R. Parthasarathy. University of Oregon

Transcription

1 Physics 161:Physics of Energy and Environment Physics 161: Physics of Energy and the Environment December 4, 2008 Prof. Raghuveer Parthasarathy

2 Physics 161:Physics of Energy and Environment Lecture 18: Announcements (1) Reading: Wolfson, Chapter 15, 16 (partial) PS7: graded (see ) Course Evaluations (on line) Study Guide for the Final Exam Posted on the web page Office hours next week: RP Tues: cancelled, Wed pm, Th pm Eryn: Thurs at the drop in center Maunta: Mon (Wil 216), Wed. 3 4 (drop in) ctr)

3 Physics 161:Physics of Energy and Environment Lecture 18: Announcements (2) Final Exam: Friday Dec. 12, 8 10am. Format: Like midterm (various question types, including short answer; very little memorization of eqns., #s) The most important part of answering any question is addressing the concept involved, not doing a calculation. Do this first! There are 3 reasons for this: (1) Understanding the concepts is the key goal of the course. (2) Describing the path to the answer often reveals to you whether the path is correct; starting a calculation rarely does. (3) You always have time to conceptually set up the answer, even if you don t have time to finish calculating something.

4 Physics 161:Physics of Energy and Environment A review question: The Atmosphere Which of the following is true: A. The atmosphere is mostly transparent to visible light B. The atmosphere is mostly transparent to infrared light C. The atmosphere is mostly opaque to the thermal radiation the Earth emits D. A & B E. A & C

5 Physics 161:Physics of Energy and Environment Atmospheric CO 2 Data on atmospheric CO 2, global temperature, etc. Large increase in atmospheric CO 2 in the past century due (mostly) to fossil fuel combustion. present: 385 ppm preindustrial: 280 ppm

6 Physics 161:Physics of Energy and Environment Temperature Global average change in temperature (ΔT)from direct measurements (since 1850) and proxies (earlier). Many different proxies: tree rings, isotope ratios, etc. Agreement between different proxies, and also recent instrumental record

7 Physics 161:Physics of Energy and Environment Temperature: 1000 Years ΔT for the past 1000 years Last few decades: unusually warm Temperature rise 0.7 C over the past century! Other phenomena (sea ice coverage, hurricane intensity, etc.) also consistent with increased greenhouse warming black: instrumental record

8 Physics 161:Physics of Energy and Environment Temperature: Further back Over long time scales (100s of 1000s of years), ice ages, interglacials. What is the historical range of ΔT (i.e. difference between ice ages, interglacials)? A. 0.7 C B. 27 C C. 7 C D. 70 C E. There is no way of knowing

9 Physics 161:Physics of Energy and Environment Temperature: Further back Reconstruct more distant history: ice core data Note scale: Ice ages, w/ 2 miles of ice over Chicago: ΔT only 7 C colder! same source as text 14 06: Petit et al., 1999

10 Physics 161:Physics of Energy and Environment Climate change: are we to blame? Yes. Reasons for attributing climate change to humans Basic physics of the greenhouse effect + known CO 2 increase due to fossil fuel use Lack of correlation between recent temperature and natural climate forcings; very good correlation before 1950 Fingerprints of changes to greenhouse effect, e.g. stratospheric cooling Climate modeling (Large programs with 3D global grids modeling physical processes.)

11 Physics 161:Physics of Energy and Environment Assessing Climate Models It s difficult to make predictions, especially about the future Niels Bohr?, Yogi Berra?,... Climate models based on well established physics (thermal radiation, etc.) Suppose we want still more assurance: How can we assess the accuracy of climate model predictions? (besides waiting...) [Ask]

12 Physics 161:Physics of Energy and Environment Assessing Climate Models How can we assess the accuracy of climate model predictions? (besides waiting...) Start models in the past, see if they reproduce present climate. (Yes!)

13 Physics 161:Physics of Energy and Environment Assessing Climate Models How can we assess the accuracy of climate model predictions? (besides waiting...) See if they reproduce present climate. Test their predictions about a variety of climatic properties distribution of T in the atmosphere, latitude dependence of precipitation, etc. (Next slides)

14 From text: Temperature structure of the atmosphere, from actual observations (thick black curve) and thirteen different climate models.

15 From text: Three months of precipitation (December to February), averaged over longitude, as a function of latitude from pole to pole. Black: actual observations. Colored: results from fifteen different climate models

16 Physics 161:Physics of Energy and Environment Assessing Climate Models How can we assess the accuracy of climate model predictions? (besides waiting...) See if they reproduce present climate. Test predictions about a variety of climatic properties See if many different, independent models agree (previous slides) See if they reproduce the effects of natural experiments, e.g. volcanic eruptions

17 Physics 161:Physics of Energy and Environment Climate Projections Many ways to assess the accuracy of climate models (besides waiting...) Are our predictions for the future certain? Certainly not! But for all these reasons, we have a good amount of confidence in projections of future climate. (Projection is a better term than prediction. ) So what do the models project? (again, don t memorize graphs)

18 Physics 161:Physics of Energy and Environment Climate Projections Pre industrial atmospheric CO 2 : 280 ppm. Present CO 2 : 385 ppm. We re on track to double the pre industrial level (i.e. 560 ppm) by mid to late century Very unprecedented in Earth s history (earlier graphs) What would doubling do? Some rough guides:...

19 Physics 161:Physics of Energy and Environment Climate Projections What would happen if CO 2 rises at 1%/year, until 560 ppm, then stays constant? T rises 3 C (Compare this to historical norms!) T takes 100 years to stabilize (i.e. effects are not immediate) 19 different models Simple model (blue) and more detailed model

20 Physics 161:Physics of Energy and Environment Projections: Increasing CO 2 At present rates, we ll more than double atmospheric CO 2. What will ΔT do? Graph: ΔT for various CO 2 scenarios. Dots: when CO 2 amount stabilizes. Several C change.

21 Physics 161:Physics of Energy and Environment Projections: Increasing CO 2 At present rates, we ll more than double atmospheric CO 2. How much CO 2 will we put into the atmosphere? Text: various scenarios (interesting, but you don t have to read them) Who knows?? Depends on social, political will.

22 Physics 161:Physics of Energy and Environment Projections: Temperature The global temperature is already rising, and this will continue. (See previous graphs) How much will it rise? Here s a way to think about the probabilities. According to the IPCC and others, the present CO 2 etc. concentration already commits the planet to an equilibrium (long term) warming of 2.4 C. This is referred to as committed warming most probable = 2.4 C, 90% probability that it s between 1.4 and 4.3 C. Graph of probabilities...

23 Physics 161:Physics of Energy and Environment Committed Warming Committed warming graph of probabilities. About 25% of this warming ( 0.6 C) has already occurred; 90% of the rest will occur during this century. V. Ramanathan & Y. Feng, On avoiding dangerous anthropogenic interference with the climate system: Formidable challenges ahead, Proceedings of the National Academy of Sciences 105: (2008).

24 Physics 161:Physics of Energy and Environment Committed Warming Based on this graph: What s more probable, that we ve committed the planet to an overall warming of ΔT = 1 C or 4 C? A. 1 C B. 4 C

25 Physics 161:Physics of Energy and Environment Committed Warming Decreasing air pollution (good for health, of course) can make the warming worse. Why? A. Pollutants like CO are not greenhouse gases B. Pollutants like CO hinder the infrared absorption of greenhouse gases. C. Pollutants like sulfate aerosols lead to cooling due to their reflectivity.

26 Physics 161:Physics of Energy and Environment Consequences of Climate Change What s so bad about climate change? ( I like warm weather... ) Changes in temperature Amount of ΔT large by historical standards Not uniform globally, by the way; cooling in some regions

27 Physics 161:Physics of Energy and Environment Consequences of Climate Change Changes in temperature More extreme temperature events high temperature extremes become much more likely in a distribution with a slightly higher mean

28 Physics 161:Physics of Energy and Environment Consequences of Climate Change Changes in temperature More extreme temperature events Changes in precipitation, weather (e.g. hurricanes) Sea level rise not due to melting icebergs: ice is less dense than water (floats), so melting floating ice lowers the water level. Melting land ice (e.g. Greenland) sliding into ocean sea level rise. Dominant mechanism isn t melting at all: thermal expansion of liquid water

29 Physics 161:Physics of Energy and Environment Consequences of Climate Change Changes in temperature More extreme temperature events Changes in precipitation, weather (e.g. hurricanes) Sea level rise predicted rise this century m. Not a lot, but enough to cause flooding in many heavily populated coastal areas (e.g. Bangladesh) Could get worse: melting of West Antarctic ice sheet 3 m rise in sea level. (Map...)

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31 Physics 161:Physics of Energy and Environment Consequences of Climate Change Changes in temperature More extreme temperature events Changes in precipitation, weather (e.g. hurricanes) Sea level rise Ocean circulation changes, e.g. the thermohaline circulation that keeps N. Europe warm, strongly dependent on temperature (convection, etc.) And more...

32 Physics 161:Physics of Energy and Environment Tipping points Climate triggered Tipping points where are they on our probability graph? Good probability that the warming we re already committed to will lead to at least a few major changes to the planet! We ll be even worse off unless present practices stop.

33 Physics 161:Physics of Energy and Environment Climate change and society Not all climate change is harmful. A rise of 1 C may lead to enhanced agricultural productivity. But ΔT rising over 2 or 3 C will cause far more damage than good. Dangerous anthropogenic interference threshold is usually considered to be 2 C. How will climate change exacerbate tensions between rich countries (which can cope better, and which are responsible for most of the warming) and poor ones? Coastal populations? Agriculture? Important questions for society...

34 Physics 161:Physics of Energy and Environment What can we do? As we ve learned: energy use and climate are fundamentally linked. We can t deal with climate change until we deal fundamentally with the way we use energy What can we do? A warning: if you think I magically possess the answer, you ll be very disappointed! Lots of pieces to any solution, some of which are yet to be discovered...

35 Physics 161:Physics of Energy and Environment What can we do? Carbon capture & sequestration. Idea: capture & store CO 2 produced by combustion, rather than allowing it to go to the atmosphere. In principle, a fine idea. Difficult, expensive. Captureof CO 2 (by chemicals that absorb it, algae, etc.) only possible at all for large, stationary sources (power plants), not mobile sources. These are half of CO 2 emissions. Sequestration: Store CO 2 in deep oceans, used oil wells, etc. Difficult, and must be sure that it works (geological, engineering concerns)

36 Physics 161:Physics of Energy and Environment What can we do? Carbon capture & sequestration. Alternative Energy Sources (Alternatives to fossil fuels) Renewable Energy, with little / no CO 2 emission? A quick survey (relax)

37 Physics 161:Physics of Energy and Environment Geothermal Power Alternative energy Heat from Earth s interior: power heat engines! Not a lot thermal energy available Low efficiency, since T H is low! Misc. environmental issues (gas release, land subsidence) Unlikely to be important

38 Physics 161:Physics of Energy and Environment Hydroelectric Power Alternative energy Physics: grav. potential kinetic electrical energy Abundance: We re already using 20 % of the max. available hydroelectric resource, so there isn t huge room for improvement. Efficient (no thermal energy involved) Greenhouse gas emissions are not zero, due to anaerobic organic decay in reservoirs (significant for hydropower in tropics), but are very low

39 Physics 161:Physics of Energy and Environment Wind Power Alternative energy Physics: kinetic electrical energy Abundant, but unevenly distributed and hard to harness Significant progress in wind power technology in recent past Efficient (no thermal energy involved)

40 Physics 161:Physics of Energy and Environment Biomass and biofuels Alternative energy Combustion of plant matter and plant derived fuels Does this combustion release CO 2? Yes. So why is it ok? [Ask] [Hint: Where is the C coming from?] Carbon: atmosphere plants (photosynthesis) atmosphere (combustion); no net change in atm CO 2. Carbon neutral IF done sustainably. A big IF. Deforestation: more C released to atmosphere Corn based ethanol in U.S.: lots of fossil fuel use, and lots of energy, involved in production (farm machinery, fertilizers, conversion to sugar,...). Energy output input! (And with little / no reduction in CO 2 emissions.) Pork barrel politics

41 Physics 161:Physics of Energy and Environment Solar Power Alternative energy Physics: EM energy electrical energy Abundant; incident solar power on Earth 10,000 human power consumption Expensive, though getting steadily cheaper. Probably the key route away from fossil fuels

42 Physics 161:Physics of Energy and Environment Nuclear Power (Fission) Alternative energy (We ve discussed this at length) Not renewable, but still worth considering

43 Physics 161:Physics of Energy and Environment Alternative energy Nuclear Fusion What about fusion? More strongly bound wikimedia commons We ve discussed nuclear fission (leftward on the graph) What about nuclear fusion? mass number

44 Physics 161:Physics of Energy and Environment Nuclear Fusion Wikimedia commons Alternative energy Combine lighter nuclei (e.g. hydrogen) into heavier ones. The sun does this. So far, not a practical energy source on earth. Reactions, e.g.

45 Physics 161:Physics of Energy and Environment Nuclear Fusion Alternative energy Lighter nuclei (e.g. hydrogen) heavier ones. Releases lots of energy 3 balloons full of 2 H and 3 H per day Entire U.S. power consumption No CO 2 emission No toxic products Abundant source material (hydrogen) What s the problem? Requires energy input for the positive nuclei to come together. Sun: provided by gravity. Us: need lasers, magnets, etc., spending more energy to fuse nuclei than is released by the fusion.

46 Physics 161:Physics of Energy and Environment Nuclear Fusion Alternative energy Lighter nuclei (e.g. hydrogen) heavier ones. Releases lots of energy So far, impractical. Fusion technology about 30 years away... but it s been 30 years away for about 70 years! Sigh... it would be wonderful!

47 Physics 161:Physics of Energy and Environment What can we do? Carbon capture & sequestration. Alternative Energy Sources Several options, esp. solar Planetary engineering manipulating climate e.g. intentional addition of reflective particles in the atmosphere Very risky. We re already conducting one uncontrolled experiment on the earth; two would greatly magnify the risks! A last resort?

48 Physics 161:Physics of Energy and Environment What can we do? Carbon capture & sequestration. Alternative Energy Sources Several options, esp. solar Planetary engineering manipulating climate Using less energy! Simple, straightforward, economical, effective Tied to other issues, e.g. urban planning Many areas in which one can implement lower energy use without lowering standard of living. Next slide: energy consumption of household refrigerators in the U.S.: dramatic drop!

49 Technology + governmental standards spurring new technology. Airplanes: 1/3 the energy per mile compared to 1970 Etc.

50 Physics 161:Physics of Energy and Environment What can we do? Carbon capture & sequestration. Planetary engineering manipulating climate Alternative Energy Sources Several options, esp. solar Using less energy!

51 Physics 161:Physics of Energy and Environment What do we need to do? What do we need to do? All of the above! No single solution to our problems of energy, the environment, and climate will be sufficient on its own.

52 Physics 161:Physics of Energy and Environment What do we need to do? Solving these problems will require science, politics, economics, and everything else we ve got and will require a populace (not just scientists) that s interested in addressing these issues, that understands the science involved, and that stays informed about scientific, political, and social developments. You: even before this course now and beyond... I ve very much enjoyed teaching this course, by the way thank you! The End