Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Physical oceanography wikipedia , lookup
Spherical Earth wikipedia , lookup
History of geology wikipedia , lookup
Age of the Earth wikipedia , lookup
Tectonic–climatic interaction wikipedia , lookup
History of Earth wikipedia , lookup
History of geodesy wikipedia , lookup
Global Energy and Water Cycle Experiment wikipedia , lookup
Global Energy Balance What determines global surface temperature? Blackbody radiation Energy emitted by an object depends on temperature. Energy Flux (W/m2) = Energy/(Time x Area) = !T4 where ! = constant = 5.67x10-8 W/(m2K4) 1 W= 1 Joule/second (Energy/time) T is temperature in K wavelength proportional to 1/T: "max = 2898/T, where " is in µm (10-6m) 1 2 Energy emitted by the sun (W) = Flux at sun's surface (W/m2) x Area of sun (m2) = !Tsun4 x 4"rs2 Flux at some distance r from sun: Flux = Energy emitted by the sun (W), area over which this energy is spread sun earth Flux = (!Tsun4)(4"rs2)/(4"r2) ~ 1/r2 Flux at the distance of the earth's orbit = ( Tsun4)(4 rs2)/(4 reo2) = S S = 1373 W/m2 = "solar constant" Energy absorbed by earth = Flux at the distance of the earth's orbit x cross section of earth = [( Tsun4)(4 rs2)/(4 reo2)][ re2] = S[ re2] Incoming energy from the sun is determined by the orbital parameters and the temperature of the sun. 3 An object will heat up if energy is added: c x dT/dt = dE/dt where c is the heat capacity If more energy is absorbed by the earth than is emitted, earth will heat up. If more energy is emitted than absorbed earth will cool down. How is a balance achieved? Emission of energy depends on the temperature of the earth 4 Global Energy Balance A temperature at the surface of the earth will be reached such that Energy in = Energy out Energy in = Energy out S[!re2] = ("Tearth4)(4!re2) Energy into/out from Earth (W) T = 275 K = 2°C 3E+17 3E+17 Energy received from sun (Watts) With albedo Energy emitted by Earth 2E+17 Earth cools down 2E+17 Earth heats up 1E+17 5E+16 0 200 220 240 260 280 300 Earth’s Temperature (K) 5 35% of sunlight reflected back out to space • Clouds [24%] • Scattering by the atmosphere [7%] • Earths surface [4%] – – – – Snow Vegetation Ocean Desert Energy in = Energy out (1-.35) S[ re2] = ( Tearth4)(4 re2) where .35 is the Albedo (reflected fraction of visible light) of the earth. T = 255 K = -18°C This is actually the temperature somewhere in the atmosphere. It is the temperature that we would see from space (emission temperature). Actual surface temperature is 15°C. Difference reflects the greenhouse effect. 6 Energy into/out from Earth (W) 3E+17 3E+17 Energy received from sun (Watts) With albedo Energy emitted by Earth 2E+17 Earth cools down 2E+17 Earth heats up 1E+17 5E+16 0 200 220 240 260 280 300 Temperature (K) Incoming shortwave Outgoing longwave Earth’s surface T = 5°C 7 8 Greenhouse gas: can absorb and emit infrared (heat) radiation Greenhouse gases: concentration (ppm) Water vapor variable CO2 350 ppm methane 1.7 N2O (nitrous oxide) .3 ozone variable Water vapor is the most important greenhouse gas. Carbon dioxide comes in second (rarer, but very effective at trapping radiation). 9 Energy Balance Energy absorbed = Energy emitted (T) How to change earth's surface temperature: 1) Change Energy coming in from the sun (increase reflectance). 2) Change amount of greenhouse gasses (emission T stays the same, but surface T is increased. More than 1 way to satisfy energy balance! 10 Positive feedback: Process in which perturbation causes system to travel further away from initial state: Negative feedback: Process which causes a system to return to it's initial state upon perturbation: Positive (de-stabilizing) feedbacks on earth's temperature: 1) Ice-albedo feedback Colder T - > more ice -> more sunlight reflected - > colder T Cold limit: Totally frozen earth Warmer T - > less ice -> less sunlight reflected - > warmer T Warm limit: Earth with no ice 11 2) Water vapor feedback Warm air can hold more moisture than cold air: Colder T -> less water vapor in atmosphere > colder T Warmer T -> more water vapor in atmosphere - > warmer T What stabilizes earth’s climate? Long term CO2 regulation by weathering and volcanism 12 What controls atmospheric CO2? 1) Partitioning of C between Deep Ocean and atmosphere/surfac e ocean (103-104 yr) 2) Partitioning of C between ocean/ atmosphere/ biosphere and sediments/rocks (>106 yr) Simplified Earth: Crust = CaSiO3 (wollastonite) Process which tends to draw down CO2 3H20 + 2CO2 + CaSiO3 -> Ca++ + 2HCO3- + H4SiO4 -> SiO2 + CaCO3 + 3H20 + CO2 1) CO2 dissolves in water to form a weak acid, which with time will break up CaSiO3 into Ca++, 2HCO3-,H4SiO4. This is called chemical weathering. These ions are soluble, and are washed into streams and eventually into the ocean by rainwater. 2) In the ocean, plants and animals form hard shells (CaCO3= SiO2). This draws the Ca++, 2HCO3-,H4SiO4 out of the ocean. These shells are eventually buried in the ocean sediments. Net reaction: CO2 + CaSiO3 -> SiO2 + CaCO3 Whole cycle: Take up 2CO2, release 1CO2 => net uptake of 1 CO2 from atmosphere. Weathering limits rate at which CO2 is drawn down 13 Weathering Rates • • • • Temperature Moisture CO2 Mechanical breakdown 14 Process which tends to build up CO2: The mantle contains CO2. As seafloor is created, this CO2 is released to the atmosphere. When seafloor sediments are subducted (subjected to heat and pressure), some CO2 from CaCO3 is released back into the atmosphere. SiO2 + CaCO3 -> CaSiO3 + CO2 This reaction will proceed faster when plate tectonics moves faster. Stabilizing mechanism: fact that uptake of CO2 is proportional to amount of CO2 in atmosphere. 15 Rate of CO2 in/out of atmosphere How is a balance achieved? g o t fr m n eri h t ea w Ou In from volcanoes CO2 16 The Carbonate-Silicate Cycle Examples • • • • • Frozen Earth Faster plate tectonics Weaker sun Continents near equator Rise of land plants 17 The Faint Young Sun Problem Faint young sun paradox Sun increases intensity with time. As more of the H is converted to He, the sun contracts. This increases the rate of fusion, and the temperature will increase. Q: Why wasn't early earth frozen?? A: More carbon was in the atmosphere. Early on, CH4 was also an important factor. How will this play out in the future as the sun gets brighter? 18