CLASS 16

HEAT BUDGET OF THE EARTH Basic budget Latitude variations Surface temperatures SEA ICE

Why is the Earth warm?

Why is Mars Colder? (avg. = 60˚C)

"

HEAT BUDGET"

Heat comes in.....

Heat goes out....

" HEAT BUDGET" Where does incoming solar radiation go?

Incoming Solar Energy can be:

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Reflected

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Absorbed (changed into heat)

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Re-radiated out to space

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The balance or imbalance of these: Controls earth surface temperatures Drives ocean and atmosphere circulation

Reflected light

THE GLOBAL HEAT BUDGET

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Of incoming solar radiation how much is....

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Reflected back out to space?

~ 30% (24% by atmos., 6% by land and sea)

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Absorbed?

~ 70% (23% in atm.; 47% by land & sea )

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ABOUT HALF

OF THE INCOMING ENERGY IS ABSORBED BY THE LAND AND SEA

1/3 reflected; ½ absorbed by land and sea

Of the energy absorbed by land & sea (47%), how much is.....

1) Re-radiated (infrared) directly to space?.... 10% 2) Transferred to the atmosphere? ...... 37% MOST OF THE SOLAR RADIATION ABSORBED BY LAND AND SEA IS TRANSFERRED BACK TO THE ATMOSPHERE

Transfer of heat from land and sea to the atmosphere happens in two ways: 1) Evaporation and condensation of water.... 24% (i.e., 24 out of the original 100 units)

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Heat uptake by evaporation -- cools surface Later…heat released by condensation -- warms atm.

WATER VAPOR VERY IMPORTANT!!!!

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2) Conduction and radiation to atmos. = 13% Much infrared energy radiated by earth’s surface is absorbed in the atmosphere by "greenhouse gases"

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In absence of this greenhouse effect, the earth would be about 10˚C!

Greenhouse effect

This is a Global Average, but....

Solar energy coming in is max. at Equator min. at poles

So… at any given latitude, heat input does not match output low latitudes: solar input > IR output high latitudes: solar input < IR output

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If heat input > output, then temperature should increase constantly

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This does not happen….

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What maintains the balance?

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Heat transferred from lower latitudes to higher latitudes by oceans and atm. currents

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Warm water/air currents: Equator --> poles

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Cool water/air currents: poles --> Equator

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Convection!!!

Heat is transferred from lower latitudes to higher latitudes by currents in oceans and atmosphere –Warm water/air currents: Equator --> poles –Cool water/air currents: poles --> Equator

•These are convection currents •They are driven by temperature differences Warm Cold

Water Vapor Transport => Heat Transport

Temperature Belts Note effects of ocean currents

Temperature variation- Winter vs. Summer

•Continents -- large T range •Oceans -- small T range – Reason : Heat capacities, land vs. water Oceans stabilize surface T of Earth

SEA ICE (NOT Icebergs)

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Layer of ice that forms annually at high lat.

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Near Antarctica; In Arctic Ocean

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SEA ICE: S

heets of ice at high latitude •Grow in winter, shrink in summer •Thickness is limited...

– < 2 meters (single season) –Ice is a thermal insulator

•Sea-ice formation creates high-S water: –Reminder: Ice formation --> high-S water.

–This forms the densest and deepest water masses in the oceans.

These are icebergs, not sea ice