Selected Slides from Prof. Broccoli s Two Guest Lectures

Transcription

1 Selected Slides from Prof. Broccoli s Two Guest Lectures Required reading for Greenhouse Effect class at Rutgers University, Spring 2004 Condensed by Sunil Somalwar

2 Global Warming Alan Robock Tony Broccoli Rutgers University, New Brunswick, New Jersey USA

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4 Mann et al. (1999)

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6 The unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more. Climate Change The IPCC Scientific Assessment (1990) The balance of evidence suggests a discernible human influence on global climate. Climate Change 1995 The Second Assessment of the Intergovernmental Panel on Climate Change (IPCC) There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. Climate Change 2000 The Third Assessment Report of the IPCC

7 At the request of U.S. President George W. Bush, the National Research Council of the U.S. National Academy of Sciences issued a special report, Climate Change Science: An Analysis of Some Key Questions, that endorsed the key conclusions of the IPCC assessment in The U.S. Environmental Protection Agency in 2002 issued a report that again supported the IPCC assessement.

8 Actual observations

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10 Climate System 1. Atmosphere 2. Hydrosphere (oceans) 3. Cryosphere (snow, ice, glaciers) 4. Biosphere (including people) 5. Lithosphere (soil, volcanoes)

11 The Climate System

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13 + Temperature Feedbacks Start with temperature increase, e.g., from more CO 2 External forcing

14 Fundamental Determinants of Climate 1. Input of solar radiation 2. Atmospheric composition (gases and aerosols) 3. Surface characteristics (albedo, roughness, potential evapotranspiration) Humans can change climate by affecting 2 or 3.

15 The climate system

16 Planetary albedo (α) is the average reflectivity of the Earth = 107/ Earth s global, annual mean energy balance

17 Greenhouse effect Earth s global, annual mean energy balance

18 Causes of Climate Change (Forcings) Natural: Solar variations Volcanic eruptions Chaotic weather variations El Niño/Southern Oscillation Other ocean-atmosphere interactions Anthropogenic: GHG: CO 2, CH 4, CFCs, N 2 O, O 3 Tropospheric aerosols Sulfates, black carbon, organics, dust Direct and indirect effects Ozone depletion (indirect effect of CFCs) Land surface modification Contrails

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20 (IPCC TAR, Chap. 3)

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32 Mountain Glacier Trends

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35 General Circulation Models (GCMs) 1 Basic Physical Laws: Conservation of energy (First law of thermodynamics) Conservation of momentum (Newton s second law of motion) Conservation of mass (Continuity equation) Conservation of moisture Hydrostatic equilibrium Gas law

36 General Circulation Models (GCMs) 2 Physical Processes That Must or Can Be Included: Wind Sea ice Radiation Snow Precipitation Glaciers Soil moisture Vegetation Ground water Ocean biota Aerosols Clouds, convective and large-scale Air-sea exchanges of moisture, energy, and momentum Air-land exchanges of moisture, energy, and momentum Chemistry, particularly O 3 and CO 2 Ocean temperature, salinity, and currents

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38 Typical grid spacing of a GCM is 4 x 5 latitude-longitude by 2 km in the vertical. In the near future, we will have global 1 x 1 models and the Japanese have designed the fastest computer in the world, the Earth Simulator. on which they will run a global 10 km x 10 km grid. Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8. When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.

39 To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be parameterized. One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box. Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.

40 Future Sea Level Projections Different scenarios Model ranges

41 Third Assessment Report of the IPCC (2001): General circulation model results

42 Third Assessment Report of the IPCC (2001): General circulation model results

43 Third Assessment Report of the IPCC (2001): General circulation model results Pinatubo

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45 Vinnikov et al. (1999)

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50 How will climate change affect us?

51 Climate Change and other Environmental Stresses Algal Blooms Land Use Change Loss of Biodiversity Invasive Species Air Pollution Acid Deposition Pollution

52 Areas of Human Endeavor That Could Be Affected by Global Warming Agriculture Water Resources Fisheries Air Pollution Human Health Recreation Insurance Wetlands Forestry Electricity Demand Wind Energy Generation Solar Energy Generation Hydroelectricity Generation Ocean Transportation Air Transportation Land Transportation Political Systems

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57 The Global Warming Dilemma (Mahlman, 2002) On the one hand, large increases in atmospheric CO 2 concentrations have occurred, with considerably more in the pipeline. Yet, the magnitude of documented warming to date is comparatively small, about 0.6 C...Thus, there has been little motivation today to resort to a major effort to reduce global CO 2 emissions. On the other hand, delaying major CO 2 emissions reductions until substantial climate warming occurs would very likely wire in the world to globally troublesome global warming for many centuries...therefore, the choices are quite daunting: we can make very large policy commitments now with little visible short-term payback, or we can delay policy action indefinitely (the de facto current strategy), with very large coping and adaptation costs decades and centuries from now.

58 The Global Warming Dilemma (Mahlman, 2002) The harsh reality of the Global Warming Dilemma: Consider the policymakers sincere question: What can we do in a mitigation context to keep global warming from happening? The blunt answer is almost nothing; climate change is well underway and it carries huge momentum. Clearly, the question needs to be restated: What are the options available for us to manage this dauntingly difficult problem in the most globally responsible way? In this form, the question is quite reasonable because it allows avenues for finding rational approaches for dealing with the real problem.

59 The Global Warming Dilemma (Mahlman, 2002) There are no quick policy fixes, nationally or globally. If we don't begin to chip away at the problem soon, it is very likely that serious consequences will be wired in for the world of our great-grandchildren and for their great-grandchildren.... The long time scales and robustness of the problem almost guarantees that our descendants in the 22 nd century will, with historical perspective, see that we were actually confronted with a major planet-scale stewardship/ management problem. They will most assuredly note how we responded, or how we did not respond to the problem.

60 Frequently Asked Questions What is the global warming controversy? Was the mild weather of some recent winters a result of global warming? Does global warming mean that there won t be snowy winters anymore? If global warming is occurring, why was January so cold? How can we project what the earth s temperature will be 50 years from now if we don t always get tomorrow s weather forecast right?

61 What is the global warming controversy?

62 Media Coverage of Global Warming Climate change is a big and very complex scientific and political issue. Media coverage naturally reports on both of these aspects often blending the two. Time Magazine April 9, 2001 Climbing temperatures. Melting glaciers. Rising Seas. All over the earth we re feeling the heat. Why isn t Washington?

63 The Global Warming Controversy Is the earth warming? (Detection) Are human activities responsible for this warming? (Attribution) What should we do about it? (Policy)

64 Was the mild weather of some recent winters a result of global warming?

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66 A Baseball Analogy John Doe is a five-year veteran with career averages of.303 BA, 9 HR, 57 RBI. He undertakes an off-season weighttraining program. In his first at-bat of the new season, he hits a towering, 470-foot home run. Was this monstrous blast a result of his off-season weight training?

67 Possible Answers Of course not. One home run doesn t prove anything. The pitcher may have thrown a batting practice fastball that anybody could crush. I knew all his off-season work would pay off. He s always been able to get his bat on the ball, he just needed some more strength. I bet he wins the home run title.

68 A Better Answer Global warming would alter the probability of warm winters, but the internal variability of the climate system is a powerful factor in year-to-year climate variations. A warm winter could be evidence of global warming, but only if it is part of a long-term trend. Time will tell.

69 No Snowy Winters Anymore? Global warming would alter the probability of snowy winters, but the internal variability of the climate system (e.g., El Niño, North Atlantic Oscillation) is a powerful factor in year-to-year climate variations.

70 If global warming is occurring, why was January so cold?

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74 Global Temperature Trends Source: NASA Goddard Institute for Space Studies

75 How can we project what the earth s temperature will be 50 years from now if tomorrow s weather forecast isn t always right?

76 X n+1 = a X n - X n 2 Consider a prediction using the above equation of the future state of the variable X, say the surface air temperature. The subscript n indicates the time, say the day, and a is a constant representing the physics of the climate system. X for any day is a times its value on the previous day minus X squared on the previous day. With such a simple equation, it should be possible to predict X indefinitely into the future. Right?

77 X n+1 = a X n - X n 2 X a Precision (decimal places) Let s assume that a is exactly and that a prediction with three decimal places is the exact solution. Then let s consider three types of errors: imprecise knowledge of the physics of the climate system, imprecise initial conditions, and rounding due to limited computer resources. This example is from Edward Lorenz.

78 X n+1 = a X n - X n 2 X a Precision (decimal places) X n+1 = a X n - X n 2 X n n Control Physics Initial Conditions Rounding

79 Sensitivity to Initial Conditions Results from three different simulations, each starting from different initial conditions. Changes in atmospheric composition are identical.

80 Global Warming Occurs in All Three The global warming signal eventually emerges in all three simulations, despite the pronounced internal variability that is evident.

81 My Global Warming Forecast The global climate will continue to warm, and as it does, any scientific controversy about the detection of climate change will end. Controversy about the attribution of climate change will last longer than controversy about the detection of climate change. The controversy will eventually shift toward the policy questions and remain for a long time.

82 However Virtually all forecasts should be expressed as probability forecasts, and mine is no exception. We still have a lot to learn about how the climate system works. More work will be required to narrow the range of uncertainties about the future spatial and temporal evolution of climate.