1 MET 112 Global Climate Change MET 112 Global Climate Change - Lecture 4 Clouds and Global Climate...

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MET 112 Global Climate Change - Lecture 4

Clouds and Global Climate

Dr. Craig ClementsSan Jose State University

In class assignment #2How does this situation affect the climate?

(2-3 sentences)

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QuestionsQuestions

What role do clouds play on the Earth’s climate?

What would happen to our climate if clouds were to increase/decrease?

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Water in the atmosphereWater in the atmosphere

Definitions:

– Evaporation:

– Condensation:

– Precipitation:

Process where a liquid changes into a gasProcess where a liquid changes into a gas

Any liquid or solid water that Any liquid or solid water that falls from the atmosphere to falls from the atmosphere to the ground. (i.e. RAIN!)the ground. (i.e. RAIN!)

Process where a gas changes into a liquidProcess where a gas changes into a liquid

Water freely Water freely evaporating and evaporating and condensingcondensing

Since more water Since more water molecules are molecules are evaporating than evaporating than condensing, then condensing, then net evaporation is net evaporation is occurring.occurring.

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Lid on:Lid on:

Now, evaporation Now, evaporation and condensation and condensation are equal. The air are equal. The air above water is above water is now called now called ‘saturated’.‘saturated’.

The humidity is The humidity is now 100%now 100%

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CondensationCondensation

The process by which water vapor changes to a cloud droplet

Water vapor molecules may ‘stick’ to

condensation nuclei and grow (billions) to eventually form cloud droplet.

Examples of condensation nuclei include:a.a. DustDustb.b. SaltSaltc.c. SmokeSmoke

Condensation occurs primarily as temperature cools:-colder the molecules more likely they are to ‘stick’ to other molecules

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http://www.ssec.wisc.edu/data/comp/cmoll/cmoll.html

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Clouds and radiationClouds and radiation

Cloud - Climate InteractionsCloud - Climate Interactions

Albedo effect - COOLINGAlbedo effect - COOLING Clouds reflect incoming solar radiation. Clouds reflect incoming solar radiation.

The cloud droplet size and total water content The cloud droplet size and total water content determine the overall reflectivity. determine the overall reflectivity.

Greenhouse effect - WARMINGGreenhouse effect - WARMING Clouds are good absorbers (and emitters) of long Clouds are good absorbers (and emitters) of long

wave (infrared) radiation.wave (infrared) radiation.

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Clouds and day to day Clouds and day to day temperaturestemperatures

Imagine that you are going camping in the Sierras Imagine that you are going camping in the Sierras with your friends. On the first day (and evening) it with your friends. On the first day (and evening) it is cloudy, while on the second day (and evening) it is cloudy, while on the second day (and evening) it is clear. Based on this information alone:is clear. Based on this information alone:

Which day would be warmer?Which day would be warmer?

Which evening would be warmer?Which evening would be warmer?

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Which day would be warmer?

1. First day (clear)

2. Second day (cloudy)

3. Both the same

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Which evening would be warmer?

1. First day (clear)

2. Second day (cloudy)

3. Both the same

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Low and High cloudsLow and High clouds

Consider two types of clouds:Consider two types of clouds:

1.1. Low levels clouds Low levels clouds

2.2. High levels cloudsHigh levels clouds

Q: How is the Earth’s surface energy budget Q: How is the Earth’s surface energy budget different for low clouds compared to high different for low clouds compared to high clouds?clouds?

Clouds and climateClouds and climate

Cloud A: Low level, (dark, thick)Cloud A: Low level, (dark, thick)

Cloud B: High level, light Cloud B: High level, light (sub visible or thin)(sub visible or thin)

Excellent reflector of incoming radiation; good absorber/emitter of infrared radiation

Fair/poor reflector of incoming radiation; good/excellent absorber/emitter of infrared radiation

So, clouds both warm and cool the earth. Overall, though, clouds act to cool the

earth

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Changes in cloudsChanges in clouds

Increases in low level clouds will:Increases in low level clouds will:–

Increases in high level clouds will:Increases in high level clouds will:

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Changes in cloudsChanges in clouds

Increases in low level clouds will:Increases in low level clouds will:– cool the surface (cooling outweighs cool the surface (cooling outweighs

warming)warming)

Increases in high level clouds will:Increases in high level clouds will:– warm the surface (warming outweighs warm the surface (warming outweighs

cooling)cooling)

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Explain how the earth’s climate would change as a result of aircarft contrails.

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1. What percentage of the sun’s radiation is a) absorbed by the Earth’s surface?b) absorbed by the atmospherec) reflected out to space?

2. What percentage of the energy received by the earth’s surface comes directly from greenhouse gas emissions?

3. If the sun’s radiation was to increase by 10%, how would the following energy units change (increase, decrease or stay the same)a) Energy gained by the Earth’s surface.b) Energy lost by the Earth’s surface.c) Energy emitted by greenhouse gases.d) Energy lost to space.

Questions