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lecture_4 - Physics 140 Lecture 4 The Temperature History...

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Unformatted text preview: Physics 140 Lecture 4 The Temperature History of the Earth Jan. 30, 2012 1 Saturday, February 4, 12 Announcements 1) For next lecture please read: Dire Predictions -- pp. 62-75 Beyond Smoke and Mirrors -- pp. 16-26 (chapter 3) 2) I will be away for the next three lectures. There will be two guest lecturers. This Wednesday Feb. 1, Prof. Sunil Somalwar who ten years ago created the Greenhouse Effect course will be guest lecturer. Next week on Monday Feb. 6 and Wednesday Feb. 8, Prof. Amit Lath who taught the Greenhouse Effect course for the past three years will be the guest lecturer. 2 Saturday, February 4, 12 The Greenhouse Effect Venus has an atmosphere that trap most of the energy being radiated by the surface. Only a small fraction, fatmos, escapes. greenhouse.gif (GIF Image, 770 517 pixels) http://astronomy.nmsu.edu/tharriso/ast110/greenhouse.gif The surface temperature, therefore, is higher so that the power escaping equals the incoming power fatmos 3 Saturday, February 4, 12 Electromagnetic Spectrum The electromagnetic spectrum covers radio waves to gamma rays. They are all the same phenomenon The difference is just the wavelength 330px-EM_Spectrum_Properties_edit.svg.png (PNG Image, 330... 4 Saturday, February 4, 12 Difference of Spectra blackbody_curve.jpg (JPEG Image, 499 316 pixels) http://chri The Sun at 6,000 K (10,000 oF) is peaked in the visible The Earth at 300 K (60 oF) is peaked in the far infrared The universe is also a blackbody. Where is its spectrum peaked? 5 Saturday, February 4, 12 Greenhouse Gases The most important greenhouse gases Water vapor -- H2O Carbon dioxide -- CO2 Methane -CH4 NO2 SO4 Ozone -- O3 Nitrous oxide -Fluorocarbons Sulfate aerosols -Soot -C The molecules of these gases absorb electromagnetic radiation in specific wavelength bands 6 Saturday, February 4, 12 Atmospheric_Transmission.png (PNG Image, 850 857 pixels) ... Absorption Bands http://4.bp.blogspot.com/_N4XvePkmKjA/TUZTNqxfDAI/A... 7 Saturday, February 4, 12 Today's Topics History of Earth's Temperature What is the Role of CO2 The Recent Past 8 Saturday, February 4, 12 History of Earth's Temperature 9 Saturday, February 4, 12 A Brief History of the Earth Formation of the Earth First life forms emerge First photosynthesis Oxygenation of atmosphere Mass extinction Demise of dinosaurs First humanoids Humans (Homo sapiens) Start of human civilization Industrial revolution 4.5 billion years ago 3.5 billion years ago 2.5 billion years ago 540 million years ago 250 million years ago 65 million years ago 4 million years ago 28.jpg (JPEG Image, 754 598 pixels) http://www.geology.wisc.edu/zircon/Earliest Piece/Images/28.jpg 100 thousand years ago 10 thousand years ago 200 years ago 10 Saturday, February 4, 12 Temperature History 500 million years of temperature 11 Saturday, February 4, 12 Causes of Change in Earth's Temperature There are only three 1) Change in the Sun's temperature 2) Change in the Earth-Sun orbital distance 3) Changes in the atmosphere 12 Saturday, February 4, 12 Time Scales We will look at temperature changes on several time scales 100 Million Years 10 Million Years 1 Million Years 100 Thousand Years 1 Thousand Years 1 Hundred Years 13 Saturday, February 4, 12 Proxies Thermometers have existed for only about 150 years. How can we measure temperature before then? Use proxies, substitutes for a direct measure of temperature. Most powerful of these is the ratio of 18O to 16O two isotopes of oxygen. 18O is heavier than 16O so water with 18O evaporates at a higher temperature. Therefore the 18O concentration in precipitation is higher with higher temperature. Measure the 18O to 16O ratio in sediments and ice core layers. 14 Saturday, February 4, 12 Phanerozoic_Climate_Change.png (PNG Image, 726 520 pixels) 100 Million Year Time Scale http://upload.wikimedia.org/wikipedia/commons/9/9c/Phanerozo... 15 Saturday, February 4, 12 100 Million Year Time Scale Measured from 18O to 16O ratio in sediment cores About a 140 million year cycle of high and low temperatures We are currently at a low What causes this is not understood Some speculation that it may be due to the solar system moving through the galactic spiral arm but this seems fairly fanciful to me Phanerozoic_Climate_Change.png (PNG Image, 726 520 pixels) http://upload.wikimedia.org/wikipedia/commons/9/9c/Phanerozo... 16 Saturday, February 4, 12 yr_Climate_Change.png (PNG Image, 650 397 pixels) 10 Million Year Time Scale http://upload.wikimedia.org/wikipedia/commons/1/1b/65_ 17 Saturday, February 4, 12 10 Million Year Time Scale Temperature has been decreasing for the past 50 million years Most recent maximum was the Eocene optimum Temperature was about 12 oC or 26 oF higher than today Notice the spike at around 58 million years. This may have been sue to the release of frozen methane hydrates from the ocean floor rapidly dumping dumping a lot of methane into the atmosphere. Notice the quick recovery. Methane doesn't stay in the atmosphere very long 65_Myr_Climate_Change.png (PNG Image, 650 397 pixels) http://upload.wikimedia.org/wikipedia/commons/1 Also notice the effect of antarctic glaciation and thawing 18 Saturday, February 4, 12 1 Million Year Time Scale 2 Equivalent Vostok T (C) http://upload.wikimedia.org/wikipedia/commons/f/f7/Five_Myr_ 2 2.5 3 0 -2 -4 -6 -8 Five Million Years of Climate Change From Sediment Cores Millions of Years Ago 4 4.5 Overall decrease 100 thousand and 41 thousand year cycles These are the ice age cycle We know what this is due to 19 Saturday, February 4, 12 18 3.5 O Benthic Carbonate (per mil) 41 kyr cycle 100 kyr cycle Variation in Earth's orbit eccentricity_cycle.jpg (JPEG Image, 972x768 pixels) - Scaled ... http://apollo.lsc.vsc.edu/classes/met130/notes/chapter16/graphic... Eccentricity of Earth's elliptical orbit varies with a 100 thousand year cycle Axis of Earth changes with 22 thousand year cycle precession.jpg (JPEG Image, 1000x633 pixels) - Scaled (96%) http://apollo.lsc.vsc.edu/classes/met130/notes/chapter16/graphic... tilt.psd.gif (GIF Image, 350 310 pixels) http://apollo.lsc.v 1 of 1 1/25/12 2:06 PM Tilt of axis changes with 41 thousand year cycle 20 Saturday, February 4, 12 Vostok Ice Cores es2105_p1_vostok_b.jpg (JPEG Image, 350x261 pixels) http:// Ratio of 18O to 16O very sensitive to temperature Can also get CO2 concentration by measuring dissolved CO2 21 Saturday, February 4, 12 100 Thousand Year Time Scale Clearly see the 100 thousand year cycle Notice that we came out of an ice age about 10,000 year ago. Should currently be heading toward another ice age. Notice the relatively rapid heating and then the relatively gradual cooling. Is this due to CO2 ? Over the past 400,000 years the Earth has 2 oC (4 oF) warmer and 8 oC (14 oF) colder than now ? 22 Saturday, February 4, 12 olocene_Temperature_Variations.png (PNG Image, 600 400 ... http://upload.wikimedia.org/wikipedia/commons/c/c 1 Thousand Year Time Scale 23 Saturday, February 4, 12 1 Thousand Year Time Scale Notice again that we came out of an ice age about 10,000 year ago. The earth has been getting colder by about 0.5 oC (1 oF) since then, until recently. The various collared lines are different proxies. Holocene_Temperature_Variations.png (PNG Image, 600 400 ... http://upload.wikimedia.org/wikipedia/commons/c/ca/H These each have sizable error so there is much fluctuation among them. The black curve is the average. 24 Saturday, February 4, 12 1 Hundred Year Time Scale 25 Saturday, February 4, 12 1 Hundred Year Time Scale Ice cores not useful on this small of a time scale 2000_Year_Temperature_Comparison.png (PNG Image, 600 4... http://upload.wikimedia.org/wikipedia/commons Need other proxies - tree rings - date of grape harvest - size of glaciers - amount of coral laid down These more or less agree For last 150 years have thermometers! 26 Saturday, February 4, 12 ...
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