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 comes in..... Heat goes out.... " HEAT BUDGET"

Incoming Solar Energy can be: ReflectedReflected Absorbed (changed into heat)Absorbed (changed into heat) Re-radiated out to space Re-radiated out to space The balance or imbalance of these:The balance or imbalance of these: Controls earth surface temperatures Drives ocean and atmosphere circulation " HEAT BUDGET" Where does incoming solar radiation go?

Reflected light

Of incoming solar radiation how much is....Of incoming solar radiation how much is.... Reflected back out to space?Reflected back out to space? ~ 30% (24% by atmos., 6% by land and sea) Absorbed?Absorbed? ~ 70% (23% in atm.; 47% by land & sea) ABOUT HALF OF THE INCOMING ENERGY IS ABSORBED BY THE LAND AND SEAABOUT HALF OF THE INCOMING ENERGY IS ABSORBED BY THE LAND AND SEA THE GLOBAL HEAT BUDGET

1/3 reflected; ½ absorbed by land and sea

1) Re-radiated (infrared) directly to space? % 2) Transferred to the atmosphere? % MOST OF THE SOLAR RADIATION ABSORBED BY LAND AND SEA IS TRANSFERRED BACK TO THE ATMOSPHERE Of the energy absorbed by land & sea (47%), how much is.....

1) Evaporation and condensation of water % (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. = 13% Much infrared energy radiated by earth’s surface is absorbed in the atmosphere by "greenhouse gases"Much infrared energy radiated by earth’s surface is absorbed in the atmosphere by "greenhouse gases" In absence of this greenhouse effect, the earth would be about -10˚C!In absence of this greenhouse effect, the earth would be about -10˚C! Transfer of heat from land and sea to the atmosphere happens in two ways:

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

If heat input > output, then temperature should increase constantlyIf heat input > output, then temperature should 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 latitudes by oceans and atm. currentsHeat transferred from lower latitudes to higher latitudes by oceans and atm. currents –Warm water/air currents: Equator --> poles –Cool water/air currents: poles --> Equator Convection!!!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 currentsThese are convection currents They are driven by temperature differencesThey 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 rangeContinents -- large T range Oceans -- small T rangeOceans -- small T range – Reason : Heat capacities, land vs. water Oceans stabilize surface T of Earth

Layer of ice that forms annually at high lat.Layer of ice that forms annually at high lat. –Near Antarctica; In Arctic Ocean SEA ICE (NOT Icebergs)

SEA ICE: Sheets of ice at high latitudeSEA ICE: Sheets 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) –Ice is a thermal insulator

Sea-ice formation creates high-S water: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