A simple explanation for why clouds are really white

By Juman Hijab

Updated on: December 11, 2021 Original date: July 18, 2021

White clouds

White clouds

White wooly sheep

White wooly sheep

Why are clouds bright white?

You know those fluffy white clouds that look like wooly sheep or whipped cream? Why are they so white? 

When I type in "why are clouds white?" into a Google search, the top 10 links all agree that the whiteness is due to the scattering of light by water droplets within the cloud. 

I would politely like to disagree. My goal in this article is to show you why this does not make sense. There is a better explanation, a simpler one. Of course, the caveat is that I am not a meteorologist.  But, read on, and see what you agree with.

White air bubbles beer

Head of beer pint

Spitting crab

Crab foaming "at the mouth"

White polar bear

White polar bear

Clouds are white because disorganized air bubbles produce the white color

First: A lot of what we see as white is due to trapped air bubbles

  • Drinks can be colored; however, shake them up or carbonate them, and they will develop a white froth. The first picture shows a beer head that is pure white, even though the beer is amber.
  • Water is clear (unless it is deep; then it is blue).  On the other hand, whitewater, wave crests, frothy saliva, and frozen water molecules with entrapped air (ice or snow) will appear white. The second picture shows a crab frothing at the mouth as the air from its gills mixes with water.
  • Many animals and birds have white camouflage. The examples include: Polar bears, Ermines, arctic foxes and hares, and myna birds. They do this as their fur and feathers are hollow and entrap air bubbles. The third picture shows a polar bear with white fur.

Of note, not all white color in nature is due to entrapped air. Read more in this course.

altostratus clouds

Altostratus clouds

Nimbostratus clouds

nimbostratus clouds

nimbostratus - altostratus

Nimbostratus - altostratus

Clouds are dark when water absorbs light

Second: Larger water droplets eat up the light --> darkness

  • Next, let's take the instance of dark or grey clouds, such as nimbostratus or cumulonimbus clouds. As soon as the sky darkens above us, we instinctively look for cover. The darkening signifies a heavy downpour.
  • Rain clouds are thicker and deeper. For example, a nimbostratus cloud often develops from the higher alto stratus cloud as it encounters a warm front. The excess warm water vapor creates increasing condensation within the cloud. This in turn encourages the formation of larger water droplets.
  • As the cloud gets heavier, it lowers itself down in the Troposphere. The air mass of the lower Troposphere pushes upwards against the lower surfaces of the cloud. This added pressure increases the condensation of water vapor into droplets. The droplets in the cloud grow even larger. 
  • This is probably the point at which the sky starts darkening.  You can see in the third picture how altostratus clouds converge into nimbostratus clouds. At this point, the water droplets are large enough to absorb the light creating a dark and foreboding presence. And that is when the rain starts falling. 

Have you noticed that as soon as the rain stops that the clouds no longer have that darkened structure?

Blue ice cave

Blue Ice cave

Clear ice cubes

Clear ice cubes: no air bubbles

white snow on deck

White snow on deck

ice cubes with central white cloud

Ice cubes with trapped white air bubbles

Snow and ice without air appear clear  or blue

Third: Add air to snow and ice ------  whiteness

  • This is last argument to support the fact that clouds are white because of the disorganized air bubbles.  Ice cubes without air bubbles are clear as shown in the second image above (it took some effort to do this at home, but I had help from here).
  •  An ice cube produced in a regular freezer with somewhat cold temperatures will freeze with air bubbles within it. It will look as if you have trapped a miniature cloud or fog within it.
  • However, if the ice is thick or deep, it appears blue. Just like ocean water looks blue. While snow looks white because of the air trapped between the snowflakes, packed snow will lose the air and appear blue.

In summary, it does not matter how much water/ice the cloud has. As long as there is a mass of disorganized air bubbles at the forefront of the cloud, the cloud will appear white. Thus, the tops of clouds - seen from an airplane -  appear very white. That is the edge of the cloud with an expanding air mass.  The bottom of a storm cloud will appear dark or grey; that is where water/ice are getting larger and weighing down the cloud. The dense number of large water drops absorb light creating the darkness effect.

Picture credits:

  1. Header image: Images by John 'K'. "Flat bottomed clouds", March 4, 2009.
  2. Vladimer Shioshvili. Clouds in Dusheti, Georgia, May 21, 2006.
  3. David Masters. Happy Sheep. One of the sheep at Styal Country Park, Cheshire, Feb 15, 2009.
  4. Martin Garrido. Beer, Dec 27, 2011.
  5. devra . Spittling crab in Morro State Park Marina, July 5, 2010.  
  6. Better Than Bacon. Polar bear in California. Apparently their hairs aren't white, they're actually translucent but hollow to better insulate, Aug 4, 2007.
  7. Maxwell Hamilton. Unusual Clouds; Altostratus undulatus, March 30, 2015.
  8. Paulo O. Storm Clouds Over Fairfax, April 27, 2011.
  9. Nicholas A. Tonelli. Convergence, Nimbostratus streaks, Easton, March 24, 2007.
  10. anoldent. Blue ice cave, 2000 New Zealand 108. 
  11. Hijab, J. Clear ice cubes, 2018.
  12. Hijab, J. White snow on deck, 2018.
  13. Hijab, J. Ice cubes with trapped air bubbles.

Juman Hijab

About the author

Juman is a retired physician after having been in clinical practice for more than four decades. Her lifelong interest has been in the chemistry of life.

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