aerosols range in size from smaller than the smallest virus to about the diameter of a human hair and can remain aloft anywhere from a few days to years.
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2. POINT OF ORIGIN

Most aerosols in the atmosphere are from human-caused pollution.

Most occur naturally, including sea salt, desert dust, wildfire smoke and sulfates from volcanic eruptions. A significant minority is from human causes such as industrial pollution, cars and deliberate burning of trees and agricultural waste. But the artificial stuff can dominate the air downwind of urban and industrial areas.
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3. SPECIAL EFFECTS

What effects do various aerosols have on the climate?

We admit that this is a tricky one, but that’s part of what makes aerosols so hard to pin down in climate models. Various kinds of aerosols have various kinds of effects, both direct and indirect. As a direct effect, aerosols scatter sunlight back into space. As an indirect effect, they can either help or hinder the development of clouds, which in turn can either cool or warm the planet.
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4. I.D., PLEASE

Which of these qualities are used to identify types of clouds?

Clouds occur in three basic shapes: puffy (cumulus), layered (stratus) and wispy (cirrus). They are also identified by the altitudes at which they form. Clouds below two kilometers (about one mile) are considered low. Those from two to six kilometers (about one to four miles) are considered mid-level, while those above that altitude are considered high. And finally, the prefix “nimbo-“ and postfix “-nimbus” signify clouds from which precipitation is falling.
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5. RADIATOR OR UMBRELLA?

Do clouds heat or cool the earth?

Different kinds of clouds at different altitudes play different roles in regulating Earth’s temperature. Wispy clouds at high altitudes tend to trap infrared radiation emitted by the sun-warmed Earth, which prevents it from escaping into space and warms the atmosphere. On the other hand, thick, low-lying clouds tend to cool the planet by shading Earth’s surface, reflecting sunlight back into space. Scientists are trying to determine how global warming will affect the balance we’ve been enjoying up to now.
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6. NIGHT LIGHT

Where are noctilucent ("night-shining") clouds found?

Noctilucent clouds form when ice crystals begin to cling to dust and particles high in the atmosphere, forming electric-blue, rippled clouds that stretch across the sky at sunset. Noctilucent or “night-shining” clouds are a delight for high-latitude sky watchers, and their season is eagerly anticipated around the Arctic Circle.
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7. GIVE ME SOME SHADE

About how much of Earth’s surface is covered by clouds at any given time?

Covering most of the Earth at any given moment, clouds have a huge—but insufficiently understood—impact on climate.
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8. SHIP SHAPE

Ships can create clouds in their atmospheric wake.

Aerosols flying out of a ship’s smokestack can seed condensation of water vapor and create long, bright clouds called “ship tracks.” They’re the nautical equivalent of an airplane’s contrails.
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9. LOCATION, LOCATION, LOCATION

Where in the atmosphere are aerosols found?

Aerosols can be found in the air over oceans, deserts, mountains, forests, ice, and every ecosystem in between. They can be found drifting in Earth’s atmosphere from the stratosphere to the troposhere to the Earth's surface.
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10. BRIGHT IDEA

The brighter a cloud looks, the less pollution it contains.

A given volume of pollution-rich cloud tends to have more numerous and smaller droplets than in more pristine clouds. The high number of small droplets provides more surfaces to reflect light, making the cloud appear brighter than a cloud consisting of fewer and larger droplets.