lecture11_ch7 - Process of Science Idea for Today: Consider...

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Unformatted text preview: Process of Science Idea for Today: Consider the difference between evidence for “correlation” and “causation”. How to predict what climate change will do to Earth • Make computer models, check them by comparing to past history & current weather. • Extrapolate trends observed on Earth. • Study other worlds, Mars and Venus, under even more extreme conditions. • Wait and see what happens to the Earth. Planets as Homes for Life A tale of three planets Why do we think Mars once had flowing water? Surface of Mars appears to have ancient river beds 1 Eroded crater Closeup of eroded crater Condition of craters indicates surface history Low-lying regions may once have had oceans Predicted mission time: 3 months Actual mission age: 48 months as of Jan 19, and still going… 100,000 pictures so far Blue regions indicate water ice near surface Spirit: 7 km Opportunity 11 km: deep within Victoria Crater 2 Where are Spirit and Opportunity now? Check at the JPL website. What determines a planet’s surface temperature? Main discoveries: “blueberry” rocks and other features: there was definitely surface water on Mars a long time ago. The energy emitted by a planet in infrared light equals the amount of sunlight energy it absorbs Conservation of energy Mercury 743 K (470 C) (878 F) 288 K ( 15 C) ( 59 F) Venus 223 K (-50 C) (-58 F) Daily variations in temperature depend on a planetʼ s rotation rate Temp vs. length The intensity of sunlight on a planet depends on its distance from the Sun Temp vs. orbital r 3 How does a planet’s reflectivity alter the surface temperature? Reflectivity Pred. Temp Venus 72% -43 C 470 C Earth 36% -17 C 15 C Moon 7% 0C Mars 25% -55 C A planetʼs reflectivity (albedo) determines how much sunlight it absorbs Actual Temp. 125 C (day) -175 C (night) How does the greenhouse effect alter surface temperature? -50 C Molecules let visible light through but can absorb infrared photons Fig 7.14 Earthʼs atmosphere absorbs light at most wavelengths. 4 Pred. Temp Greenhouse effect: Actual Temp. Warming (H2O, CO2, CH4) Venus -43 C 470 C 513 C Earth -17 C 15 C 32 C Moon 0C Mars Certain molecules let sunlight through but trap escaping infrared photons -55 C 125 C (day) -175 C (night) -50 C -- 5C Mars has seasons: CO2 can freeze in polar caps Mars has weather in a thin atmosphere of CO2 Mars once had a much thicker CO2 atmosphere Dramatic climate change occurred about 3 billion years ago The CO2 probably came from volcanoes Why Mars lost its atmosphere is still under investigation 5 Was Mars too small? Thick CO2 clouds of Venus lock heat in Marsʼ interior cooled off, lost its magnetic field, atmosphere lost to stripping by early solar wind? Where is Earthʼs CO2? Plants, Rocks, & Ocean CO2 dissolves in ocean and gets locked into rocks How has Earth’s climate changed during its history? A runaway greenhouse effect would occur if Earth moved to Venusʼ orbit 6 Earthʼs ice ages end as oceans freeze over and volcanoes release CO2 into the atmosphere Greenland, then and now How is human activity affecting Earth’s climate? CO2 content of Earthʼs atmosphere is steadily increasing. The rate of increase is higher now than in the last 400,000 years We are conducting a planet-sized climate experiment. The choice to act or not is ours. And the consequences will be experienced by us & our children. Increased CO2 is causing global warming: causation established by testing the model “Fossil record” of CO2 from ice cores 7 CO2 at 450 ppm • Melt Greenland, West Antarctic ice sheets • Catastrophic rise in sea levels • 35 years away at current rate of 2 ppm/year (now=380 ppm) • Need to reduce CO2 emissions by 50% to avert disaster (Princeton’s Socolow & Pacala: “12 of 15 wedges” ; 1 wedge = 1 billion metric tons of CO2 per year) What saves a billion tons/year? “1 wedges”: Nat. Geo. 10/2007 Efficiency and Conservation Improve fuel economy: 2 billion cars expected by 2057, get 60 mpg Reduce miles/car/year from 10,000 to 5,000 Increase efficiency of household power use by 25% What’s being done now? • Not much - Europe and Japan have begun to reduce emissions • US contributes 25% of total emissions, will increase carbon output by 20% by 2020 • China building 1 coal-fired plant/week What can be done? Carbon Capture and Storage Capture CO2 and store underground at 800 large coalfired plants or 1600 natural gas plants Low Carbon fuels Replace 1400 large coal-fired plants with natural gas fired plants. Displace coal by increasing nuclear power generation to 3 times current capacity Improve coal-fired power plant efficiency to 60% from 40% What can be done? Renewables and Biostorage Increase wind-generated power to 25x current capacity. Increase solar power to 700x current capacity Sources of CO2 that you control Combustion puts 6 million tons of C02 in the atmosphere every year. Increase wind power to 50x current capacity to make hydrogen for fuel-cell cars. Increase ethanol biofuel production to 50x current (1/6 of ALL cropland required.) Corn is not the way, though!!! Stop all deforestation. Stop normal plowing (speeds decomposition.) 8 Examples of human success in environmental change • Lead controls in emissions & gasoline & paint reduced lead levels in blood, improved IQ scores in children • CFC regulation led to (slowly) smaller ozone hole. • Insurance industries have a stake in changing behavior: reducing emissions, smarter land use, changing perception of risk • Note that Carbon cost is not included in fuel cost now: actual fuel costs would motivate change. Change is possible! (But we need to start now, make it economically necessary.) What can you do? • • • • • • • • • Drive (and fly) less. Walk, bike, take public transportation. Eat less meat (especially red meat) Thermostat management: cooler in winter, warmer in summer Turn stuff off, unplug when not in use. Invest in alternative energy, renewables, carbon offsets. Buy a hybrid car. Let your government know how you feel. Vote: registration deadline is Oct 6 Investor Alert (Fortune Mag.) “Climate change is no longer a fringe issue…these trends present enormous risks and opportunities.” Cost of natural disasters 2005: $225 billion, in 2004: $118 billion Reinsurance giant Swiss Re: “Global warming has accelerated from a problem which might affect our grandchildren, to one that could significantly disturb the social and economic conditions of our lifetime.” www.ceres.org Be able to answer • What is the evidence for (surface) water on Mars? • What factors affect the temperature on a planet (and how)? • Explain the greenhouse effect of atmospheres, including runaway greenhouse. • What is the evidence for global warming and human’s influence on greenhouse gases in the atmosphere? • Why are conditions on Mars and Venus so different from those on Earth? 9 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.

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