chapter_12 - Long-Term Climate Regulation Regulation...

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Unformatted text preview: Long-Term Climate Regulation Regulation Chapter 12 Dr. Emily Berndt Fundamentals of the Climate System EAS 253 I. Overview I. A. Solar evolution models predict the sun: i. was 30% dimmer when it formed ii. has increased luminosity linearly with has age age B. Earth had liquid water as far back as Earth 4.2 b.y.a 4.2 I. Overview I. C. Warm temperatures were maintained by: i. Greenhouse gases ii. CH4 concentrations fell abruptly 2.4 b.y.a. iii. Cause the first major glaciation iv. Earth recovered as CO2 levels rose due to Earth volcanic eruptions volcanic v. As the sun brightened, CO2 As concentrations decreased concentrations I. Overview I. D. Over the past 400 million years, Earth’s D. climate has fluctuated between warm and cold conditions and E. The result of changes in the E. atmospheric CO2 concentration induced by plate tectonics and the carbonate-silicate cycle carbonate-silicate II. Introduction II. A. Life requires water B. This implies Earth’s surface This temperature has remained warm enough to support liquid water enough C. The sun was about 30% less bright, so The why did the climate remain relatively warm enough to support liquid water? warm II. Introduction II. D. Possible solutions to the Faint Young D. Sun Paradox Sun i. Stronger greenhouse effect ii. Lower planetary albedo iii. Either are needed to balance the planetary Either energy balance energy iv. Why would either of these factors change? II. Introduction II. E. Strong negative feedback E. between atmospheric CO2 and the rate of silicate weathering silicate i. Tendency to stabilize Tendency climate over long time scales scales iii. Causes atmospheric i. CO2 levels to change CO2 ii. II. Introduction II. F. Earth’s surface has experienced F. substantial swings where polar ices was present, absent, or ice sheets were in the tropics were G. How stable has Earth’s climate been? H. How have plate tectonics and biological H. evolution caused large climatic shifts? evolution III. Faint Young Sun Paradox III. The sun was 30% less luminous 4.6 bya Now the sun is brightening by about 1% Now every hundred million years every What are the effects of Solar Luminosity What Changes? Changes? Early Earth should have been colder than it is Early today today Faint Young Sun Paradox – how did liquid Faint water exist if the sun was 70% as intense as today today Does Earth have a built in stability Does mechanism? mechanism? III. Faint Young Sun Paradox III. A. The sun gets brighter as it ages B. Luminosity increase is a direct result of Luminosity density changes due to the conversion of H to He of Changes in Solar Luminosity Changes The sun’s brightness increases as it The depletes it’s hydrogen fuel depletes As H decreases in the core, there is less As pressure (core contracts and heats up) pressure A temperature rises, increases the pressure As temperature increases, the rate of fusion As increases increases More energy and a brighter sun! http://www.physicsoftheunivers III. Faint Young Sun Paradox III. C. Defining the problem mathematically III. Faint Young Sun Paradox III. C. Defining the problem mathematically i. Assumptions 1. 2. Constant CO2 concentration of 340 ppm Constant surface albedo ii. Increase in magnitude of green house effect Increase due to the water vapor feedback due iii. Surface temperature fall below the freezing Surface point prior to 1.9 b.y.a. point iv. Prediction at odds with geological evidence 1. 2. Liquid water present 3.8 b.y.a. Life present as well III. Faint Young Sun Paradox III. D. Possible Solutions to the problem: 1. Lower Albedo a. b. c. How could a water covered planet have an albedo near zero If temperature was below freezing there would be ice present Unlikely it could have kept the planet warm Most likely solution Water vapor is not the solution i. ii. Close to saturation Acts as a feedback rather than a forcing Good absorber of IR Reduced gas More abundant prior to 2.4 b.y.a. Rapidly destroyed by UV radiation 2. Larger Greenhouse Effect a. b. c. Larger concentration of ammonia? i. ii. iii. iv. 3. Additional heat sources besides the Sun a. b. c. d. Geothermal heat from interior decay of radioactive elements Both sources were larger in the past Geothermal heat flux is too small III. Faint Young Sun Paradox III. E. A CO2-Rich Early Atmosphere i. Reasons for higher CO2 concentrations: 1. 2. Smaller continents and reduced silicate weathering and Smaller carbonate storage carbonate Degassing and enhance volcanism subduction of carbonate material into the mantle hard to say of concentrations were higher or lower little early geological evidence ii. Counterarguments 1. 2. 3. III. Faint Young Sun Paradox III. E. A CO2-Rich Early Atmosphere iii. Carbonate-silicate cycle 1. 2. 3. Impacts CO2 concentrations over long time scales Strong negative feedback Consider lower surface temperature a. b. c. Slower rate of silicate weathering Lower CO2 loss rate Accumulations of CO2 emitted emitted from volcanoes until a balance of silicate weathering with outgassing 1. What if Earth were ice covered? a. b. c. c. d. e. No silicate weathering Accumulation of CO2 Enhancement of green house effect and ice melt Natural process to recover from glaciation Most of the time the feedback is strong enough to avoid global glaciation III. Faint Young Sun Paradox III. E. A CO2-Rich Early Atmosphere iiv. How much atmospheric CO2 would have been necessary v. to keep the early oceans from freezing? to 1. If only CO2 and water vapor as greenhouse gases 2. Minimum CO2 to compensate for reduced solar luminosity is 0.3 bar bar a. a. a. a. 1,000 times present amount of CO2 not a large amount compared to amount of carbon available Only 0.5% of the CO2 is is needed to resolved the problem III. Faint Young Sun Paradox III. F. Effect of Methane on the Archean Climate III. Faint Young Sun Paradox III. F. Effect of Methane on the Archean Climate i. Methane could have been prevalent prior to 2.3 b.y.a. when O2 levels were low levels ii. Strong warming effect on global temperature 1. Supplemented by warming die to ethane 2. Offset by cooling die to organic haze iii. Asdf 1. Of CH4 was not present a CO2 concentration of 0.02 would be needed to keep surface temperature >0 needed a. 60 times present level 3 2. If CH4 was present as 10--3 mixing ratio needed CO2 mixing concentration of 0.005 bar concentration a. 15 times present level 3. Keeping the archean climate at 288 K would require about 0.03 Keeping bar of CO2 concentration bar a. 100 times present value III. Faint Young Sun Paradox III. G. A pink sky during the Archean? i. Interaction of sunlight with the atmosphere 1. Today rayleigh scattering- effective scattering of shorter Today wavelengths (blue sky) wavelengths 2. Mie scattering- scattering by particles comparable in Mie size to wavelength being scattered (pink, orange) size ii. CH4 can polymerize to form higher hydrocarbons - Carbon atoms in long chains i. ii. Creates orange haze Positive feedback 1. 2. 3. 4. Increase in surface temperaute More CH4 produceers Increase in CH4 Increase in green house effect III. Faint Young Sun Paradox III. H. Climate regulation by the “Anti-Greenhouse H. Effect” Effect” III. Faint Young Sun Paradox III. H. Climate regulation by the “Anti-Greenhouse Effect” i. As CH4 increases, organic haze develops ii. CH4 and haze are strong absorbers of (visible) radiation iii. Absorption produces an anti-GH effect 1. Sunlight absorbed high in the atmosphere 2. Radiated to space as IR energy 3. Never reaches the surface and surface cools iv. Climate regulated by a (-) feedback 1. Increase in temperature 2. Increase in CH4 but decrease in CO2 3. 3. 4. 5. 6. 7. Formation of haze Absorption of solar radiation Cooling of surface Overall effect is to stabilize climate Doesn’t tell us actual climate, but that it was stable for longer Doesn’t periods of time periods III. Faint Young Sun Paradox III. I. Comparing the Archean climate to Daisyworld + CH4 - CH4 III. Faint Young Sun Paradox III. I. Comparing the Archean climate to Daisyworld i. If methane producers were keeping the early climate warm, and If they depended on warmth to flourish, they modified the climate for their benefit their ii. Gaian nature of Archean climate iii. Line shows increase in temperature leads to increase in CH4 iv. Curve shows impact of CH4 on temperature 1. At low CH4 levels a. Increase CH4, increase temperature b. Enhanced GH effect c. P1 is unstable 2. At high CH4 levels a. Increase CH4, decrease temperature b. Haze formation Haze c. Ps is stable c. v. Predicts the climate should have stabilized once haze was present ...
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This note was uploaded on 04/11/2011 for the course EAS 253 taught by Professor Dr.emilyberndt during the Spring '11 term at Saint Louis.

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