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“Good things come to those who wait… greater things come to those who get off their rear and do anything to make it happen.” - Unknown. MOST OF THE ENERGY THAT WARMS THE EARTH COMES FROM THE SUN.
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“Good things come to those who wait… greater things come to those who get off their rear and do anything to make it happen.” - Unknown
MOST OF THE ENERGY THAT WARMS THE EARTH COMES FROM THE SUN. THERE IS A SMALL AMOUNT OF ENERGY FROM THE RADIOACTIVE MATERIAL IN THE INTERIOR OF THE EARTH, BUT BY FAR AND AWAY, MOST OF THE ENERGY COMES FROM THE SUN. THE SUN’S ENERGY IS GENERATED BY NUCLEAR FUSION REACTIONS TAKING PLACE IN THE SUN’S CORE. THIS ENERGY EVENTUALLY REACHES THE SURFACE OF THE SUN AND IS RADIATED INTO SPACE.
THE SUN IS EMITTING ENERGY AT THE RATE OF 3.85 X 1026 WATTS. HOWEVER, THE SUN IS 1.5 X 108 KM FROM EARTH. SO, THE EARTH ONLY RECEIVES A SMALL FRACTION OF THE ENERGY THE SUN EMITS. IF WE IMAGINE A DISK WITH A DIAMETER EQUAL TO THE EARTH’S DIAMETER AT RIGHT ANGLES TO THE SUN’S RAYS JUST OUTSIDE THE EARTH’S ATMOSPHERE, WE CAN CALCULATE THE ENERGY INPUT PER UNIT AREA. 1368 WATTS M-2 .
HOWEVER, THE EARTH IS A ROTATING SPHERE, AND NOT A FLAT DISK, SO IF WE ALLOW FOR THIS, THE RADIATION AVERAGE (SOLAR CONSTANT) IS 342 WATTS M-2. THIS IS THE ENERGY COMING TO THE EARTH FROM THE SUN. IT IS IN THE FORM OF ELECTROMAGNETIC RADIATION (LIGHT), WHICH IS THE ONLY FORM OF ENERGY THAT CAN BE TRANSMITTED THROUGH THE VACUUM OF SPACE.
GLOBAL MEAN SURFACE TEMPERATURE, GMST – THE AVERAGE TEMPERATURE OF THE ENTIRE SURFACE OF THE EARTH. THIS TEMPERATURE IS RELATIVELY CONSTANT. FOR AN OBJECT TO MAINTAIN A CONSTANT TEMPERTURE, IT MUST BE IN ENERGY BALANCE. ENERGY LOST = ENERGY GAINED THIS IS TRUE OF ANY OBJECT AT CONSTANT TEMPERATURE, INCLUDING THE EARTH.
ANY WARM BODY EMITS LIGHT. THE INTENSITY OF THE LIGHT EMITTED IS DEPENDS ON T4. IN OTHER WORDS, AS THE TEMPERATURE OF AN OBJECT INCREASES, THE INTENSITY OF LIGHT EMITTED INCREASES IN PROPORTIONAL TO THE TEMPERATURE RAISED TO THE 4TH POWER. AS THE TEMPERATURE INCREASES, THE RADIATION EMITTED IS ALSO SHIFTED FROM THE INFRARED TO SHORTER WAVELENGTHS.
SO, AS THE SUN HEATS THE SURFACE OF THE EARTH, THE SURFACE TEMPERATURE INCREASES, AND THE AMOUNT OF ENERGY RE-EMITTED TO SPACE INCREASES UNTIL A BALANCE IS REACHED. ENERGY LOST = ENERGY GAINED THE SURFACE OF THE EARTH REACHES A CONSTANT TEMPERATURE. WITH NO ATMOSPHERE, THIS TEMPERATURE WOULD BE 255o K OR 0o F.
BUT, WE HAVE AN ATMOSPHERE! NITROGEN 78% OXYGEN 21% ARGON 0.93% CO2 390 ppm METHANE 1.8 ppm N2O 314 ppb OZONE 10-100 ppb WATER VAPOR VARIES WITH TIME AND PLACE, BUT AVERAGED OVER BOTH, THE WATER VAPOR REPRESENTS 0.5% OF THE ATMOSPHERIC GASES.
NITROGEN (N2) AND OXYGEN (O2) ARE LARGELY TRANSPARENT TO INCOMING SOLAR RADIATION AND TO OUTGOING INFRARED RADIATION. BUT, THERE ARE TRACE GASES IN THE ATMOSPHERE THAT CAN ABSORB SOME OF THE OUTGOING INFRARED RADIATION, IN PARTICULAR H2O AND CO2. THIS ABSORBED RADIATION IS RE-EMITTED – AS MUCH BACK TO THE EARTH’S SURFACE AS INTO SPACE. THE RESULT IS A WARMING OF THE EARTH’S SURFACE.
THE EARTH IS WARMER THAN IT WOULD BE WITHOUT AN ATMOSPHERE. THIS NATURAL GREENHOUSE EFFECT IS AROUND 55o F. MAJOR IDEA: GREENHOUSE GASES ACT AS AN INSULATING BLANKET AND CAUSE THE SURFACE OF THE EARTH TO BE WARMER THAN IT WOULD BE OTHERWISE.
THE NATURAL GREENHOUSE EFFECT IS A GOOD THING. IMAGINE EARTH IF THE GMST AVERAGED OVER 30o C (55o F) COLDER. DURING THE LAST ICE AGE, THE GMST AVERAGED 6o C COLDER. IT IS THE ADDITIONAL WARMING OR THE ENHANCED GREENHOUSE EFFECT THAT IS A CONCERN.
THE CONCENTRATION OF CO2 WAS RELATIVELY CONSTANT FOR HUNDREDS OF YEARS. AT AROUND 1750 AT THE START OF THE INDUSTRIAL REVOLUTION, IT STARTED TO INCREASE. IN A LITTLE OVER 200 YEARS, FROM 1750 TO AROUND 1975, IT INCREASED FROM 280 ppm TO 330 ppm. IN JUST 30 YEARS, IT HAS INCREASED AN ADDITIONAL 50 ppm.
WHEN COMPARING GREENHOUSE GASES, WE RATE THE ABILITY OF CO2 TO ABSORB ENERGY AS 1. THEN, WE RATE THE OTHER GREENHOUSE GASES RELATIVE TO IT. SOME HALOCARBONS HAVE VALUES OF AT LEAST 1000. METHANE HAS A VALUE OF 21. CO2 IS AN IMPORTNT GREENHOUSE GASE BECAUSE WE PRODUCE SO MUCH OF IT. ALSO, CO2, METHANE, AND N2O HAVE NATURAL SINKS. HOWEVER, CO2 HAS A VERY LONG LIFETIME IN THE ATMOSPHERE – HUNDREDS OF YEARS. METHANE AND N2O HAVE SHORT LIFETIMES IN THE ATMOSPHERE.
PRIOR TO THE INDUSTRIAL REVOLUTIION, THE CONCENTRATIONS OF THESE GASES IN THE ATMOSPHERE WERE RELATIVELY BALANCED. THE SOURCES AND SINKS WERE RELATIVELY BALANCED. POPULATION TELLS PART OF THE STORY. AT THE END OF THE 18TH CENTURY, THERE WERE LESS THAT 1 BILLION PEOPLE ON EARTH. NOW THERE ARE OVER 7 BILLION. BEST ESTIMATES PUT THE POPULATION AT 9 BILLION BY 2050.
WHERE DO THESE GREENHOUSE GASES COME FROM? CARBON DIOXIDE COMES FROM BURNING FOSSIL FUELS. METHANE – 30% COMES FROM ANAEROBIC BREAKDOWN OF ORGANIC MATTER (SWAMPS AND WETLANDS). RICE PADDIES CONTRIBUTE 11%. LIVESTOCK FLATULENCE CONTRIBUTES 16%. LANDFILLS CONTRIBUTE 17%. NATURAL GAS PRODUCTION AND COAL MINES PRODUCE 19%. NITROUS OXIDE, N2O – AGRICULTURAL ACTIVITIES AND BURNING FOSSIL FUELS. OZONE – GROUND LEVEL AMOUNTS ARE PRODUCED BY PHOTOCHEMICAL SMOG.
CONTRIUBTIONS OF GREENHOUSE GASES TO INCREASE IN GMST: CARBON DIOXIDE – 53% METHANE – 17% NITROUS OXIDE – 5% HALOCARBONS – 12% TROPOSPHERIC OZONE – 13% WE TALK A LOT ABOUT CARBON DIOXIDE, BUT IT IS IMPORTANT NOT TO FORGET ABOUT THE OTHER GASES. WE HAVEN’T MENTIONED WATER VAPOR. HUMANS DON’T DIRECTLY IMPACT WATER VAPOR CONTENT, BUT HUMANS DO INDIRECTLY INFLUENCE IT. THE AMOUNT DEPENDS ON TEMPERATURE.
