CLASSCLASS 1616

HEAT BUDGET OF THE EARTHHEAT BUDGET OF THE EARTHBasic budgetBasic budget

Latitude variationsLatitude variations

Surface temperaturesSurface temperatures

SEA ICESEA ICE

Why is the Earth warm?

Why is Mars Colder? (avg. = - 60˚C)

Heat comes in.....Heat comes in.....

Heat goes out....Heat goes out....

""HEAT BUDGET" HEAT BUDGET"

Incoming Solar Energy can be:Incoming Solar Energy can be:•ReflectedReflected•Absorbed (changed into heat)Absorbed (changed into heat)• Re-radiated out to spaceRe-radiated out to space

•The balance or imbalance of these:The balance or imbalance of these:

Controls earth surface temperaturesControls earth surface temperatures

Drives ocean and atmosphere circulationDrives ocean and atmosphere circulation

""HEAT BUDGET" HEAT BUDGET" Where does incoming solar radiation go?Where does incoming solar radiation go?

Reflected light

•Of Of incoming solar radiationincoming solar radiation how much is.... how much is....•ReflectedReflected back out to space? back out to space?

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

~ 70% (23% in atm.; ~ 70% (23% in atm.; 47% by land & sea47% by land & sea))

•ABOUT HALFABOUT HALF OF THE INCOMING ENERGY IS OF THE INCOMING ENERGY IS ABSORBED BY THE LAND AND SEAABSORBED BY THE LAND AND SEA

THE GLOBAL HEAT BUDGETTHE GLOBAL HEAT BUDGET

1/3 reflected; ½ absorbed by land and sea

1) Re-radiated1) Re-radiated (infrared) directly to space?.... (infrared) directly to space?.... 10%10%2) Transferred to the atmosphere? ...... 2) Transferred to the atmosphere? ...... 37%37%

MOST OF THE SOLAR RADIATION ABSORBED MOST OF THE SOLAR RADIATION ABSORBED BY LAND AND SEA IS TRANSFERRED BACK BY LAND AND SEA IS TRANSFERRED BACK TO THE ATMOSPHERETO THE ATMOSPHERE

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

1) 1) Evaporation and condensationEvaporation and condensation of water.... of water.... 24% (i.e., 24 out of the original 100 units)24% (i.e., 24 out of the original 100 units)

• Heat uptake by evaporation -- cools surfaceHeat uptake by evaporation -- cools surface• Later…heat released by condensation -- warms atm.Later…heat released by condensation -- warms atm.• WATER VAPOR VERY IMPORTANT!!!!WATER VAPOR VERY IMPORTANT!!!!

2) Conduction and radiation to atmos.2) Conduction and radiation to atmos. = 13% = 13%• Much infrared energy radiated by earth’s surface is Much infrared energy radiated by earth’s surface is

absorbed in the atmosphere by "greenhouse gases" absorbed in the atmosphere by "greenhouse gases" • In absence of this greenhouse effect, the earth In absence of this greenhouse effect, the earth

would be about -10˚C!would be about -10˚C!

Transfer of heat from land and sea to the Transfer of heat from land and sea to the atmosphere happens in two ways:atmosphere happens in two ways:

Greenhouse effect

This is a Global Average, but....

Solar energy coming in isSolar energy coming in is

max. at Equatormax. at Equator

min. at polesmin. at poles

So… at any given latitude, heat input So… at any given latitude, heat input does not does not matchmatch output output

low latitudes: solar input > IR outputlow latitudes: solar input > IR output

high latitudes: solar input < IR outputhigh latitudes: solar input < IR output

•If heat input > output, then temperature If heat input > output, then temperature should increase constantlyshould increase constantly•This does not happen…. This does not happen…. •What maintains the balance?What maintains the balance?

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

–Warm water/air currents: Equator --> polesWarm water/air currents: Equator --> poles–Cool water/air currents: poles --> EquatorCool water/air currents: poles --> Equator

•Convection!!!Convection!!!

Heat is transferred from lower latitudes to Heat is transferred from lower latitudes to higher latitudes by currents in oceans and higher latitudes by currents in oceans and atmosphereatmosphere

–Warm water/air currents: Equator --> Warm water/air currents: Equator --> polespoles–Cool water/air currents: poles --> EquatorCool water/air currents: poles --> Equator

•These are convection currentsThese are convection currents•They are driven by temperature They are driven by temperature differencesdifferences

WarmWarm

ColdCold

Water Vapor Transport => Heat Transport

Temperature BeltsTemperature Belts

Note effects of ocean currents

Temperature variation- Winter vs. SummerTemperature variation- Winter vs. Summer

•Continents -- large T rangeContinents -- large T range

•Oceans -- small T rangeOceans -- small T range

– Reason : Heat capacities, land vs. water Reason : Heat capacities, land vs. water

Oceans Oceans stabilize stabilize surface T of surface T of EarthEarth

•Layer of ice that forms annually at high lat.Layer of ice that forms annually at high lat.–Near Antarctica; In Arctic OceanNear Antarctica; In Arctic Ocean

SEA ICE (NOT Icebergs)SEA ICE (NOT Icebergs)

•SEA ICESEA ICE: S: Sheets of ice at high latitudeheets of ice at high latitude

•Grow in winter, shrink in summerGrow in winter, shrink in summer

•Thickness is limited...Thickness is limited...

– < 2 meters (single season)< 2 meters (single season)

–Ice is a thermal insulatorIce is a thermal insulator

•Sea-ice formation creates high-S water:Sea-ice formation creates high-S water:

–Reminder: Ice formation --> high-S water.Reminder: Ice formation --> high-S water.

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

These are icebergs, not sea ice