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Consider the following statements:

  1. High clouds primarily reflect solar radiation and cool the surface of the Earth.
  2. Low clouds have a high absorption of infrared radiation emanating from the Earth’s surface and thus cause warming effect.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Explanation

  • High clouds are often thin and do not reflect very much. They let lots of the Sun’s warmth in. Low clouds are often quite thick and reflect lots of sunlight back into space.
  • The main difference between high and low clouds is that the high clouds are colder. This means that they radiate less energy into space than the lower, warmer clouds. Therefore, high clouds work to “trap” more energy than low clouds.
  • High clouds are not good at reflecting short waves. But, they are very good at blocking long waves. This also traps heat. Thus, high clouds will cause a warming of the Earth’s surface. Hence, Statement 2 is not correct.
  • Low clouds are excellent reflectors. But, they don’t stop the longwave energy from escaping to space. Therefore, low clouds help to cool the Earth. Hence, Statement 1 is not correct.

Learn more

Types of clouds

  • High clouds: Also known as cirrus clouds, they lie above 20,000 ft. They are thin, made of ice crystals, and do not produce rain. They have warming effect.
  • Middle clouds: Also known as altostratus clouds, they occur between 6,500 – 20,000 ft. They are made of water droplets and ice crystals. They sometimes produce virga, precipitation that evaporates before reaching the ground.
  • Low clouds: Also known as stratus clouds, they occur below 6,500 ft. They are dense and dark. They produce rain and snow. They have cooling effect.

How clouds affect climate

  • Cloud amount: More widespread clouds reflect more sunlight back to space causing cooling.
  • Cloud reflectivity: Clouds with more water droplets (whiter clouds) reflect more sunlight causing cooling.
  • Cloud height: Higher clouds are colder so they emit less infrared radiation. This greenhouse effect causes warming.

Uncertainties

  • Greatest uncertainty about impact of low clouds over subtropical oceans. Climate models differ on how much these will decrease with warming.
  • Organization of clouds over hundreds of kms scales not well simulated yet. This can significantly impact climate.

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